Philip Evans

Prof Philip Evans

CVSSP and NPL Professor of Medical Radiation Imaging
31 BA 00



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Phone: +44 (0)1483 684380 / 688914 / 684378
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Senate House, University of Surrey
Guildford, Surrey GU2 7XH


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Postgraduate research supervision

Postgraduate research supervision

My publications


Gildersleve J, Dearnaley DP, Evans PM, Swindell W (1995) Reproducibility of patient positioning during routine radiotherapy, as assessed by an integrated megavoltage imaging system., Radiother Oncol 35 (2) pp. 151-160
A portal imaging system has been used, in conjunction with a movie measurement technique to measure set-up errors for 15 patients treated with radiotherapy of the pelvis and for 12 patients treated with radiotherapy of the brain. The pelvic patients were treated without fixation devices and the brain patients were treated with individually-moulded plastic shells. As would be expected the brain treatments were found to be more accurate than the pelvic treatments. Results are presented in terms of five error types: random error from treatment to treatment, error between mean treatment position and simulation position, random simulation error, systematic simulator-to-treatment errors and total treatment error. For the brain patients the simulation-to-treatment error predominates and random treatment errors were small (95%
Swindell W, Morton EJ, Evans PM, Lewis DG (1991) The Design of Megavoltage Projection Imaging Systems: Some theOretical Aspects, Medical Physics 18 (5) pp. 855-866
This study investigates factors associated with the imaging of a patient using a high-energy radiotherapy treatment beam. Both single-stage (e.g., solid-state detector) and two-stage (e.g., scintillation screen plus TV) systems are considered. First an expression is derived that relates dose at the buildup depth in the object to the structure of the object, the scatter-to-primary signal-variance ratio and the differential-signal-to-noise ratio in the image. Second the number of bits required to digitize the image is derived. Third the effect of scattered radiation is investigated for photon counting, photopeak, and Compton detector types. Fourth the effect of noise in the detection process is considered. Finally, the relationship between x-ray source size, detector aperture, and image magnification is derived. The optimum magnification for given source size and detector aperture is discussed in terms of the system transfer function. The study indicates that at a primary beam energy of 2 MeV, a dose of 10-3cGy is required to detect reliably the presence of a bone section of area 10 x 10 mm and thickness 4 mm in 250 mm of soft tissue. For this example, it is also estimated that a digitization accuracy of 10 bits is required. The calculations indicate that for a Compton detector, the scatter-to-primary signal-variance ratio drops from a value of around 30% at the exit surface of the object to 5% at a distance of 80 cm from the object with a consequent small reduction in the dose required to form the image. © 1991, American Association of Physicists in Medicine. All rights reserved.
Tahavoria F, Adams E, Dabbs M, Aldridge L, Liversidge N, Donovan E, Jordan T, Evans PM, Wells K (2015) Combining Marker-less Patient Setup and Respiratory Motion Monitoring Using Low Cost 3D Camera Technology, MEDICAL IMAGING 2015: IMAGE-GUIDED PROCEDURES, ROBOTIC INTERVENTIONS, AND MODELING 9415 SPIE-INT SOC OPTICAL ENGINEERING
Bohndiek SE, Blue A, Cabello J, Clark AT, Guerrini N, Evans PM, Harris EJ, Konstantinidis A, Maneuski D, Osmond J, O'Shea V, Speller RD, Turchetta R, Wells K, Zin H, Allinson NM (2009) Characterization and Testing of LAS: A Prototype 'Large Area Sensor' With Performance Characteristics Suitable for Medical Imaging Applications, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 56 (5) pp. 2938-2946 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Evans PM, Donovan EM, Fenton N, Hansen VN, Moore I, Partridge M, Reise S, Suter B, Symonds-Tayler JR, Yarnold JR (1998) Practical implementation of compensators in breast radiotherapy., Radiother Oncol 49 (3) pp. 255-265
BACKGROUND AND PURPOSE: A method of using electronic portal imaging to design compensators for tangential breast irradiation has been developed. We describe how this has been implemented. MATERIALS AND METHODS: The compensator design method generates wedged and unwedged beam weights, in conjunction with templates for multiple lead-sheet compensators and pseudo-CT outlines. The latter describe the breast and lung profiles in a set of transverse slices. The layers of the compensator and pseudo-CT outlines are transferred to a treatment planning system for verification. The accuracy of the planning system for the high transmission blocks used to describe the compensators has been verified using a plotting tank system. Dose volume histogram data and transaxial and sagittal plan slices have been compared for both standard and compensated treatments for a sample set of five patients. RESULTS: The planning system predicted the dose at depths of 1.5 and 5 cm to within 2% for the compensators tested. The biggest source of discrepancy was a consequence of the planning system requiring blocks to have integer percentage transmission. For all patients studied, the compensated treatment resulted in a significant reduction in the percentage volume outside the 95-105% dose, with an average reduction of 10.2%. The percentage volume outside the 95-107% dose was also reduced by typically 3.4%. The implementation was found to yield a convenient automatic method of designing compensators using electronic portal imaging and verifying the results using a planning system. CONCLUSIONS: These results indicate that this method of implementation can be used in practice. The dosimetric accuracy of the treatment planning system is limited by the requirement that blocks should be of integer transmission, but this effect is small.
Zin HM, Konstantinidis AC, Harris EJ, Osmond JPF, Olivo A, Bohndiek SE, Clark AT, Turchetta R, Guerrini N, Crooks J, Allinson NM, Speller R, Evans PM (2010) Characterisation of regional variations in a stitched CMOS active pixel sensor, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 620 (2-3) pp. 540-548
McQuaid D, Partridge M, Symonds-Tayler JR, Evans PM, Webb S (2009) Target-tracking deliveries on an Elekta linac: a feasibility study, PHYSICS IN MEDICINE AND BIOLOGY 54 (11) pp. 3563-3578
Harris EJ, Miller NR, Bamber JC, Evans PM, Symonds-Tayler JRN (2007) Performance of ultrasound based measurement of 3D displacement using a curvilinear probe for organ motion tracking, PHYSICS IN MEDICINE AND BIOLOGY 52 (18) pp. 5683-5703 IOP PUBLISHING LTD
Parent L, Seco J, Evans PM, Dance DR, Fielding A (2006) Evaluation of two methods of predicting MLC leaf positions using EPID measurements, MEDICAL PHYSICS 33 (9) pp. 3174-3182 American Association of Physicists in Medicine
Poludniowski GG, Evans PM (2013) Optical photon transport in powdered-phosphor scintillators. Part 1. Multiple-scattering and validity of the Boltzmann transport equation., Med Phys 40 (4) American Association of Physicists in Medicine
Purpose: In Part 1 of this two-part work, predictions for light transport in powdered-phosphor screens are made, based on three distinct approaches. Predictions of geometrical optics-based ray tracing through an explicit microscopic model (EMM) for screen structure are compared to a Monte Carlo program based on the Boltzmann transport equation (BTE) and Swank's diffusion equation solution. The purpose is to: (I) highlight the additional assumptions of the BTE Monte Carlo method and Swank's model (both previously used in the literature) with respect to the EMM approach; (II) demonstrate the equivalences of the approaches under well-defined conditions and; (III) identify the onset and severity of any discrepancies between the models. A package of computer code (called phsphr) is supplied which can be used to reproduce the BTE Monte Carlo results presented in this work.Methods: The EMM geometrical optics ray-tracing model is implemented for hypothesized microstructures of phosphor grains in a binder. The BTE model is implemented as a Monte Carlo program with transport parameters, derived from geometrical optics, as inputs. The analytical solution of Swank to the diffusion equation is compared to the EMM and BTE predictions. Absorbed fractions and MTFs are calculated for a range of binder-to-phosphor relative refractive indices (n = 1.1-5.0), screen thicknesses (t = 50-200 ¼m), and packing fill factors (pf = 0.04-0.54).Results: Disagreement between the BTE and EMM approaches increased with n and pf. For the largest relative refractive index (n = 5) and highest packing fill (pf = 0.5), the BTE model underestimated the absorbed fraction and MTF50, by up to 40% and 20%, respectively. However, for relative refractive indices typical of real phosphor screens (n d 2), such as Gd2O2S:Tb, the BTE and EMM predictions agreed well at all simulated packing densities. In addition, Swank's model agreed closely with the BTE predictions when the screen was thick enough to be considered turbid.Conclusions: Although some assumptions of the BTE are violated in realistic powdered-phosphor screens, these appear to lead to negligible effects in the modeling of optical transport for typical phosphor and binder refractive indices. Therefore it is reasonable to use Monte Carlo codes based on the BTE to treat this problem. Furthermore, Swank's diffusion equation solution is an adequate approximation if a turbidity condition, presented here, is satisfied.
O'Shea TP, Garcia LJ, Rosser KE, Harris EJ, Evans PM, Bamber JC (2014) 4D ultrasound speckle tracking of intra-fraction prostate motion: A phantom-based comparison with x-ray fiducial tracking using CyberKnife, Physics in Medicine and Biology 59 (7) pp. 1701-1720
This study investigates the use of a mechanically-swept 3D ultrasound (3D-US) probe for soft-tissue displacement monitoring during prostate irradiation, with emphasis on quantifying the accuracy relative to CyberKnife® x-ray fiducial tracking. An US phantom, implanted with x-ray fiducial markers was placed on a motion platform and translated in 3D using five real prostate motion traces acquired using the Calypso system. Motion traces were representative of all types of motion as classified by studying Calypso data for 22 patients. The phantom was imaged using a 3D swept linear-array probe (to mimic trans-perineal imaging) and, subsequently, the kV x-ray imaging system on CyberKnife. A 3D cross-correlation block-matching algorithm was used to track speckle in the ultrasound data. Fiducial and US data were each compared with known phantom displacement. Trans-perineal 3D-US imaging could track superior-inferior (SI) and anterior-posterior (AP) motion to d0.81 mm root-mean-square error (RMSE) at a 1.7 Hz volume rate. The maximum kV x-ray tracking RMSE was 0.74 mm, however the prostate motion was sampled at a significantly lower imaging rate (mean: 0.04 Hz). Initial elevational (right-left; RL) US displacement estimates showed reduced accuracy but could be improved (RMSE
Donovan EM, Yarnold JR, Adams EJ, Morgan A, Warrington APJ, Evans PM (2008) An investigation into methods of IMRT planning applied to breast radiotherapy, BRITISH JOURNAL OF RADIOLOGY 81 (964) pp. 311-322 BRITISH INST RADIOLOGY
Seco J, Evans PM, Webb S (2002) An optimization algorithm that incorporates IMRT delivery constraints., Phys Med Biol 47 (6) pp. 899-915
An intensity-modulated beam optimization algorithm is presented which incorporates the delivery constraints into the optimization cycle. The optimization algorithm is based on the quasi-Newton method of iteratively solving minimization problems. The developed algorithm iteratively corrects the incident, pencil-beam-like, fluence to incorporate the delivery constraints. In the present study, the goal of the optimization algorithm is to achieve the best deliverable radiotherapy plan, subject to the constraints of the delivery technique described by a leaf-sequencing algorithm being applied concurrently. In general, if they are applied after, rather than during, the optimization cycle, the delivery constraints associated with the IMRT technique can produce local variations up to 6% in the 'optimized' dose (i.e., distribution without applied constraints) and reduce the degree of conformity, of the dose, to the PTV region. The optimization method has been applied to three IMRT delivery techniques: dynamic multileaf (DMLC), multiple-static-field (MSF) and slice-by-slice tomotherapy (NOMOS MIMiC). The beam profiles were generated for a prostate tumour with organs at risk being the rectum, bladder and femoral heads. The optimization method described was shown to generate optimum and deliverable IMRT plans for these three delivery techniques. In the case of the DMLC and MSF the optimization converged within 3-5 iterations to a mean PTV dose of 69.60 +/- 1.34 Gy and 69.71 +/- 1.34 Gy, respectively, while for NOMOS MIMiC approximately 10 iterations were needed to obtain 69.68 +/- 1.55 Gy. In addition to this, the IMRT optimization also yielded optimum fluence profiles when clustering was performed concurrently with the leaf-sequencer. An optimum between 8 and 15 clusters of equal fluence 'intensity' was shown to establish the best compromise between the number of fluence levels and the PTV dose coverage.
Castellano IA, Dance DR, Skinner CL, Evans PM (2005) Patient radiation doses for electron beam CT, MEDICAL PHYSICS 32 (8) pp. 2517-2527 AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS
Harris EJ, Donovan EM, Coles CE, de Boer HCJ, Poynter A, Rawlings C, Wishart GC, Evans PM (2012) How does imaging frequency and soft tissue motion affect the PTV margin size in partial breast and boost radiotherapy?, RADIOTHERAPY AND ONCOLOGY 103 (2) pp. 166-171
Yamold J, Donovan E, Bleackley N, Reise S, Peckitt C, Patel S, Sharp G, Ross G, Tait D, Evans P (2005) Randomised trial of standard 2D radiotherapy (RT) versus 3D intensity modulated radiotherapy (IMRT) in patients prescribed breast radiotherapy, EJC SUPPLEMENTS 3 (2) pp. 390-390 PERGAMON-ELSEVIER SCIENCE LTD
Evans PM, Symonds-Tayler JR, Colgan R, Hugo GD, Letts N, Sandin C (2010) Gating characteristics of an Elekta radiotherapy treatment unit measured with three types of detector., Phys Med Biol 55 (8) pp. N201-N210 Institute of Physics
The characteristics of an Elekta Precise treatment machine with a gating interface were investigated. Three detectors were used: a Farmer ionization chamber, a MatriXX ionization chamber array and an in-house, single pulse-measurement ionization chamber (IVC). Measurements were made of dosimetric accuracy, flatness and symmetry characteristics and duty cycle for a range of beam-on times and gating periods. Results were compared with a standard ungated delivery as a reference. For all beam-on times, down to 0.5 s, dosimetric differences were below +/-1% and flatness and symmetry parameter variations were below +/-1.5%. For the shorter beam-on times the in-house detector deviated from the other two detectors, suggesting that this device should be used in conjunction with other detectors for absolute dosimetry purposes. However, it was found to be useful for studying gated beam characteristics pulse by pulse.
Evans PM, Hansen VN, Swindell W (1997) The optimum intensities for multiple static multileaf collimator field compensation., Med Phys 24 (7) pp. 1147-1156
A method of determining the optimum beam intensities for compensation using multiple static multileaf collimator fields is presented. In this method a histogram of the number of beam pixels against beam intensity is generated for the intensity-modulated beam (IMB). The intensity of each beam to be used is chosen to minimize the mean square deviation between each bin in the histogram and the closest beam intensity. This method has been applied to sample IMBs possessing one maximum and two maxima. For both cases, the use of uniform beam intensity increments is shown to be close to optimal. In the case with two maxima, the efficacy of irradiating both peaks simultaneously, rather than separately, has been studied and shown to be of potential benefit. The optimum intensities for an IMB for breast radiotherapy are also presented.
Coolens C, Evans PM, Seco J, Webb S, Blackall JM, Rietzel E, Chen GT (2006) The susceptibility of IMRT dose distributions to intrafraction organ motion: an investigation into smoothing filters derived from four dimensional computed tomography data., Med Phys 33 (8) pp. 2809-2818
This study investigated the sensitivity of static planning of intensity-modulated beams (IMBs) to intrafraction deformable organ motion and assessed whether smoothing of the IMBs at the treatment-planning stage can reduce this sensitivity. The study was performed with a 4D computed tomography (CT) data set for an IMRT treatment of a patient with liver cancer. Fluence profiles obtained from inverse-planning calculations on a standard reference CT scan were redelivered on a CT scan from the 4D data set at a different part of the breathing cycle. The use of a nonrigid registration model on the 4D data set additionally enabled detailed analysis of the overall intrafraction motion effects on the IMRT delivery during free breathing. Smoothing filters were then applied to the beam profiles within the optimization process to investigate whether this could reduce the sensitivity of IMBs to intrafraction organ motion. In addition, optimal fluence profiles from calculations on each individual phase of the breathing cycle were averaged to mimic the convolution of a static dose distribution with a motion probability kernel and assess its usefulness. Results from nonrigid registrations of the CT scan data showed a maximum liver motion of 7 mm in superior-inferior direction for this patient. Dose-volume histogram (DVH) comparison indicated a systematic shift when planning treatment on a motion-frozen, standard CT scan but delivering over a full breathing cycle. The ratio of the dose to 50% of the normal liver to 50% of the planning target volume (PTV) changed up to 28% between different phases. Smoothing beam profiles with a median-window filter did not overcome the substantial shift in dose due to a difference in breathing phase between planning and delivery of treatment. Averaging of optimal beam profiles at different phases of the breathing cycle mainly resulted in an increase in dose to the organs at risk (OAR) and did not seem beneficial to compensate for organ motion compared with using a large margin. Additionally, the results emphasized the need for 4D CT scans when aiming to reduce the internal margin (IM). Using only a single planning scan introduces a systematic shift in the dose distribution during delivery. Smoothing beam profiles either based on a single scan or over the different breathing phases was not beneficial for reducing this shift.
Kirby AM, Evans PM, Helyer SJ, Donovan EM, Convery HM, Yarnold JR (2011) A randomised trial of Supine versus Prone breast radiotherapy (SuPr study): Comparing set-up errors and respiratory motion, RADIOTHERAPY AND ONCOLOGY 100 (2) pp. 221-226
McNair H, Harris E, Evans P (2005) An investigation into the efficacy of automatic marker detection methods applied to intra-fractional prostate motion tracking., RADIOTHERAPY AND ONCOLOGY 76 pp. S58-S58 ELSEVIER IRELAND LTD
Mukesh MB, Harris E, Collette S, Coles CE, Bartelink H, Wilkinson J, Evans PM, Graham P, Haviland J, Poortmans P, Yarnold J, Jena R (2013) Normal tissue complication probability (NTCP) parameters for breast fibrosis: Pooled results from two randomised trials, Radiotherapy and Oncology 108 (2) pp. 293-298
Introduction The dose-volume effect of radiation therapy on breast tissue is poorly understood. We estimate NTCP parameters for breast fibrosis after external beam radiotherapy. Materials and methods We pooled individual patient data of 5856 patients from 2 trials including whole breast irradiation followed with or without a boost. A two-compartment dose volume histogram model was used with boost volume as the first compartment and the remaining breast volume as second compartment. Results from START-pilot trial (n = 1410) were used to test the predicted models. Results 26.8% patients in the Cambridge trial (5 years) and 20.7% patients in the EORTC trial (10 years) developed moderate-severe breast fibrosis. The best fit NTCP parameters were BEUD3(50) = 136.4 Gy, ³50 = 0.9 and n = 0.011 for the Niemierko model and BEUD 3(50) = 132 Gy, m = 0.35 and n = 0.012 for the Lyman Kutcher Burman model. The observed rates of fibrosis in the START-pilot trial agreed well with the predicted rates. Conclusions This large multi-centre pooled study suggests that the effect of volume parameter is small and the maximum RT dose is the most important parameter to influence breast fibrosis. A small value of volume parameter 'n' does not fit with the hypothesis that breast tissue is a parallel organ. However, this may reflect limitations in our current scoring system of fibrosis. © 2013 Elsevier Ireland Ltd. All rights reserved.
Bodey RK, Evans PM, Flux GD (2005) Spatial aspects of combined modality radiotherapy., Radiother Oncol 77 (3) pp. 301-309
BACKGROUND AND PURPOSE: A combined modality radiotherapy (CMRT) incorporates both external beam radiotherapy (EBT) and targeted radionuclide therapy (TRT) components. The spatial aspects of this combination were explored by utilising intensity modulated radiotherapy (IMRT) to provide a non-uniform EBT dose distribution. PATIENTS AND METHODS: Three methods of prescribing the required non-uniform distribution of EBT dose are described, based on both physical and biological criteria according to the distribution of TRT uptake. The results and consequences of these prescriptions are explored by application to three examples of patient data. RESULTS: The planning procedure adopted allowed IMRT plans to be produced that met the prescription requirements. However, when the treatment was planned as a CMRT, compared with the use of EBT alone, more satisfactory target doses could be achieved with lower doses to normal tissues. The effects of errors in EBT delivery and in the functional data were found to cause a non-uniform prescription to tend towards the uniform case. CONCLUSIONS: The methods and results are relevant for more general biological treatment planning, in which IMRT may be used to produce dose distributions prescribed according to tumour function. The effects of delivery and dose calculation errors can have a significant impact on how such treatments should be planned.
McNair HA, Brock J, Symonds-Taylor JRN, Ashley S, Eagle S, Evans PM, Kavanagh A, Panakis N, Brada M (2009) Feasibility of the use of the Active Breathing Co ordinator (TM) (ABC) in patients receiving radical radiotherapy for non-small cell lung cancer (NSCLC), RADIOTHERAPY AND ONCOLOGY 93 (3) pp. 424-429 Elsevier
Smyth G, Evans PM, Bamber JC, Saran FH, Mandeville HC, Bedford JL (2015) Fluence-Based Trajectory Optimization for Non-Coplanar VMAT, MEDICAL PHYSICS 42 (6) pp. 3434-3434 AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS
Harris E, Mukesh M, Jena R, Baker A, Bartelink H, Brooks C, Dean J, Donovan E, Collette S, Eagle S, Fenwick J, Graham P, Haviland J, Kirby A, Mayles H, Mitchell RA, Perry R, Poortmans P, Poynter A, Shentall G, Titley J, Thompson A, Yarnold JR, Coles CE, Evans PM (2014) A multicentre observational study evaluating image-guided radiotherapy for more accurate partial-breast intensity-modulated radiotherapy: comparison with standard imaging technique, Efficacy and Mechanisms Evaluation 1 (3) 1 pp. i-73 NIHR
Whole-breast radiotherapy (WBRT) is the standard treatment for breast cancer following breast-conserving surgery. Evidence shows that tumour recurrences occur near the original cancer: the tumour bed. New treatment developments include increasing dose to the tumour bed during WBRT (synchronous integrated boost) and irradiating only the region around the tumour bed, for patients at high and low risk of tumour recurrence, respectively. Currently, standard imaging uses bony anatomy to ensure accurate delivery of WBRT. It is debatable whether or not more targeted treatments such as synchronous integrated boost and partial-breast radiotherapy require image-guided radiotherapy (IGRT) focusing on implanted tumour bed clips (clip-based IGRT).

Primary ? to compare accuracy of patient set-up using standard imaging compared with clip-based IGRT. Secondary ? comparison of imaging techniques using (1) tumour bed radiotherapy safety margins, (2) volume of breast tissue irradiated around tumour bed, (3) estimated breast toxicity following development of a normal tissue control probability model and (4) time taken.

Multicentre observational study embedded within a national randomised trial: IMPORT-HIGH (Intensity Modulated and Partial Organ Radiotherapy ? HIGHer-risk patient group) testing synchronous integrated boost and using clip-based IGRT.

Five radiotherapy departments, participating in IMPORT-HIGH.

Two-hundred and eighteen patients receiving breast radiotherapy within IMPORT-HIGH.

There was no direct intervention in patients? treatment. Experimental and control intervention were clip-based IGRT and standard imaging, respectively. IMPORT-HIGH patients received clip-based IGRT as routine; standard imaging data were obtained from clip-based IGRT images.

Main outcome measures
Difference in (1) set-up errors, (2) safety margins, (3) volume of breast tissue irradiated, (4) breast toxicity and (5) time, between clip-based IGRT and standard imaging.

The primary outcome of overall mean difference in clip-based IGRT and standard imaging using daily set-up errors was 2?2.6 mm (p

Lewis DG, Swindell W, Morton EJ, Evans PM, Xiao ZR (1992) A megavoltage CT scanner for radiotherapy verification., Phys Med Biol 37 (10) pp. 1985-1999
We have further developed a system for generating megavoltage CT images immediately prior to the administration of external beam radiotherapy. The detector is based on the scanner of Simpson (Simpson et al 1982)--the major differences being a significant reduction in dose required for image formation, faster image formation and greater convenience of use in the clinical setting. Attention has been paid to the problem of ring artefacts in the images. Specifically, a Fourier-space filter has been applied to the sinogram data. After suitable detector calibration, it has been shown that the device operates close to its theoretical specification of 3 mm spatial resolution and a few percent contrast resolution. Ring artefacts continue to be a major source of image degradation. A number of clinical images have been presented. The next stage of this work is to use the system to make clinical measurements of patient set-up inaccuracies building on our work making such measurements from digital portal images (Evans et al 1992).
Webb S, Evans PM, Swindell W, Deasy JO (1994) A proof that uniform dose gives the greatest TCP for fixed integral dose in the planning target volume., Phys Med Biol 39 (11) pp. 2091-2098
In this note it is shown that for a fixed integral dose to the planning target volume, the highest tumour control probability (TCP) arises when the dose is spatially uniform. This 'uniform dose theorem' is proved both for (i) a specific TCP model based on Poisson/independent voxel statistics, and (ii) any model for voxel control probability having a specific shape with respect to increasing dose.
McQuaid D, Partridge M, Symonds-Tayler JRN, Evans PM, Webb S (2009) Experimental Validation of a Target Tracking IMRT Delivery with Conventional MLCs, CLINICAL ONCOLOGY 21 (3) pp. 243-244 Elsevier
Introduction: This study assessed complex, target-tracking, intensity-
modulated delivery by the Elekta MLCi system. For treatment
sites where intrafraction tissue motion is a significant problem,
target-tracking deliveries have the potential of reducing motion
margins used in radiotherapy planning.
Method: A toroidally shaped target surrounding an organ at risk
(OAR), necessitating multiple field segments to irradiate the target
and spare the OAR, was defined in a solid water phantom. The
phantom was programmed to move in a reproducible 2D elliptical
trajectory. A static and target-tracking delivery were planned for
delivery on a standard Elekta Precise series linac with integrated
MLCi system. Dose was delivered in 3 ways: (i) static delivery to the
static phantom, (ii) static delivery to the moving phantom and
(iii) tracking delivery to a moving phantom, and was assessed by
film measurement. The dose delivery was quantified by measurement
of the mean and standard deviation of the dose on the central
plane through the target.
Results: The mean target doses measured were: 100% 2.8%,
95.8% 7.2% and 98.5% 2.6%, respectively, for the three cases
listed above, whereas the mean doses to the OAR from the three
delivery scenarios were: 38.2% 24.4%, 54.0% 18.1% and 38.2% 19.7%. All dose measurements are quoted relative to the static
target dose from a static delivery.
Conclusion: Target-tracking deliveries have been shown to be
realisable on the current generation of Elekta linacs. The tracking
techniques have been shown to remove the negative effects of
tissue motion. In this case, reducing the mean dose to the OAR by
15.8% whilst restoring the target dose homogeneity to the static
case. However, many obstacles remain before the technique can
be safely used in the clinic and these are the subject of further
research in the field.
Roberts DA, Hansen VN, Thompson MG, Poludniowski G, Niven A, Seco J, Evans PM (2011) Comparative study of a low-Z cone-beam computed tomography system., Phys Med Biol 56 (14) pp. 4453-4464 Institute of Physics
Computed tomography images have been acquired using an experimental (low atomic number (Z) insert) megavoltage cone-beam imaging system. These images have been compared with standard megavoltage and kilovoltage imaging systems. The experimental system requires a simple modification to the 4 MeV electron beam from an Elekta Precise linac. Low-energy photons are produced in the standard medium-Z electron window and a low-Z carbon electron absorber located after the window. The carbon electron absorber produces photons as well as ensuring that all remaining electrons from the source are removed. A detector sensitive to diagnostic x-ray energies is also employed. Quantitative assessment of cone-beam computed tomography (CBCT) contrast shows that the low-Z imaging system is an order of magnitude or more superior to a standard 6 MV imaging system. CBCT data with the same contrast-to-noise ratio as a kilovoltage imaging system (0.15 cGy) can be obtained in doses of 11 and 244 cGy for the experimental and standard 6 MV systems, respectively. Whilst these doses are high for everyday imaging, qualitative images indicate that kilovoltage like images suitable for patient positioning can be acquired in radiation doses of 1-8 cGy with the experimental low-Z system.
Parent L, Evans P, Dance DR, Fielding A, Seco J (2004) Effect of spectral variation with field size on dosimetric response of an amorphous silicon electronic portal imaging device, RADIOTHERAPY AND ONCOLOGY 73 pp. S154-S155 ELSEVIER IRELAND LTD
Coolens C, Webb S, Shirato H, Nishioka K, Evans PM (2008) A margin model to account for respiration-induced tumour motion and its variability., Phys Med Biol 53 (16) pp. 4317-4330
In order to reduce the sensitivity of radiotherapy treatments to organ motion, compensation methods are being investigated such as gating of treatment delivery, tracking of tumour position, 4D scanning and planning of the treatment, etc. An outstanding problem that would occur with all these methods is the assumption that breathing motion is reproducible throughout the planning and delivery process of treatment. This is obviously not a realistic assumption and is one that will introduce errors. A dynamic internal margin model (DIM) is presented that is designed to follow the tumour trajectory and account for the variability in respiratory motion. The model statistically describes the variation of the breathing cycle over time, i.e. the uncertainty in motion amplitude and phase reproducibility, in a polar coordinate system from which margins can be derived. This allows accounting for an additional gating window parameter for gated treatment delivery as well as minimizing the area of normal tissue irradiated. The model was illustrated with abdominal motion for a patient with liver cancer and tested with internal 3D lung tumour trajectories. The results confirm that the respiratory phases around exhale are most reproducible and have the smallest variation in motion amplitude and phase (approximately 2 mm). More importantly, the margin area covering normal tissue is significantly reduced by using trajectory-specific margins (as opposed to conventional margins) as the angular component is by far the largest contributor to the margin area. The statistical approach to margin calculation, in addition, offers the possibility for advanced online verification and updating of breathing variation as more data become available.
Webb S, Evans PM (2006) Innovative techniques in radiation therapy: Editorial, overview, and crystal ball gaze to the future, SEMINARS IN RADIATION ONCOLOGY 16 (4) pp. 193-198
Partridge M, Evans PM, Symonds-Tayler JR (1999) Optical scattering in camera-based electronic portal imaging., Phys Med Biol 44 (10) pp. 2381-2396
An investigation of scintillation light scattering within camera-based electronic portal imaging devices is presented. A simple analytical scatter model is adapted for the precise geometries of two different camera-based imaging systems and the results of modelling and experimental measurements are compared. The results of the study strongly suggest that the main source of optical scattering is multiple reflection between the scintillation screen and 45 degree mirror in both systems. The scattered light has a highly non-uniform distribution, which is strongly dependent upon field size. For large radiation fields the scatter contribution can be over 20% of the primary signal scintillation light intensity in the centre of the field. A purely optical method of removing the scattered light signal using a louvre grid on the surface of the scintillation screen is then presented and experimentally demonstrated to be effective.
Parent L, Fielding AL, Dance DR, Seco J, Evans PM (2007) Amorphous silicon EPID calibration for dosimetric applications: comparison of a method based on Monte Carlo prediction of response with existing techniques, PHYSICS IN MEDICINE AND BIOLOGY 52 (12) pp. 3351-3368 Institute of Physics
Poludniowski G, Landry G, DeBlois F, Evans PM, Verhaegen F (2009) SpekCalc: a program to calculate photon spectra from tungsten anode x-ray tubes., Physics in Medicine and Biology 54 (19) pp. N433-N438 Institute of Physics
A software program, SpekCalc, is presented for the calculation of x-ray spectra from tungsten anode x-ray tubes. SpekCalc was designed primarily for use in a medical physics context, for both research and education purposes, but may also be of interest to those working with x-ray tubes in industry. Noteworthy is the particularly wide range of tube potentials (40-300 kVp) and anode angles (recommended: 6-30 degrees) that can be modelled: the program is therefore potentially of use to those working in superficial/orthovoltage radiotherapy, as well as diagnostic radiology. The utility is free to download and is based on a deterministic model of x-ray spectrum generation (Poludniowski 2007 Med. Phys. 34 2175). Filtration can be applied for seven materials (air, water, Be, Al, Cu, Sn and W). In this note SpekCalc is described and illustrative examples are shown. Predictions are compared to those of a state-of-the-art Monte Carlo code (BEAMnrc) and, where possible, to an alternative, widely-used, spectrum calculation program (IPEM78).
Osmond JPF, Lupica G, Harris EJ, Zin H, Allinson NM, Evans PM (2011) High-Speed Tracking of Moving Markers During Radiotherapy Using a CMOS Active Pixel Sensor, INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 81 (2) pp. S763-S764 Elsevier
Purpose/Objective(s): In order to minimize the dose delivered to healthy tissue near amoving tumor during radiotherapy it is first
necessary to accurately measure tumor position as a function of time. For example, a portal imager can be used to detect surrogate
markers implanted around the tumor in order to track its motion with a moving collimator. Lung tumors can move at up to 30
mm/s, requiring a sampling rate of 30 frame/s to achieve mm accuracy. However the passive a-Si Flat Panel Imagers (FPIs) available
with current linear accelerators operate at 2 - 10 frames/s, significantly slower than the required rate. Furthermore a-Si FPIs
provide low image quality at their fastest frame rates and are susceptible to damage by the treatment beam, requiring replacement
every 1 - 2 years. Emerging CMOS active pixel sensors use an addressable and partial read-out architecture to achieve significantly
improved frame-rates relative to their passive counterparts. They are also capable of higher resolution, image quality
and radiation-hardness. This study investigates the feasibility of using a CMOS APS to quickly and accurately track radio-opaque
markers during radiotherapy.
Materials/Methods: A custom CMOS imaging system was designed and constructed in collaboration with the MI3 consortium.
The performance of this system was characterized and compared with an a-Si FPI. Four cylindrical gold markers of diameter 0.8
to 2 mm and length 8 mm were positioned on a motion-platform and moved according to the Lujan approximation to respiratory motion. Images were acquired using the megavoltage treatment beam at a range of frame and dose rates. The success rate of an
automatic detection routine, absolute mean-error from the expected position and contrast-to-noise ratio of the marker images were
then evaluated as a function of marker size, marker speed, frame rate and dose rate.
Results: TheCMOSimager was found to offer improved resolution and signal-to-noise than the standard a-Si FPI at a comparable
dose. The long integration time of the FPI resulted in marker images being too blurred to detect. The CMOS was able to detect the
three largest markers 100% of the time and estimate their position to within 0.3 mm at 150 - 300 MU/min and 20 - 50 frame/s.
However success rate declined with decreasing dose or frame rate.
Conclusions: A CMOS megavoltage imaging system was found to offer superior signal-noise and resolution than the standard
a-Si FPI. Furthermore the high speed of C
Evans PM, Partridge M (2000) A method of improving the spatial resolution of treatments that involve a multileaf collimator., Phys Med Biol 45 (3) pp. 609-622
In this paper we present a novel method of reducing the dosimetric effects of the finite leaf width of a multileaf collimator (MLC) in conformal and intensity modulated radiotherapy (IMRT). This is achieved by decomposing the required high-resolution fluence distribution into two orthogonal components, which are delivered with two leaf sweeps with head-twists differing by 90 degrees. Before the decomposition stage, a filter is applied to the required beam to force it to have a constant gradient in the two delivery directions. The component deliveries were found to be very spiky in nature, resulting in very inefficient delivery with the scanning leaves of our MLC. This method was evaluated using film dosimetry of four idealized beams: a 45 degree edge, a circle, a hemispherical intensity modulated beam (IMB) and a sine-like IMB. The measurements showed that this method had significantly reduced the effects of the 1 cm leaf width of our MLC at the 50% isodose level, but there was significant overdosage at the edge of the field and immediately inside the held edge. This method shows promise but further work is required before it may find clinical utility.
Juneja P, Harris EJ, Kirby AM, Evans PM (2012) Adaptive Breast Radiation Therapy Using Modeling of Tissue Mechanics: A Breast Tissue Segmentation Study, INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 84 (3) pp. E419-E425 ELSEVIER SCIENCE INC
Panakis N, McNair H, Mendes R, Symonds-Tayler R, Evans P, Bedford J, Brada M (2006) Radiotherapy treatment margins for non-small cell lung cancer (NSCLC): Controlling tumour motion with active breathing control (ABC) cannot be considered in isolation, RADIOTHERAPY AND ONCOLOGY 81 pp. S395-S395 ELSEVIER IRELAND LTD
Nioutsikou E, Seppenwoolde Y, Symonds-Tayler R, Heijmen B, Evans P, Webb S (2007) Dosimetric investigation of lung tumour motion compensation with the cyberknife/synchrony respiratory tracking system measured experimentally, RADIOTHERAPY AND ONCOLOGY 84 pp. S76-S77 ELSEVIER IRELAND LTD
Hector CL, Evans PM, Webb S (2000) The dosimetric consequences of patient movement on three classes of intensity-modulated delivery techniques in breast radiotherapy, USE OF COMPUTERS IN RADIATION THERAPY pp. 289-291 SPRINGER-VERLAG BERLIN
Esposito M, Anaxagoras T, Evans PM, Green S, Manolopoulos S, Nieto-Camero J, Parker DJ, Poludniowski G, Price T, Waltham C, Allinson NM (2015) CMOS Active Pixel Sensors as energy-range detectors for proton Computed Tomography, JOURNAL OF INSTRUMENTATION 10 IOP PUBLISHING LTD
Since the first proof of concept in the early 70s, a number of technologies has been proposed to perform proton CT (pCT), as means of mapping tissue stopping power for accurate treatment planning in proton therapy. Previous prototypes of energy-range detectors for pCT have been mainly based on the use of scintillator-based calorimeters, to measure proton residual energy. However, such an approach is limited by the need for only a single proton passing through the
energy-range detector per read-out cycle. A novel approach to this problem could be the use of pixelated detectors, where the independent read-out of each pixel allows to measure simultaneously
the residual energy of a number of protons in the same read-out cycle, facilitating a faster and more efficient pCT scan.
This paper investigates the suitability of CMOS Active Pixel Sensors (APSs) to track individual protons as they go through a number of CMOS layers, forming an energy-range telescope. Measurements performed at the iThemba Laboratories will be presented and analysed in terms of
correlation, to confirm capability of proton tracking for CMOS APSs.
Harris E, Miller N, Evans P, Bamber J, Symonds-Tayler R (2007) Performance of ultrasound based 3D intra-fraction organ motion tracking, RADIOTHERAPY AND ONCOLOGY 84 pp. S176-S176 ELSEVIER IRELAND LTD
Partridge M, Evans PM, van Herk M, Ploeger LS, Budgell GJ, James HV (2000) Leaf position verification during dynamic beam delivery: a comparison of three applications using electronic portal imaging., Med Phys 27 (7) pp. 1601-1609
The use of a dynamic multileaf collimator (MLC) to deliver intensity-modulated beams presents a problem for conventional verification techniques. The use of electronic portal imaging to track MLC leaves during beam delivery has been shown to provide a solution to this problem. An experimental comparison of three different verification systems, each using a different electronic portal imaging technology, is presented. Two of the systems presented are commercially available imagers with in-house modifications, with the third system being an in-house built experimental system. The random and systematic errors present in each of the verifications systems are measured and presented, together with the study of the effects of varying dose rate and leaf speed on verification system performance. The performance of the three systems is demonstrated to be very similar, with an overall accuracy in comparing measured and prescribed collimator trajectories of approximately +/-1.0 mm. Systematic errors in the percentage delivered dose signal provided by the accelerator are significant and must be corrected for good performance of the current systems. It is demonstrated that, with suitable modifications, commercially available portal imaging systems can be used to verify dynamic MLC beam delivery.
Muller L, Adams E, Evans P, Partridge M, Pichenot M, Anebajagane SK, Lefkopoulos D, Monti AF (2003) Clinical implementation of a new IMRT verification concept, RADIOTHERAPY AND ONCOLOGY 68 pp. S105-S106 ELSEVIER IRELAND LTD
Flampouri S, Evans PM, Verhaegen F, Nahum AE, Spezi E, Partridge M (2002) Optimization of accelerator target and detector for portal imaging using Monte Carlo simulation and experiment., Phys Med Biol 47 (18) pp. 3331-3349
Megavoltage portal images suffer from poor quality compared to those produced with kilovoltage x-rays. Several authors have shown that the image quality can be improved by modifying the linear accelerator to generate more low-energy photons. This work addresses the problem of using Monte Carlo simulation and experiment to optimize the beam and detector combination to maximize image quality for a given patient thickness. A simple model of the whole imaging chain was developed for investigation of the effect of the target parameters on the quality of the image. The optimum targets (6 mm thick aluminium and 1.6 mm copper) were installed in an Elekta SL25 accelerator. The first beam will be referred to as A16 and the second as Cu1.6. A tissue-equivalent contrast phantom was imaged with the 6 MV standard photon beam and the experimental beams with standard radiotherapy and mammography film/screen systems. The arrangement with a thin Al target/mammography system improved the contrast from 1.4 cm bone in 5 cm water to 19% compared with 2% for the standard arrangement of a thick, high-Z target/radiotherapy verification system. The linac/phantom/detector system was simulated with the BEAM/EGS4 Monte Carlo code. Contrast calculated from the predicted images was in good agreement with the experiment (to within 2.5%). The use of MC techniques to predict images accurately, taking into account the whole imaging system, is a powerful new method for portal imaging system design optimization.
Gulliford S, Morgan R, Sydes M, Partridge M, Webb S, Dearnaley D, Evans P (2007) Dose-volume relationships for common late rectal complications resulting from radiotherapy for prostate cancer: Analysis of data from a multi-centre randomised controlled trial (MRC RT01, ISRCTN 47772397), RADIOTHERAPY AND ONCOLOGY 84 pp. S157-S157 ELSEVIER IRELAND LTD
Harris E, Evans P, Seco J (2005) Analytical model of electronic portal imaging device response, RADIOTHERAPY AND ONCOLOGY 76 pp. S199-S199 ELSEVIER IRELAND LTD
Hansen VN, Swindell W, Evans PM (1997) Extraction of primary signal from EPIDs using only forward convolution., Med Phys 24 (9) pp. 1477-1484
A model is presented in which the scatter signal in images obtained obtained by electronic portal imaging devices (EPIDs) is removed by a forward convolution method. The convolution kernel, kt(r) is a cylindrically symmetric kernel, generated by Monte Carlo, representing the scattered signal of a pencil beam at the image plane after the photons have gone through an object of thickness, t. A set of the kernels is presented and used to extract the primary signal. The signal from primary photons in the image, P(r), is extracted by an iterative method in which the essential assumption is that the scatter signal S(r) can be described by a superposition of the signal that would be obtained with the object removed from the beam, O(r), and the kernel kt(r). The thickness, t, that is used to choose the kernel, is directly related to P(r) by a simple exponential relationship; hence the thickness, t, of the object and the primary signal, P(r), are both iterated to better estimates through this procedure. The model is tested on Monte Carlo simulated data, where the extracted primary signal is compared with the "true" primary signal. Results are presented for a set of phantoms of uniform thicknesses up to 35 cm, and for field areas up to 320 cm(2), and for an inhomogeneous phantom containing a sphere of different density. The primary signal can be extracted to better than 1.5%, even when the original Scatter-to-Primary Ratio (SPR) is more than 25%. Finally, we have tested the model on EPID images, a nonuniform (breast) phantom is presented here. The breast phantom both have a curved external contour and contains a structure of a different density (lung). The radiological thickness of this breast phantom, as extracted using the above convolution model, was found to be within 2.8 mm (1 sd) of the true radiological thickness.
Fielding A, Evans P, Clark C (2004) Verification of patient position and delivery of IMRT by electronic portal imaging, RADIOTHERAPY AND ONCOLOGY 73 (3) pp. 339-347 ELSEVIER SCI IRELAND LTD
BACKGROUND AND PURPOSE: The purpose of the work presented in this paper was to determine whether patient positioning and delivery errors could be detected using electronic portal images of intensity modulated radiotherapy (IMRT). PATIENTS AND METHODS: We carried out a series of controlled experiments delivering an IMRT beam to a humanoid phantom using both the dynamic and multiple static field method of delivery. The beams were imaged, the images calibrated to remove the IMRT fluence variation and then compared with calibrated images of the reference beams without any delivery or position errors. The first set of experiments involved translating the position of the phantom both laterally and in a superior/inferior direction a distance of 1, 2, 5 and 10 mm. The phantom was also rotated 1 and 2 degrees . For the second set of measurements the phantom position was kept fixed and delivery errors were introduced to the beam. The delivery errors took the form of leaf position and segment intensity errors. RESULTS: The method was able to detect shifts in the phantom position of 1 mm, leaf position errors of 2 mm, and dosimetry errors of 10% on a single segment of a 15 segment IMRT step and shoot delivery (significantly less than 1% of the total dose). CONCLUSIONS: The results of this work have shown that the method of imaging the IMRT beam and calibrating the images to remove the intensity modulations could be a useful tool in verifying both the patient position and the delivery of the beam.
Flampouri S, McNair HA, Donovan EM, Evans PM, Partridge M, Verhaegen F, Nutting CM (2005) Initial patient imaging with an optimised radiotherapy beam for portal imaging., Radiother Oncol 76 (1) pp. 63-71
BACKGROUND AND PURPOSE: To investigate the feasibility and the advantages of a portal-imaging mode on a medical accelerator, consisting of a thin low-Z bremsstrahlung target and a thin Gd2O2S/film detector, for patient imaging. PATIENTS AND METHODS: The international code of practice for high-energy photon dosimetry was used to calibrate dosimetry instruments for the imaging beam produced by 4.75 MeV electrons hitting a 6mm thick aluminium target. Images of the head and neck of a humanoid phantom were taken with a mammography film system and the dose in the phantom was measured with TLDs calibrated for this beam. The first head and neck patient images are compared with conventional images (taken with the treatment beam on a film radiotherapy verification detector). Visibility of structures for six patients was evaluated. RESULTS: Images of the head and neck of a humanoid phantom, taken with both imaging systems showed that the contrast increased dramatically for the new system while the dose required to form an image was less than 10(-2)Gy. The patient images taken with the new and the conventional systems showed that air-tissue interfaces were better defined in the new system image. Anatomical structures, visible on both films, are clearer with the new system. Additionally, bony structures, such as vertebrae, were clearly visible only with the new system. The system under evaluation was significantly better for all features in lateral images and most features in anterior images. CONCLUSIONS: This pilot study of the new portal imaging system showed the image quality is significantly improved.
Mcnair HA, Hansen VN, Parker CC, Evans PM, Norman A, Miles E, Harris EJ, Del-Acroix L, Smith E, Keane R, Khoo VS, Thompson AC, Dearnaley DP (2008) A comparison of the use of bony anatomy and internal markers for offline verification and an evaluation of the potential benefit of online and offline verification protocols for prostate radiotherapy, INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 71 (1) pp. 41-50 ELSEVIER SCIENCE INC
Morton EJ, Evans PM, Ferraro M, Young EF, Swindell W (1991) Development of video frame store and distortion correction facilities for an external-beam radiotherapy treatment simulator., Br J Radiol 64 (764) pp. 747-750
Evans PM, Bleackley N, Convery DJ, Donovan EM, Hansen VN, Partridge M, Reise S, Symonds-Tayler JRN, Yarnold JR (2000) The use of compensators and multiple static fields for IMRT of the breast, USE OF COMPUTERS IN RADIATION THERAPY pp. 208-209 SPRINGER-VERLAG BERLIN
Coolens C, Evans PM, Seco J, Webb S, Blackall J, Rietzel E, Chen GTY (2004) Susceptibility of IMRT dose distributions to deformable organ motion and the impact of beam smoothing, RADIOTHERAPY AND ONCOLOGY 73 pp. S176-S177 ELSEVIER IRELAND LTD
Poludniowski GG, Evans PM (2013) Optical photon transport in powdered-phosphor scintillators. Part II. Calculation of single-scattering transport parameters., Med Phys 40 (4) American Association of Physicists in Medicine
Purpose: Monte Carlo methods based on the Boltzmann transport equation (BTE) have previously been used to model light transport in powdered-phosphor scintillator screens. Physically motivated guesses or, alternatively, the complexities of Mie theory have been used by some authors to provide the necessary inputs of transport parameters. The purpose of Part II of this work is to: (i) validate predictions of modulation transform function (MTF) using the BTE and calculated values of transport parameters, against experimental data published for two Gd2O2S:Tb screens; (ii) investigate the impact of size-distribution and emission spectrum on Mie predictions of transport parameters; (iii) suggest simpler and novel geometrical optics-based models for these parameters and compare to the predictions of Mie theory. A computer code package called phsphr is made available that allows the MTF predictions for the screens modeled to be reproduced and novel screens to be simulated.Methods: The transport parameters of interest are the scattering efficiency (Qsct), absorption efficiency (Qabs), and the scatter anisotropy (g). Calculations of these parameters are made using the analytic method of Mie theory, for spherical grains of radii 0.1-5.0 ¼m. The sensitivity of the transport parameters to emission wavelength is investigated using an emission spectrum representative of that of Gd2O2S:Tb. The impact of a grain-size distribution in the screen on the parameters is investigated using a Gaussian size-distribution (Ã = 1%, 5%, or 10% of mean radius). Two simple and novel alternative models to Mie theory are suggested: a geometrical optics and diffraction model (GODM) and an extension of this (GODM+). Comparisons to measured MTF are made for two commercial screens: Lanex Fast Back and Lanex Fast Front (Eastman Kodak Company, Inc.).Results: The Mie theory predictions of transport parameters were shown to be highly sensitive to both grain size and emission wavelength. For a phosphor screen structure with a distribution in grain sizes and a spectrum of emission, only the average trend of Mie theory is likely to be important. This average behavior is well predicted by the more sophisticated of the geometrical optics models (GODM+) and in approximate agreement for the simplest (GODM). The root-mean-square differences obtained between predicted MTF and experimental measurements, using all three models (GODM, GODM+, Mie), were within 0.03 for both Lanex screens in all cases. This is e
Partridge M, Evans PM, Mosleh-Shirazi A, Convery D (1998) Independent verification using portal imaging of intensity-modulated beam delivery by the dynamic MLC technique., Med Phys 25 (10) pp. 1872-1879
The use of intensity-modulated radiation fields in radiotherapy treatment has been shown to have the potential to deliver highly conformal dose distributions. One technique for delivering these intensity-modulated beams is a computerized dynamic multileaf collimator (MLC). A major current impediment to the development of dynamic MLC therapy is verification of these highly complex treatments. Electronic portal imaging is shown here to be a solution to this verification problem. Experimental results are presented showing that leaf penumbra measured with a portal imager can be used to accurately define the positions of moving leaves. The random error in these leaf positions is compared with mean leaf positions along each leaf bank and specified leaf positions at prescription control points to check mechanical performance. Individual leaves are also checked for systematic motion errors. All leaf positions are found to be well within the manufacturer's specifications at all times. Finally, integral intensity images are presented that can be related to the dose distribution delivered. Portal imaging is shown to have the potential to become a valuable tool for the verification of dynamic MLC irradiation.
Panakis N, McNair HA, Christian JA, Mendes R, Symonds-Tayler JRN, Knowles C, Evans PM, Bedford J, Brada M (2008) Defining the margins in the radical radiotherapy of non-small cell lung cancer (NSCLC) with active breathing control (ABC) and the effect on physical lung parameters, RADIOTHERAPY AND ONCOLOGY 87 (1) pp. 65-73 ELSEVIER IRELAND LTD
Juneja P, Evans PM, Harris EJ (2013) The validation index: A new metric for validation of segmentation algorithms using two or more expert outlines with application to radiotherapy planning, IEEE Transactions on Medical Imaging 32 (8) pp. 1481-1489
Validation is required to ensure automated segmentation algorithms are suitable for radiotherapy target definition. In the absence of true segmentation, algorithmic segmentation is validated against expert outlining of the region of interest. Multiple experts are used to overcome inter-expert variability. Several approaches have been studied in the literature, but the most appropriate approach to combine the information from multiple expert outlines, to give a single metric for validation, is unclear. None consider a metric that can be tailored to case-specific requirements in radiotherapy planning. Validation index (VI), a new validation metric which uses experts' level of agreement was developed. A control parameter was introduced for the validation of segmentations required for different radiotherapy scenarios: for targets close to organs-at-risk and for difficult to discern targets, where large variation between experts is expected. VI was evaluated using two simulated idealized cases and data from two clinical studies. VI was compared with the commonly used Dice similarity coefficient (DSCpair-wise) and found to be more sensitive than the DSCpair-wise to the changes in agreement between experts. VI was shown to be adaptable to specific radiotherapy planning scenarios. © 1982-2012 IEEE.
Evans PM, Partridge M, Symonds-Tayler JR (2001) Sampling considerations for intensity modulated radiotherapy verification using electronic portal imaging., Med Phys 28 (4) pp. 543-552
A model has been developed to describe the sampling process that occurs when intensity modulated radiotherapy treatments (delivered with a multileaf collimator) are imaged with an electronic portal imaging device that acquires a set of frames with a finite dead-time between them. The effects of the imaging duty cycle and frame rate on the accuracy of dosimetric verification have been studied. A frame interval of 1 s with 25%, 50% and 75% duty cycle, and a 50% duty cycle with frame intervals of 1, 2, 4, 8, and 16 s have been studied for a smoothly varying hemispherical intensity profile, and a 50% duty cycle with frame intervals of 1, 2, 4, and 8 s for a pixellated distribution. In addition an intensity modulated beam for breast radiotherapy has been modeled and imaged for 0.33 s frame time and 1, 2, and 3 s frame separation. The results show that under sparse temporal sampling conditions, errors of the order of 10% may ensue and occur with an oscillatory pattern. For the beams studied, imaging with a 1 or 2 s frame interval resulted in small errors at the 1%-2% level, for all duty cycles shown.
Smyth G, Evans PM, Bamber JC, Saran FH, Mandeville HC, Bedford JL (2015) SU-E-T-436: Fluence-Based Trajectory Optimization for Non-Coplanar VMAT., Medical Physics 42 (6) pp. 3434-3434 Wiley / American Association of Physicists in Medicine
PURPOSE: To investigate a fluence-based trajectory optimization technique for non-coplanar VMAT for brain cancer. METHODS: Single-arc non-coplanar VMAT trajectories were determined using a heuristic technique for five patients. Organ at risk (OAR) volume intersected during raytracing was minimized for two cases: absolute volume and the sum of relative volumes weighted by OAR importance. These trajectories and coplanar VMAT formed starting points for the fluence-based optimization method. Iterative least squares optimization was performed on control points 24° apart in gantry rotation. Optimization minimized the root-mean-square (RMS) deviation of PTV dose from the prescription (relative importance 100), maximum dose to the brainstem (10), optic chiasm (5), globes (5) and optic nerves (5), plus mean dose to the lenses (5), hippocampi (3), temporal lobes (2), cochleae (1) and brain excluding other regions of interest (1). Control point couch rotations were varied in steps of up to 10° and accepted if the cost function improved. Final treatment plans were optimized with the same objectives in an in-house planning system and evaluated using a composite metric - the sum of optimization metrics weighted by importance. RESULTS: The composite metric decreased with fluence-based optimization in 14 of the 15 plans. In the remaining case its overall value, and the PTV and OAR components, were unchanged but the balance of OAR sparing differed. PTV RMS deviation was improved in 13 cases and unchanged in two. The OAR component was reduced in 13 plans. In one case the OAR component increased but the composite metric decreased - a 4 Gy increase in OAR metrics was balanced by a reduction in PTV RMS deviation from 2.8% to 2.6%. CONCLUSION: Fluence-based trajectory optimization improved plan quality as defined by the composite metric. While dose differences were case specific, fluence-based optimization improved both PTV and OAR dosimetry in 80% of cases.
Coolens C, Evans P, Webb S, Bidmead M (2005) Clinical feasibility of a proposed internal margin model to account for variability in respiratory motion in gated radiotherapy delivery, RADIOTHERAPY AND ONCOLOGY 76 pp. S92-S92 ELSEVIER IRELAND LTD
Partridge M, Symonds-Tayler JR, Evans PM (2000) IMRT verification with a camera-based electronic portal imaging system., Phys Med Biol 45 (12) pp. N183-N196
An evaluation of the capabilities of a commercially available camera-based electronic portal imaging system for intensity-modulated radiotherapy verification is presented. Two modifications to the system are demonstrated which use a novel method to tag each image acquired with the delivered dose measured by the linac monitor chamber and reduce optical cross-talk in the imager. A detailed performance assessment is presented, including measurements of the optical decay characteristics of the system. The overall geometric accuracy of the system is determined to be +/-2.0 mm, with a dosimetric accuracy of +/-1.25 MU. Finally a clinical breast IMRT treatment, delivered by dynamic multileaf collimation, is successfully verified both by tracking the position of each leaf during beam delivery and recording the integrated intensity observed over the entire beam.
Donovan E, Bleakley N, Denholm E, Evans P, Gothard L, Hanson J, Peckitt C, Reise S, Ross G, Sharp G, Symonds-Tayler R, Tait D, Yarnold J (2007) Randomised trial of standard 2D radiotherapy (RT) versus intensity modulated radiotherapy (IMRT) in patients prescribed breast radiotherapy, RADIOTHERAPY AND ONCOLOGY 82 (3) pp. 254-264 ELSEVIER IRELAND LTD
BACKGROUND: Radiation dose distributions created by two dimensional (2D) treatment planning are responsible for partial volumes receiving >107% of the prescribed dose in a proportion of patients prescribed whole breast radiotherapy after tumour excision of early breast cancer. These may contribute to clinically significant late radiation adverse effects. AIM: To test three dimensional (3D) intensity modulated radiotherapy (IMRT) against 2D dosimetry using standard wedge compensators in terms of late adverse effects after whole breast radiotherapy. METHODS: Three hundred and six women prescribed whole breast radiotherapy after tumour excision for early stage cancer were randomised to 3D IMRT (test arm) or 2D radiotherapy delivered using standard wedge compensators (control arm). All patients were treated with 6 or 10MV photons to a dose of 50Gy in 25 fractions to 100% in 5 weeks followed by an electron boost to the tumour bed of 11.1Gy in 5 fractions to 100%. The primary endpoint was change in breast appearance scored from serial photographs taken before radiotherapy and at 1, 2 and 5 years follow up. Secondary endpoints included patient self-assessments of breast discomfort, breast hardness, quality of life and physician assessments of breast induration. Analysis was by intention to treat. RESULTS: 240 (79%) patients with 5-year photographs were available for analysis. Change in breast appearance was identified in 71/122 (58%) allocated standard 2D treatment compared to only 47/118 (40%) patients allocated 3D IMRT. The control arm patients were 1.7 times more likely to have a change in breast appearance than the IMRT arm patients after adjustment for year of photographic assessment (95% confidence interval 1.2-2.5, p=0.008). Significantly fewer patients in the 3D IMRT group developed palpable induration assessed clinically in the centre of the breast, pectoral fold, infra-mammary fold and at the boost site. No significant differences between treatment groups were found in patient reported breast discomfort, breast hardness or quality of life. CONCLUSION: This analysis suggests that minimisation of unwanted radiation dose inhomogeneity in the breast reduces late adverse effects. Incidence of change in breast appearance was statistically significantly higher in patients in the standard 2D treatment arm compared with the IMRT arm. A beneficial effect on quality of life remains to be demonstrated.
Zin HM, Harris EJ, Osmond JP, Allinson NM, Evans PM (2013) Towards real-time VMAT verification using a prototype, high-speed CMOS active pixel sensor., Phys Med Biol 58 (10) pp. 3359-3375
This work investigates the feasibility of using a prototype complementary metal oxide semiconductor active pixel sensor (CMOS APS) for real-time verification of volumetric modulated arc therapy (VMAT) treatment. The prototype CMOS APS used region of interest read out on the chip to allow fast imaging of up to 403.6 frames per second (f/s). The sensor was made larger (5.4 cm × 5.4 cm) using recent advances in photolithographic technique but retains fast imaging speed with the sensor's regional read out. There is a paradigm shift in radiotherapy treatment verification with the advent of advanced treatment techniques such as VMAT. This work has demonstrated that the APS can track multi leaf collimator (MLC) leaves moving at 18 mm s(-1) with an automatic edge tracking algorithm at accuracy better than 1.0 mm even at the fastest imaging speed. Evaluation of the measured fluence distribution for an example VMAT delivery sampled at 50.4 f/s was shown to agree well with the planned fluence distribution, with an average gamma pass rate of 96% at 3%/3 mm. The MLC leaves motion and linac pulse rate variation delivered throughout the VMAT treatment can also be measured. The results demonstrate the potential of CMOS APS technology as a real-time radiotherapy dosimeter for delivery of complex treatments such as VMAT.
Smyth G, Bamber JC, Evans PM, Bedford JL (2013) Trajectory optimization for dynamic couch rotation during volumetric modulated arc radiotherapy., Phys Med Biol 58 (22) pp. 8163-8177
Non-coplanar radiation beams are often used in three-dimensional conformal and intensity modulated radiotherapy to reduce dose to organs at risk (OAR) by geometric avoidance. In volumetric modulated arc radiotherapy (VMAT) non-coplanar geometries are generally achieved by applying patient couch rotations to single or multiple full or partial arcs. This paper presents a trajectory optimization method for a non-coplanar technique, dynamic couch rotation during VMAT (DCR?VMAT), which combines ray tracing with a graph search algorithm. Four clinical test cases (partial breast, brain, prostate only, and prostate and pelvic nodes) were used to evaluate the potential OAR sparing for trajectory-optimized DCR?VMAT plans, compared with standard coplanar VMAT. In each case, ray tracing was performed and a cost map reflecting the number of OAR voxels intersected for each potential source position was generated. The least-cost path through the cost map, corresponding to an optimal DCR?VMAT trajectory, was determined using Dijkstra's algorithm. Results show that trajectory optimization can reduce dose to specified OARs for plans otherwise comparable to conventional coplanar VMAT techniques. For the partial breast case, the mean heart dose was reduced by 53%. In the brain case, the maximum lens doses were reduced by 61% (left) and 77% (right) and the globes by 37% (left) and 40% (right). Bowel mean dose was reduced by 15% in the prostate only case. For the prostate and pelvic nodes case, the bowel V50 Gy and V60 Gy were reduced by 9% and 45% respectively. Future work will involve further development of the algorithm and assessment of its performance over a larger number of cases in site-specific cohorts.
Evans PM, Donovan EM, Partridge M, Bidmead AM, Garton A, Mubata C (1999) Radiological thickness measurement using a liquid ionization chamber electronic portal imaging device., Phys Med Biol 44 (6) pp. N89-N97
We present a method of calibrating the Portal Vision electronic portal imaging device to obtain radiological thickness maps for compensator design. In this method, coefficients are derived to describe the relationship between intensity and thickness for a set of water-equivalent blocks. The effects of four parameters were studied: (a) The dose response of the system was measured and found to be describable by a square-root function. (b) The calibration data and images were taken with a wedge in situ. The effects of using different wedges and different wedge orientations were investigated. The intrinsic accuracy of the accelerator/imager system was found to be 1.9 mm, for both 15 degrees and 30 degrees wedges. Changing the wedge orientation between calibration and imaging and rotating the calibration coefficients accordingly led to an error of 3.5 mm. (c) The variation in detector response with gantry angle was measured and corrected. The residual error in this process was 2.4 mm. (d) The use of a model to correct the effects of imaging with different field sizes was investigated and found to yield a residual error of 2.9 mm. The overall error in image calibrations was approximately 4 mm or 2% in dose. This is considered to be sufficiently small for the intended use of designing compensators for tangential breast irradiation.
Partridge M, Symonds-Tayler JRN, Evans PM (2000) Verification of dynamic MLC beam delivery using electronic portal imaging, USE OF COMPUTERS IN RADIATION THERAPY pp. 556-557 SPRINGER-VERLAG BERLIN
Harris EJ, Mukesh MB, Donovan EM, Kirby AM, Haviland JS, Jena R, Yarnold J, Baker A, Dean J, Eagle S, Mayles H, Griffin C, Perry R, Poynter A, Coles CE, Evans PM (2015) A multicentre study of the evidence for customized margins in photon breast boost radiotherapy., The British journal of radiology 89 (1058)
To determine if subsets of patients may benefit from smaller or larger margins when using laser setup and bony anatomy verification of breast tumour bed (TB) boost radiotherapy (RT).Verification imaging data acquired using cone-beam CT, megavoltage CT or two-dimensional kilovoltage imaging on 218 patients were used (1574 images). TB setup errors for laser-only setup (dlaser) and for bony anatomy verification (dbone) were determined using clips implanted into the TB as a gold standard for the TB position. Cases were grouped by centre-, patient- and treatment-related factors, including breast volume, TB position, seroma visibility and surgical technique. Systematic (£) and random (Ã) TB setup errors were compared between groups, and TB planning target volume margins (MTB) were calculated.For the study population, £laser was between 2.8 and 3.4 mm, and £bone was between 2.2 and 2.6 mm, respectively. Females with larger breasts (p = 0.03), easily visible seroma (p d 0.02) and open surgical technique (p d 0.04) had larger £laser. £bone was larger for females with larger breasts (p = 0.02) and lateral tumours (p = 0.04). Females with medial tumours (p
Hansen VN, Evans PM, Budgell GJ, Mott JHL, Williams PC, Brugmans MJP, Wittkamper FW, Mijnheer BJ, Brown K (1998) Quality assurance of the dose delivered by small radiation segments, PHYSICS IN MEDICINE AND BIOLOGY 43 (9) pp. 2665-2675 IOP PUBLISHING LTD
Juneja P, Evans P, Windridge D, Harris E (2016) Classification of fibroglandular tissue distribution in the breast based on radiotherapy planning CT, BMC MEDICAL IMAGING 16 ARTN 6 BIOMED CENTRAL LTD
Mukesh M, Harris E, Jena R, Evans P, Coles C (2012) Relationship between irradiated breast volume and late normal tissue complications: A systematic review, RADIOTHERAPY AND ONCOLOGY 104 (1) pp. 1-10 ELSEVIER IRELAND LTD
Alexander EJ, McNair HA, Kavanagh A, Ingram W, Evans PM, Dearnaley DP (2011) Initial Results of a Comparison of Localisation of the Prostate Gland Using an Electromagnetic Tracking System With Cone Beam CT, EUROPEAN JOURNAL OF CANCER 47 pp. S494-S494
Ott R, Evans N, Evans P, Osmond J, Clark A, Crooks J, Prydderich M, Turchetta R (2009) Active Pixel Sensors in Nuclear Medicine Imaging, 2008 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE (2008 NSS/MIC), VOLS 1-9 pp. 4149-4152 IEEE
Poludniowski G, Allinson NM, Evans PM (2015) Proton radiography and tomography with application to proton therapy., Br J Radiol 88 (1053)
Proton radiography and tomography have long promised benefit for proton therapy. Their first suggestion was in the early 1960s and the first published proton radiographs and CT images appeared in the late 1960s and 1970s, respectively. More than just providing anatomical images, proton transmission imaging provides the potential for the more accurate estimation of stopping-power ratio inside a patient and hence improved treatment planning and verification. With the recent explosion in growth of clinical proton therapy facilities, the time is perhaps ripe for the imaging modality to come to the fore. Yet many technical challenges remain to be solved before proton CT scanners become commonplace in the clinic. Research and development in this field is currently more active than at any time with several prototype designs emerging. This review introduces the principles of proton radiography and tomography, their historical developments, the raft of modern prototype systems and the primary design issues.
Bodey RK, Flux GD, Evans PM (2003) Combining dosimetry for targeted radionuclide and external beam therapies using the biologically effective dose., Cancer Biother Radiopharm 18 (1) pp. 89-97
It is not uncommon for a patient to receive both external beam and targeted radionuclide therapy during the course of a cancer treatment. The total dose received by the tumor and by normal tissues will therefore be subject to the contributions of both treatment modalities. However, the two treatments are generally applied independently of one another, with little attention paid to the combined effect. With the availability of patient-specific three-dimensional dosimetry for radionuclide therapies, it is pertinent now to consider the combined effect of the two treatments, and to investigate how dosimetry for this situation may be carried out. Methodology has been developed to allow a combination of dose information from the two types of therapy. The biologically effective dose (BED) has been employed to address the issue of inequivalence of biological effect of the two therapies. Dose distributions have been represented as distributions of BED, and the net effect resulting from the combination of these two therapies demonstrated through a combination of BED maps. Examples are presented of cases in which this analysis of a combined therapy provides a more favorable treatment than either therapy alone. For one patient the ratio of the mean spinal cord dose to the mean CTV dose was calculated for both an external beam therapy alone and for a combined therapy and was found to be 0.40 and 0.16, respectively.
Love PA, Evans PM, Leach MO, Webb S (2003) Polymer gel measurement of dose homogeneity in the breast: comparing MLC intensity modulation with standard wedged delivery., Phys Med Biol 48 (8) pp. 1065-1074
Polymer gel dosimetry has been used to measure the radiotherapy dose homogeneity in a breast phantom for two different treatment methods. The first 'standard' method uses two tangential wedged fields while the second method has three static fields shaped by multileaf collimators (MLCs) in addition to the standard wedged fields to create intensity modulated fields. Gel dose distributions from the multileaf modulation treatment show an improved dose uniformity in comparison to the standard treatment with a decreased volume receiving doses over 105%.
Poludniowski G, Evans PM, Kavanagh A, Webb S (2011) Removal and effects of scatter-glare in cone-beam CT with an amorphous-silicon flat-panel detector., Phys Med Biol 56 (6) pp. 1837-1851 Institute of Physics
Scatter in a detector and its housing can result in image degradation. Typically, such scatter leads to a low-spatial frequency 'glare' superimposed on the primary signal. We infer the glare-spread function (GSF) of an amorphous-silicon flat-panel detector via an edge-spread technique. We demonstrate that this spread (referred to as 'scatter-glare' herein) causes a low-spatial frequency drop in the associated modulation-transfer function. This results in a compression of the range of reconstructed CT (computed tomography) numbers and is an impediment to accurate CT-number calibration. We show that it can also lead to visual artefacts. This explains previously unresolved CT-number discrepancies in an earlier work (Poludniowski et al 2009 Phys. Med. Biol. 54 3847). We demonstrate that after deconvolving the GSF from the projection images, in conjunction with a correction for phantom-scatter, the CT-number discrepancies disappear. We show results for an in-house-built phantom with inserts of tissue-equivalent materials and for a patient scan. We conclude that where scatter-glare has not been accounted for, the calibration of cone-beam CT numbers to material density will be compromised. The scatter-glare measurement method we propose is simple and requires no special equipment. The deconvolution process is also straightforward and relatively quick (60 ms per projection on a desktop PC).
Evans PM, Coolens C, Nioutsikou E (2006) Effects of averaging over motion and the resulting systematic errors in radiation therapy., Phys Med Biol 51 (1) pp. N1-N7
The potential for systematic errors in radiotherapy of a breathing patient is considered using the statistical model of Bortfeld et al (2002 Phys. Med. Biol. 47 2203-20). It is shown that although averaging over 30 fractions does result in a narrow Gaussian distribution of errors, as predicted by the central limit theorem, the fact that one or a few samples of the breathing patient's motion distribution are used for treatment planning (in contrast to the many treatment fractions that are likely to be delivered) may result in a much larger error with a systematic component. The error distribution may be particularly large if a scan at breath-hold is used for planning.
Poludniowski G, Allinson NM, Anaxagoras T, Esposito M, Green S, Manolopoulos S, Nieto-Camero J, Parker DJ, Price T, Evans PM (2014) Proton-counting radiography for proton therapy: a proof of principle using CMOS APS technology., Phys Med Biol 59 (11) pp. 2569-2581
Despite the early recognition of the potential of proton imaging to assist proton therapy (Cormack 1963 J. Appl. Phys. 34 2722), the modality is still removed from clinical practice, with various approaches in development. For proton-counting radiography applications such as computed tomography (CT), the water-equivalent-path-length that each proton has travelled through an imaged object must be inferred. Typically, scintillator-based technology has been used in various energy/range telescope designs. Here we propose a very different alternative of using radiation-hard CMOS active pixel sensor technology. The ability of such a sensor to resolve the passage of individual protons in a therapy beam has not been previously shown. Here, such capability is demonstrated using a 36 MeV cyclotron beam (University of Birmingham Cyclotron, Birmingham, UK) and a 200 MeV clinical radiotherapy beam (iThemba LABS, Cape Town, SA). The feasibility of tracking individual protons through multiple CMOS layers is also demonstrated using a two-layer stack of sensors. The chief advantages of this solution are the spatial discrimination of events intrinsic to pixelated sensors, combined with the potential provision of information on both the range and residual energy of a proton. The challenges in developing a practical system are discussed.
Donovan EM, Brooks C, Mitchell RA, Mukesh M, Coles CE, Evans PM, Harris EJ, IMPORT Trials Management Group (2014) The effect of image guidance on dose distributions in breast boost radiotherapy., Clin Oncol (R Coll Radiol) 26 (11) pp. 671-676
AIMS: To determine the effect of image-guided radiotherapy on the dose distributions in breast boost treatments. MATERIALS AND METHODS: Computed tomography images from a cohort of 60 patients treated within the IMPORT HIGH trial (CRUK/06/003) were used to create sequential and concomitant boost treatment plans (30 cases each). Two treatment plans were created for each case using tumour bed planning target volume (PTV) margins of 5 mm (achieved with image-guided radiotherapy) and 8 mm (required for bony anatomy verification). Dose data were collected for breast, lung and heart; differences with margin size were tested for statistical significance. RESULTS: A median decrease of 29 cm(3) (range 11-193 cm(3)) of breast tissue receiving 95% of the prescribed dose was observed where image-guided radiotherapy margins were used. Decreases in doses to lungs, contralateral breast and heart were modest, but statistically significant (P 91%) of the prescribed dose in 12 cases; in addition, the required partial breast median dose was exceeded in nine concomitant boost cases by 0.5-3.7 Gy. CONCLUSIONS: The use of image guidance and, hence, a reduced tumour bed PTV margin, in breast boost radiotherapy resulted in a modest reduction in radiation dose to breast, lung and heart tissues. Reduced margins enabled by image guidance were necessary to discriminate between dose levels to multiple PTVs in the concomitant breast boost plans investigated.
Osmond JPF, Harris EJ, Clark AT, Ott RJ, Holland AD, Evans PM (2008) An investigation into the use of CMOS active pixel technology in image-guided radiotherapy, PHYSICS IN MEDICINE AND BIOLOGY 53 (12) pp. 3159-3174
Evans P, Mosleh-Shirazi A (2005) Models of the light output from scintillation crystals, RADIOTHERAPY AND ONCOLOGY 76 pp. S76-S76 ELSEVIER IRELAND LTD
Roberts DA, Hansen VN, Niven AC, Thompson MG, Seco J, Evans PM (2008) A low Z linac and flat panel imager: comparison with the conventional imaging approach, PHYSICS IN MEDICINE AND BIOLOGY 53 (22) pp. 6305-6319 IOP PUBLISHING LTD
Kirby AM, Evans PM, Nerurkar AY, Desai SS, Krupa J, Devalia H, della Rovere GQ, Harris EJ, Kyriakidou J, Yarnold JR (2010) How does knowledge of three-dimensional excision margins following breast conservation surgery impact upon clinical target volume definition for partial-breast radiotherapy?, RADIOTHERAPY AND ONCOLOGY 94 (3) pp. 292-299 ELSEVIER IRELAND LTD
Mukesh MB, Coles CE, Wilkinson J, Jena R, Harris E, Collette S, Bartelink H, Evans PM, Graham P, Haviland J, Poortmans P, Yarnold J (2013) Normal tissue complication probability (NTCP) parameters for breast fibrosis: Pooled results from two randomised trials, Radiotherapy and Oncology
Introduction: The dose-volume effect of radiation therapy on breast tissue is poorly understood. We estimate NTCP parameters for breast fibrosis after external beam radiotherapy. Materials and methods: We pooled individual patient data of 5856 patients from 2 trials including whole breast irradiation followed with or without a boost. A two-compartment dose volume histogram model was used with boost volume as the first compartment and the remaining breast volume as second compartment. Results from START-pilot trial (n = 1410) were used to test the predicted models. Results: 26.8% patients in the Cambridge trial (5 years) and 20.7% patients in the EORTC trial (10 years) developed moderate-severe breast fibrosis. The best fit NTCP parameters were BEUD(50) = 136.4 Gy, ³50 = 0.9 and n = 0.011 for the Niemierko model and BEUD(50) = 132 Gy, m = 0.35 and n = 0.012 for the Lyman Kutcher Burman model. The observed rates of fibrosis in the START-pilot trial agreed well with the predicted rates. Conclusions: This large multi-centre pooled study suggests that the effect of volume parameter is small and the maximum RT dose is the most important parameter to influence breast fibrosis. A small value of volume parameter 'n' does not fit with the hypothesis that breast tissue is a parallel organ. However, this may reflect limitations in our current scoring system of fibrosis. © 2013 Elsevier Ireland Ltd.
Mosleh-Shirazi MA, Swindell W, Evans PM (1998) Optimization of the scintillation detector in a combined 3D megavoltage CT scanner and portal imager., Med Phys 25 (10) pp. 1880-1890
A parametric study is described leading to the optimization of a custom-made scintillation detector with a relatively high quantum efficiency (QE) for megavoltage photons and light output toward a remote lens. This detector allows low-dose portal imaging and continuous cone-beam megavoltage CT acquisition. The EGS4 Monte Carlo code was used to simulate the x-ray and electron transport in the detector. A Monte Carlo model of optical photon transport in a detector element was devised and used as well as various irradiation experiments on scintillators. Different detector materials and configurations were compared in terms of the optical photon irradiance on the lens from on- and off-axis detector elements and the practical constraints regarding detector construction and weight. Effects of scintillator material, detector element size, crystal coating type, and reflectivity, combinations of different coatings on detector faces, scintillator doping level, and crystal transparency were studied. With scintillator thickness adjusted to give an 18% x-ray QE at 6 MV, the light output of CsI(Tl) was at least eight times higher than ZnWO4, BGO and NE118 plastic. Further, CsI(Tl) showed the smallest decrease in QE going from 6 to 24 MV. The off-axis reduction in emittance from the periphery of the detector was relatively small with a slight dependence on the type and reflectivity of the coating and the crystal thickness for a fixed detector element cross section. Light output was more strongly dependent on the reflectivity of lambertian coatings than specular ones. For a fixed detector element cross section, optimum coating type depended on crystal thickness. Typical CsI(Tl) crystals showed a relatively small variation in light output with changes in optical attenuation length. The optimum detector element was found to be CsI(Tl) coated on five faces with TiO2-loaded epoxy resin offering about a ten-fold improvement in light output per incident photon compared to typical metal/phosphor screens.
Bodey RK, Flux GD, Evans PM (2004) Spatial optimisation of combined modality radiotherapy, EUROPEAN JOURNAL OF NUCLEAR MEDICINE AND MOLECULAR IMAGING 31 pp. S475-S475 SPRINGER
Partridge M, Aldridge S, Donovan E, Evans PM (2001) An intercomparison of IMRT delivery techniques: a case study for breast treatment., Phys Med Biol 46 (7) pp. N175-N185
Intensity-modulated radiotherapy beams can be delivered using a multileaf collimator by one of two methods: either by superposition of a series of multiple-static fields, or by moving the collimators while the beam is on to produce 'dynamically' modulated beams. The leaf trajectories in this dynamic mode are given by a series of linear steps between control points defining each collimator position at known intervals throughout an exposure. The complexity of the resulting modulation is limited in the first case by the number of fields superposed and in the second case by the number of control points defined. Results are presented for an experimental study that investigates the effect of changing both the number of fields for the multiple-static technique, and the number of control points for a dynamic 'close-in' technique. All deliveries studied are clinical intensity-modulated breast fields. The effect of using a universal wedge in conjunction with the multileaf collimator is also studied, together with a comparison of the relative efficiency, time taken and the absolute dosimetric accuracy of the various delivery options. It is shown that all delivery techniques produce equivalent dose distributions when using 15 control points, with 10 control points being sufficient to produce an adequate breast compensator distribution. Except for the case of a four-control-point dynamic delivery, the universal wedge makes no significant difference to the dose distribution. However, it makes the delivery less efficient. The close-in interpreter consistently produces deliveries that are more efficient than the more conventional sliding-window technique and faster than the multiple-static-field technique. Finally the close-in technique is compared to the more 'standard' leaf-sweep technique and shown to be equivalent.
Esposito M, Anaxagoras T, Konstantinidis AC, Zheng Y, Speller RD, Evans PM, Allinson NM, Wells K (2014) Performance of a novel wafer scale CMOS active pixel sensor for bio-medical imaging., Phys Med Biol 59 (13) pp. 3533-3554
Recently CMOS active pixels sensors (APSs) have become a valuable alternative to amorphous silicon and selenium flat panel imagers (FPIs) in bio-medical imaging applications. CMOS APSs can now be scaled up to the standard 20 cm diameter wafer size by means of a reticle stitching block process. However, despite wafer scale CMOS APS being monolithic, sources of non-uniformity of response and regional variations can persist representing a significant challenge for wafer scale sensor response. Non-uniformity of stitched sensors can arise from a number of factors related to the manufacturing process, including variation of amplification, variation between readout components, wafer defects and process variations across the wafer due to manufacturing processes. This paper reports on an investigation into the spatial non-uniformity and regional variations of a wafer scale stitched CMOS APS. For the first time a per-pixel analysis of the electro-optical performance of a wafer CMOS APS is presented, to address inhomogeneity issues arising from the stitching techniques used to manufacture wafer scale sensors. A complete model of the signal generation in the pixel array has been provided and proved capable of accounting for noise and gain variations across the pixel array. This novel analysis leads to readout noise and conversion gain being evaluated at pixel level, stitching block level and in regions of interest, resulting in a coefficient of variation }1.9%. The uniformity of the image quality performance has been further investigated in a typical x-ray application, i.e. mammography, showing a uniformity in terms of CNR among the highest when compared with mammography detectors commonly used in clinical practice. Finally, in order to compare the detection capability of this novel APS with the technology currently used (i.e. FPIs), theoretical evaluation of the detection quantum efficiency (DQE) at zero-frequency has been performed, resulting in a higher DQE for this detector compared to FPIs. Optical characterization, x-ray contrast measurements and theoretical DQE evaluation suggest that a trade off can be found between the need of a large imaging area and the requirement of a uniform imaging performance, making the DynAMITe large area CMOS APS suitable for a range of bio-medical applications.
Donovan EM, Johnson U, Shentall G, Evans PM, Neal AJ, Yarnold JR (2000) Evaluation of compensation in breast radiotherapy: a planning study using multiple static fields., Int J Radiat Oncol Biol Phys 46 (3) pp. 671-679
PURPOSE: A method that uses electronic portal imaging to design intensity-modulated beams for compensation in breast radiotherapy was implemented using multiple static fields in a planning study. We present the results of the study to verify the algorithm, and to assess improvements to the dosimetry. METHODS AND MATERIALS: Fourteen patients were imaged with computed tomography (CT) and on a treatment unit using an electronic portal imager. The portal imaging data were used to design intensity-modulated beams to give an ideal dose distribution in the breast. These beams were implemented as multiple static fields added to standard wedged tangential fields. Planning of these treatments was performed on a commercial treatment planning system (Target 2, IGE Medical Systems, Slough, U.K.) using the CT data for each patient. Dose-volume histogram (DVH) analysis of the plans with and without multileaf collimator (MLC) compensation was carried out. This work has been used as the basis for a randomized clinical trial investigating whether improvements in dosimetry are correlated with the reduction of long-term side effects from breast radiotherapy. RESULTS: The planning analysis showed a mean increase in target volume receiving 95-105% of prescribed dose of 7.5% (range -0.8% to 15.9%) when additional MLC compensation was applied. There was no change to the minimum dose for all 14 patient data sets. The change in the volume of breast tissue receiving over 105% of prescribed dose, when applying MLC compensation, was between -1.4% and 11.9%, with positive numbers indicating an improvement. These effects showed a correlation with breast size; the larger the breast the greater the amount of improvement. CONCLUSIONS: The method for designing compensation for breast treatments using an electronic portal imager has been verified using planning on CT data for 14 patients. An improvement was seen in planning when applying MLC compensation and this effect was greater the larger the breast size.
Esposito M, Anaxagoras T, Fant A, Wells K, Konstantinidis A, Osmond JPF, Evans PM, Speller RD, Allinson NM (2011) DynAMITe: A wafer scale sensor for biomedical applications, Journal of Instrumentation 6 (12) C12064 IOP Publishing
In many biomedical imaging applications Flat Panel Imagers (FPIs) are currently the most common option. However, FPIs possess several key drawbacks such as large pixels, high noise, low frame rates, and excessive image artefacts. Recently Active Pixel Sensors (APS) have gained popularity overcoming such issues and are now scalable up to wafer size by appropriate reticule stitching. Detectors for biomedical imaging applications require high spatial resolution, low noise and high dynamic range. These figures of merit are related to pixel size and as the pixel size is fixed at the time of the design, spatial resolution, noise and dynamic range cannot be further optimized. The authors report on a new rad-hard monolithic APS, named DynAMITe (Dynamic range Adjustable for Medical Imaging Technology), developed by the UK MI-3 Plus consortium. This large area detector (12.8 cm × 12.8 cm) is based on the use of two different diode geometries within the same pixel array with different size pixels (50 ¼m and 100 ¼m). Hence the resulting device can possess two inherently different resolutions each with different noise and saturation performance. The small and the large pixel cameras can be reset at different voltages, resulting in different depletion widths. The larger depletion width for the small pixels allows the initial generated photo-charge to be promptly collected, which ensures an intrinsically lower noise and higher spatial resolution. After these pixels reach near saturation, the larger pixels start collecting so offering a higher dynamic range whereas the higher noise floor is not important as at higher signal levels performance is governed by the Poisson noise of the incident radiation beam. The overall architecture and detailed characterization of DynAMITe will be presented in this paper.
Partridge M, Evans PM (1998) The practical implementation of a scatter model for portal imaging at 10 MV., Phys Med Biol 43 (9) pp. 2685-2693
A detailed validation of a physical model for scattered radiation in portal images at 10 MV is presented. The ratio of the signal due to scattered radiation to the signal due to primary radiation (SPR) in an electronic portal image is defined. A simple physical model for SPR on the central axis (SPR*) was presented by Swindell and Evans for 6 MV and validated for field sizes up to 320 cm2. In this paper, the model is extended to 10 MV and validated for field sizes up to 625 cm2. The model is first compared with Monte Carlo modelled data for field areas A from 40 to 320 cm2, scatterer thicknesses d of 5 to 35 cm water and scatterer to detector distances L2 of 40 to 100 cm. The physical model has one free parameter, which is fitted empirically using these data. Second, experimental measurements are performed with A from 40 to 625 cm2, d from 4.6 to 27.4 cm and L2 fixed at 100 cm. The root mean square (rms) difference between the physical model and the Monte Carlo calculations was less than 0.001 for all L2 greater than 60 cm. Agreement between experimentally measured and physically modelled data amounts to a radiological thickness error of at best 0.7 mm in 273.6 mm and at worst 0.4 in 45.6 mm. The model performs equally well at all field sizes tested. This study shows that the Swindell and Evans SPR* model is accurate at 10 MV for L2 greater than 60 cm for all A up to 625 cm2.
Bedford JL, Oldham M, Hoess A, Evans PM, Shentall GS, Webb S (1997) Methods for transferring patient and plan data between radiotherapy treatment planning systems., Br J Radiol 70 (835) pp. 740-749
The effectiveness of conformal radiotherapy can ultimately only be assessed by the use of clinical trials. As large multicentre clinical trials become more widespread, methods of transferring patient and plan data between radiotherapy treatment planning systems become increasingly important. In this paper, the general strategy for the transfer of data is discussed, and also illustrated with reference to two specific systems: TARGET 2 (GE Medical Systems) and VOXELPLAN (DKFZ-Heidelberg). The transfer method involves using a computer program to translate the data formats used by each of the two systems for CT scans, patient outlines, plan information and block descriptions. This paper does not address the question of transferring beam data between systems: beam data must first be entered separately into both machines. The physical concepts encountered when transferring plans are described, with specific reference to the two planning systems used. Differences in the strategies used by the two planning systems for definition of irregular field shapes are compared. The dose calculations used by the two systems are also briefly evaluated. Isodoses produced by VOXELPLAN around a circular target volume are found to be up to 3 mm different in location to those produced by TARGET 2, owing to the use of a smooth field shape contour as opposed to a stepped field shape which closely models the leaves of a multileaf collimator. In general, dose distributions generated by both systems are comparable, but some differences are found in the presence of large tissue inhomogeneities. It is concluded that the transfer of patient and plan data between two different treatment planning systems is feasible, provided that any differences in field shape definition methods or dose calculation methods between the two systems are understood.
Harris EJ, Symonds-Taylor R, Treece GM, Gee AH, Prager RW, Brabants P, Evans PM (2009) Evaluation of a three-dimensional ultrasound localisation system incorporating probe pressure correction for use in partial breast irradiation., Br J Radiol 82 (982) pp. 839-846 British Institute of Radiology
This work evaluates a three-dimensional (3D) freehand ultrasound-based localisation system with new probe pressure correction for use in partial breast irradiation. Accuracy and precision of absolute position measurement was measured as a function of imaging depth (ID), object depth, scanning direction and time using a water phantom containing crossed wires. To quantify the improvement in accuracy due to pressure correction, 3D scans of a breast phantom containing ball bearings were obtained with and without pressure. Ball bearing displacements were then measured with and without pressure correction. Using a single scan direction (for all imaging depths), the mean error was
Trapp JV, Michael G, Evans PM, Baldock C, Leach MO, Webb S (2004) Dose resolution in gel dosimetry: effect of uncertainty in the calibration function., Phys Med Biol 49 (10) pp. N139-N146
Dose resolution, DdeltaP, is becoming a common method for characterizing the performance of a gel dosimeter. In this note we examine how the goodness of fit of the calibration function affects DdeltaP and show that its inclusion in the calculation of DdeltaP is essential to avoid overestimating the performance of the gel.
Gulliford SL, Partridge M, Sydes MR, Webb S, Evans PM, Dearnaley DP (2012) Parameters for the Lyman Kutcher Burman (LKB) model of Normal Tissue Complication Probability (NTCP) for specific rectal complications observed in clinical practise, RADIOTHERAPY AND ONCOLOGY 102 (3) pp. 347-351
Seco J, Evans PM, Webb S (2001) Analysis of the effects of the delivery technique on an IMRT plan: comparison for multiple static field, dynamic and NOMOS MIMiC collimation., Phys Med Biol 46 (12) pp. 3073-3087
The process of delivering an IMRT treatment may involve various beam-modifying techniques such as multileaf collimators (MLCs), the NOMOS MIMiC, blocks, wedges, etc. In the case of the MLC, the spatial/temporal variation of the position of the leaves and diaphragms in the beam allows the delivery of modulated beam profiles either by the multiple-static-field (MSF) method or by the dynamic multileaf collimator (DMLC) method. The constraints associated with the IMRT delivery technique are usually neglected in the process of obtaining the 'optimal' inverse treatment plan. Consequently, dose optimization may be significantly reduced when the 'optimal' beam profiles are converted to leaf/diaphragm positions via a leaf-sequencing interpreter. The paper presented here assesses the effects on the optimum treatment plan of the following leaf-sequencing algorithms: MSF, DMLC and NOMOS MIMiC. The results obtained suggest that the delivery of an 'optimum' plan produces an overdosage of the PTV region due to various factors such as leaf/diaphragm transmission effects, head-scatter and phantom-scatter contributions. The overdosage observed for a cohort of ten patients was 2.5, 3.7 and 5.7%, respectively, for the DMLC, MSF and NOMOS MIMiC, after normalizing the delivered fluence to account for IMRT effects (using the method of Convery et al (Convery D J, Cogrove V P and Webb S 2000 Proc. 13th Int. Conf. on Computers in Radiotherapy (Heidelberg, 2000)) such as to obtain 70 Gy at the isocentre. The IMRT techniques DMLC, MIMiC and MSF were compared for the organs at risk: rectum, bladder, and left and right femoral heads.
Mosleh-Shirazi MA, Evans PM, Swindell W, Symonds-Tayler JR, Webb S, Partridge M (1998) Rapid portal imaging with a high-efficiency, large field-of-view detector., Med Phys 25 (12) pp. 2333-2346
The design, construction, and performance evaluation of an electronic portal imaging device (EPID) are described. The EPID has the same imaging geometry as the current mirror-based systems except for the x-ray detection stage, where a two-dimensional (2D) array of 1 cm thick CsI(Tl) detector elements are utilized. The approximately 18% x-ray quantum efficiency of the scintillation detector and its 30 x 40 cm2 field-of-view at the isocenter are greater than other area-imaging EPIDs. The imaging issues addressed are theoretical and measured signal-to-noise ratio, linearity of the imaging chain, influence of frame-summing on image quality and image calibration. Portal images of test objects and a humanoid phantom are used to measure the performance of the system. An image quality similar to the current devices is achieved but with a lower dose. With approximately 1 cGy dose delivered by a 6 MV beam, a 2 mm diam structure of 1.3% contrast and an 18 mm diam object of 0.125% contrast can be resolved without using image-enhancement methods. A spatial resolution of about 2 mm at the isocenter is demonstrated. The capability of the system to perform fast sequential imaging, synchronized with the radiation pulses, makes it suitable for patient motion studies and verification of intensity-modulated beams as well as its application in cone-beam megavoltage computed tomography.
Evans PM, Gildersleve JQ, Morton EJ, Swindell W, Coles R, Ferraro M, Rawlings C, Xiao ZR, Dyer J (1992) Image comparison techniques for use with megavoltage imaging systems., Br J Radiol 65 (776) pp. 701-709
In this paper we describe software facilities for enabling patient positioning studies using the megavoltage imaging system developed at the Royal Marsden Hospital and Institute of Cancer Research. The study focuses on the use of the system for three purposes: patient position verification (by comparing images taken at treatment simulation with megavoltage images taken at treatment time); reproducibility studies (by analysing a set of megavoltage images); and set-up correction (by adjusting the set-up until the megavoltage image obtained at treatment registers with the simulation image). The need is discussed for suitably presented simulator images, a method of determining field boundaries and the possibility of delineating soft-tissue interfaces. Several algorithms of different types, developed specifically for the purpose of intercomparison of planar projection images, are presented. The techniques employed and their usefulness, in both the qualitative and the quantitative sense, are discussed. The results are presented of a phantom and clinical study, to evaluate the rigour and reproducibility of the algorithms. These results indicate that measurements can be made to an accuracy of about 1-2 mm, with a similar value for interobserver reproducibility for the best image comparison techniques available.
Fielding A, Clark C, Evans P (2003) Verification of patient position and delivery of IMRT by electronic portal Imaging, MEDICAL PHYSICS 30 (6) pp. 1352-1352 AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS
South CP, Partridge M, Evans PM (2008) A theoretical framework for prescribing radiotherapy dose distributions using patient-specific biological information, MEDICAL PHYSICS 35 (10) pp. 4599-4611 AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS
Seco J, Evans PM (2007) Assessing the effect of electron density in photon dose calculations (vol 33, pg 540, 2006), MEDICAL PHYSICS 34 (7) pp. 3121-3121 American Association of Physicists in Medicine
Evans PM (2008) Anatomical imaging for radiotherapy, PHYSICS IN MEDICINE AND BIOLOGY 53 (12) pp. R151-R191 IOP PUBLISHING LTD
Nioutsikou E, Seppenwoolde Y, Symonds-Tayler JRN, Heijmen B, Evans P, Webb S (2008) Dosimetric investigation of lung tumor motion compensation with a robotic respiratory tracking system: An experimental study, MEDICAL PHYSICS 35 (4) pp. 1232-1240 AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS
Alobaidli S, McQuaid S, South C, Prakash V, Evans P, Nisbet A (2014) The role of texture analysis in imaging as an outcome predictor and potential tool in radiotherapy treatment planning., Br J Radiol 87 (1042)
Predicting a tumour's response to radiotherapy prior to the start of treatment could enhance clinical care management by enabling the personalization of treatment plans based on predicted outcome. In recent years, there has been accumulating evidence relating tumour texture to patient survival and response to treatment. Tumour texture could be measured from medical images that provide a non-invasive method of capturing intratumoural heterogeneity and hence could potentially enable a prior assessment of a patient's predicted response to treatment. In this article, work presented in the literature regarding texture analysis in radiotherapy in relation to survival and outcome is discussed. Challenges facing integrating texture analysis in radiotherapy planning are highlighted and recommendations for future directions in research are suggested.
Juneja P, Harris EJ, Evans PM (2014) Investigation of the accuracy of breast tissue segmentation methods for the purpose of developing breast deformation models for use in adaptive radiotherapy, Journal of Physics: Conference Series 489 (1)
Realistic modelling of breast deformation requires the breast tissue to be segmented into fibroglandular and fatty tissue and assigned suitable material properties. There are a number of breast tissue segmentation methods proposed and used in the literature. The purpose of this study was to validate and compare the accuracy of various segmentation methods and to investigate the effect of the tissue distribution on the segmentation accuracy. Computed tomography (CT) data for 24 patients, both in supine and prone positions were segmented into fibroglandular and fatty tissue. The segmentation methods explored were: physical density thresholding; interactive thresholding; fuzzy c-means clustering (FCM) with three classes (FCM3) and four classes (FCM4); and k-means clustering. Validation was done in two-stages: firstly, a new approach, supine-prone validation based on the assumption that the breast composition should appear the same in the supine and prone scans was used. Secondly, outlines from three experts were used for validation. This study found that FCM3 gave the most accurate segmentation of breast tissue from CT data and that the segmentation accuracy is adversely affected by the sparseness of the fibroglandular tissue distribution. © Published under licence by IOP Publishing Ltd.
Donovan EM, Harris EJ, Mukesh MB, Haviland JS, Titley J, Griffin C, Coles CE, Evans PM, IMPORT Trials Management Group (2014) The IMPORT HIGH image-guided radiotherapy study: a model for assessing image-guided radiotherapy., Clin Oncol (R Coll Radiol) 27 (1) pp. 3-5
Hector CL, Webb S, Evans PM (2000) The dosimetric consequences of inter-fractional patient movement on conventional and intensity-modulated breast radiotherapy treatments., Radiother Oncol 54 (1) pp. 57-64
BACKGROUND AND PURPOSE: A method has been developed to enable a comparison to be made between the effects of movement on conventional tangential breast treatments and intensity-modulated treatments delivered using compensators. MATERIALS AND METHODS: The effects of set-up error and organ motion were studied for a set of six patients. Images were taken of these patients over the course of their treatment and conventional wedged and compensated treatment plans were designed for each. Dose-volume statistics were used to evaluate each of the treatment plans by examining the volume outside the dose range 95-105%. To assess the effects of movement alone, the volume change from day 1 was also calculated. RESULTS: Thirty-six estimated CT-sets were available for evaluation. Measurements of breast volume showed the volume to increase to a peak between fraction 4 and 8 and then decrease back below the initial volume. The standard treatment was found to yield 29/36 plans (81%) with greater than 5% volume outside the dose range 95-105%. For the compensated plans this dropped to 11/36 plans (31%). The analysis of the volume changes from day 1 showed that for both standard and compensated treatments 7/30 plans (23%) had an increase in volume outside the dose range 95-105% of greater than 5% of the total planning target volume. CONCLUSIONS: The compensated treatment is more susceptible to patient movement. However, the actual volume of tissue outside 95-105% dose is less when compared to standard treatment implying the compensated treatment is still superior.
Parent L, Seco J, Evans PM, Fielding A, Dance DR (2006) Monte Carlo modelling of a-Si EPID response: The effect of spectral variations with field size and position, MEDICAL PHYSICS 33 (12) pp. 4527-4540
Evans PM, Donovan EM, Partridge M, Childs PJ, Convery DJ, Eagle S, Hansen VN, Suter BL, Yarnold JR (2000) The delivery of intensity modulated radiotherapy to the breast using multiple static fields., Radiother Oncol 57 (1) pp. 79-89
BACKGROUND AND PURPOSE: To develop a method of using a multileaf collimator (MLC) to deliver intensity modulated radiotherapy (IMRT) for tangential breast fields, using an MLC to deliver a set of multiple static fields (MSFs). MATERIALS AND METHODS: An electronic portal imaging device (EPID) is used to obtain thickness maps of medial and lateral tangential breast fields. From these IMRT deliveries are designed to minimize the volume of breast above 105% of prescribed dose. The deliveries are universally-wedged beams augmented with a set of low dose shaped irradiations. Dosimetric and planning QA of this method has been compared with the standard, wedged treatment and the corresponding treatment using physical compensators. Several options for delivering the MSF treatment are presented. RESULTS: The MSF technique was found to be superior to the standard technique (P value=0.002) and comparable with the compensated technique. Both IMRT methods reduced the volume of breast above 105% dose from a mean value of 12.0% of the total breast volume to approximately 2.8% of the total breast volume. CONCLUSIONS: This MSF method may be used to reduce the high dose volume in tangential breast irradiation significantly. This may have consequences for long-term side effects, particularly cosmesis.
Seco J, Adams L, Partridge M, Evans P, Verhaegen F (2005) Evaluation of pencil beam, collapsed cone and Monte Carlo IMRT dose calculation algorithms for dual target sites, RADIOTHERAPY AND ONCOLOGY 76 pp. S18-S18 ELSEVIER IRELAND LTD
Evans PM, Gildersleve JQ, Rawlings C, Swindell W (1993) Technical note: the implementation of patient position correction using a megavoltage imaging device on a linear accelerator., Br J Radiol 66 (789) pp. 833-838
The problem of using information from the analysis of megavoltage images to adjust patient set-up has been addressed. In the case of rotational corrections it has been assumed that the treatment head is to be adjusted, although for gantry angles of 0 degree and 180 degrees couch rotation may be used. In the case of translational shifts adjustment of the collimator jaws or of the couch have both been considered for arbitrary combinations of couch and gantry angle. For couch movement the case has been considered where it is desirable to minimize both the number of parameters to be adjusted and also the magnitude of the change in the patient's position. Values obtained for frequently used set-up parameters have been presented. Adjustment of the treatment couch positioning is the most desirable option, as this should bring the patient closer to the correct position for subsequent treatment fields. However, rotational errors are not correctable for all gantry angles and furthermore the collimator settings may be set more accurately than those of the treatment couch. Hence, in some cases, adjustment of the collimation system may be desirable or necessary. The formulae given in Equations (13) to (18) are currently being used in an intervention study to correct patient set-up during the course of a treatment fraction.
Colgan R, McClelland J, McQuaid D, Evans PM, Hawkes D, Brock J, Landau D, Webb S (2008) Planning lung radiotherapy using 4D CT data and a motion model., Phys Med Biol 53 (20) pp. 5815-5830
This work is a feasibility study to use a four-dimensional computed tomography (4D CT) dataset generated by a continuous motion model for treatment planning in lung radiotherapy. The model-based 4D CT data were derived from multiple breathing cycles. Four patients were included in this retrospective study. Treatment plans were optimized at end-exhale for each patient and the effect of respiratory motion on the dose delivery investigated. The accuracy of the delivered dose as determined by the number of intermediate respiratory phases used for the calculation was considered. The time-averaged geometry of the anatomy representing the mid-ventilation phase of the breathing cycle was generated using the motion model and a treatment plan was optimized for this phase for one patient. With respiratory motion included, the mid-ventilation plan achieved better target coverage than the plan optimized at end-exhale when standard margins were used to expand the clinical target volume (CTV) to planning target volume (PTV). Using a margin to account for set-up uncertainty only, resulted in poorer target coverage and healthy tissue sparing. For this patient cohort, the results suggest that conventional three-dimensional treatment planning was sufficient to maintain target coverage despite respiratory motion. The motion model has proved a useful tool in 4D treatment planning.
Gulliford S, Foo K, Morgan RC, Aird EG, Bidmead AM, Critchley H, Evans PM, Gianolini S, Mayles WP, Moore AR, Sanchez B, Partridge M, Sydes MR, Webb S, Dearnaley DP (2009) Independent Validation of Rectal Dose-volume Constraints using MRC RT01 (ISRCTN47772397) Trial Data, CLINICAL ONCOLOGY 21 (3) pp. 249-249 Elsevier
Introduction: Treatment plan evaluation requires knowledge of the
effect of the plan, not only on the intended target, but also the
surrounding normal tissues that are unavoidably irradiated. Recent
literature has provided estimations of tolerance doses and
proposed dose-volume constraints for many of the organs at risk.
However, very few of these recommendations have been independently
validated. This study details how constraints proposed
for the rectum were tested using data from the RT01 randomised
prostate radiotherapy trial.
Method: An independent validation of the rectal dose-volume
constraints used in the CHHiP trial and proposed recently by
Fiorino et al. was performed. The constraints were applied
retrospectively to the treatment plans collected from the RT01
trial. Odds ratios (OR) were calculated to compare the reported
incidence of specific late rectal toxicity end points in the group of
patients whose treatment plan met a specified dose-volume
constraint compared to the group of patients who failed that
Results: Statistically significant ORs were observed for every
constraint tested (except 75 Gy) for at least one clinical end point.
For the CHHiP constraints between 60 and 70 Gy, the ORs
calculated for rectal bleeding (RMH score defined in protocol)
exceeded 2.5 (P!0.02). Similarly the ORs for CHHiP constraints
between 30 and 65 Gy exceeded 2.4 (P!0.021) for urgency (UCLA
PCI). The Fiorino constraints between 40 and 60 Gy resulted in ORs
O2 (P!0.02) for loose stools (UCLA PCI)
Conclusion: Implementing rectal dose-volume constraints from
30 Gy up to the prescription dose will result in a decrease in the
incidence of late rectal toxicity. Constraints for doses as low as
30 Gy were statistically significant, further challenging the concept
that the rectum is a serial structure where the maximum dose to
the organ is the only consideration.
Hansen VN, Evans PM, Shentall GS, Helyer SJ, Yarnold JR, Swindell W (1997) Dosimetric evaluation of compensation in radiotherapy of the breast: MLC intensity modulation and physical compensators., Radiother Oncol 42 (3) pp. 249-256
BACKGROUND AND PURPOSE: Electronic portal images may be used to design the compensation required to maximise dose uniformity in the breast from opposed tangential beams. MATERIALS AND METHODS: Four methods of implementing the desired compensation have been studied: a simple wedge, a physical compensator in conjunction with a wedge; one open field plus four shaped multi-leaf-collimated (MLC) fields, and one wedged field in conjunction with three shaped MLC fields. Evaluation was performed using thermoluminescent dosimeters (TLDs) placed inside a phantom which was designed to mimic the human breast. The measured results are compared with both the prediction of the in-house compensation design software and with the dose predicted by the GE Target II planning system. The implications of each method for the time taken to plan and deliver treatment were analysed. RESULTS: The dose inhomogeneity, as measured at seven points in the central plane was greatest for the simple wedge (root mean square (rms) = 4.5%) compared to an open field plus four shaped MLC fields (rms = 2.2%), a wedged field plus three shaped MLC fields (rms = 3.3%), and the physical compensator (rms = 2.4%). The times required to plan and prepare these treatments varied considerably. The standard wedged treatment required under 15 min; both MLC-based and the physical compensator treatments required approximately 50 min. Differences of treatment delivery times were up to 8 min. CONCLUSIONS: These results indicate that the dose inhomogeneity can be reduced by beam intensity modulation designed using EPIDs.
Parent L, Evans P, Dance D, Seco J, Fielding A (2005) Calibration of the true leaf positions in Monte Carlo simulations of an MLC, RADIOTHERAPY AND ONCOLOGY 76 pp. S175-S175 ELSEVIER IRELAND LTD
Webb S, Convery DJ, Evans PM (1998) Inverse planning with constraints to generate smoothed intensity-modulated beams., Phys Med Biol 43 (10) pp. 2785-2794
Highly conformal dose distributions can be generated by intensity-modulated radiotherapy. Intensity-modulated beams (IMBs) are generally determined by inverse-planning techniques designed to maximize conformality. Usually such techniques apply no constraints on the form of the IMBs which may then develop fine-scale modulation. In this paper we present a technique for generating smoother IMBs, which yields a dose distribution almost identical to that without the constraint on the form of the IMBs. The method applies various filters successively at intervals throughout the iterative inverse planning. It is shown that the IMBs so determined using a simple median window filter have desirable properties in terms of increasing the efficiency of delivery by the dynamic multileaf collimator method and may be 'more like conventional beams' than unconstrained, highly modulated IMBs.
Gildersleve J, Dearnaley D, Evans P, Morton E, Swindell W (1994) Preliminary clinical performance of a scanning detector for rapid portal imaging., Clin Oncol (R Coll Radiol) 6 (4) pp. 245-250
A scanning megavoltage imaging detector, with associated image storage and analysis facilities has been developed. This produces images of the treatment portals in under 10 seconds, in a digital format, facilitating rapid, quantitative image analysis. Image quality is comparable to, and at some sites improves upon, that available from film. Clinical problems in the use of megavoltage imaging include limited field of view, loss of information at the field edge due to penumbra effects, degradation of the image by bowel gas, and difficulties in the detection of soft tissue-air interfaces. Possible solutions to these problems are discussed. The imaging system has been used to assess the random errors occurring during routine para-aortic nodal irradiation. The errors detected are small, with over 95% of set-ups lying within +/- 4.5 mm of the mean daily position. No differences were detected in the magnitude of random errors between anterior and posterior treatment fields.
Bartlett FR, Yarnold JR, Donovan EM, Evans PM, Locke I, Kirby AM (2013) Multileaf Collimation Cardiac Shielding in Breast Radiotherapy: Cardiac Doses are Reduced, But at What Cost?, Clin Oncol (R Coll Radiol) 25 (12) pp. 690-696
To measure cardiac tissue doses in left-sided breast cancer patients receiving supine tangential field radiotherapy with multileaf collimation (MLC) cardiac shielding of the heart and to assess the effect on target volume coverage.
Evans PM, Hansen VN, Mayles WP, Swindell W, Torr M, Yarnold JR (1995) Design of compensators for breast radiotherapy using electronic portal imaging., Radiother Oncol 37 (1) pp. 43-54
A novel method of designing intensity modulated beams (IMBs) to achieve compensation in external beam radiotherapy of the breast, without the need for CT scans, is presented. The design method comprises three parts: (1) an electronic portal image is used to generate a map of radiological thickness; (2) this map is then used to obtain an estimate of the breast and lung outline; (3) a TMR-based dose calculation algorithm is then used to determine the optimum beam profile to achieve the best dose distribution. The dose distributions calculated for IMBs were compared with those calculated for the use of simple wedges. The results for two patients studied indicate that the dose inhomogeneity for IMBs is +/- 5%, compared with a value of +/- 10% for a wedged plan. The uncertainty in radiological thickness measurement corresponds to a dosimetric error of +/- 2%. Other errors associated with outline estimation are typically less than 2%, with a largest value of +5% for one of the patients who had a large and highly asymmetrical breast. The results for the two patients studied suggest that the uncertainties in the method are significantly smaller than the improvement in dose uniformity produced.
Coolens C, Webb S, Evans PM, Seco J (2003) Combinational use of conformal and intensity-modulated beams in radiotherapy planning., Phys Med Biol 48 (12) pp. 1795-1807
Intensity-modulated (IM) beam profiles computed by inverse-planning systems tend to be complex and may have multiple spatial minima and maxima. In addition to the structure originating from the treatment objectives, beam profiles might contain stochastic structure or noise and numerical artefacts, which present certain practical difficulties. The combinational use of conformal and intensity-modulated beams could be a different method of making the total fluence distribution less noisy and deliverable without compromising the advantages of IMRT. The investigation of this possibility provided the basis for this paper. A treatment-planning study was performed to compare plans combining modulated and unmodulated beams with a 5-field, equally spaced, full IMRT plan for treating the prostate and seminal vesicles in three patients. Beam angles for this study were 0 degrees, 72 degrees, 144 degrees, 216 degrees and 288 degrees. Additionally, a study was performed on a patient with a different beam arrangement (36 degrees, 108 degrees, 180 degrees, 252 degrees, 324 degrees) from the first study to test the obtained results. This study has demonstrated that it is possible to substitute up to two conformal beams in the originally full IMRT plan when carefully selecting the conformal beam angles. Making the anterior beam (0 degrees) and an anterior oblique beam (between 0 degrees and 90 degrees) conformal leads to a reduction in the total number of monitor units and segments of about 15% and 39%, respectively. Additionally, these two open fields can be used for simpler treatment verification.
Evans PM, Mosleh-Shirazi MA, Harris EJ, Seco J (2006) Monte Carlo and Lambertian light guide models of the light output from scintillation crystals at megavoltage energies, MEDICAL PHYSICS 33 (6) pp. 1797-1809 AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS
Juneja P, Harris EJ, Evans PM (2014) Investigation of the accuracy of breast tissue segmentation methods for the purpose of developing breast deformation models for use in adaptive radiotherapy, XVII INTERNATIONAL CONFERENCE ON THE USE OF COMPUTERS IN RADIATION THERAPY (ICCR 2013) 489 IOP PUBLISHING LTD
Beck JA, Budgell GJ, Roberts DA, Evans PM (2009) Electron beam quality control using an amorphous silicon EPID, MEDICAL PHYSICS 36 (5) pp. 1859-1866 American Association of Physicists in Medicine
Kavanagh A, Evans PM, Hansen VN, Webb S (2009) Obtaining breathing patterns from any sequential thoracic x-ray image set, PHYSICS IN MEDICINE AND BIOLOGY 54 (16) pp. 4879-4888
Swindell W, Evans PM (1996) Scattered radiation in portal images: a Monte Carlo simulation and a simple physical model., Med Phys 23 (1) pp. 63-73
The scattered radiation in 6 MV radiotherapy portal images is analyzed. First, a quantity SPR* is studied, by means of Monte Carlo (MC) modeling. SPR* is defined as the ratio, on the central axis, of the signal due to scattered radiation to that due to the primary radiation. The detector model mimics a high-energy photon detector in the context of transit dosimetry. Second, a physical model of SPR* has been developed from first principles. For a cylindrical phantom, placed symmetrically about the isocenter, it predicts that SPR* depends on the area A at the isocenter of the circular field and the phantom thickness d as follows. SPR* = k0Ad(1 + k1d)(1 + k2A), where k0 = 0.0266(L1 + L2)2/(L1L2)2, k2 = - [L1(-2) + L2(-2) + (L1(-1) + L2(-1))2((2/3) + (3 kappa/2))]/2pi, L1 is the source-to-isocenter distance, L2 is the isocenter-to-detector distance, and kappa is the mean energy of the radiation beam (MeV/0.511). Constant k1, for which there is no simple expression, depends on L2. Comparison to the MC data shows that for 60 or= 50 cm. Third, experimental measurements of the scatter-to-primary ratio were obtained using our custom built imaging system mounted on a Philips SL25 linear accelerator. In the first experiment, A was varied from 40 to 400 cm2 with L1 = L2 = 100 cm with d = 20 cm. In the second experiment water depth d was varied from 0 to 28 cm with L1 = L2 = 100 cm and A = 200 cm2. The rms agreements between the MC data and the experiments were 0.0015 and 0.0045, respectively.
Osmond JP, Zin HM, Harris EJ, Lupica G, Allinson NM, Evans PM (2011) Imaging of moving fiducial markers during radiotherapy using a fast, efficient active pixel sensor based EPID., Medical Physics 38 (11) pp. 6152-6159 American Association of Physicists in Medicine
The purpose of this work was to investigate the use of an experimental complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) for tracking of moving fiducial markers during radiotherapy.
Seco J, Clark CH, Evans PM, Webb S (2006) A quantitative study of IMRT delivery effects in commercial planning systems for the case of oesophagus and prostate tumours, BRITISH JOURNAL OF RADIOLOGY 79 (941) pp. 401-408 BRITISH INST RADIOLOGY
Symonds-Tayler JR, Partridge M, Evans PM (1997) An electronic portal imaging device for transit dosimetry., Phys Med Biol 42 (11) pp. 2273-2283
An electronic portal imaging device has been designed and constructed. It consists of an array of 128 CsI scintillation crystals coupled to photodiodes which is scanned across the field in 4 seconds. The linac is operated at a dose rate of 400 cGy min-1 and the dose delivered for image acquisition is approximately 27 cGy. The data acquisition controller is a stand-alone STE computer located within the scan arm. Sample images are presented showing contrast and spatial resolution of the system together with a humanoid phantom image and a clinical image of a breast cancer patient. The phantom images show the detector has a contrast resolution of 0.3% (at 15 mm diameter) and a spatial resolution of 2.5-3.2 mm. Images of uniform Perspex blocks have also been calibrated for thickness, indicating the system can measure radiological thickness to an accuracy of 2-3 mm of water. These results indicate the detector may be used for transit dosimetry applications including compensator design.
Bartlett FR, Colgan RM, Donovan EM, Carr K, Landeg S, Clements N, McNair HA, Locke I, Evans PM, Haviland JS, Yarnold JR, Kirby AM (2014) Voluntary breath-hold technique for reducing heart dose in left breast radiotherapy., J Vis Exp (89)
Breath-holding techniques reduce the amount of radiation received by cardiac structures during tangential-field left breast radiotherapy. With these techniques, patients hold their breath while radiotherapy is delivered, pushing the heart down and away from the radiotherapy field. Despite clear dosimetric benefits, these techniques are not yet in widespread use. One reason for this is that commercially available solutions require specialist equipment, necessitating not only significant capital investment, but often also incurring ongoing costs such as a need for daily disposable mouthpieces. The voluntary breath-hold technique described here does not require any additional specialist equipment. All breath-holding techniques require a surrogate to monitor breath-hold consistency and whether breath-hold is maintained. Voluntary breath-hold uses the distance moved by the anterior and lateral reference marks (tattoos) away from the treatment room lasers in breath-hold to monitor consistency at CT-planning and treatment setup. Light fields are then used to monitor breath-hold consistency prior to and during radiotherapy delivery.
Hsu A, Miller NR, Evans PM, Bamber JC, Webb S (2005) Feasibility of using ultrasound for real-time tracking during radiotherapy., Med Phys 32 (6) pp. 1500-1512
This study was designed to examine the feasibility of utilizing transabdominal ultrasound for real-time monitoring of target motion during a radiotherapy fraction. A clinical Acuson 128/XP ultrasound scanner was used to image various stationary and moving phantoms while an Elekta SL25 linear accelerator radiotherapy treatment machine was operating. The ultrasound transducer was positioned to image from the outer edge of the treatment field at all times. Images were acquired to videotape and analyzed using in-house motion tracking algorithms to determine the effect of the SL25 on the quality of the displacement measurements. To determine the effect on the dosimetry of the presence of the transducer, dose distributions were examined using thermoluminescent dosimeters loaded into an Alderson Rando phantom and exposed to a 10 x 10 cm2 treatment field with and without the ultrasound transducer mounted 2.5 cm outside the field edge. The ultrasound images acquired a periodic noise that was shown to occur at the pulsing frequency of the treatment machine. Images of moving tissue were analyzed and the standard deviation on the displacement estimates within the tissue was identical with the SL25 on and off. This implies that the periodic noise did not significantly degrade the precision of the tracking algorithm (which was better than 0.01 mm). The presence of the transducer at the surface of the phantom presented only a 2.6% change to the dose distribution to the volume of the phantom. The feasibility of ultrasonic motion tracking during radiotherapy treatment is demonstrated. This presents the possibility of developing a noninvasive, real-time and low-cost method of tracking target motion during a treatment fraction.
Harris EJ, McNair HA, Evans PM (2006) Feasibility of fully automated detection of fiducial markers implanted into the prostate using electronic portal imaging: A comparison of methods, INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 66 (4) pp. 1263-1270 ELSEVIER SCIENCE INC
Allinson N, Anaxagoras T, Aveyard J, Arvanitis C, Bates R, Blue A, Bohndiek S, Cabello J, Chen L, Chen S, Clark A, Clayton C, Cook E, Cossins A, Crooks J, El-Gomati M, Evans PM, Faruqi W, French M, Gow J, Greenshaw T, Greig T, Guerrini N, Harris EJ, Henderson R, Holland A, Jeyasundra G, Karadaglic D, Konstantinidis A, Liang HX, Maini KMS, McMullen G, Olivo A, O'Shea V, Osmond J, Ott RJ, Prydderch M, Qiang L, Riley G, Royle G, Segneri G, Speller R, Symonds-Tayler JRN, Triger S, Turchetta R, Venanzi C, Wells K, Zha X, Zin H (2009) The Multidimensional Integrated Intelligent Imaging project (MI-3), NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 604 (1-2) pp. 196-198 ELSEVIER SCIENCE BV
Kavanagh A, McQuaid D, Evans P, Webb S, Guckenberger M (2011) Dosimetric consequences of inter-fraction breathing-pattern variation on radiotherapy with personalized motion-assessed margins., Phys Med Biol 56 (22) pp. 7033-7043
The data from eight patients who had undergone stereotactic body radiotherapy were selected due to their 4D-CT planning scans showing that their tumours had respiratory induced motion trajectories of large amplitude (greater than 9 mm in cranio-caudal direction). Radiotherapy plans with personalized motion-assessed margins were generated for these eight patients. The margins were generated by inverse 4D planning on an eight-bin phase-sorted 4D-CT scan. The planning was done on an in-house software system with a non-rigid registration stage being completed using freely available software. The resultant plans were then recalculated on a 4D-CT scan taken later during the course of treatment. Simulated image-guided patient set-up was used to align the geometric centres of the tumour region and minimize any misalignment between the two reconstructions. In general, the variation in the patient breathing patterns was found to be very small. Consequently, the degradation of the mean dose to the tumour region was found to be around a few percent (
Donovan EM, Bleackley NJ, Evans PM, Reise SF, Yarnold JR (2002) Dose-position and dose-volume histogram analysis of standard wedged and intensity modulated treatments in breast radiotherapy., Br J Radiol 75 (900) pp. 967-973
The aim of this work was to evaluate the positional distribution of dose in a concise manner and to analyse dose-histogram results in tangential breast radiotherapy in 300 patients, randomized to standard wedged or intensity modulated radiotherapy (IMRT), for future correlation with clinical outcome data. A simple method for analysing the dose-position relationship in the treatment volume was used to compare the spatial distribution of dose in patients. The breast was divided into equal thirds (upper, middle and lower) and dose was assessed using three dose bands; 95-105%, >105-110% and >110% of the prescription dose. The effect of using IMRT on the dosimetry was assessed from dose-volume histogram data using the following parameters: percentage of the target volume receiving a dose less than 95%, greater than 105%, either less than 95% or greater than 105% of that prescribed; the mean dose; and the maximum dose. Doses greater than 105% were predominantly in the upper and lower regions of the breast in the standard wedged treatment. 96% of these patients received doses greater than 105% in the upper region of the breast and 70% received doses greater than 105% in the lower breast. Only 4% of patients allocated IMRT received doses greater than 105% in either region. Analysis of dose-volume histogram data showed that IMRT reduced the volume receiving a dose greater than 105% by a mean of 10.7% (p= or
Hector CL, Evans PM, Webb S (2001) The dosimetric consequences of inter-fractional patient movement on three classes of intensity-modulated delivery techniques in breast radiotherapy., Radiother Oncol 59 (3) pp. 281-291
BACKGROUND AND PURPOSE: A comparison between three classes of intensity-modulated delivery techniques was undertaken to examine the dosimetric consequences of using a multileaf collimator (MLC) reshaped on each imaged fraction as opposed to compensators designed on the first day of treatment potentially giving a treatment technique whose accuracy is thus degraded by movement. MATERIALS AND METHODS: The effects of inter-fractional patient movement for a cohort of six breast patients were studied. Five treatment techniques were evaluated, two using a compensator, two using multiple static fields (MSF) and one using a dynamic multileaf collimator (DMLC). The compensated techniques consisted of (i) the use of compensators designed on day 1 only and used each fraction thereafter and (ii) the use of a compensator redesigned for each imaged fraction. The two MSF techniques were (i) a four-field-component design and (ii) a method where the fluence interval between the MLC field components was set so they were equivalent to the compensator ('quantized' MSF-MLC). The final technique investigated was the DMLC. Plans were produced for each of the five methods and a paired t-test was used to assess the reduction in the breast volume outside the dose range 95-105% between sets of pairs of techniques. An on-line correction strategy was simulated to determine the number of treatments that required intervention. The action levels were calculated using the difference between the volume outside the dose range 95-105% calculated for treatments where the DMLC was designed on day 1 only and for each imaged fraction. Differences of greater than 2%, greater than 5% and greater than 10% were investigated. RESULTS: Thirty-five plans were evaluated for each technique. Results showed that a statistically significant mean reduction in the volume of the breast outside the dose range 95-105% could be achieved if the compensators were designed on each imaged fraction rather than on day 1 only (P=0.0045). When the comparison was made between the 'quantized' MSF-MLC and the technique where the compensators were designed on day 1 only, a statistically significant mean reduction in the volume of the breast tissue outside the dose range 95-105% was not achieved (P=0.21). Comparison of the DMLC technique to the technique where the compensators were designed on day 1 only results in a statistically significant mean reduction in the volume outside the dose range 95-105% (P=0.024). This correspon
Juneja P, Bonora M, Haviland JS, Harris E, Evans P, Somaiah N (2016) Does breast composition influence late adverse effects in breast radiotherapy?, The Breast 26 pp. 25-30 Elsevier
BACKGROUND: Large breast size is associated with increased risk of late adverse effects after surgery and radiotherapy for early breast cancer. It is hypothesised that effects of radiotherapy on adipose tissue are responsible for some of the effects seen. In this study, the association of breast composition with late effects was investigated along with other breast features such as fibroglandular tissue distribution, seroma and scar. METHODS: The patient dataset comprised of 18 cases with changes in breast appearance at 2 years follow-up post-radiotherapy and 36 controls with no changes, from patients entered into the FAST-Pilot and UK FAST trials at The Royal Marsden. Breast composition, fibroglandular tissue distribution, seroma and scar were assessed on planning CT scan images and compared using univariate analysis. The association of all features with late-adverse effect was tested using logistic regression (adjusting for confounding factors) and matched analysis was performed using conditional logistic regression. RESULTS: In univariate analyses, no statistically significant differences were found between cases and controls in terms of breast features studied. A statistically significant association (p 
Perrin R, Evans PM, Webb S, Partridge M (2010) The use of PET images for radiotherapy treatment planning: An error analysis using radiobiological endpoints, MEDICAL PHYSICS 37 (2) pp. 516-531
Donovan EM, James H, Bonora M, Yarnold JR, Evans PM (2012) Second cancer incidence risk estimates using BEIR VII models for standard and complex external beam radiotherapy for early breast cancer, Medical Physics 39 (10) pp. 5814-5824
Purpose: To compare organ specific cancer incidence risks for standard and complex external beam radiotherapy (including cone beam CT verification) following breast conservation surgery for early breast cancer. Method: Doses from breast radiotherapy and kilovoltage cone beam CT (CBCT) exposures were obtained from thermoluminescent dosimeter measurements in an anthropomorphic phantom in which the positions of radiosensitive organs were delineated. Five treatment deliveries were investigated: (i) conventional tangential field whole breast radiotherapy (WBRT), (ii) noncoplanar conformal delivery applicable to accelerated partial beast irradiation (APBI), (iii) two-volume simultaneous integrated boost (SIB) treatment, (iv) forward planned three-volume SIB, and (v) inverse-planned three volume SIB. Conformal and intensity modulated radiotherapy methods were used to plan the complex treatments. Techniques spanned the range from simple methods appropriate for patient cohorts with a low cancer recurrence risk to complex plans relevant to cohorts with high recurrence risk. Delineated organs at risk included brain, salivary glands, thyroid, contralateral breast, left and right lung, esophagus, stomach, liver, colon, and bladder. Biological Effects of Ionizing Radiation (BEIR) VII cancer incidence models were applied to the measured mean organ doses to determine lifetime attributable risk (LAR) for ages at exposure from 35 to 80 yr according to radiotherapy techniques, and included dose from the CBCT imaging. Results: All LAR decreased with age at exposure and were lowest for brain, thyroid, liver, and bladder (
Roberts DA, Hansen VN, Seco J, Thompson MG, Evans PM, Verhaegen F, Seuntjens J (2008) A simple Monte Carlo based optimisation model to determine image contrast in an imaging system, INTERNATIONAL WORKSHOP ON MONTE CARLO TECHNIQUES IN RADIOTHERAPY DELIVERY AND VERIFICATION - THIRD MCGILL INTERNATIONAL WORKSHOP 102
Poludniowski G, Evans PM, Webb S (2009) Rayleigh scatter in kilovoltage x-ray imaging: is the independent atom approximation good enough?, Physics in Medicine and Biology 54 (22) pp. 6931-6942 Institute of Physics
Monte Carlo simulation is the gold standard method for modelling scattering processes in medical x-ray imaging. General-purpose Monte Carlo codes, however, typically use the independent atom approximation (IAA). This is known to be inaccurate for Rayleigh scattering, for many materials, in the forward direction. This work addresses whether the IAA is sufficient for the typical modelling tasks in medical kilovoltage x-ray imaging. As a means of comparison, we incorporate a more realistic 'interference function' model into a custom-written Monte Carlo code. First, we conduct simulations of scatter from isolated voxels of soft tissue, adipose, cortical bone and spongiosa. Then, we simulate scatter profiles from a cylinder of water and from phantoms of a patient's head, thorax and pelvis, constructed from diagnostic-quality CT data sets. Lastly, we reconstruct CT numbers from simulated sets of projection images and investigate the quantitative effects of the approximation. We show that the IAA can produce errors of several per cent of the total scatter, across a projection image, for typical x-ray beams and patients. The errors in reconstructed CT number, however, for the phantoms simulated, were small (typically
Hsu A, Miller N, Evans P, Bamber J, Webb S (2003) Ultrasound guided radiotherapy - A feasibility evaluation (WIP), MEDICAL PHYSICS 30 (6) pp. 1384-1384 AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS
Poludniowski G, Allinson NM, Evans PM (2014) Proton computed tomography reconstruction using a backprojection-then-filtering approach., Phys Med Biol 59 (24) pp. 7905-7918
A novel approach to proton CT reconstruction using backprojection-then-filtering (BPF) is proposed. A list-mode algorithm is formulated accommodating non-linear proton paths. The analytical form is derived for the deblurring kernel necessary for the filtering step. Further, a finite matrix correction is derived to correct for the limited size of the backprojection matrix. High quantitative accuracy in relative stopping power is demonstrated (}0.1%) using Monte Carlo simulations. This accuracy makes the algorithm a promising candidate for future proton CT systems in proton therapy applications. For the purposes of reconstruction, each proton path in the object-of-interest was estimated based on a cubic spline fit to the proton entry and exit vectors. The superior spatial-resolution of the BPF method over the standard filtering-then-backprojection approach is demonstrated. As the BPF algorithm requires only one backprojection and filtering operation on a scan data set, it also offers computational advantages over an iterative reconstruction approach.
Donovan EM, Brabants P, Evans PM, Symonds-Tayler JR, Wilks R (2006) Accuracy and precision of an external-marker tracking-system for radiotherapy treatments., Br J Radiol 79 (946) pp. 808-817
The purpose of this work was to determine the accuracy and precision of a real-time motion-tracking system (Osiris+) for the monitoring of external markers used on patients receiving radiotherapy treatments. Random and systematic errors in the system were evaluated for linear (1D), circular (2D) and elliptical (3D) continuous motions, and for a set of static positions offset from an origin. A Wellhofer beam data measurement system and a computer controlled platform (which could be programmed to give motion in 3D) were used to move a hemi-spherical test object. The test object had four markers of the type used on patients. Three markers were aligned in the central plane and a fourth was positioned out of plane. Errors were expressed as deviations from the planned positions at the sampled time points. The marked points on the test object were tracked for the linear motion case with a variation from the true position of less than +/-1 mm, except for two extreme situations. The variation was within +/-2 mm when the lights were dimmed and when the amplitude of the movement was +/-5.0 cm. The 2D circular motion was tracked with a standard deviation of 1 mm or less over four cycles. The sampling rates of the system were found to be 0.3-0.4 s when it was monitoring actively and 1.5-1.6 s otherwise. The recorded Osiris+ measurements of known static positions were within +/-1 mm of the value from the computer controlled platform moving the test object. The elliptical motions in 3D were tracked to +/-1 mm in two directions (Y,Z), and generally to within +/-2 mm for the third direction (X); however, specific marked points could display an error of up to 5 mm at certain positions in X. The overall displacement error for the 3D motion was +/-1 mm with a standard deviation of 2.5 mm. The system performance is satisfactory for use in tracking external marker motion during radiotherapy treatments.
Gildersleve J, Dearnaley DP, Evans PM, Law M, Rawlings C, Swindell W (1994) A randomised trial of patient repositioning during radiotherapy using a megavoltage imaging system., Radiother Oncol 31 (2) pp. 161-168
Effectiveness of radiotherapy is dependent on the accuracy of beam alignment. Recent developments in megavoltage imaging allow real-time monitoring of beam placement. Maximum gains from this new technology can only be made if the information is utilised to correct patient positioning prospectively before the majority of a treatment fraction is delivered. We have developed and utilised an integrated megavoltage imaging system to perform a randomised trial demonstrating significant improvements in accuracy using treatment intervention techniques for pelvic radiotherapy. The mean field-placement accuracy improved from 4.3 mm to 2 mm and the proportion of treatments given with a field-placement error of > or = 5 mm decreased from 69% to 7%. This improvement in accuracy may enable smaller margins around the target volume to be chosen whilst ensuring complete target coverage at each treatment fraction.
Ott RJ, Evans N, Harris E, Evans P, Osmond J, Holland A, Prydderch M, Clark A, Crooks J, Halsall R, Key-Charriere M, Martin S, Turchetta R (2006) A CsI-Active Pixel Sensor Based Detector for Gamma Ray Imaging, 2006 IEEE NUCLEAR SCIENCE SYMPOSIUM CONFERENCE RECORD, VOL 1-6 pp. 2990-2992 IEEE
Evans P, Osmond J, Harris E, Symonds-Tayler R, Ott RJ, Holland A (2007) The application of active pixel sensors to precision radiotherapy, RADIOTHERAPY AND ONCOLOGY 84 pp. S116-S116 ELSEVIER IRELAND LTD
Zin H, Harris E, Osmond J, Evans P (2014) Fast regional readout CMOS Image Sensor for dynamic MLC tracking, Journal of Physics: Conference Series 489 (1)
Advanced radiotherapy techniques such as volumetric modulated arc therapy (VMAT) require verification of the complex beam delivery including tracking of multileaf collimators (MLC) and monitoring the dose rate. This work explores the feasibility of a prototype Complementary metal-oxide semiconductor Image Sensor (CIS) for tracking these complex treatments by utilising fast, region of interest (ROI) read out functionality. An automatic edge tracking algorithm was used to locate the MLC leaves edges moving at various speeds (from a moving triangle field shape) and imaged with various sensor frame rates. The CIS demonstrates successful edge detection of the dynamic MLC motion within accuracy of 1.0 mm. This demonstrates the feasibility of the sensor to verify treatment delivery involving dynamic MLC up to
Davies GA, Clowes P, McQuaid D, Evans PM, Webb S, Poludniowski G (2013) An experimental comparison of conventional two-bank and novel four-bank dynamic MLC tracking, PHYSICS IN MEDICINE AND BIOLOGY 58 (5) pp. 1635-1648 IOP PUBLISHING LTD
Bodey RK, Evans PM, Flux GD (2004) Application of the linear-quadratic model to combined modality radiotherapy., Int J Radiat Oncol Biol Phys 59 (1) pp. 228-241
PURPOSE: Methods of performing dosimetry for a combined modality radiotherapy (CMRT) consisting of a targeted radionuclide therapy (TRT) and separately delivered external beam therapy (EBT) have been established using the biologically effective dose (BED). However, a concurrent delivery of the two therapies may influence the radiobiologic effect of the treatment resulting from interaction between the therapies, and this situation has been modeled to assess the likely consequences of this regime. METHODS AND MATERIALS: A general form of the linear-quadratic model with a dose protraction factor was applied to concurrent delivery of EBT and TRT. Contributions to total BED from intra- and intermodality effects were calculated, and parameter values varied to determine conditions under which the intermodality contributions were likely to be most significant. A Poisson model of tumor control probability (TCP) was used to assess the predicted effect of concurrent delivery on treatment outcome. RESULTS: In general, over a wide range of parameter values, the effect of intermodality interactions in CMRT is small, increasing total BED delivered to tumor by approximately 1%, and producing a negligible increase in TCP. Synergistic effects could be greater in normal tissues if high doses were received from both therapies, with intermodality terms increasing total BED delivered by approximately 6% in the general case, and by approximately 18% for the case of slow repair in the spinal cord. A significant synergistic effect was predicted between EBT and I-125 seed therapy of the prostate when values of alpha/beta = 1.2 Gy, alpha = 0.026 Gy, mu = 0.36 h(-1) and N(0) = 138 clonogens were used, with TCP increasing from approximately 0.5 to 0.6. CONCLUSIONS: Under most clinical conditions, the relative temporal delivery of these two therapies is unlikely to significantly influence the overall radiobiologic effect to tumor at the cellular level. Synergistic effects may, however, be more significant in normal tissues and for tumors with low values of alpha/beta and alpha.
Harris EJ, Miller NR, Bamber JC, Symonds-Tayler JR, Evans PM (2010) Speckle tracking in a phantom and feature-based tracking in liver in the presence of respiratory motion using 4D ultrasound., Phys Med Biol 55 (12) pp. 3363-3380
We have evaluated a 4D ultrasound-based motion tracking system developed for tracking of abdominal organs during therapy. Tracking accuracy and precision were determined using a tissue-mimicking phantom, by comparing tracked motion with known 3D sinusoidal motion. The feasibility of tracking 3D liver motion in vivo was evaluated by acquiring 4D ultrasound data from four healthy volunteers. For two of these volunteers, data were also acquired whilst simultaneously measuring breath flow using a spirometer. Hepatic blood vessels, tracked off-line using manual tracking, were used as a reference to assess, in vivo, two types of automated tracking algorithm: incremental (from one volume to the next) and non-incremental (from the first volume to each subsequent volume). For phantom-based experiments, accuracy and precision (RMS error and SD) were found to be 0.78 mm and 0.54 mm, respectively. For in vivo measurements, mean absolute distance and standard deviation of the difference between automatically and manually tracked displacements were less than 1.7 mm and 1 mm respectively in all directions (left-right, anterior-posterior and superior-inferior). In vivo non-incremental tracking gave the best agreement. In both phantom and in vivo experiments, tracking performance was poorest for the elevational component of 3D motion. Good agreement between automatically and manually tracked displacements indicates that 4D ultrasound-based motion tracking has potential for image guidance applications in therapy.
Subiel A, Moskvin V, Welsh GH, Cipiccia S, Reboredo D, Evans P, Partridge M, DesRosiers C, Anania MP, Cianchi A, Mostacci A, Chiadroni E, Di Giovenale D, Villa F, Pompili R, Ferrario M, Belleveglia M, Di Pirro G, Gatti G, Vaccarezza C, Seitz B, Isaac RC, Brunetti E, Wiggins SM, Ersfeld B, Islam MR, Mendonca MS, Sorensen A, Boyd M, Jaroszynski DA (2014) Dosimetry of very high energy electrons (VHEE) for radiotherapy applications: Using radiochromic film measurements and Monte Carlo simulations, Physics in Medicine and Biology 59 (19) pp. 5811-5829
© 2014 Institute of Physics and Engineering in Medicine.Very high energy electrons (VHEE) in the range from 100-250 MeV have the potential of becoming an alternative modality in radiotherapy because of their improved dosimetry properties compared with MV photons from contemporary medical linear accelerators. Due to the need for accurate dosimetry of small field size VHEE beams we have performed dose measurements using EBT2 Gafchromic® film. Calibration of the film has been carried out for beams of two different energy ranges: 20 MeV and 165 MeV from conventional radio frequency linear accelerators. In addition, EBT2 film has been used for dose measurements with 135 MeV electron beams produced by a laser-plasma wakefield accelerator. The dose response measurements and percentage depth dose profiles have been compared with calculations carried out using the general-purpose FLUKA Monte Carlo (MC) radiation transport code. The impact of induced radioactivity on film response for VHEEs has been evaluated using the MC simulations. A neutron yield of the order of 10-5 neutrons cm-2 per incident electron has been estimated and induced activity due to radionuclide production is found to have a negligible effect on total dose deposition and film response. Neutron and proton contribution to the equivalent doses are negligible for VHEE. The study demonstrates that EBT2 Gafchromic film is a reliable dosimeter that can be used for dosimetry of VHEE. The results indicate an energy-independent response of the dosimeter for 20 MeV and 165 MeV electron beams and has been found to be suitable for dosimetry of VHEE.
Flampouri S, Evans P, Fielding A, Partridge M, Verhaegen F (2004) Investigation of megavoltage beams and detectors for electronic portal imaging, MEDICAL PHYSICS 31 (6) pp. 1832-1832 AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS
Seco J, Evans PM, Webb S (2000) Modelling the effects of IMRT delivery: Constraints and incorporation of beam smoothing into inverse planning, USE OF COMPUTERS IN RADIATION THERAPY pp. 542-544 SPRINGER-VERLAG BERLIN
Davies GA, Clowes P, Bedford JL, Evans PM, Webb S, Poludniowski G (2013) An experimental evaluation of the Agility MLC for motion-compensated VMAT delivery., Phys Med Biol 58 (13) pp. 4643-4657
An algorithm for dynamic multileaf-collimator (dMLC) tracking of a target performing a known a priori, rigid-body motion during volumetric modulated arc therapy (VMAT), has been experimentally validated and applied to investigate the potential of the Agility (Elekta AB, Stockholm, Sweden) multileaf-collimator (MLC) for use in motion-compensated VMAT delivery. For five VMAT patients, dosimetric measurements were performed using the Delta(4) radiation detector (ScandiDos, Uppsala, Sweden) and the accuracy of dMLC tracking was evaluated using a gamma-analysis, with threshold levels of 3% for dose and 3 mm for distance-to-agreement. For a motion trajectory with components in two orthogonal directions, the mean gamma-analysis pass rate without tracking was found to be 58.0%, 59.0% and 60.9% and was increased to 89.1%, 88.3% and 93.1% with MLC tracking, for time periods of motion of 4 s, 6 s and 10 s respectively. Simulations were performed to compare the efficiency of the Agility MLC with the MLCi MLC when used for motion-compensated VMAT delivery for the same treatment plans and motion trajectories. Delivery time increases from a static-tumour to dMLC-tracking VMAT delivery were observed in the range 0%?20% for the Agility, and 0%?57% with the MLCi, indicating that the increased leaf speed of the Agility MLC is beneficial for MLC tracking during lung radiotherapy.
Seco J, Evans PM (2006) Assessing the effect of electron density in photon dose calculations, MEDICAL PHYSICS 33 (2) pp. 540-552
Taylor JT, Poludniowski G, Price T, Waltham C, Allport PP, Casse GL, Esposito M, Evans PM, Green S, Manger S, Manolopoulos S, Nieto-Camero J, Parker DJ, Symons J, Allinson NM (2016) An experimental demonstration of a new type of proton computed tomography using a novel large-area silicon tracking detector, Medical Physics 43 (11) pp. 6129-6136 American Association of Physicists in Medicine
Purpose: Radiography and tomography using proton beams promises benefit to image-guidance and treatment
planning for proton therapy. A novel proton tracking detector is described and experimental demonstrations
at a therapy facility reported. A new type of proton CT reconstructing relative ?scattering-power?
rather than ?stopping-power? is also demonstrated. Notably, this new type of imaging does not require the
55 measurement of the residual energies of the protons.Methods: A large area, silicon micro-strip tracker with high spatial and temporal resolution has been developed
by the PRaVDA consortium and commissioned using beams of protons at iThemba LABS, Medical
Radiation Department, South Africa. The tracker comprises twelve planes of silicon developed using technology from high energy physics with each plane having an active area of micro-strips. The tracker is organised into four separate units each containing three detectors at 60æ
60 to one
another creating an x-u-v co-ordinate system. Pairs of tracking units are used to reconstruct vertices for
protons entering and exiting a phantom containing tissue equivalent inserts. By measuring the position and
direction of each proton before and after the phantom, the non-linear path for each proton through an object
can be reconstructed. Results: Experimental results are reported for tracking the path of protons with initial energies of 125 MeV
and 191 MeV. A spherical phantom of 75 mm diameter was imaged by positioning it between the entrance
and exit detectors of the tracker. Positions and directions of individual protons were used to create angular
distributions and 2D fluence maps of the beam. These results were acquired for 36 equally spaced projections
spanning 180æ
, allowing, for the the first time, an experimental CT image based upon the relative scattering
70 power of protons to be reconstructed. Conclusions: Successful tracking of protons through a thick target (phantom) has demonstrated that the
tracker discussed in this paper can provide the precise directional information needed to perform proton
radiography and tomography. When synchronized with a range telescope, this could enable the reconstruction
of proton CT images of stopping power. Furthermore, by measuring the deflection of many protons through
75 a phantom it was demonstrated that it is possible to reconstruct a new kind of CT image (scattering power)
based upon this tracking information alone.
Harris EJ, Miller NR, Bamber JC, Symonds-Tayler JR, Evans PM (2011) The effect of object speed and direction on the performance of 3D speckle tracking using a 3D swept-volume ultrasound probe., Phys Med Biol 56 (22) pp. 7127-7143 Institute of Physics
Three-dimensional (3D) soft tissue tracking using 3D ultrasound is of interest for monitoring organ motion during therapy. Previously we demonstrated feature tracking of respiration-induced liver motion in vivo using a 3D swept-volume ultrasound probe. The aim of this study was to investigate how object speed affects the accuracy of tracking ultrasonic speckle in the absence of any structural information, which mimics the situation in homogenous tissue for motion in the azimuthal and elevational directions. For object motion prograde and retrograde to the sweep direction of the transducer, the spatial sampling frequency increases or decreases with object speed, respectively. We examined the effect object motion direction of the transducer on tracking accuracy. We imaged a homogenous ultrasound speckle phantom whilst moving the probe with linear motion at a speed of 0-35 mm s{¹. Tracking accuracy and precision were investigated as a function of speed, depth and direction of motion for fixed displacements of 2 and 4 mm. For the azimuthal direction, accuracy was better than 0.1 and 0.15 mm for displacements of 2 and 4 mm, respectively. For a 2 mm displacement in the elevational direction, accuracy was better than 0.5 mm for most speeds. For 4 mm elevational displacement with retrograde motion, accuracy and precision reduced with speed and tracking failure was observed at speeds of greater than 14 mm s{¹. Tracking failure was attributed to speckle de-correlation as a result of decreasing spatial sampling frequency with increasing speed of retrograde motion. For prograde motion, tracking failure was not observed. For inter-volume displacements greater than 2 mm, only prograde motion should be tracked which will decrease temporal resolution by a factor of 2. Tracking errors of the order of 0.5 mm for prograde motion in the elevational direction indicates that using the swept probe technology speckle tracking accuracy is currently too poor to track homogenous tissue over a series of volume images as these errors will accumulate. Improvements could be made through increased spatial sampling in the elevational direction.
Kirby AM, deSouza NM, Evans PM, Yarnold JR (2009) MRI Delineation of Tumour Bed for Partial Breast Irradiation: Fusion/Comparison with CT/Titanium Clip-based Method, CLINICAL ONCOLOGY 21 (3) pp. 251-251 Elsevier
Introduction: A standard method of tumour bed (TB) delineation for
partial-breast irradiation (PBI) involves outlining titanium clips and
architectural abnormalities on CT images. Uncertainties remain
regarding delineation of TB/normal tissue interface between clips.
MRI offers greater soft-tissue contrast.We investigated whether MRI
adds information leading to changes in CT/clip-defined target
volumes, and evaluated the clinical significance of differences.
Methods: 30 women with breast invasive ductal carcinoma/DCIS
underwent lumpectomy during which 6e12 titanium clips were
secured in the four radial, anterior and deep excision margins of
the TB. Patients underwent CT imaging and MRI in the same prone
position. 3D-MRI datasets (T1-weighted [standard and fat-suppressed]
and T2-weighted) were co-registered with CT data
(matched using clips). TB was delineated separately on CT, MR,
and fused MR-CT datasets. Clinical (CTV) (TB + 15 mm) and planning
target volumes (PTV) (CTV + 10 mm) were generated. The primary
endpoint was conformity index (CI) between CT and fused-MRCT TB
(volume of agreement divided by total delineated volume
[volumetotal]). DiscordanceCT was defined as percentage of volumetotal missed by CT, and discordanceMRCT as percentage of
volumetotal missed by MRCT. Partial-breast dose distributions were
generated for CT/clip-CTV, and percentage of MRCT-CTV receiving
O95% of isocentre dose.
Results: Median CT/clip and MRCT-TB volumes were 5.7 cm3 and
9.7 cm3, respectively (mean percentage volume increase ¼ 55.1%).
Mean CIs for CT vs MRCT were 0.54 (TB), 0.84 (CTV) and 0.89 (PTV).
For CT vs MRCT TB, discordanceCT (i.e. geographical miss of
seroma/haemorrhage seen on MR) was 37.1%. DiscordanceMRCT
(i.e. inappropriate inclusion of normal breast tissue on CT) was
9.2%. Median coverage of CT/clip-CTV by 95% isodose was 97.1%
(30/30 CTV covered). Median coverage of MRCT-CTV was 96.5%. 4/
30 MRCT-CTV were inadequately covered (worst coverage ¼ 89.0%).
Conclusions: Addition of MR to CT/clip data increases TB volume by
identifying additional seroma/haemorrhage. TB discordance rarely
translates into clinically significant differences in CTV/PTV. CT/
clip-based PBI plans adequately cover MRCT-defined target
volumes in most cases. CT/clip-based TB delineation should remain the current standard for PBI.
Hector C, Webb S, Evans PM (2001) A simulation of the effects of set-up error and changes in breast volume on conventional and intensity-modulated treatments in breast radiotherapy., Phys Med Biol 46 (5) pp. 1451-1471
The effect of interfractional patient movement on dosimetry has been investigated for breast radiotherapy. Errors in patient set-up and changes in breast volume were simulated individually to determine how each contributes to the total dosimetric error. Two treatment techniques were investigated: a conventional treatment and an intensity-modulated treatment delivered using compensators. Six patients were investigated and anterior-posterior (AP) and superior-inferior (SI) displacements were simulated by displacing the isocentre in both directions by 2, 5 and 10 mm. A model of the breast was developed from the six patients to simulate changes in breast volume. In this model, the breast was described as a set of semi-ellipses. The volume of the breast was changed by varying the magnitude of the semi-major and semi-minor axes. Anisotropic changes in breast volume were also investigated. The dosimetric error was evaluated for each dose plan by calculating the volume outside the 95-105% dose range resulting from the simulations. A number of parameters describing the size and shape of the breast were also investigated to determine whether a susceptibility of outline sets to interfractional patient movement could be predicted. A parameter describing the increase in the breast volume outside the 95-105% dose range was calculated for AP a
Kirby AM, Evans PM, Haviland J, Yarnold JR (2009) Left Anterior Descending Coronary Artery (LAD) Doses from Breast Radiotherapy: is Prone Treatment Beneficial?, CLINICAL ONCOLOGY 21 (3) pp. 251-252 Elsevier
Breast radiotherapy increases risks of late cardiovascular
mortality/morbidity. LAD irradiation is implicated in pathogenesis, but the effects of prone positioning on its dosimetry
are unknown. We compared LAD and heart doses from whole (WBI)
and partial (PBI) breast radiotherapy planned prone and supine.
Methods: Thirty-nine (14 left-breast-affected) patients had titanium
clips placed in excision cavity walls at breast-conservation surgery.
Each underwent standard supine CT scanning before repositioning
and re-imaging prone on an in-house platform with an aperture
through which index breast falls. Partial-breast (PB) CTV was defined
as tumour bed (clips/architectural distortion) plus 15 mm margin.
WBclinical target volume (CTV) was defined using radio-opaque wire
marking clinically palpable breast tissue. Heart and LAD were
outlined. Conventional tangential-field PBI and WBI plans and dosevolume
histograms were produced for each position (total: 156
plans). Mean heart/LAD, and maximum LAD doses were compared.
Results: In left-breast-affected patients, mean (SD) LADmean
doses were 11.5 (8.4) Gy (supineWB), 12.1 (7.4) Gy (proneWB),
1.7 (1.6) Gy (supinePB), and 3.2 (3.0) Gy (pronePB). Mean (SD)
LADmax doses were 47.5 (5.7) Gy (supineWB), 47.4 (3.7) Gy
(proneWB), 22.8 (19.3) Gy (supinePB) and 32.1 (17.1) Gy
(pronePB). Prone positioning improved heart and LAD doses in 6/
14 WBI (mean improvement in LADmean ¼ 12.0 Gy) and 3/14 PBI
cases (mean improvement in LADmax ¼ 25.3 Gy), but worsened
doses in 7/14 WBI (mean increase in LADmean¼ 9.8 Gy) and 8/14
PBI (mean increase in LADmax¼ 24.7 Gy) cases. Breast volume
O1000 cm3 correlated with a benefit of prone treatment
(P ¼ 0.02). Heart and LAD parameters agreed on the best plan in
24/28 instances. PBI reduced heart and LAD doses in 100% of
patients compared to WBI.
Conclusions: LAD doses from WBI are significant. Prone positioning
is likely to improve heart and LAD dosimetry in women with breast
volumes O1000 cm3 (RE cup), but to increase heart/LAD doses in
women with breast volumes !1000 cm3. PBI universally improves
cardiac dosimetry compared to WBI and all eligible women should
be offered participation in PBI trials where available.
Bell MA, Byram BC, Harris EJ, Evans PM, Bamber JC (2012) In vivo liver tracking with a high volume rate 4D ultrasound scanner and a 2D matrix array probe., Phys Med Biol 57 (5) pp. 1359-1374 IOP PUBLISHING LTD
The effectiveness of intensity-modulated radiation therapy (IMRT) is compromised by involuntary motion (e.g. respiration, cardiac activity). The feasibility of processing ultrasound echo data to automatically estimate 3D liver motion for real-time IMRT guidance was previously demonstrated, but performance was limited by an acquisition speed of 2 volumes per second due to hardware restrictions of a mechanical linear array probe. Utilizing a 2D matrix array probe with parallel receive beamforming offered increased acquisition speeds and an opportunity to investigate the benefits of higher volume rates. In vivo livers of three volunteers were scanned with and without respiratory motion at volume rates of 24 and 48 Hz, respectively. Respiration was suspended via voluntary breath hold. Correlation-based, phase-sensitive 3D speckle tracking was applied to consecutively acquired volumes of echo data. Volumes were omitted at fixed intervals and 3D speckle tracking was re-applied to study the effect of lower scan rates. Results revealed periodic motion that corresponded with the heart rate or breathing cycle in the absence or presence of respiration, respectively. For cardiac-induced motion, volume rates for adequate tracking ranged from 8 to 12 Hz and was limited by frequency discrepancies between tracking estimates from higher and lower frequency scan rates. Thus, the scan rate of volume data acquired without respiration was limited by the need to sample the frequency induced by the beating heart. In respiratory-dominated motion, volume rate limits ranged from 4 to 12 Hz, interpretable from the root-mean-squared deviation (RMSD) from tracking estimates at 24 Hz. While higher volume rates yielded RMSD values less than 1 mm in most cases, lower volume rates yielded RMSD values of 2-6 mm.
Bartlett F, Donovan E, Colgan R, McNair H, Carr K, Locke I, Evans P, Haviland J, Yarnold J, Kirby A (2013) Partial breast irradiation margins with two deep-inspiratory breath-hold techniques, EUROPEAN JOURNAL OF CANCER 49 pp. S235-S235 ELSEVIER SCI LTD
Poludniowski G, Evans PM, Hansen VN, Webb S (2009) An efficient Monte Carlo-based algorithm for scatter correction in keV cone-beam CT., Physics in Medicine and Biology 54 (12) pp. 3847-3864 Institute of Physics
A new method is proposed for scatter-correction of cone-beam CT images. A coarse reconstruction is used in initial iteration steps. Modelling of the x-ray tube spectra and detector response are included in the algorithm. Photon diffusion inside the imaging subject is calculated using the Monte Carlo method. Photon scoring at the detector is calculated using forced detection to a fixed set of node points. The scatter profiles are then obtained by linear interpolation. The algorithm is referred to as the coarse reconstruction and fixed detection (CRFD) technique. Scatter predictions are quantitatively validated against a widely used general-purpose Monte Carlo code: BEAMnrc/EGSnrc (NRCC, Canada). Agreement is excellent. The CRFD algorithm was applied to projection data acquired with a Synergy XVI CBCT unit (Elekta Limited, Crawley, UK), using RANDO and Catphan phantoms (The Phantom Laboratory, Salem NY, USA). The algorithm was shown to be effective in removing scatter-induced artefacts from CBCT images, and took as little as 2 min on a desktop PC. Image uniformity was greatly improved as was CT-number accuracy in reconstructions. This latter improvement was less marked where the expected CT-number of a material was very different to the background material in which it was embedded.
Poludniowski G, Webb S, Evans PM (2012) Technical note: suppression of artifacts arising from simultaneous cone-beam imaging and RF transponder tracking in prostate radiotherapy., Med Phys 39 (3) pp. 1646-1649 American Association of Physicists in Medicine
Artifacts in treatment-room cone-beam reconstructions have been observed at the authors' center when cone-beam acquisition is simultaneous with radio frequency (RF) transponder tracking using the Calypso 4D system (Calypso Medical, Seattle, WA). These artifacts manifest as CT-number modulations and increased CT-noise. The authors present a method for the suppression of the artifacts.
Mosleh-Shirazi MA, Evans PM, Swindell W, Webb S, Partridge M (1998) A cone-beam megavoltage CT scanner for treatment verification in conformal radiotherapy., Radiother Oncol 48 (3) pp. 319-328
PURPOSE: A prototype scanner for large-volume megavoltage computed tomography (MVCT) in a clinical set-up is described. The ultimate aim is to improve treatment accuracy in conformal radiotherapy through patient set-up error reduction and transit dosimetry. MATERIALS AND METHODS: The scanner consists of a custom-built 2D CsI(Tl) crystal array viewed by a lens and a CCD camera. Image acquisition is synchronized with radiation pulses. The 2D projections resulting from a single continuous 360 degrees gantry rotation are reconstructed using a cone-beam tomography algorithm. Prior to reconstruction, the raw projections are calibrated and corrected for centre of rotation movement and accelerator output fluctuation. The performance of the system has been evaluated by reconstructing projections of open fields, test objects and a humanoid phantom. RESULTS: Hundreds of 2D projections can be acquired with a clinically-acceptable data collection time (about 2 min) and dose (approximately 40 cGy, with a possible four-fold reduction). A maximum density resolution of about 2% is achieved offering some soft tissue discrimination without using image enhancement tools. A spatial resolution of 2.5 mm is obtained. The reconstructed image intensity is linear with electron density over the range of interest. Coronal or sagittal slices through the 3D reconstruction of the humanoid phantom show a better delineation of structures than the corresponding portal images taken at the same orientation. CONCLUSIONS: A similar image quality to our current single-slice MVCT scanner is achieved with the advantage of providing tens of tomographic slices for a single gantry rotation. This work demonstrates the feasibility of clinical cone-beam MVCT and indicates how this prototype can be improved.
Ott R, Evans N, Evans P, Osmond J, Clark A, Turchetta R (2009) Preliminary investigations of active pixel sensors in Nuclear Medicine imaging, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 604 (1-2) pp. 86-88 ELSEVIER SCIENCE BV
Parent L, Seco J, Fielding A, Dance D, Evans P (2005) A-Si EPID image prediction for fields of various sizes and off-axis positions using Monte Carlo methods, RADIOTHERAPY AND ONCOLOGY 76 pp. S148-S148 ELSEVIER IRELAND LTD
Fielding AL, Evans PM, Clark CH (2002) The use of electronic portal imaging to verify patient position during intensity-modulated radiotherapy delivered by the dynamic MLC technique., Int J Radiat Oncol Biol Phys 54 (4) pp. 1225-1234
PURPOSE: The precise shape of the three-dimensional dose distributions created by intensity-modulated radiotherapy means that the verification of patient position and setup is crucial to the outcome of the treatment. In this paper, we investigate and compare the use of two different image calibration procedures that allow extraction of patient anatomy from measured electronic portal images of intensity-modulated treatment beams. METHODS AND MATERIALS: Electronic portal images of the intensity-modulated treatment beam delivered using the dynamic multileaf collimator technique were acquired. The images were formed by measuring a series of frames or segments throughout the delivery of the beams. The frames were then summed to produce an integrated portal image of the delivered beam. Two different methods for calibrating the integrated image were investigated with the aim of removing the intensity modulations of the beam. The first involved a simple point-by-point division of the integrated image by a single calibration image of the intensity-modulated beam delivered to a homogeneous polymethyl methacrylate (PMMA) phantom. The second calibration method is known as the quadratic calibration method and required a series of calibration images of the intensity-modulated beam delivered to different thicknesses of homogeneous PMMA blocks. Measurements were made using two different detector systems: a Varian amorphous silicon flat-panel imager and a Theraview camera-based system. The methods were tested first using a contrast phantom before images were acquired of intensity-modulated radiotherapy treatment delivered to the prostate and pelvic nodes of cancer patients at the Royal Marsden Hospital. RESULTS: The results indicate that the calibration methods can be used to remove the intensity modulations of the beam, making it possible to see the outlines of bony anatomy that could be used for patient position verification. This was shown for both posterior and lateral delivered fields. CONCLUSIONS: Very little difference between the two calibration methods was observed, so the simpler division method, requiring only the single extra calibration measurement and much simpler computation, was the favored method. This new method could provide a complementary tool to existing position verification methods, and it has the advantage that it is completely passive, requiring no further dose to the patient and using only the treatment fields.
Bartlett FR, Carr K, McNair HA, Locke I, Yarnold JR, Kirby AM, Colgan RM, Donovan EM, Evans PM, Haviland JS (2013) The UK HeartSpare Study: Randomised evaluation of voluntary deep-inspiratory breath-hold in women undergoing breast radiotherapy, Radiotherapy and Oncology
Purpose: To determine whether voluntary deep-inspiratory breath-hold (v_DIBH) and deep-inspiratory breath-hold with the active breathing coordinator" (ABC_DIBH) in patients undergoing left breast radiotherapy are comparable in terms of normal-tissue sparing, positional reproducibility and feasibility of delivery. Methods: Following surgery for early breast cancer, patients underwent planning-CT scans in v_DIBH and ABC_DIBH. Patients were randomised to receive one technique for fractions 1-7 and the second technique for fractions 8-15 (40 Gy/15 fractions total). Daily electronic portal imaging (EPI) was performed and matched to digitally-reconstructed radiographs. Cone-beam CT (CBCT) images were acquired for 6/15 fractions and matched to planning-CT data. Population systematic (£) and random errors (Ã) were estimated. Heart, left-anterior-descending coronary artery, and lung doses were calculated. Patient comfort, radiographer satisfaction and scanning/treatment times were recorded. Within-patient comparisons between the two techniques used the paired t-test or Wilcoxon signed-rank test. Results: Twenty-three patients were recruited. All completed treatment with both techniques. EPI-derived £ were d1.8 mm (v_DIBH) and d2.0 mm (ABC_DIBH) and à d2.5 mm (v_DIBH) and d2.2 mm (ABC_DIBH) (all p non-significant). CBCT-derived £ were d3.9 mm (v_DIBH) and d4.9 mm (ABC_DIBH) and à d 4.1 mm (v_DIBH) and d 3.8 mm (ABC_DIBH). There was no significant difference between techniques in terms of normal-tissue doses (all p non-significant). Patients and radiographers preferred v_DIBH (p = 0.007, p = 0.03, respectively). Scanning/treatment setup times were shorter for v_DIBH (p = 0.02, p = 0.04, respectively). Conclusions: v_DIBH and ABC_DIBH are comparable in terms of positional reproducibility and normal tissue sparing. v_DIBH is preferred by patients and radiographers, takes less time to deliver, and is cheaper than ABC_DIBH. © 2013 Elsevier Ireland Ltd. All rights reserved.
Morton EJ, Swindell W, Lewis DG, Evans PM (1991) A linear array, scintillation crystal-photodiode detector for megavoltage imaging, Medical Physics 18 (4) pp. 681-691
An imaging device has been developed to acquire images during external photon-beam radiotherapy treatments. It consists of a linear array of 128 zinc tungstate (ZnW04) scintillation crystals each of which is individually optically coupled to a photodiode and associated electronics. The image is formed by scanning the linear array across the radiation field using a stepping motor under the control of a microcomputer. Image archive, display, and analysis are performed using a microVAX II computer. Results from a general theoretical analysis are presented before a detailed description of the particular detector construction. The mechanical design of the detector is such that the detector is automatically positioned to within a millimeter relative to the treatment source. This simplifies procedures for analyzing setup variations when comparing a treatment image to any other treatment, or planning, images. Image acquisition takes under 4 s with a contrast resolution of better than 1% at a spatial resolution of 2.5 mm in the object plane. The primary dose used to form these images is 0.55 cGy although the dose received by the patient will be closer to 25 cGy due to the linear scanning geometry and 3.8-s scan time that is used. © 1991, American Association of Physicists in Medicine. All rights reserved.
Hansen VN, Evans PM, Swindell W (1996) The application of transit dosimetry to precision radiotherapy., Med Phys 23 (5) pp. 713-721
A method of using electronic portal imaging (EPI) for transit dosimetry is described. In this method, a portal image of the treatment field is first aligned with a digitally reconstructed radiograph (DRR) to geometrically relate the computed tomography (CT) scan, used to generate the DRR, with the EPI. Then the EPI is corrected for scatter within the patient to yield a map of primary fluence striking the detector. This is backprojected through the planning CT data set to yield a distribution of primary fluence within the patient. This distribution is then convolved with dose deposition kemels to yield a map of dose delivery within the patient. Such a distribution may be compared with the dose distribution resulting from the original treatment plan in order to evaluate the adequacy of the treatment. This method has been evaluated using a humanoid phantom. We find the transit dosimetry relative dose distribution when compared with film and thermoluminescent dosimeter (TLD) measurements and compared with our planning system to agree within 2% in the pelvic region of a humanoid phantom.
Kirby AM, Crowley C, Jena R, Gregory DL, Coles CE, Harris EJ, Evans PM (2013) Tumour bed delineation for partial breast/breast boost radiotherapy: What is the optimal number of implanted markers?, Radiotherapy and Oncology pp. 231-235 Elsevier
Purpose: International consensus has not been reached regarding the optimal number of implanted tumour bed (TB) markers for partial breast/breast boost radiotherapy target volume delineation. Four common methods are: insertion of 6 clips (4 radial, 1 deep and 1 superficial), 5 clips (4 radial and 1 deep), 1 clip at the chest wall, and no clips. We compared TB volumes delineated using 6, 5, 1 and 0 clips in women who have undergone wide-local excision (WLE) of breast cancer (BC) with full-thickness closure of the excision cavity, in order to determine the additional margin required for breast boost or partial breast irradiation (PBI) when fewer than 6 clips are used. Methods: Ten patients with invasive ductal BC who had undergone WLE followed by implantation of six fiducial markers (titanium clips) each underwent CT imaging for radiotherapy planning purposes. Retrospective processing of the DICOM image datasets was performed to remove markers and associated imaging artefacts, using an in-house software algorithm. Four observers outlined TB volumes on four different datasets for each case: (1) all markers present (CT); (2) the superficial marker removed (CT); (3) all but the chest wall marker removed (CT); (4) all markers removed (CT). For each observer, the additional margin required around each of TB, TB, and TB in order to encompass TB was calculated. The conformity level index (CLI) and differences in centre-of-mass (COM) between observers were quantified for CT, CT, CT, CT. Results: The overall median additional margins required to encompass TB were 8 mm (range 0-28 mm) for TB, 5 mm (range 1-13 mm) for TB, and 2 mm (range 0-7 mm) for TB. CLI were higher for TB volumes delineated using CT (0.31) CT (0.32) than for CT (0.19) and CT (0.15). Conclusions: In women who have undergone WLE of breast cancer with full-thickness closure of the excision cavity and who are proceeding to PBI or breast boost RT, target volume delineation based on 0 or 1 implanted markers is not recommended as large additional margins are required to account for uncertainty over true TB location. Five implanted markers (one deep and four radial) are likely to be adequate assuming the addition of a standard 10-15 mm TB-CTV margin. Low CLI values for all TB volumes reflect the sensitivity of low volumes to small differences in delineation and are unlikely to be clinically significant for TB and TB in the context of adequate TB-CTV margins. © 2013 Elsevier Ireland Ltd. All rights reserved
Kirby AM, Evans PM, Donovan EM, Convery HM, Haviland JS, Yarnold JR (2010) Prone versus supine positioning for whole and partial-breast radiotherapy: A comparison of non-target tissue dosimetry, RADIOTHERAPY AND ONCOLOGY 96 (2) pp. 178-184
Partridge M, Evans PM, Mosleh-Shirazi MA (1998) Linear accelerator output variations and their consequences for megavoltage imaging., Med Phys 25 (8) pp. 1443-1452
An experimental study of radiation output intensity fluctuations of a Philips SL25 linear accelerator is presented. Measurements are obtained using an electronic portal imaging device, and the consequences of the measured fluctuations for various different applications of megavoltage imaging including portal imaging, transit dosimetry and megavoltage computed tomography (MVCT) are discussed with examples. Fluctuations in output of +/- 0.7% (1 SD) are seen on every radiation pulse after photon noise and uncertainties caused by the detection system have been accounted for. Large fluctuations are also seen during the initial beam stabilization period (15%), during normal accelerator operation after the beam has been on for more than 1 min (4.5%) and during are therapy as a repeatable function of gantry angle (9%). Such output intensity fluctuations are shown to produce image artifacts in portal imaging devices with scanned detector readout and can also produce systematic errors in detector calibration that would lead to uncertainty in transit dose calculations. The propagation of these intensity fluctuations through MVCT image reconstruction is shown to produce ring artifacts in the reconstructed image. Sample portal and MVCT images are presented. All observed fluctuations in accelerator output are well within the manufacturer's specifications and do not affect the total dose delivered during normal treatment. Finally, megavoltage imaging is shown to be a powerful tool for accelerator quality assurance and treatment verification.
Coolens C, Evans P, Seco J, Webb S (2004) Analysis of stochastic noise in intensity-modulated beams, PHYSICS IN MEDICINE AND BIOLOGY 49 (17) PII S0031- pp. 3857-3875 IOP PUBLISHING LTD
Inverse planning techniques are known to produce intensity-modulated beams (IMBs) that are highly modulated. They are characterized by the fact that they contain high-frequency modulations that are absent in the profiles that are easier to deliver. For the purpose of this study these clinically unwanted fluctuations are being defined as 'noise'. Although these highly modulated solutions are also optimal solutions, as soon as the profiles are being delivered, they become unfavourable with respect to delivery efficiency and the analysis and verification of treatment. The aim of this work was therefore to understand the origins of the structure and complexity of IMBs. Ultimately, if one can characterize the essential features in optimum beam profiles, it might be possible to control the frequency distribution of IMBs and simplify the IMRT planning and delivery process. The study was based on two common optimization techniques: simulated annealing (SA) and gradient-descent (GD). The assumptions made at the start of this work were that the stochastic noise caused by the SA optimization technique is dominant over other sources of noise and that it could be separated out from the essential modulation after convergence of the cost function by averaging minimum-cost fluence profiles. The results indicate that there are three possible sources of stochastic noise in IMBs, i.e. the optimization technique, the cost function and the definition of convergence of that cost function. In terms of the optimization technique itself, it was confirmed that the gradient-descent technique does not introduce stochastic noise in the IMBs. The SA technique does introduce stochastic noise but averaging of minimum-cost fluence profiles does not result in smoother beam profiles. This originates from the fact that this type of noise is not the dominant factor in the optimization, but rather the curvature of the cost function close to the global minimum. It is shown that the choice of initial temperature in the SA optimization technique is crucial for the convergence of the cost function and the frequency distribution of the fluence profiles. If the initial temperature is too small the stochastic noise will get frozen into the fluence profiles and become the dominant component of noise, resulting in very random-looking and difficult to deliver patterns.
Bartlett FR, Colgan RM, Donovan EM, Carr K, Landeg S, Clements N, McNair HA, Locke I, Evans PM, Haviland JS, Yarnold JR, Kirby AM (2014) Voluntary breath-hold technique for reducing heart dose in left breast radiotherapy, Journal of Visualized Experiments (89)
Breath-holding techniques reduce the amount of radiation received by cardiac structures during tangential-field left breast radiotherapy. With these techniques, patients hold their breath while radiotherapy is delivered, pushing the heart down and away from the radiotherapy field. Despite clear dosimetric benefits, these techniques are not yet in widespread use. One reason for this is that commercially available solutions require specialist equipment, necessitating not only significant capital investment, but often also incurring ongoing costs such as a need for daily disposable mouthpieces. The voluntary breath-hold technique described here does not require any additional specialist equipment. All breath-holding techniques require a surrogate to monitor breath-hold consistency and whether breath-hold is maintained. Voluntary breath-hold uses the distance moved by the anterior and lateral reference marks (tattoos) away from the treatment room lasers in breath-hold to monitor consistency at CT-planning and treatment setup. Light fields are then used to monitor breath-hold consistency prior to and during radiotherapy delivery. © JoVE 2006-2014. All Rights Reserved.
Price T, Esposito M, Poludniowski G, Taylor J, Waltham C, Parker DJ, Green S, Manolopoulos S, Allinson NM, Anaxagoras T, Evans P, Nieto-Camero J (2015) Expected proton signal sizes in the PRaVDA Range Telescope for proton Computed Tomography, Journal of Instrumentation 10 (5)
Proton radiotherapy has demonstrated benefits in the treatment of certain cancers. Accurate measurements of the proton stopping powers in body tissues are required in order to fully optimise the delivery of such treaments. The PRaVDA Consortium is developing a novel, fully solid state device to measure these stopping powers. The PRaVDA Range Telescope (RT), uses a stack of 24 CMOS Active Pixel Sensors (APS) to measure the residual proton energy after the patient. We present here the ability of the CMOS sensors to detect changes in the signal sizes as the proton traverses the RT, compare the results with theory, and discuss the implications of these results on the reconstruction of proton tracks.
Poludniowski GG, Evans PM (2007) Calculation of x-ray spectra emerging from an x-ray tube. Part I. electron penetration characteristics in x-ray targets., Medical Physics 34 (6) pp. 2164-2174 American Association of Physicists in Medicine
The penetration characteristics of electron beams into x-ray targets are investigated for incident electron kinetic energies in the range 50-150 keV. The frequency densities of electrons penetrating to a depth x in a target, with a fraction of initial kinetic energy, u, are calculated using Monte Carlo methods for beam energies of 50, 80, 100, 120 and 150 keV in a tungsten target. The frequency densities for 100 keV electrons in Al, Mo and Re targets are also calculated. A mixture of simple modeling with equations and interpolation from data is used to generalize the calculations in tungsten. Where possible, parameters derived from the Monte Carlo data are compared to experimental measurements. Previous electron transport approximations in the semiempirical models of other authors are discussed and related to this work. In particular, the crudity of the use of the Thomson-Whiddington law to describe electron penetration and energy loss is highlighted. The results presented here may be used towards calculating the target self-attenuation correction for bremsstrahlung photons emitted within a tungsten target.
Roberts DA, Hansen VN, Thompson MG, Poludniowski G, Niven A, Seco J, Evans PM (2012) Kilovoltage energy imaging with a radiotherapy linac with a continuously variable energy range, MEDICAL PHYSICS 39 (3) pp. 1218-1226 AMER ASSOC PHYSICISTS MEDICINE AMER INST PHYSICS
Partridge M, Evans PM, MoslehShirazi MA (1997) Accelerator output fluctuation: The effect on megavoltage CT and portal image quality., PROCEEDINGS OF THE XIITH INTERNATIONAL CONFERENCE ON THE USE OF COMPUTERS IN RADIATION THERAPY pp. 288-290 MEDICAL PHYSICS PUBLISHING
Poludniowski G, Thomas MD, Evans PM, Webb S (2010) CT reconstruction from portal images acquired during volumetric-modulated arc therapy., Phys Med Biol 55 (19) pp. 5635-5651 Institute of Physics
Volumetric-modulated arc therapy (VMAT), a form of intensity-modulated arc therapy (IMAT), has become a topic of research and clinical activity in recent years. As a form of arc therapy, portal images acquired during the treatment fraction form a (partial) Radon transform of the patient. We show that these portal images, when used in a modified global cone-beam filtered backprojection (FBP) algorithm, allow a surprisingly recognizable CT-volume to be reconstructed. The possibility of distinguishing anatomy in such VMAT-CT reconstructions suggests that this could prove to be a valuable treatment position-verification tool. Further, some potential for local-tomography techniques to improve image quality is shown.
Castellano IA, Dance DR, Evans PM (2005) CT dosimetry: Getting the best from the adult cristy phantom, RADIATION PROTECTION DOSIMETRY 114 (1-3) pp. 321-325 OXFORD UNIV PRESS
Poludniowski GG, Evans PM, Webb S (2012) Cone Beam Computed Tomography Number Errors and Consequences for Radiotherapy Planning: An Investigation of Correction Methods, International Journal of Radiation Oncology, Biology, Physics
Purpose: The potential of keV cone beam computed tomography (CBCT) for guiding adaptive replanning is well-known. There are impediments to this, one being CBCT number accuracy. The purpose of this study was to investigate CBCT number correction methods and the affect of residual inaccuracies on dose deposition. Four different correction strategies were applied to the same patient data to compare performance and the sophistication of correction-method needed for acceptable dose errors. Methods and Materials: Planning CT and CBCT reconstructions were used for 12 patients (6 brain, 3 prostate, and 3 bladder cancer patients). All patients were treated using Elekta linear accelerators and XVI imaging systems. Two of the CBCT number correction methods investigated were based on an algorithm previously proposed by the authors but only previously applied to phantoms. Two further methods, based on an approach previously suggested in the research literature, were also examined. Dose calculations were performed using scans of a "worst" subset of patients using the Pinnacle
version 9.0 treatment planning system and the patients' clinical plans. Results: All mean errors in CBCT number were
Coolens C, Evans P, Seco J, Webb S (2003) Analysis of stochastic noise in intensity-modulated beams, RADIOTHERAPY AND ONCOLOGY 68 pp. S100-S101 ELSEVIER IRELAND LTD
Partridge M, Symonds-Tayler JR, Evans PM (1999) A large-area ionization chamber for portal image calibration., Phys Med Biol 44 (1) pp. 271-279
Methods of removing the effects of linear accelerator (linac) output fluctuation from electronic portal images are described and compared. The output of the linac is measured using a specially constructed large-area ionization chamber during imaging and recorded with the image. The use of a dose-rate signal directly from the linac monitor chamber is discussed. Various versions of a quadratic thickness calibration scheme are tested, incorporating linac output data measured by the ionization chamber. Experimental results are presented showing that the incorporation of data from the ionization chamber gives improved absolute calibration accuracy and flatness. Immediately after calibration, the mean systematic thickness error in calibration of a uniform 136.8 mm water-equivalent slab was shown to be no more than 0.6 mm with a thickness variation within each image also of no more than +/-0.8 mm. This was true even when imaging with an unstable linac beam giving mean thickness errors between images of 8.8 mm and variations within each image of +/-4.9 mm without the ionization chamber correction. Up to one month after calibration, use of the ionization chamber to remove short-term linac fluctuations is shown to still keep mean thickness errors to less than 1.6 mm with variations within each image of no more than +/-1.4 mm.
Spies L, Evans PM, Partridge M, Hansen VN, Bortfeld T (2000) Direct measurement and analytical modeling of scatter in portal imaging, MEDICAL PHYSICS 27 (3) pp. 462-471 AMER INST PHYSICS
McNair HA, Kavanagh A, Powell C, Symonds-Tayler JRN, Brada M, Evans PM (2012) Fluoroscopy as a surrogate for lung tumour motion, BRITISH JOURNAL OF RADIOLOGY 85 (1010) pp. 168-175
South CP, Evans PM, Partridge M (2009) Dose prescription complexity versus tumor control probability in biologically conformal radiotherapy, MEDICAL PHYSICS 36 (10) pp. 4379-4388 American Association of Physicists in Medicine
McQuaid S, Scuffham J, Alobaidli S, Prakash V, Ezhil V, Nisbet A, South C, Evans P (2017) Factors influencing the robustness of P-value measurements in CT texture prognosis studies, Physics in Medicine and Biology 62 (13) 5403 IOP Publishing
Several studies have recently reported on the value of CT texture analysis in predicting survival, although the topic remains controversial, with further validation needed in order to consolidate the evidence base. The aim of this study was to investigate the effect of varying the input parameters in the Kaplan?Meier analysis, to determine whether the resulting P-value can be considered to be a robust indicator of the parameter's prognostic potential. A retrospective analysis of the CT-based normalised entropy of 51 patients with lung cancer was performed and overall survival data for these patients were collected. A normalised entropy cut-off was chosen to split the patient cohort into two groups and log-rank testing was performed to assess the survival difference of the two groups. This was repeated for varying normalised entropy cut-offs and varying follow-up periods. Our findings were also compared with previously published results to assess robustness of this parameter in a multi-centre patient cohort. The P-value was found to be highly sensitive to the choice of cut-off value, with small changes in cut-off producing substantial changes in P. The P-value was also sensitive to follow-up period, with particularly noisy results at short follow-up periods. Using matched conditions to previously published results, a P-value of 0.162 was obtained. Survival analysis results can be highly sensitive to the choice in texture cut-off value in dichotomising patients, which should be taken into account when performing such studies to avoid reporting false positive results. Short follow-up periods also produce unstable results and should therefore be avoided to ensure the results produced are reproducible. Previously published findings that indicated the prognostic value of normalised entropy were not replicated here, but further studies with larger patient numbers would be required to determine the cause of the different outcomes.
Bartlett F, Donovan E, McNair H, Corsini L, Colgan R, Evans P, Maynard L, Griffin C, Haviland J, Yarnold J, Kirby A (2016) The UK HeartSpare Study (Stage II): Multicentre Evaluation of a Voluntary Breath-hold Technique in Patients Receiving Breast Radiotherapy, Clinical Oncology 29 (3) pp. e51-e56 Elsevier
Aims To evaluate the feasibility and heart-sparing ability of the voluntary breath-hold (VBH) technique in a multicentre setting. Materials and methods Patients were recruited from 10 UK centres. Following surgery for early left breast cancer, patients with any heart inside the 50% isodose from a standard free-breathing tangential field treatment plan underwent a second planning computed tomography (CT) scan using the VBH technique. A separate treatment plan was prepared on the VBH CT scan and used for treatment. The mean heart, left anterior descending coronary artery (LAD) and lung doses were calculated. Daily electronic portal imaging (EPI) was carried out and scanning/treatment times were recorded. The primary end point was the percentage of patients achieving a reduction in mean heart dose with VBH. Population systematic (£) and random errors (Ã) were estimated. Within-patient comparisons between techniques used Wilcoxon signed-rank tests. Results In total, 101 patients were recruited during 2014. Primary end point data were available for 93 patients, 88 (95%) of whom achieved a reduction in mean heart dose with VBH. Mean cardiac doses (Gy) for free-breathing and VBH techniques, respectively, were: heart 1.8 and 1.1, LAD 12.1 and 5.4, maximum LAD 35.4 and 24.1 (all P
Smyth G, Evans PM, Bamber J, Mandeville H, Welsh L, Saran F, Bedford J (2016) Non-coplanar trajectories to improve organ at risk sparing in volumetric modulated arc therapy for primary brain tumours, Radiotherapy and Oncology 121 (1) pp. 124-131 Elsevier
Background and purpose: To evaluate non-coplanar volumetric modulated arc radiotherapy (VMAT) trajectories for organ at risk (OAR) sparing in primary brain tumour radiotherapy. Materials and methods: Fifteen patients were planned using coplanar VMAT and compared against non-coplanar VMAT plans for three trajectory optimization techniques. A geometric heuristic technique (GH) combined beam scoring and Dijkstra's algorithm to minimize the importance-weighted sum of OAR volumes irradiated. Fluence optimization was used to perform a local search around coplanar and GH trajectories, producing fluence-based local search (FBLS) and FBLS+GH trajectories respectively. Results: GH, FBLS, and FBLS+GH trajectories reduced doses to the contralateral globe, optic nerve, hippocampus, temporal lobe, and cochlea. However, FBLS increased dose to the ipsilateral lens, optic nerve and globe. Compared to GH, FBLS+GH increased dose to the ipsilateral temporal lobe and hippocampus, contralateral optics, and the brainstem and body. GH and FBLS+GH trajectories reduced bilateral hippocampi normal tissue complication probability (p = 0.028 and p = 0.043, respectively). All techniques reduced PTV conformity; GH and FBLS+GH trajectories reduced homogeneity but less so for FBLS+GH. Conclusions: The geometric heuristic technique best spared OARs and reduced normal tissue complication probability, however incorporating fluence information into non-coplanar trajectory optimization maintained PTV homogeneity.
Donovan E, Brooks C, Mitchell R, Mukesh M, Coles C, Evans PM, Harris E (2014) The effect of image guidance on dose distributions in breast boost radiotherapy, Clinical Oncology 26 (11) pp. 671-676 Elsevier
Aims: To determine the effect of image-guided radiotherapy on the dose distributions in breast boost treatments. Materials and methods: Computed tomography images from a cohort of 60 patients treated within the IMPORT HIGH trial (CRUK/06/003) were used to create sequential and concomitant boost treatment plans (30 cases each). Two treatment plans were created for each case using tumour bed planning target volume (PTV) margins of 5 mm (achieved with image-guided radiotherapy) and 8 mm (required for bony anatomy verification). Dose data were collected for breast, lung and heart; differences with margin size were tested for statistical significance. Results: A median decrease of 29 cm (range 11-193 cm) of breast tissue receiving 95% of the prescribed dose was observed where image-guided radiotherapy margins were used. Decreases in doses to lungs, contralateral breast and heart were modest, but statistically significant (P 91%) of the prescribed dose in 12 cases; in addition, the required partial breast median dose was exceeded in nine concomitant boost cases by 0.5-3.7 Gy. Conclusions: The use of image guidance and, hence, a reduced tumour bed PTV margin, in breast boost radiotherapy resulted in a modest reduction in radiation dose to breast, lung and heart tissues. Reduced margins enabled by image guidance were necessary to discriminate between dose levels to multiple PTVs in the concomitant breast boost plans investigated.
Phillips I, Ajaz M, Ezhil V, Prakash V, Alobaidli S, McQuaid S, South C, Scuffham J, Nisbet A, Evans P (2017) Clinical Applications of textural analysis in Non-Small Cell Lung cancer, British Journal of Radiology 91 (1081) British Institute of Radiology
Lung cancer is the leading cause of cancer mortality worldwide. Treatment pathways include regular cross-sectional imaging, generating large data sets which present intriguing possibilities for exploitation beyond standard visual interpretation. This additional data mining has been termed ?radiomics? and includes semantic and agnostic approaches. Texture Analysis (TA) is an example of the latter, and uses a range of mathematically derived features to describe an image or region of an image. Often TA is used to describe a suspected or known tumour. TA is an attractive tool as large existing image sets can be submitted to diverse techniques for data processing, presentation, interpretation and hypothesis testing with annotated clinical outcomes. There is a growing anthology of published data using different TA techniques to differentiate between benign and malignant lung nodules, differentiate tissue sub-types of lung cancer, prognosticate and predict outcome and treatment response, as well as predict treatment side effects and potentially aid radiotherapy planning. The aim of this systematic review is to summarise the current published data and understand the potential future role of TA in managing lung cancer.
Phillips I, Ajaz M, Ezhil V, Prakash V, Alobaidli S, McQuaid S, South C, Scuffham J, Nisbet A, Evans P (2017) Clinical Applications of textural analysis in Non-Small Cell Lung cancer, British Journal of Radiology 91 (1081) British Institute of Radiology
Lung cancer is the leading cause of cancer mortality worldwide. Treatment pathways include regular cross-sectional imaging, generating large data sets which present intriguing possibilities for exploitation beyond standard visual interpretation. This additional data mining has been termed ?radiomics? and includes semantic and agnostic approaches. Texture Analysis (TA) is an example of the latter, and uses a range of mathematically derived features to describe an image or region of an image. Often TA is used to describe a suspected or known tumour. TA is an attractive tool as large existing image sets can be submitted to diverse techniques for data processing, presentation, interpretation and hypothesis testing with annotated clinical outcomes. There is a growing anthology of published data using different TA techniques to differentiate between benign and malignant lung nodules, differentiate tissue sub-types of lung cancer, prognosticate and predict outcome and treatment response, as well as predict treatment side effects and potentially aid radiotherapy planning. The aim of this systematic review is to summarise the current published data and understand the potential future role of TA in managing lung cancer.
Alobaidli S (2017) Functional imaging and texture analysis in radiotherapy planning.,
In this thesis, a methodology is developed to generate optimised three-dimensional voxel-based CT texture maps (3D-VTM) to examine regional heterogeneity information within tumours and their relation to tumour metabolism measured as 18F-fluoro-deoxy glucose (18F-FDG) Positron Emission Tomography (PET) distributions. Ten patients diagnosed with advanced non-small cell lung cancer (NSCLC) were investigated. For optimal texture information decoding, an optimised quantisation method is presented. The texture feature that reflects heterogeneity and which showed correlation with patients? survival was chosen for this thesis. To account for respiratory motion effects, an in-house designed phantom was used to characterise the effects of motion on texture analysis and consequently adapt our method in that regard.
Amos R, Bulbeck H, Burnet N, Crellin A, Eaton D, Evans P, Hall E, Hawkins M, Mackay R, Kirkby K, Sharma R, Sebag-Montefiore D (2018) Proton Beam Therapy ? the Challenges of Delivering High-quality Evidence of Clinical Benefit, Clinical Oncology 30 (5) pp. 280-284 Elsevier
The use of proton beam therapy (PBT) offers the opportunity to improve greater conformality of radiotherapy treatment delivery in some patients. However, it is associated with a high capital cost and the need to build new dedicated facilities. We discuss how the global radiotherapy community can respond to the challenge of producing high-quality evidence of clinical benefit from PBT in adult patients. In the UK, the National Cancer Research Institute-funded Clinical and Radiotherapy Translational group has established the PBT Clinical Trial Strategy Group. An eight-point framework is described that can assist the development and delivery of high-quality clinical trials.