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Prof Andrew Nisbet


Professor of Medical Physics

Biography

Biography

Professor Andrew Nisbet was appointed Head of Medical Physics at the Royal Surrey County Hospital NHS Foundation Trust and Professor of Medical Physics at Surrey University in 2006. He graduated in Physics at the University of Edinburgh before completing an MSc in Medical Physics at the University of Aberdeen and subsequently a PhD from the same University. Prior to taking up appointment in Guildford he was Head of Radiotherapy Physics within the Medical Physics Department at the Oxford Radcliffe Hospitals NHS Trust.

The Department of Medical Physics includes the Regional Radiation Protection Service, Radiotherapy Physics, Radiopharmacy & Nuclear Medicine Physics, Scientific Computing, Technical Services and the Department also hosts the National Coordinating Centre for the Physics of Mammography on behalf of the NHS Breast Screening Programme.

Professor Nisbet has been a member of the Technology Subgroup of the National Radiotherapy Advisory Group, which produced an influential report on planning future radiotherapy services in England. He is an expert in the implementation of advanced radiotherapy techniques and the assessment of risk from such treatments. He has worked closely with the National Physical Laboratory in providing national recommendations on the measurement of dose for radiotherapy. He has been a consultant for the International Atomic Energy Agency producing guidelines for the on-site auditing of radiotherapy departments and has sat on the Panel of Scientific Experts for a European Union funded grant with the objectives of performing an EU-wide study on the implementation of Medical Exposure Directive requirements aimed at the reduction of the probability and the magnitude of accidents in radiotherapy and developing guidelines on a risk analysis of accidental and unintended exposures in external beam radiotherapy and, therefore, improving patient safety.

As Principal or co-Investigator he has held grants in excess of £6m. As Head of the Medical Physics Department and Co-Investigator he has been involved in two CRUK / EPSRC /MRC/ NIHR Cancer Imaging Programme Grants investigating the optimisation of digital technology for mammographic screening. He has helped develop the dosimetric methodology for determining cardiac dose from breast radiotherapy employed in a major international epidemiological study funded by the European Union, for which he was Partner and lead medical physicist, and which has recently published its results in the New England Journal of Medicine. He has been a co-investigator on a Department of Health funded grant examining the adaption of medical imaging systems for body monitoring in the event of a radiological incident. He has also been PI for two NIHR invention for innovation grants, in collaboration with the National Physical Laboratory, developing a novel superconducting quantum interference device (SQUID) based microbolometer for the measurement of radiobiological effect from particle therapy beams.

He has supervised 12 PhD, 3 MD and numerous MSc postgraduate students and has published over 80 papers in peer reviewed journals. He is currently primary or co-supervisor to a further 8 PhD students and 1 MD fellow.

My publications

Publications

Dimitriadis A, Kirkby KJ, Nisbet A, Clark CH (2015) Current status of cranial stereotactic radiosurgery in the UK, BRITISH JOURNAL OF RADIOLOGY 89 (1058) ARTN 20150452 BRITISH INST RADIOLOGY
Issa F, Nisbet A, Bradley DA, Hugtenburg RP (2013) Novel high resolution I brachytherapy source dosimetry using Ge-doped optical fibres, Radiation Physics and Chemistry 92 pp. 48-53
The steep dose gradients close to brachytherapy sources limit the ability to obtain accurate measurements of dose. Here we use a novel high spatial resolution dosimeter to measure dose around a I source and compare against simulations. Ge-doped optical fibres, used as thermoluminescent dosimeters, offer sub-mm spatial resolution, linear response from 10cGy to >1kGy and dose-rate independence. For a I brachytherapy seed in a PMMA phantom, doses were obtained for source-dosimeter separations from 0.1cm up to several cm, supported by EGSnrc/DOSRZznrc Monte Carlo simulations and treatment planning system data. The measurements agree with simulations to within 2.3%±0.3% along the transverse and perpendicular axes and within 3.0%±0.5% for measurements investigating anisotropy in angular dose distribution. Measured and Veriseed" brachytherapy treatment planning system (TPS) values agreed to within 2.7%±0.5%.Ge-doped optical fibre dosimeters allow detailed dose mapping around brachytherapy sources, not least in situations of high dose gradient. © 2013 Elsevier Ltd.
Nisbet A, Ward A (2001) Radiotherapy equipment--purchase or lease?, Br J Radiol 74 (884) pp. 735-744
Against a background of increasing demand for radiotherapy equipment, this study was undertaken to investigate options for equipment procurement, in particular to compare purchase with lease. The perceived advantages of lease are that equipment can be acquired within budget and cashflow constraints, with relatively low amounts of cash leaving the NHS in the first year, avoiding the necessity of capitalizing the equipment and providing protection against the risk of obsolescence associated with high technology equipment. The perceived disadvantages of leasing are that the Trust does not own the equipment, leasing can be more expensive in revenue terms, the tender process is extended and there may be lease conditions to be met, which may be costly and/or restrictive. There are also a number of technical considerations involved in the leasing of radiotherapy equipment that influence the financial analysis and practical operation of the radiotherapy service. The technical considerations include servicing and planned preventative maintenance, upgrades, spare parts, subsequent purchase of "add ons", modification of equipment, research and development work, commencement of the lease period, return of equipment at the end of the lease period and negotiations at the end of the lease period. A study from Raigmore Hospital, Inverness is described, which involves the procurement of new, state-of-the-art radiotherapy equipment. This provides an overview of the procurement process, including a summary of the advantages and disadvantages of leasing, with the figures from the financial analysis presented and explained. In addition, a detailed description is given of the technical considerations to be taken into account in the financial analysis and negotiation of any lease contract.
Nisbet A, Thwaites DI, Nahum AE, Pitchford WG (1998) An experimental evaluation of recent electron dosimetry codes of practice, PHYSICS IN MEDICINE AND BIOLOGY 43 (8) pp. 1999-2014 IOP PUBLISHING LTD
Jafari SM, Alalawi AI, Hussein M, Alsaleh W, Najem MA, Hugtenburg RP, Bradley DA, Spyrou NM, Clark CH, Nisbet A (2014) Glass beads and Ge-doped optical fibres as thermoluminescence dosimeters for small field photon dosimetry., Phys Med Biol 59 (22) pp. 6875-6889
An investigation has been made of glass beads and optical fibres as novel dosimeters for small-field photon radiation therapy dosimetry. Commercially available glass beads of largest dimension 1.5 mm and GeO2-doped SiO2 optical fibres of 5 mm length and 120 µm diameter were characterized as thermoluminescence dosimeters. Results were compared against Monte-Carlo simulations with BEAMnrc/DOSXYZnrc, EBT3 Gafchromic film, and a high-resolution 2D-array of liquid-filled ionization chambers. Measurements included relative output factors and dose profiles for square-field sizes of 1, 2, 3, 4, and 10 cm. A customized Solid-Water® phantom was employed, and the beads and fibres were placed at defined positions along the longitudinal axis to allow accurate beam profile measurement. Output factors and the beam profile parameters were compared against those calculated by BEAMnrc/DOSXYZnrc. The output factors and field width measurements were found to be in agreement with reference measurements to within better than 3.5% for all field sizes down to 2 cm2 for both dosimetric systems, with the beads showing a discrepancy of no more than 2.8% for all field sizes. The results confirm the potential of the beads and fibres as thermoluminescent dosimeters for use in small photon radiation field sizes.
Taylor CW, Nisbet A, McGale P, Darby SC (2007) Dosimetry based on radiotherapy treatment planning, RADIATION RESEARCH 167 (3) pp. 359-359 RADIATION RESEARCH SOC
Taylor CW, Brønnum D, Darby SC, Gagliardi G, Hall P, Jensen MB, McGale P, Nisbet A, Ewertz M (2011) Cardiac dose estimates from Danish and Swedish breast cancer radiotherapy during 1977-2001., Radiotherapy and Oncology 100 (2) pp. 176-183 Elsevier
To estimate target and cardiac doses from breast cancer radiotherapy in Denmark and in the Stockholm and Umeå areas of Sweden during 1977-2001.
Nisbet A, Aukett RJ, Davison A, Glendinning A, Thwaites DI, Bonnett DE (1998) An Experimental Intercomparison of Kilovoltage X-ray Dosimetry Protocols, pp. 43-54 Medical Physics Pub
Clark CH, Hussein M, Tsang Y, Thomas R, Wilkinson D, Bass G, Snaith J, Gouldstone C, Bolton S, Nutbrown R, Venables K, Nisbet A (2014) A multi-institutional dosimetry audit of rotational intensity-modulated radiotherapy., Radiother Oncol 113 (2) pp. 272-278
Rotational IMRT (VMAT and Tomotherapy) has now been implemented in many radiotherapy centres. An audit to verify treatment planning system modelling and treatment delivery has been undertaken to ensure accurate clinical implementation.
Weatherburn H, Nisbet A (1991) The Protocols and Codes of Practice Used for the Determination of Absorbed Dose in Megavoltage Photon and Electron Beams, Critical Reviews in Biomedical Engineering 19 (2,3) pp. 147-180
Lei M, Clark C, Adams E, Freeman K, Jamieson C, Dabbs M, Jordan T, Whitaker S, Nisbet A, Urbano TG (2010) CBCT Evaluation of Dose-Volume Changes in Contralateral Parotid Gland during Head and Neck IG-IMRT, INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 78 (3) pp. S481-S482 ELSEVIER SCIENCE INC
Palmer AL, Diez P, Gandon L, Wynn-Jones A, Bownes P, Lee C, Aird E, Bidmead M, Lowe G, Bradley D, Nisbet A (2015) A multicentre 'end to end' dosimetry audit for cervix HDR brachytherapy treatment., Radiother Oncol 114 (2) pp. 264-271
PURPOSE: To undertake the first multicentre fully 'end to end' dosimetry audit for HDR cervix brachytherapy, comparing planned and delivered dose distributions around clinical treatment applicators, with review of local procedures. MATERIALS AND METHODS: A film-dosimetry audit was performed at 46 centres, including imaging, applicator reconstruction, treatment planning and delivery. Film dose maps were calculated using triple-channel dosimetry and compared to RTDose data from treatment planning systems. Deviations between plan and measurement were quantified at prescription Point A and using gamma analysis. Local procedures were also discussed. RESULTS: The mean difference between planned and measured dose at Point A was -0.6% for plastic applicators and -3.0% for metal applicators, at standard uncertainty 3.0% (k=1). Isodose distributions agreed within 1mm over a dose range 2-16Gy. Mean gamma passing rates exceeded 97% for plastic and metal applicators at 3% (local) 2mm criteria. Two errors were found: one dose normalisation error and one applicator library misaligned with the imaged applicator. Suggestions for quality improvement were also made. CONCLUSIONS: The concept of 'end to end' dosimetry audit for HDR brachytherapy has been successfully implemented in a multicentre environment, providing evidence that a high level of accuracy in brachytherapy dosimetry can be achieved.
Al-Nowais S, Nisbet A, Adamovics J, Doran SJ (2009) An attempt to determine the saturation dose for PRESAGE, Journal of Physics: Conference Series 164 (1) 012043
This brief work-in-progress outlines two methods that we have attempted for determining the dose at which the linear relation between optical density of a PRESAGE" dosimeter and the dose deposited breaks down. Both methods were equally successful in mapping the linear relation up to an optical density of approximately 6.25 cm?1 (absorbance 2..5), but no saturation was found in this region.
Abdul Rahman A, Hugtenburg R, Abdul Sani S, Alalawi A, Issa F, Thomas R, Barry M, Nisbet A, Bradley DA (2012) An investigation of the thermoluminescence of Ge-doped SiO(2) optical fibres for application in interface radiation dosimetry., Applied Radiation and Isotopes 70 (7) pp. 1436-1441
We investigate the ability of high spatial resolution (
Jafari SM, Jordan TJ, Distefano G, Bradley DA, Spyrou NM, Nisbet A, Clark CH (2015) Feasibility of using glass-bead thermoluminescent dosimeters for radiotherapy treatment plan verification, BRITISH JOURNAL OF RADIOLOGY 88 (1055) ARTN 20140804 BRITISH INST RADIOLOGY
Dalah EZ, Nisbet A, Bradley D (2010) Effect of window level on target volume delineation in treatment planning, APPLIED RADIATION AND ISOTOPES 68 (4-5) pp. 602-604 PERGAMON-ELSEVIER SCIENCE LTD
Agency IAE (2007) On-site Visits to Radiotherapy Centres - Medical Physics Procedures,
The Quality Assurance Team for Radiation Oncology (QUATRO) provides independent quality audits both proactive (comprehensive reviews of the radiotherapy practices) and reactive (focused investigations in response to suspected or actual ...
Merrett J, Fenwick A, Scuffham J, Johansson L, Nisbet A (2015) One Size Fits All? Assessment of the Use of a Simple Calibration Protocol for Quantitative SPECT/CT Imaging of 177Lu in European Hospitals, EUROPEAN JOURNAL OF NUCLEAR MEDICINE AND MOLECULAR IMAGING 42 pp. S184-S184 SPRINGER
Noor NM, Hussein M, Bradley DA, Nisbet A, Kadni T (2014) Characterization of Ge-doped optical fibres for MV radiotherapy dosimetry, Radiation Physics and Chemistry 98 pp. 33-41
Ge-doped optical fibres offer promising thermoluminescence (TL) properties together with small physical size and modest cost. Their use as dosimeters for postal radiotherapy dose audits of megavoltage photon beams has been investigated. Key dosimetric characteristics including reproducibility, linearity, dose rate, temperature and angular dependence have been established. A methodology of measuring absorbed dose under reference conditions was developed. The Ge-doped optical fibres offer linearity between TL yield and dose, with a reproducibility of better than 5%, following repeated measurements (n=5) for doses from 5cGy to 1000cGy. The fibres also offer dose rate, angular and temperature independence, while an energy-dependent response of 7% was found over the energy range 6MV to 15MV (TPR of 0.660, 0.723 and 0.774 for 6, 10 and 15MV respectively). The audit methodology has been developed with an expanded uncertainty of 4.22% at 95% confidence interval for the photon beams studied. © 2013 Elsevier Ltd.
Abdul Rahman AT, Nisbet A, Bradley DA (2011) Dose-rate and the reciprocity law: TL response of Ge-doped SiO2 optical fibers at therapeutic radiation doses, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 652 (1) pp. 891-895
Al-Ahbabi SS, Bradley DA, Nisbet A (2013) Tomotherapy evaluation for head and neck cases using two types of phantoms, Radiation Physics and Chemistry
The use of rotational therapy as an important method of treatment delivery is expected to increase due in a large part to the development and utilisation of tomotherapy. Rotational therapy minimises the occurrence of hotspots and the irradiation of critical organs, providing more uniform dosing while sparing critical organs. Two important characteristics of rotational radiation are its dynamic nature and dosimetric variability in radiation delivery, both of which present a considerable challenge for clinical physicists seeking appropriate tools to meet the demands of quality assurance. In this paper 15 Delivery Quality Assurance (DQA) plans of head and neck patients were assessed for the Hi-Art tomotherapy system using Kodak X-Omat V film and an A1SL Ref F92722 ion chamber versus MapCheck. Absolute dose measurement showed average differences of 3.42 cGy and 98% Gamma (³) factor for the Cheese phantom technique. For the MapCheck technique the average difference and Gamma factor were 0.74 cGy and 96%, respectively. Gamma (³) matrix distribution was used to evaluate the difference between measured and calculated dose distribution. © 2013 Elsevier Ltd. All rights reserved.
Alalawi A, Nisbet A, Alzimami K, Bradley DA, Hugtenburg R, Abdul Rahman A, Barry M (2014) Measurement of dose enhancement close to high atomic number media using optical fibre thermoluminescence dosimeters, Radiation Physics and Chemistry 95 pp. 145-147
Present interest concerns development of a system to measure photoelectron-enhanced dose close to a tissue interface using analogue gold-coated doped silica-fibre thermoluminescence detectors and an X-ray set operating at 250. kVp. Study is made of the dose enhancement factor for various thicknesses of gold; measurements at a total gold thickness of 160. nm (accounting for incident and exiting photons) produces a mean measured dose enhancement factor of 1.33±0.01 To verify results, simulations of the experimental setup have been performed. © 2013 Elsevier Ltd.
Nowais SA, Kacperek A, Brunt JNH, Adamovics J, Nisbet A, Doran SJ (2010) An investigation of the response of the radiochromic dosimeter PRESAGE" to irradiation by 62 MeV protons, Journal of Physics: Conference Series 250 pp. 155-159
Palmer AL, Lee C, Ratcliffe AJ, Bradley D, Nisbet A (2013) Design and implementation of a film dosimetry audit tool for comparison of planned and delivered dose distributions in high dose rate (HDR) brachytherapy., Phys Med Biol 58 (19) pp. 6623-6640
A novel phantom is presented for 'full system' dosimetric audit comparing planned and delivered dose distributions in HDR gynaecological brachytherapy, using clinical treatment applicators. The brachytherapy applicator dosimetry test object consists of a near full-scatter water tank with applicator and film supports constructed of Solid Water, accommodating any typical cervix applicator. Film dosimeters are precisely held in four orthogonal planes bisecting the intrauterine tube, sampling dose distributions in the high risk clinical target volume, points A and B, bladder, rectum and sigmoid. The applicator position is fixed prior to CT scanning and through treatment planning and irradiation. The CT data is acquired with the applicator in a near clinical orientation to include applicator reconstruction in the system test. Gamma analysis is used to compare treatment planning system exported RTDose grid with measured multi-channel film dose maps. Results from two pilot audits are presented, using Ir-192 and Co-60 HDR sources, with a mean gamma passing rate of 98.6% using criteria of 3% local normalization and 3 mm distance to agreement (DTA). The mean DTA between prescribed dose and measured film dose at point A was 1.2 mm. The phantom was funded by IPEM and will be used for a UK national brachytherapy dosimetry audit.
Saeed Al-Ahbabi S, Bradley DA, Beyomi M, Alkatib Z, Adhaheri S, Darmaki M, Nisbet A (2012) A comparison of protocols for external beam radiotherapy beam calibrations., Appl Radiat Isot 70 (7) pp. 1331-1336
A number of codes of practice (CoP) for electron and photon radiotherapy beam dosimetry are currently in use. Comparison is made of the more widely used of these, specifically those of the International Atomic Energy Agency (IAEA TRS-398), the American Association of Physicists in Medicine (AAPM TG-51) and the Institute of Physics and Engineering in Medicine (IPEM 2003). All are based on calibration of ionization chambers in terms of absorbed dose to water, each seeking to reduce uncertainty in delivered dose, providing an even stronger system of primary standards than previous air-kerma based approaches. They also provide a firm, traceable and straight-forward formalism (Radiology, 1996). Included in making dose assessments for the three CoP are calibration coefficients for a range of beam quality indices. Measurements have been performed using clinical photon and electron beams, the absorbed dose to water being obtained following the recommendations given by each code. Electron beam comparisons have been carried out using measurements for electron beams of nominal energies 6, 9, 12, 16 and 20 MeV. Comparisons were also carried out for photon beams of nominal energies 6 and 18 MV. For photon beams use was made of NE2571 cylindrical graphite walled ionization chambers, cross-calibrated against an NE2611 Secondary Standard; for electron beams, PTW Markus and NACP-02 plane-parallel chambers were used. Irradiations were made using Varian 600C/2100C linacs, supported by water tanks and Virtual Water" phantoms. The absorbed doses for photon and electron beams obtained following these CoP are all in good agreement, with deviations of less than 2%. A number of studies have been carried out by different groups in different countries to examine the consistency of dosimetry codes of practice or protocols. The aim of these studies is to confirm that the goal of those codes is met, namely uniformity in establishment of dosimetry of all radiation beam types used in cancer therapy in the world, and this is one of the studies.
Palmer AL, Bradley D, Nisbet A (2014) Evaluation and implementation of triple-channel radiochromic film dosimetry in brachytherapy, JOURNAL OF APPLIED CLINICAL MEDICAL PHYSICS 15 (4) pp. 280-296 MULTIMED INC
Mills CA, Chan YF, Intaniwet A, Shkunov M, Nisbet A, Keddie JL, Sellin PJ (2013) Direct detection of 6 MV x-rays from a medical linear accelerator using a semiconducting polymer diode, Physics in Medicine and Biology 58 (13) pp. 4471-4482
Recently, a new family of low-cost x-radiation detectors have been developed, based on semiconducting polymer diodes, which are easy to process, mechanically flexible, relatively inexpensive, and able to cover large areas. To test their potential for radiotherapy applications such as beam monitors or dosimeters, as an alternative to the use of solid-state inorganic detectors, we present the direct detection of 6 MV x-rays from a medical linear accelerator using a thick film, semiconducting polymer detector. The diode was subjected to 4 ms pulses of 6 MV x-rays at a rate of 60 Hz, and produces a linear increase in photocurrent with increasing dose rate (from 16.7 to 66.7 mGy s-1). The sensitivity of the diode was found to range from 13 to 20 nC mGy -1 cm-3, for operating voltages from -50 to -150 V, respectively. The diode response was found to be stable after exposure to doses up to 15 Gy. Testing beyond this dose range was not carried out. Theoretical calculations show that the addition of heavy metallic nanoparticles to polymer films, even at low volume fractions, increases the x-ray sensitivity of the polymer film/nanoparticle composite so that it exceeds that for silicon over a wide range of x-ray energies. The possibility of detecting x-rays with energies relevant to medical oncology applications opens up the potential for these polymer detectors to be used in detection and imaging applications using medical x-ray beams. © 2013 Institute of Physics and Engineering in Medicine.
Teoh M, Clark CH, Wood K, Whitaker S, Nisbet A (2011) Volumetric modulated arc therapy: a review of current literature and clinical use in practice., Br J Radiol 84 (1007) pp. 967-996
Volumetric modulated arc therapy (VMAT) is a novel radiation technique, which can achieve highly conformal dose distributions with improved target volume coverage and sparing of normal tissues compared with conventional radiotherapy techniques. VMAT also has the potential to offer additional advantages, such as reduced treatment delivery time compared with conventional static field intensity modulated radiotherapy (IMRT). The clinical worldwide use of VMAT is increasing significantly. Currently the majority of published data on VMAT are limited to planning and feasibility studies, although there is emerging clinical outcome data in several tumour sites. This article aims to discuss the current use of VMAT techniques in practice and review the available data from planning and clinical outcome studies in various tumour sites including prostate, pelvis (lower gastrointestinal, gynaecological), head and neck, thoracic, central nervous system, breast and other tumour sites.
Alalawi AI, Nisbet A, Alzimami KS, Bradley DA, Abdul Rahman AT, Barry MA, Hugtenburg RP (2013) Measurement of dose enhancement close to high atomic number media using optical fibre thermo luminescence dosimeters, Radiation Physics and Chemistry
Present interest concerns development of a system to measure photoelectron-enhanced dose close to a tissue interface using analogue gold-coated doped silica-fibre thermo luminescence detectors and an X-ray set operating at 250 kVp. Study is made of the dose enhancement factor for various thickness of gold; measurements at a total gold thickness of 160 nm produces a mean dose enhancement factor of 3.19. To verify results, simulations of the experimental setup have been performed. © 2013 Elsevier Ltd. All rights reserved.
Aldridge S, Ismail A, Nobes J, Langley S, Nisbet A, Laing R (2007) Comparison of two prostate seed brachytherapy techniques using dosimetric analysis, RADIOTHERAPY AND ONCOLOGY 84 pp. S144-S145 ELSEVIER IRELAND LTD
Irvine C, Morgan A, Crellin A, Nisbet A, Beange I (2004) The clinical implications of the collapsed cone planning algorithm, CLINICAL ONCOLOGY 16 (2) pp. 148-154 ELSEVIER SCIENCE LONDON
Patel T, Li B, Gallop J, Cox D, Kirkby K, Romans E, Chen J, Nisbet A, Hao L (2015) Investigating the intrinsic noise limit of Dayem bridge NanoSQUIDs, IEEE Transactions on Applied Superconductivity 25 (3)
© 2014 IEEE.NanoSQUIDs made from Nb thin films have been produced with nanometre loop sizes down to 200 nm, using weak-link junctions with dimensions less than 60 nm. These composite (W/Nb) single layer thin film devices, patterned by FIB milling, show extremely good low-noise performance ~170 n¦0 at temperatures between 5 and 8.5 K and can operate in rather high magnetic fields (at least up to 1 T). The devices produced so far have a limited operating temperature range, typically only 1-2 K. We have the goal of achieving operation at 4.2 K, to be compatible with the best SQUID series array (SSA) preamplifier available. Using the SSA to readout the nanoSQUIDs provides us with a means of investigating the intrinsic noise of the former. In this paper we report improved white noise levels of these nanoSQUIDs, enabling potential detection of a single electronic spin flip in a 1-Hz bandwidth. At low frequencies the noise performance is already limited by SSA preamplifier noise.
Alshanqity M, Duane S, Nisbet A (2012) A simple approach for EPID dosimetric calibration to overcome the effect of image-lag and ghosting., Appl Radiat Isot 70 (7) pp. 1154-1157
EPID dosimetry has known drawbacks. The main issue is that a measurable residual signal is observed after the end of irradiation for prolonged periods of time, thus making measurement difficult. We present a detailed analysis of EPID response and suggest a simple, yet accurate approach for calibration that avoids the complexity of incorporating ghosting and image-lag using the maximum integrated signal instead of the total integrated signal. This approach is linear with dose and independent of dose rate.
Noor NM, Hussein M, Bradley DA, Nisbet A (2010) The potential of Ge-doped optical fibre TL dosimetry for 3D verification of high energy IMRT photon beams, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 619 (1-3) pp. 157-162 ELSEVIER SCIENCE BV
Issa F, Abdul Rahman AT, Hugtenburg RP, Bradley DA, Nisbet A (2012) Establishment of Ge-doped optical fibres as thermoluminescence dosimeters for brachytherapy., Appl Radiat Isot 70 (7) pp. 1158-1161 Elsevier
This study aims to establish the sensitive,
Lei M, Adams E, Clark C, Cranshaw J, Reise S, Rickard D, Jena R, Kirkby N, Hatt M, Hall J, Jordan T, Whittaker S, Nisbet A, Guerrero-Urbano T (2010) 18F-FDG-PET Guided dose painting IMRT in oropharyngeal SCC: TCP and NTCP variations with dose and automated segmentation, Radiotherapy & Oncology 96 (Supplement 1) pp. S 308-S 308 Elsevier
Palmer A, Bradley D, Nisbet A (2015) Evaluation and mitigation of potential errors in radiochromic film dosimetry due to film curvature at scanning., J Appl Clin Med Phys 16 (2) pp. 5141-?
This work considers a previously overlooked uncertainty present in film dosimetry which results from moderate curvature of films during the scanning process. Small film samples are particularly susceptible to film curling which may be undetected or deemed insignificant. In this study, we consider test cases with controlled induced curvature of film and with film raised horizontally above the scanner plate. We also evaluate the difference in scans of a film irradiated with a typical brachytherapy dose distribution with the film naturally curved and with the film held flat on the scanner. Typical naturally occurring curvature of film at scanning, giving rise to a maximum height 1 to 2 mm above the scan plane, may introduce dose errors of 1% to 4%, and considerably reduce gamma evaluation passing rates when comparing film-measured doses with treatment planning system-calculated dose distributions, a common application of film dosimetry in radiotherapy. The use of a triple-channel dosimetry algorithm appeared to mitigate the error due to film curvature compared to conventional single-channel film dosimetry. The change in pixel value and calibrated reported dose with film curling or height above the scanner plate may be due to variations in illumination characteristics, optical disturbances, or a Callier-type effect. There is a clear requirement for physically flat films at scanning to avoid the introduction of a substantial error source in film dosimetry. Particularly for small film samples, a compression glass plate above the film is recommended to ensure flat-film scanning. This effect has been overlooked to date in the literature.
Wai P, Adamovics J, Krstajic N, Ismail A, Nisbet A, Doran S (2009) Dosimetry of the microSelectron-HDR Ir-192 source using PRESAGE (TM) and optical CT, APPLIED RADIATION AND ISOTOPES 67 (3) pp. 419-422 PERGAMON-ELSEVIER SCIENCE LTD
Daar E, Kaabar W, Lei C, Keddie JL, Nisbet A, Bradley DA (2010) AFM and uni-axial testing of pericardium exposed to radiotherapy doses, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 652 (1) pp. 874-877 Elsevier
Nisbet A, Thwaites DI (1997) A dosimetric intercomparison of electron beams in UK radiotherapy centres, PHYSICS IN MEDICINE AND BIOLOGY 42 (12) pp. 2393-2409 IOP PUBLISHING LTD
Issa F, Latip NAA, Bradley DA, Nisbet A (2010) Ge-doped optical fibres as thermoluminescence dosimeters for kilovoltage X-ray therapy irradiations, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 652 (1) pp. 834-837 Elsevier
Dalah E, Bradley D, Nisbet A (2010) Simulation of tissue activity curves of Cu-64-ATSM for sub-target volume delineation in radiotherapy, PHYSICS IN MEDICINE AND BIOLOGY 55 (3) pp. 681-694 IOP PUBLISHING LTD
Dalah E, Gundogdu O, Bradley D, Nisbet A (2009) A Study of the Inherent Limitations of Image Fusion Software in Volume Delineation for Radiotherapy, Clinical Oncology (Vol 21(3), Suppl 1) pp. 267-267 Elsevier
Dalah E, Bradley D, Nisbet A (2010) A mathematical approach towards simulating a realistic tissue activity curve of Cu-64-ATSM for the purpose of sub-target volume delineation in radiotherapy, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 619 (1-3) pp. 283-286 ELSEVIER SCIENCE BV
Daar E, Kaabar W, Nisbet A, Bradley DA, Woods E, Lei C (2014) Atomic force microscopy and mechanical testing of bovine pericardium irradiated to radiotherapy doses, Radiation Physics and Chemistry 96 pp. 176-180
Within the context of radiotherapy our work investigates the feasibility of identifying changes in structural and biomechanical properties of pericardium resulting from exposure to penetrating photon irradiation. Collagen fibres extracted from bovine pericardium were chosen as a model of pericardium extracellular matrix as these form the main fibrous component of the medium. Tests of mechanical properties, controlled by the various structural elements of the tissues, were performed on frontal pericardium, including uni-axial tests and atomic force microscopy (AFM). While the irradiated collagen fibres showed no significant change in D-band spacing up to doses of 80. Gy, the fibre width was found to increase by 34±9% at 80. Gy when compared with that for un-irradiated samples. © 2013 Elsevier Ltd.
Nisbet A, Pitchford G (2012) Electron Beam Physics, 9 pp. 102-113 Oxford University Press, USA
This series of practical handbooks are aimed at physicians both training and practising in radiotherapy, as well as medical physicists, dosimetrists, radiographers and senior nurses.
Taylor CW, Nisbet A, McGale P, Goldman U, Darby SC, Hall P, Gagliardi G (2009) Cardiac doses from Swedish breast cancer radiotherapy since the 1950s, RADIOTHERAPY AND ONCOLOGY 90 (1) pp. 127-135 ELSEVIER IRELAND LTD
Palmer AL, Dimitriadis A, Nisbet A, Clark CH (2015) Evaluation of Gafchromic EBT-XD film, with comparison to EBT3 film, and application in high dose radiotherapy verification, PHYSICS IN MEDICINE AND BIOLOGY 60 (22) pp. 8741-8752 IOP PUBLISHING LTD
Galer S, Hao L, Gallop J, Palmans A, Kirkby KJ, Nisbet A (2011) Design Concept for a novel SQUID based Micobolometer, Radiation Protection Dosimetry 143 (2-4) pp. 427-431 Oxford University Press
Hussein M, Nisbet A, Clark CH, Tsang Y, Thomas RAS, Gouldstone C, Maughan D, Snaith JAD, Bolton SC (2013) A methodology for dosimetry audit of rotational radiotherapy using a commercial detector array, Radiotherapy and Oncology 108 (1) pp. 78-85 Elsevier
Purpose To develop a methodology for the use of a commercial detector array in dosimetry audits of rotational radiotherapy. Materials and methods The methodology was developed as part of the development of a national audit of rotational radiotherapy. Ten cancer centres were asked to create a rotational radiotherapy treatment plan for a three-dimensional treatment-planning-system (3DTPS) test and audited. Phantom measurements using a commercial 2D ionisation chamber (IC) array were compared with measurements using 0.125 cm IC, Gafchromic film and alanine pellets in the same plane. Relative and absolute gamma index (³) comparisons were made for Gafchromic film and 2D-Array planes, respectively. Results Comparisons between individual detectors within the 2D-Array against the corresponding IC and alanine measurement showed a statistically significant concordance correlation coefficient (both Á > 0.998, p
Beange I, Nisbet A (2000) A collision prevention software tool for complex three-dimensional isocentric set-ups., Br J Radiol 73 (869) pp. 537-541
During treatment planning it can be difficult to check whether a particular plan is workable, that is it avoids obstructing treatment beams with parts of the patient couch and it avoids collisions between the treatment machine head and the patient couch. To overcome this problem, the trigonometric relationships between the placement of treatment beams and the patient couch are examined. From these relationships a set of useful equations that can be generally applied is derived. The application of these equations practically as a simple (non-graphical) planning tool is described. The resulting tool enables the feasibility of a plan to be checked during treatment planning, and gives guidance as to how a patient could be repositioned to allow the use of a plan when potential beam obstructions are detected, prior to verification of the treatment on a simulator.
Galer S, Hao L, Gallop J, Palmans H, Kirkby K, Nisbet A (2011) DESIGN CONCEPT FOR A NOVEL SQUID-BASED MICRODOSEMETER, RADIATION PROTECTION DOSIMETRY 143 (2-4) pp. 427-431 OXFORD UNIV PRESS
Nisbet A (2006) Dosimetric Measurements (Electrons), 7
Chan O, Adams E, Clark C, Freeman K, Dabbs M, Jamieson C, Hussein M, Jordan T, Money-Kyrle J, Khaksar S, Laing R, Langley S, Nisbet A, Guerrero-urbano T (2010) CBCt Evaluation of Interfraction Changes in Rectal and Bladder Volume in Prostate Cancer patients Receiving IG-IMRT, Radiotherapy & Oncology 96 (Supplement 1) pp. S 395-S 395 Elsevier
Alalawi AI, Nisbet A, Alzimami KS, Bradley DA, Hugtenburg RP, Abdul Rahman AT, Barry MA (2013) Measurement of dose enhancement close to high atomic number media using optical fibre thermoluminescence dosimeters, Radiation Physics and Chemistry
Present interest concerns development of a system to measure photoelectron-enhanced dose close to a tissue interface using analogue gold-coated doped silica-fibre thermoluminescence detectors and an X-ray set operating at 250 kVp. Study is made of the dose enhancement factor for various thicknesses of gold; measurements at a total gold thickness of 160 nm (accounting for incident and exiting photons) produces a mean measured dose enhancement factor of 1.33±0.01 To verify results, simulations of the experimental setup have been performed. © 2013 Elsevier Ltd. All rights reserved.
Dalah E, Lloyd D, Bradley D, Nisbet A (2009) Computational simulation of tumour hypoxia as applied to radiation therapy applications, IFMBE Proceedings 25 (1) pp. 64-66
It has long been appreciated that hypoxia plays a significant role in tumour resistance to radiotherapy treatment, chemotherapy treatment and also in surgery. For present interests, it is noted that tumour radio-sensitivity increases with the increase of oxygen concentration across tumour regions. A theoretical representation of oxygen distribution in 2D vascular architecture using a reaction diffusion model enables relationships between tissue diffusivity, tissue metabolism, anatomical structure of blood vessels and oxygen gradients to be characterized quantitatively. We present a refinement to the work of Kelly and Brady (2006) and demonstrate the significant effect of the role of the venules supply on the microcirculation process at the intracellular level. With our representation of the two latter forces, the model is being developed to simulate the uptake of various PET reagents, such as 64Cu-ATSM, to demonstrate their potential use in radiation therapy treatment planning as an indicator of tumour hypoxic regions.
Allahverdi M, Nisbet A, Thwaites DI (1999) An evaluation of epoxy resin phantom materials for megavoltage photon dosimetry., Phys Med Biol 44 (5) pp. 1125-1132
Epoxy resin phantom materials have been available for some time and are widely used for dosimetry purposes, not least in audit phantoms. Information on their behaviour is partly available in the literature, but there are different mixes and formulations often given similar names and it may not be appropriate to transfer information from one material to another. Five commercially available water substitute materials have been evaluated for use in megavoltage photon beams: WT1, WTe, RMI 451, RMI 457 and 'plastic water'. Four independent experiments were carried out to compare these materials with water in megavoltage photon beams ranging in energy from cobalt 60 to nominal 16 MV x-rays, and some general conclusions are drawn from the results as to their use. All are suitable for relative dosimetry in megavoltage photon beams. However, differences of up to 1% are observed for absolute measurements. The newer formulations, developed for electron beam use, are also closer to water for megavoltage photon beams.
Clark CH, Aird EGA, Bolton S, Miles EA, Nisbet A, Snaith JAD, Thomas RAS, Venables K, Thwaites DI (2015) Radiotherapy dosimetry audit: three decades of improving standards and accuracy in UK clinical practice and trials, BRITISH JOURNAL OF RADIOLOGY 88 (1055) ARTN 20150251 BRITISH INST RADIOLOGY
Taylor CW, Nisbet A, Povall JM, McGale P, Dodwell D, Darby SC (2007) Cardiac irradiation in breast radiotherapy, CLINICAL ONCOLOGY 19 (4) pp. S3-S3 ELSEVIER SCIENCE LONDON
Nisbet A, Weatherburn H, Fenwick JD, McVey G (1998) Spectral reconstruction of clinical megavoltage photon beams and the implications of spectral determination on the dosimetry of such beams., Phys Med Biol 43 (6) pp. 1507-1521
An analysis technique, based on simulated annealing, is described which is employed to derive megavoltage photon beam spectral information from narrow beam attenuation measurements. Megavoltage photon beam spectra have been determined using this technique for linear accelerators from different manufacturers, and different models from individual manufacturers at a range of energies from nominal 6 MV to nominal 25 MV. All of the photon beams included in the study are in routine clinical use. The subsequent effects on dosimetry of employing derived primary spectra to specify beam quality are examined. The results suggest that the quality index TPR(20)10 may be insensitive to beam quality changes for high-energy beams in the range of 15 MV to 25 MV. Although the quality index may be insensitive as a beam quality specifier at these higher qualities, the actual difference in the calculated dose delivered using derived spectra as the quality specifier rather than TPR(20)10 is likely to be small, the results obtained indicating a difference of between 0.2% and 0.7% in the calculated dose delivered.
Nisbet A, Thwaites DI (1998) An evaluation of epoxy resin phantom materials for electron dosimetry., Phys Med Biol 43 (6) pp. 1523-1528
The use of epoxy resin 'solid water' (water substitute) phantoms is becoming increasingly common in radiotherapy dosimetry, and depth ionization curves and conversion factors from ionization to dose identical to water have often been assumed. Fluence ratios of water to solid water for WTe (produced by Radiation Physics, St Bartholomew's Hospital, London) and RMI 457 (produced by Radiation Measurements Inc., Middleton, Wisconsin) have therefore been determined and have been found to decrease with energy, which, within measurement uncertainty, can be described with a linear function dependent on mean electron beam energy at the depth of measurement, Ed. The fluence ratios for WTe are very close to unity (i.e. within the measuring uncertainty) for most of the energies examined, the exception being a nominal 20 MeV beam. The results also show that an assumption of unity for the fluence ratios of RMI 457 may introduce a systematic error of the order of 1% in electron beam dosimetry at lower energies. As regards the depth ionization curves measured in the respective solid water materials, these are shown to be in agreement with those measured in water within the limits of the measuring uncertainty.
Nisbet A, Cocker M (2004) Experiences of a proactive IR(ME)R inspection in radiotherapy., British Journal of Radiology 77 (916) pp. 329-332 British Institute of Radiology
The Ionizing Radiation (Medical Exposure) Regulations 2000, IR(ME)R, apply to the safety of the patient referred for a medical exposure to ionizing radiation. In Scotland, the Scottish Executive (Department of Health) is responsible for carrying out inspections of compliance with these regulations. IR(ME)R specifically addresses issues concerned with Employer's duties, responsibilities of the Practitioner, Operator and Referrer, justification of individual medical exposures for diagnosis and treatment, optimization of all procedures, clinical audit and adequate training of all duty holders. A proactive IR(ME)R inspection of the Clinical Oncology Department, Raigmore Hospital, Inverness, was carried out in November 2001 by inspectors based at the Department of Health, London, and seconded by the Scottish Executive, Department of Health. The aim of the inspection was to assess the degree of compliance with the regulations. In this case study the experiences of a proactive inspection are described in detail and some of the important elements of implementing IR(ME)R in a department that operates an ISO 9000-2000 Quality Management System addressed. The identification of IR(ME)R Duty Holders' responsibilities is one important aspect which may be inadequately described by the existing Quality Management System documentation. Other key elements of the inspection include the methods of authorizing the justification, the importance of the treatment prescription sheets in the demonstration of compliance with IR(ME)R, patient identification and pregnancy questions and dose recording procedures. The integration of the standard operating procedures as described in Schedule 1 of the regulations is also important. Where the existing Quality Management System documentation is written to include the IR(ME)R requirements of duty holder's responsibilities and the allocation of all the important tasks, then there is no need to re-badge these documents for IR(ME)R purposes. IR(ME)R encourages departments to focus on the safety of the patient and to document good practice. In order to comply, departments will have to show evidence of optimization of their procedures and must address the clinical governance issues associated with delivery of treatment.
Saeed Al-Ahbabi S, Bradley DA, Beyomi M, Alkatib Z, Adhaheri S, Darmaki M, Nisbet A (2012) A comparison of protocols for external beam radiotherapy beam calibrations, Applied Radiation and Isotopes 70 (7) pp. 1331-1336
A number of codes of practice (CoP) for electron and photon radiotherapy beam dosimetry are currently in use. Comparison is made of the more widely used of these, specifically those of the International Atomic Energy Agency (IAEA TRS-398), the American Association of Physicists in Medicine (AAPM TG-51) and the Institute of Physics and Engineering in Medicine (IPEM 2003). All are based on calibration of ionization chambers in terms of absorbed dose to water, each seeking to reduce uncertainty in delivered dose, providing an even stronger system of primary standards than previous air-kerma based approaches. They also provide a firm, traceable and straight-forward formalism (Radiology, 1996). Included in making dose assessments for the three CoP are calibration coefficients for a range of beam quality indices. Measurements have been performed using clinical photon and electron beams, the absorbed dose to water being obtained following the recommendations given by each code. Electron beam comparisons have been carried out using measurements for electron beams of nominal energies 6, 9, 12, 16 and 20. MeV. Comparisons were also carried out for photon beams of nominal energies 6 and 18. MV. For photon beams use was made of NE2571 cylindrical graphite walled ionization chambers, cross-calibrated against an NE2611 Secondary Standard; for electron beams, PTW Markus and NACP-02 plane-parallel chambers were used. Irradiations were made using Varian 600C/2100C linacs, supported by water tanks and Virtual Water" phantoms. The absorbed doses for photon and electron beams obtained following these CoP are all in good agreement, with deviations of less than 2%.A number of studies have been carried out by different groups in different countries to examine the consistency of dosimetry codes of practice or protocols. The aim of these studies is to confirm that the goal of those codes is met, namely uniformity in establishment of dosimetry of all radiation beam types used in cancer therapy in the world, and this is one of the studies. © 2011 Elsevier Ltd.
Daar E, Woods E, Keddie JL, Nisbet A, Bradley DA (2010) Effect of penetrating ionising radiation on the mechanical properties of pericardium, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 619 (1-3) pp. 356-360 ELSEVIER SCIENCE BV
Thwaites DI, Nisbet A (2003) The Scottish plus radiotherapy dosimetry audit system: recent results and pilot audit studies for MLC dosimetry and in-vivo dosimetry, RADIOTHERAPY AND ONCOLOGY 68 pp. S26-S26 ELSEVIER IRELAND LTD
Darby SC, Ewertz M, McGale P, Bennet AM, Blom-Goldman U, Brnønum D, Correa C, Cutter D, Gagliardi G, Gigante B, Jensen MB, Nisbet A, Peto R, Rahimi K, Taylor C, Hall P (2013) Risk of ischemic heart disease in women after radiotherapy for breast cancer, New England Journal of Medicine 368 (11) pp. 987-998
Background: Radiotherapy for breast cancer often involves some incidental exposure of the heart to ionizing radiation. The effect of this exposure on the subsequent risk of ischemic heart disease is uncertain. Methods: We conducted a population-based case-control study of major coronary events (i.e., myocardial infarction, coronary revascularization, or death from ischemic heart disease) in 2168 women who underwent radiotherapy for breast cancer between 1958 and 2001 in Sweden and Denmark; the study included 963 women with major coronary events and 1205 controls. Individual patient information was obtained from hospital records. For each woman, the mean radiation doses to the whole heart and to the left anterior descending coronary artery were estimated from her radiotherapy chart. Results: The overall average of the mean doses to the whole heart was 4.9 Gy (range, 0.03 to 27.72). Rates of major coronary events increased linearly with the mean dose to the heart by 7.4% per gray (95% confidence interval, 2.9 to 14.5; P
Hussein M, Adams EJ, Jordan TJ, Clark CH, Nisbet A (2013) A critical evaluation of the PTW 2D-ARRAY seven29 and OCTAVIUS II phantom for IMRT and VMAT verification, Journal of Applied Clinical Medical Physics 14 (6) pp. 274-292
Quality assurance (QA) for intensity- and volumetric-modulated radiotherapy (IMRT and VMAT) has evolved substantially. In recent years, various commercial 2D and 3D ionization chamber or diode detector arrays have become available, allowing for absolute verification with near real time results, allowing for streamlined QA. However, detector arrays are limited by their resolution, giving rise to concerns about their sensitivity to errors. Understanding the limitations of these devices is therefore critical. In this study, the sensitivity and resolution of the PTW 2D-ARRAY seven29 and OCTAVIUS II phantom combination was comprehensively characterized for use in dynamic sliding window IMRT and RapidArc verification. Measurement comparisons were made between single acquisition and a multiple merged acquisition techniques to improve the effective resolution of the 2D-ARRAY, as well as comparisons against GAFCHROMIC EBT2 film and electronic portal imaging dosimetry (EPID). The sensitivity and resolution of the 2D-ARRAY was tested using two gantry angle 0° modulated test fields. Deliberate multileaf collimator (MLC) errors of 1, 2, and 5 mm and collimator rotation errors were inserted into IMRT and RapidArc plans for pelvis and head & neck sites, to test sensitivity to errors. The radiobiological impact of these errors was assessed to determine the gamma index passing criteria to be used with the 2D-ARRAY to detect clinically relevant errors. For gamma index distributions, it was found that the 2D-ARRAY in single acquisition mode was comparable to multiple acquisition modes, as well as film and EPID. It was found that the commonly used gamma index criteria of 3% dose difference or 3 mm distance to agreement may potentially mask clinically relevant errors. Gamma index criteria of 3%/2 mm with a passing threshold of 98%, or 2%/2 mm with a passing threshold of 95%, were found to be more sensitive. We suggest that the gamma index passing thresholds may be used for guidance, but also should be combined with a visual inspection of the gamma index distribution and calculation of the dose difference to assess whether there may be a clinical impact in failed regions.
Chan O, Adams E, Clark C, Dabbs M, Jamieson C, Hussein M, Laing R, Langley S, Nisbet A, Urbano TG (2010) Impact of Intrafraction Motion on TCP and Rectal NTCP Values in Patients Receiving IG-IMRT for Prostate Cancer, INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 78 (3) pp. S363-S364 ELSEVIER SCIENCE INC
Doran SJ, Abdul Rahman AT, Bräuer-Krisch E, Brochard T, Adamovics J, Nisbet A, Bradley D (2013) Establishing the suitability of quantitative optical CT microscopy of PRESAGE® radiochromic dosimeters for the verification of synchrotron microbeam therapy., Phys Med Biol 58 (18) pp. 6279-6297
Previous research on optical computed tomography (CT) microscopy in the context of the synchrotron microbeam has shown the potential of the technique and demonstrated high quality images, but has left two questions unanswered: (i) are the images suitably quantitative for 3D dosimetry? and (ii) what is the impact on the spatial resolution of the system of the limited depth-of-field of the microscope optics? Cuvette and imaging studies are reported here that address these issues. Two sets of cuvettes containing the radiochromic plastic PRESAGE® were irradiated at the ID17 biomedical beamline of the European Synchrotron Radiation facility over the ranges 0-20 and 0-35 Gy and a third set of cuvettes was irradiated over the range 0-20 Gy using a standard medical linac. In parallel, three cylindrical PRESAGE® samples of diameter 9.7 mm were irradiated with test patterns that allowed the quantitative capabilities of the optical CT microscope to be verified, and independent measurements of the imaging modulation transfer function (MTF) to be made via two different methods. Both spectrophotometric analysis and imaging gave a linear dose response, with gradients ranging from 0.036-0.041 cm(-1) Gy(-1) in the three sets of cuvettes and 0.037 (optical CT units) Gy(-1) for the imaging. High-quality, quantitative imaging results were obtained throughout the 3D volume, as illustrated by depth-dose profiles. These profiles are shown to be monoexponential, and the linear attention coefficient of PRESAGE® for the synchrotron-generated x-ray beam is measured to be (0.185 ± 0.02) cm(-1) in excellent agreement with expectations. Low-level (
Alalawi AI, Jafari SM, Najem MA, Nisbet A, Hussein M, Alzimami KS, Bradley DA, Spyrou NM, Alsaleh W, Hugtenburg RP, Clark CH, Abolaban F (2014) Preliminary investigations of two types of silica-based dosimeter for small-field radiotherapy, Radiation Physics and Chemistry 104 pp. 139-144
Two thermoluminescent dosimeters (SiO-GeO doped fibres and glass beads (GB)) were used to measure small photon field doses and compared against GAFCHROMIC film, a small ionisation chamber (RK-018) and a p-type silicon diode (SCANDITRONIX, F1356), as well as Monte Carlo simulations with FLUKA and BEAMnrc/DOSXYZnrc. Ge-doped SiO fibres have been shown by this group to offer a viable system for use as dosimeters. The fibres and GB offer good spatial resolution (~120¼m and 2mm respectively), large dynamic dose range (with linearity from tens of mGy up to well in excess of many tens of Gy), are non-hygroscopic and are of low cost. Measurements of beam profiles for field sizes of 10mm×10mm, 20mm×20mm, 30mm×30mm, 40mm×40mm, and 100mm×100mm were carried out. Through the use of a customised solid water phantom, doped optical fibres and GBs were placed at defined positions along the x-and y-axes to allow accurate beam profile measurement. The maximum difference between FWHM measurements was 1.8mm. For penumbra measurements (measured between 80% and 20% isodoses), the maximum difference was
Palmer AL, Nisbet A, Bradley DA (2013) Semi-3D dosimetry of high dose rate brachytherapy using a novel Gafchromic EBT3 film-array water phantom, 7TH INTERNATIONAL CONFERENCE ON 3D RADIATION DOSIMETRY (IC3DDOSE) 444 IOP PUBLISHING LTD
Nisbet A, Galer S, Palmans H, Hao L, Kirkby K, Gallop J (2010) Development of a Microbolometer for Microdosimetry., Radiotherapy and Oncology (Vol 96, Suppl 1) pp. S453-S453 Elsevier
Noor NM, Hussein M, Bradley DA, Nisbet A (2011) Investigation of the use of Ge-doped optical fibre for in vitro IMRT prostate dosimetry, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 652 (1) pp. 819-823 Elsevier
Teoh M, Beveridge S, Wood K, Whitaker S, Adams E, Rickard D, Jordan T, Nisbet A, Clark C (2012) Volumetric-modulated arc therapy (RapidArc) vs. conventional fixed-field intensity-modulated radiotherapy for (18)F-FDG-PET-guided dose escalation in oropharyngeal cancer: A planning study., Med Dosim
Fluorine-18-fluorodeoxyglucose-positron emission tomography ((18)F-FDG-PET)-guided focal dose escalation in oropharyngeal cancer may potentially improve local control. We evaluated the feasibility of this approach using volumetric-modulated arc therapy (RapidArc) and compared these plans with fixed-field intensity-modulated radiotherapy (IMRT) focal dose escalation plans. Materials and methods: An initial study of 20 patients compared RapidArc with fixed-field IMRT using standard dose prescriptions. From this cohort, 10 were included in a dose escalation planning study. Dose escalation was applied to (18)F-FDG-PET-positive regions in the primary tumor at dose levels of 5% (DL1), 10% (DL2), and 15% (DL3) above standard radical dose (65 Gy in 30 fractions). Fixed-field IMRT and double-arc RapidArc plans were generated for each dataset. Dose-volume histograms were used for plan evaluation and comparison. The Paddick conformity index (CI(Paddick)) and monitor units (MU) for each plan were recorded and compared. Both IMRT and RapidArc produced clinically acceptable plans and achieved planning objectives for target volumes. Dose conformity was significantly better in the RapidArc plans, with lower CI(Paddick) scores in both primary (PTV1) and elective (PTV2) planning target volumes (largest difference in PTV1 at DL3; 0.81 ± 0.03 [RapidArc] vs. 0.77 ± 0.07 [IMRT], p = 0.04). Maximum dose constraints for spinal cord and brainstem were not exceeded in both RapidArc and IMRT plans, but mean doses were higher with RapidArc (by 2.7 ± 1 Gy for spinal cord and 1.9 ± 1 Gy for brainstem). Contralateral parotid mean dose was lower with RapidArc, which was statistically significant at DL1 (29.0 vs. 29.9 Gy, p = 0.01) and DL2 (29.3 vs. 30.3 Gy, p = 0.03). MU were reduced by 39.8-49.2% with RapidArc (largest difference at DL3, 641 ± 94 vs. 1261 ± 118, p
Nisbet A, Beange I, Vollmar HS, Irvine C, Morgan A, Thwaites DI (2004) Dosimetric verification of a commercial collapsed cone algorithm in simulated clinical situations., Radiother Oncol 73 (1) pp. 79-88
BACKGROUND AND PURPOSE: This work reports a detailed study carried out in two UK radiotherapy centres of the dosimetric accuracy of the collapsed cone algorithm of a commercial treatment planning system (Helax-TMS) in simulated clinical situations. MATERIALS AND METHODS: Initially the accuracy of the collapsed cone algorithm in homogeneous media is evaluated for an extensive set of simple and complex fields. Water, lung and bone substitute epoxy resin material were then used to assess the algorithm in inhomogeneous media and compare its accuracy with the pencil beam algorithm currently in clinical use. Finally a semi-anatomic phantom and an anthropomorphic phantom were employed to assess the dosimetric accuracy using simulated clinical set ups. Thermoluminescence dosimeter (TLD) measurements were made with the anthropomorphic phantom and ionisation chambers otherwise. Nominal 4, 6 and 15 MV photon beams were studied. RESULTS: For most homogeneous cases agreement between measured and calculated dose is within +/-2% or +/-2 mm. In cases with heterogeneities and simulated clinical situations it is observed that the accuracy is also generally within +/-2% or +/-2 mm. Specific instances where the difference between measured and calculated values exceed this are highlighted. CONCLUSIONS: It can be concluded that in clinical treatment planning situations where lung is present the collapsed cone algorithm should be considered in preference to pencil beam algorithms normally used but that there may still be some discrepancy between calculations and measurement.
Bradley DA, Hugtenburg RP, Nisbet A, Abdul Rahman AT, Issa F, Mohd Noor N, Alalawi A (2012) Review of doped silica glass optical fibre: Their TL properties and potential applications in radiation therapy dosimetry., Appl Radiat Isot
Review is made of dosimetric studies of Ge-doped SiO(2) telecommunication fibre as a 1-D thermoluminescence (TL) system for therapeutic applications. To-date, the response of these fibres has been investigated for UV sources, superficial X-ray beam therapy facilities, a synchrotron microbeam facility, electron linear accelerators, protons, neutrons and alpha particles, covering the energy range from a few eV to several MeV. Dosimetric characteristics include, reproducibility, fading, dose response, reciprocity between TL yield and dose-rate and energy dependence. The fibres produce a flat response to fixed photon and electron doses to within better than 3% of the mean TL distribution. Irradiated Ge-doped SiO(2) optical fibres show limited signal fading, with an average loss of TL signal of
Palmer AL, Bradley DA, Nisbet A (2015) Evaluation and mitigation of potential errors in radiochromic film dosimetry due to film curvature at scanning, Journal of Applied Clinical Medical Physics 16 (2) pp. 425-431
This work considers a previously overlooked uncertainty present in film dosimetry which results from moderate curvature of films during the scanning process. Small film samples are particularly susceptible to film curling which may be undetected or deemed insignificant. In this study, we consider test cases with controlled induced curvature of film and with film raised horizontally above the scanner plate. We also evaluate the difference in scans of a film irradiated with a typical brachytherapy dose distribution with the film naturally curved and with the film held flat on the scanner. Typical naturally occurring curvature of film at scanning, giving rise to a maximum height 1 to 2 mm above the scan plane, may introduce dose errors of 1% to 4%, and considerably reduce gamma evaluation passing rates when comparing film-measured doses with treatment planning system-calculated dose distributions, a common application of film dosimetry in radiotherapy. The use of a triple-channel dosimetry algorithm appeared to mitigate the error due to film curvature compared to conventional single-channel film dosimetry. The change in pixel value and calibrated reported dose with film curling or height above the scanner plate may be due to variations in illumination characteristics, optical disturbances, or a Callier-type effect. There is a clear requirement for physically flat films at scanning to avoid the introduction of a substantial error source in film dosimetry. Particularly for small film samples, a compression glass plate above the film is recommended to ensure flat-film scanning. This effect has been overlooked to date in the literature.
Palmer AL, Di Pietro P, Alobaidli S, Issa F, Doran S, Bradley D, Nisbet A (2013) Comparison of methods for the measurement of radiation dose distributions in high dose rate (HDR) brachytherapy: Ge-doped optical fiber, EBT3 Gafchromic film, and PRESAGE® radiochromic plastic., Med Phys 40 (6)
Dose distribution measurement in clinical high dose rate (HDR) brachytherapy is challenging, because of the high dose gradients, large dose variations, and small scale, but it is essential to verify accurate treatment planning and treatment equipment performance. The authors compare and evaluate three dosimetry systems for potential use in brachytherapy dose distribution measurement: Ge-doped optical fibers, EBT3 Gafchromic film with multichannel analysis, and the radiochromic material PRESAGE(®) with optical-CT readout.
Hussein M, Aldridge S, Nisbet A (2009) The Effect of Beam Energy on IMRT Treatment Plans and the Risk of Secondary-induced Malignancies, Clinical Oncology (Vol 21(3), Suppl 1) pp. 246-246 Elsevier
Jafari SM, Bradley DA, Alalawi A, Clark CH, Nisbet A, Spyrou NM, Gouldstone CA, Sharpe PHG, Jordan TJ (2014) Low-cost commercial glass beads as dosimeters in radiotherapy, Radiation Physics and Chemistry 97 pp. 95-101
Recent developments in advanced radiotherapy techniques using small field photon beams, require small detectors to determine the delivered dose in steep dose gradient fields. Commercially available glass jewellery beads exhibit thermoluminescent properties and have the potential to be used as dosimeters in radiotherapy due to their small size (
Palmer AL, Bidmead M, Nisbet A (2012) A survey of quality control practices for high dose rate (HDR) and pulsed dose rate (PDR) brachytherapy in the United Kingdom., J Contemp Brachytherapy 4 (4) pp. 232-240
A survey of quality control (QC) currently undertaken in UK radiotherapy centres for high dose rate (HDR) and pulsed dose rate (PDR) brachytherapy has been conducted. The purpose was to benchmark current accepted practice of tests, frequencies and tolerances to assure acceptable HDR/PDR equipment performance. It is 20 years since a similar survey was conducted in the UK and the current review is timed to coincide with a revision of the IPEM Report 81 guidelines for quality control in radiotherapy.
Darby SC, Bronnum D, Correa C, Ewertz M, Gagliardi G, Gigante B, McGale P, Nisbet A, Taylor C, Hall P (2010) A Dose-response Relationship for the Incidence of Radiation-related Heart Disease, INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 78 (3) pp. S49-S50 ELSEVIER SCIENCE INC
Taylor CW, Povall JM, McGale P, Nisbet A, Dodwell D, Smith JT, Darby SC (2008) Cardiac dose from tangential breast cancer radiotherapy in the year 2006, INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 72 (2) pp. 501-507 ELSEVIER SCIENCE INC
Jafari SM, Hussein M, Bradley DA, Nisbet A, Spyrou NM, Jordan TJ, Clark CH (2014) Energy response of glass bead TLDs irradiated with radiation therapy beams, Radiation Physics and Chemistry 104 pp. 208-211
Glass beads are a novel TL dosimeter in radiotherapy. An important characteristic of TL dosimeters is their energy response, especially when intended for use in radiotherapy applications over a wide range of energies (typically from X-rays generated at 80kVp up to 25MV photon and MeV electron beams). In this paper, the energy response of glass beads (Mill Hill, Japan) is investigated for their TL response to kV X-rays from an orthovoltage radiotherapy unit and also for MV photon and MeV electron beams from a medical linear accelerator. The experimental findings show that for photon and electron beams, the TL response of this particular glass bead, normalised to unity for 6MV X-rays (TPR=0.670), decreases to 0.96±0.02 for 15MV X-rays (TPR=0.761) and to 0.95±0.01 for 20MeV electron beams (R=8.35cm). This compares favourably with other TLD materials such as LiF and also alanine dosimeters that are readout with an EPR system. For kV X-rays, the response increases to 4.52±0.05 for 80kV X-rays (HVL=2.4mm Al) which approaches 3 times that of LiF TLDs and 5 times that of alanine. In conclusion, the particular glass beads, when used as a dosimeter material, show a relatively small energy dependence over the megavoltage range of clinically relevant radiation qualities, being clearly advantageous for accurate dosimetry. Conversely, the energy response is significant for photon beam energies covering the kV range. In both circumstances, in dosimetric evaluations the energy response needs to be taken into account. © 2014 Elsevier Ltd.
Palmer AL, Bradley DA, Nisbet A (2014) Dosimetric audit in brachytherapy., Br J Radiol 87 (1041)
Dosimetric audit is required for the improvement of patient safety in radiotherapy and to aid optimization of treatment. The reassurance that treatment is being delivered in line with accepted standards, that delivered doses are as prescribed and that quality improvement is enabled is as essential for brachytherapy as it is for the more commonly audited external beam radiotherapy. Dose measurement in brachytherapy is challenging owing to steep dose gradients and small scales, especially in the context of an audit. Several different approaches have been taken for audit measurement to date: thimble and well-type ionization chambers, thermoluminescent detectors, optically stimulated luminescence detectors, radiochromic film and alanine. In this work, we review all of the dosimetric brachytherapy audits that have been conducted in recent years, look at current audits in progress and propose required directions for brachytherapy dosimetric audit in the future. The concern over accurate source strength measurement may be essentially resolved with modern equipment and calibration methods, but brachytherapy is a rapidly developing field and dosimetric audit must keep pace.
Palmer A, Bradley D, Nisbet A (2012) Physics-aspects of dose accuracy in high dose rate (HDR) brachytherapy: Source dosimetry, treatment planning, equipment performance and in vivo verification techniques, Journal of Contemporary Brachytherapy 4 (2) pp. 81-91 Termedia Publishing House
This study provides a review of recent publications on the physics-aspects of dosimetric accuracy in high dose rate (HDR) brachytherapy. The discussion of accuracy is primarily concerned with uncertainties, but methods to improve dose conformation to the prescribed intended dose distribution are also noted. The main aim of the paper is to review current practical techniques and methods employed for HDR brachytherapy dosimetry. This includes work on the determination of dose rate fields around brachytherapy sources, the capability of treatment planning systems, the performance of treatment units and methods to verify dose delivery. This work highlights the determinants of accuracy in HDR dosimetry and treatment delivery and presents a selection of papers, focusing on articles from the last five years, to reflect active areas of research and development. Apart from Monte Carlo modelling of source dosimetry, there is no clear consensus on the optimum techniques to be used to assure dosimetric accuracy through all the processes involved in HDR brachytherapy treatment. With the exception of the ESTRO mailed dosimetry service, there is little dosimetric audit activity reported in the literature, when compared with external beam radiotherapy verification.
Daar E, King L, Nisbet A, Thorpe R, Bradley D (2010) Viscosity changes in hyaluronic acid: Irradiation and rheological studies, APPLIED RADIATION AND ISOTOPES 68 (4-5) pp. 746-750 PERGAMON-ELSEVIER SCIENCE LTD
Abdul Rahman AT, Abdul Sani SF, Alalawi AIM, Issa F, Nisbet A, Bradley DA, Hugtenburg RP, Thomas R, Barry MA (2012) An investigation of the thermoluminescence of Ge-doped SiO
optical fibres for application in interface radiation dosimetry,
Applied Radiation and Isotopes 70 (7) pp. 1436-1441
We investigate the ability of high spatial resolution (~120¼m) Ge-doped SiO
TL dosimeters to measure photoelectron dose enhancement resulting from the use of a moderate to high-Z target (an iodinated contrast media) irradiated by 90kVp X-rays. We imagine its application in a novel radiation synovectomy technique, modelled by a phantom containing a reservoir of I
molecules at the interface of which the doped silica dosimeters are located. Measurements outside of the iodine photoelectron range are provided for using a stepped-design that allows insertion of the fibres within the phantom. Monte Carlo simulation (MCNPX) is used for verification. At the phantom medium I
-interface additional photoelectron generation is observed, ~60% above that in the absence of the I
, simulations providing agreement to within 3%. Percentage depth doses measured away from the iodine contrast medium reservoir are bounded by published PDDs at 80kVp and 100kVp. © 2011 Elsevier Ltd.
Hussein M, Aldridge S, Guerrero Urbano T, Nisbet A (2011) The effect of 6 and 15 MV on intensity-modulated radiation therapy prostate cancer treatment: plan evaluation, tumour control probability and normal tissue complication probability analysis, and the theoretical risk of secondary induced malignancies., British Journal of Radiology 85 (1012) pp. 423-432 British Institute of Radiology
Objective: To investigate the effect of 6 and 15 MV photon energies on intensity-modulated radiation therapy (IMRT) prostate cancer treatment plan outcome and to compare the theoretical risks of secondary induced malignancies. Methods: Separate prostate cancer IMRT plans were prepared for 6 and 15 MV beams. Organ equivalent doses were obtained through thermoluminescent dosimeter (TLD) measurements in a Rando phantom. The neutron dose contribution at 15 MV was measured using polyallyl-diglycol-carbonate (PADC) neutron track etch detectors. Risk coefficients from ICRP Report 103 were used to compare the risk of fatal secondary induced malignancies in out-of-field organs and tissues for 6 and 15 MV. For the bladder and the rectum, a comparative evaluation of the risk using three separate models was carried out. Dose-volume parameters for the rectum, bladder and prostate planning-target-volume were evaluated, as well as normal tissue complication probability (NTCP) and tumour control probability (TCP) calculations. Results: There is a small increased theoretical risk of developing a fatal cancer from 6 MV compared with 15 MV, taking into account all the organs. Dose-volume parameters for the rectum and bladder show that 15 MV results in better volume sparing in the regions below 70 Gy, but the volume exposed increases slightly beyond this in comparison to 6 MV, resulting in a higher NTCP for the rectum of 3.6% versus 3.0% (p
=
0.166). Conclusion: The choice to treat using IMRT at 15 MV should not be excluded, but should be based on risk versus benefit, considering the age and life expectancy of the patient together with the relative risk of radiation-induced cancer and NTCPs.
Nisbet A, Hall C, Kirby M, Hatton J, Rembowska A, Illes A, Aspradakis M, Townley J, Blake S, Mayles P (2002) Guidelines for the Provision of a Physics Service to Radiotherapy,
Abolaban F, Zaman S, Cashmore J, Nisbet A, Clark CH (2016) Changes in Patterns of Intensity-modulated Radiotherapy Verification and Quality Assurance in the UK, CLINICAL ONCOLOGY 28 (8) pp. E28-E34 ELSEVIER SCIENCE LONDON
Taylor CW, Nisbet A, Mcgale P, Darby SC (2007) Cardiac exposures in breast cancer radiotherapy: 1950s-1990s, INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 69 (5) pp. 1484-1495 ELSEVIER SCIENCE INC
Thwaites DI, DuSatouy AR, Jordan T, McEwen MR, Nahum AE, Nisbet A, Pitchford WG (2003) The IPEM code of practice for electron dosimetry for radiotherapy beams of initial energy from 4 to 25 MeV based on an absorbed dose to water calibration, Physics in Medicine and Biology 48 (18) pp. 2929-2970
This report contains the recommendations of the Electron Dosimetry Working Party of the UK Institute of Physics and Engineering in Medicine (IPEM). The recommendations consist of a code of practice for electron dosimetry for radiotherapy beams of initial energy from 4 to 25 MeV. The code is based on the absorbed dose to water calibration service for electron beams provided by the UK standards laboratory, the National Physical Laboratory (NPL). This supplies direct N(D,w) calibration factors, traceable to a calorimetric primary standard, at specified reference depths over a range of electron energies up to approximately 20 MeV. Electron beam quality is specified in terms of R(50,D), the depth in water along the beam central axis at which the dose is 50% of the maximum. The reference depth for any given beam at the NPL for chamber calibration and also for measurements for calibration of clinical beams is 0.6R(50.D) - 0.1 cm in water. Designated chambers are graphite-walled Farmer-type cylindrical chambers and the NACP- and Roos-type parallel-plate chambers. The practical code provides methods to determine the absorbed dose to water under reference conditions and also guidance on methods to transfer this dose to non-reference points and to other irradiation conditions. It also gives procedures and data for extending up to higher energies above the range where direct calibration factors are currently available. The practical procedures are supplemented by comprehensive appendices giving discussion of the background to the formalism and the sources and values of any data required. The electron dosimetry code improves consistency with the similar UK approach to megavoltage photon dosimetry, in use since 1990. It provides reduced uncertainties, approaching 1% standard uncertainty in optimal conditions, and a simpler formalism than previous air kerma calibration based recommendations for electron dosimetry
Doran S, Thomas R, Hollingdale R, Adamovics J, Nisbet A (2010) Electron dosimetry in the presence of small cavities, Journal of Physics: Conference Series 250 pp. 447-451
Noor NM, Shukor NA, Hussein M, Nisbet A, Bradley DA (2012) Comparison of the TL fading characteristics of Ge-doped optical fibres and LiF dosimeters, Appl Radiat Isot 70 (7) pp. 1384-1387 Elsevier
Fading is important in choosing appropriate thermoluminescence (TL) materials for particular applications. Comparison is made herein of changes due to fading in the TL yield of Ge-doped fibres and lithium fluoride (LiF) dosimeters, for varying temperature and dose. The fading is independent of dose for all investigated dosimeters while the loss in TL yield reduces for lower storage temperatures. At room temperature and for 133 days of storage, a maximum signal loss of 5% has been observed for both forms of LiF dosimeter, while 9 and 50¼m core diameter Ge-doped fibres produced a loss of 11% and 8%, respectively.
Taylor C, Nisbet A, Povall J, McGale P, Dodwell D, Darby S (2006) Heart and coronary artery doses from breast radiotherapy, RADIOTHERAPY AND ONCOLOGY 81 pp. S283-S283 ELSEVIER IRELAND LTD
Nisbet A, Thwaites DI (1998) Polarity and ion recombination correction factors for ionization chambers employed in electron beam dosimetry., Phys Med Biol 43 (2) pp. 435-443
Polarity and ion recombination correction factors for the NACP (type-02) design parallel-plate ionization chamber employed in a recent UK national electron beam dosimetry intercomparison are derived over the full range of energies and measurement conditions encountered. In addition, these effects have been studied for a further four NACP chambers, a Markus parallel-plate chamber, a Roos parallel-plate chamber and a NE2571 graphite walled cylindrical ionization chamber.
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.
Tariq I, Humbert-Vidan L, Chen T, South CP, Ezhil V, Kirkby NF, Jena R, Nisbet A (2015) Mathematical modelling of tumour volume dynamics in response to stereotactic ablative radiotherapy for non-small cell lung cancer., Physics in medicine and biology 60 (9) pp. 3695-3713
This paper reports a modelling study of tumour volume dynamics in response to stereotactic ablative radiotherapy (SABR). The main objective was to develop a model that is adequate to describe tumour volume change measured during SABR, and at the same time is not excessively complex as lacking support from clinical data. To this end, various modelling options were explored, and a rigorous statistical method, the Akaike information criterion, was used to help determine a trade-off between model accuracy and complexity. The models were calibrated to the data from 11 non-small cell lung cancer patients treated with SABR. The results showed that it is feasible to model the tumour volume dynamics during SABR, opening up the potential for using such models in a clinical environment in the future.
Nisbet A, Galer S, Palmans H, Hao L, Kirkby K, Gallop J (2010) Development of a Microbolometer for Microdosimetry, Radiotherapy & Oncology 96 (Supple) pp. S 453-S 453 Elsevier
Hussein M, Rowshanfarzad P, Ebert MA, Nisbet A, Clark CH (2013) A comparison of the gamma index analysis in various commercial IMRT/VMAT QA systems., Radiother Oncol 109 (3) pp. 370-376
To investigate the variability of the global gamma index (³) analysis in various commercial IMRT/VMAT QA systems and to assess the impact of measurement with low resolution detector arrays on ³.
Teoh M, Wood K, Whitaker S, Beveridge S, Adams E, Rickard D, Jordan T, Nisbet A, Clark CH (2013) Volumetric-modulated arc therapy (RapidArc) vs. conventional fixed-field intensity-modulated radiotherapy for F-FDG-PET-guided dose escalation in oropharyngeal cancer: A planning study, Medical Dosimetry 38 (1) pp. 18-24
Fluorine-18-fluorodeoxyglucose-positron emission tomography (F-FDG-PET)-guided focal dose escalation in oropharyngeal cancer may potentially improve local control. We evaluated the feasibility of this approach using volumetric-modulated arc therapy (RapidArc) and compared these plans with fixed-field intensity-modulated radiotherapy (IMRT) focal dose escalation plans. Materials and methods: An initial study of 20 patients compared RapidArc with fixed-field IMRT using standard dose prescriptions. From this cohort, 10 were included in a dose escalation planning study. Dose escalation was applied to F-FDG-PET-positive regions in the primary tumor at dose levels of 5% (DL1), 10% (DL2), and 15% (DL3) above standard radical dose (65 Gy in 30 fractions). Fixed-field IMRT and double-arc RapidArc plans were generated for each dataset. Dose-volume histograms were used for plan evaluation and comparison. The Paddick conformity index (CI) and monitor units (MU) for each plan were recorded and compared. Both IMRT and RapidArc produced clinically acceptable plans and achieved planning objectives for target volumes. Dose conformity was significantly better in the RapidArc plans, with lower CI scores in both primary (PTV1) and elective (PTV2) planning target volumes (largest difference in PTV1 at DL3; 0.81 ± 0.03 [RapidArc] vs. 0.77 ± 0.07 [IMRT], p = 0.04). Maximum dose constraints for spinal cord and brainstem were not exceeded in both RapidArc and IMRT plans, but mean doses were higher with RapidArc (by 2.7 ± 1 Gy for spinal cord and 1.9 ± 1 Gy for brainstem). Contralateral parotid mean dose was lower with RapidArc, which was statistically significant at DL1 (29.0 vs. 29.9 Gy, p = 0.01) and DL2 (29.3 vs. 30.3 Gy, p = 0.03). MU were reduced by 39.8-49.2% with RapidArc (largest difference at DL3, 641 ± 94 vs. 1261 ± 118, p
Merrett JL, Fenwick AJ, Yatigammana DNB, Scuffham JW, Johansson LC, Nisbet A (2014) Quantitative Imaging of Lu-177 on a Symbia T6 SPECT/CT, EUROPEAN JOURNAL OF NUCLEAR MEDICINE AND MOLECULAR IMAGING 41 pp. S222-S222 SPRINGER
Lei M, Clark C, Adams E, Freeman K, Jamieson C, Dabbs M, Jordan T, Whitaker S, Nisbet A, Urbano TG (2010) CBCT Evaluation of Dose-Volume Changes in Contralateral Parotid Gland during Head and Neck IG-IMRT, INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 78 (3) pp. S481-S482 ELSEVIER SCIENCE INC
Dalah EZ, Nisbet A, Reise S, Bradley D (2008) Evaluating commercial image registration packages for radiotherapy treatment planning, APPLIED RADIATION AND ISOTOPES 66 (12) pp. 1948-1953 PERGAMON-ELSEVIER SCIENCE LTD
Alshanqity M, Duane S, Nisbet A (2012) A simple approach for EPID dosimetric calibration to overcome the effect of image-lag and ghosting, Applied Radiation and Isotopes 70 (7) pp. 1154-1157
EPID dosimetry has known drawbacks. The main issue is that a measurable residual signal is observed after the end of irradiation for prolonged periods of time, thus making measurement difficult. We present a detailed analysis of EPID response and suggest a simple, yet accurate approach for calibration that avoids the complexity of incorporating ghosting and image-lag using the maximum integrated signal instead of the total integrated signal. This approach is linear with dose and independent of dose rate. © 2012 Elsevier Ltd.
Nisbet A, Roberts R, Costelloe M, Hopewell J (2006) A radiobiological and clinical assessment of quality assurance tolerances in head and neck radiotherapy techniques, RADIOTHERAPY AND ONCOLOGY 81 pp. S460-S460 ELSEVIER IRELAND LTD
Issa F, Hugtenburg RP, Bradley DA, Nisbet A (2011) Investigating radionuclide source shielding performance using Ge-doped optical fibre thermoluminescence dosimeters, AIP Conference Proceedings 1423 pp. 401-405 American Institute of Physics
Nisbet A, Thwaites DI, Sheridan ME (1998) A dosimetric intercomparison of kilovoltage X-rays, megavoltage photons and electrons in the Republic of Ireland., Radiother Oncol 48 (1) pp. 95-101
BACKGROUND AND PURPOSE: A comprehensive dosimetry intercomparison has been carried out involving all the radiotherapy centres, all external beam modalities and every radiotherapy treatment unit in the Republic of Ireland. MATERIALS AND METHODS: Reference point measurements were made for all megavoltage photon beams. Doses were also investigated in planned three-field distributions. One of these was in a homogeneous epoxy resin solid water phantom, whilst the second included a lung equivalent insert. The intercomparison was also carried out for three electron energies in each centre. The position of the depth of maximum dose for a standard field size was independently determined, as was the beam energy and a subsequent beam calibration was made. In addition, a kilovoltage X-ray intercomparison was carried out on every kilovoltage quality. RESULTS: For 13 megavoltage photon beams a mean ratio of intercomparison measured dose to locally measured dose of 1.002 was obtained (standard deviation 1.2%). For 12 electron beam measurements a mean ratio of intercomparison measured dose to locally measured dose of 1.018 was obtained (standard deviation 0.8%). For four kilovoltage beams a mean ratio of intercomparison measured dose to locally measured dose of 0.997 was obtained (standard deviation 1.9%). CONCLUSIONS: The intercomparison has given confidence in the basis of clinical delivery of radiation dose in radiotherapy treatment and in the consistency (precision) of dosimetry between different centres within the Republic of Ireland. In addition, it has established a methodology for subsequent ongoing routine radiotherapy dosimetry audit and a baseline set of results to act as an initial reference point.
Skeldon AC, Chaffey G, Lloyd DJ, Mohan V, Bradley DA, Nisbet A (2012) Modelling and detecting tumour oxygenation levels., PLoS One 7 (6)
Tumours that are low in oxygen (hypoxic) tend to be more aggressive and respond less well to treatment. Knowing the spatial distribution of oxygen within a tumour could therefore play an important role in treatment planning, enabling treatment to be targeted in such a way that higher doses of radiation are given to the more radioresistant tissue. Mapping the spatial distribution of oxygen in vivo is difficult. Radioactive tracers that are sensitive to different levels of oxygen are under development and in the early stages of clinical use. The concentration of these tracer chemicals can be detected via positron emission tomography resulting in a time dependent concentration profile known as a tissue activity curve (TAC). Pharmaco-kinetic models have then been used to deduce oxygen concentration from TACs. Some such models have included the fact that the spatial distribution of oxygen is often highly inhomogeneous and some have not. We show that the oxygen distribution has little impact on the form of a TAC; it is only the mean oxygen concentration that matters. This has significant consequences both in terms of the computational power needed, and in the amount of information that can be deduced from TACs.
Palmer AL, Nisbet A, Bradley D (2013) Verification of high dose rate brachytherapy dose distributions with EBT3 Gafchromic film quality control techniques, Physics in Medicine and Biology 58 (3) pp. 497-511
It is essential that quality control (QC) techniques are developed to keep pace with modern high dose rate (HDR) brachytherapy. Current QC methods may be insufficient to fully assure the accuracy of 3D-optimized dose delivery. This work presents an evaluation of Gafchromic EBT3 film, with multi-channel analysis, in HDR dose environments for advanced QC and commissioning. 'Film-array in water' and 'three-channel Solid Water block' purpose-designed phantoms are utilized. Dose and dose-rate dependency and practical film usage has been evaluated. EBT3 measurements of dose with radial distance from a HDR source are compared to Monte Carlo data. Semi-3D dose distributions around clinical HDR applicators are compared to treatment plans. The measurement of delivery accuracy for inverse-planned pseudo-clinical test cases, with correct delivery and simulated treatment errors, has also been investigated. Local gamma criteria of 3%, 3 mm is recommended with passing rates of at least 96% typically achieved. The system is sensitive to simulated errors in HDR delivery, with significant reductions of passing rate. It has been demonstrated that EBT3 Gafchromic film, in combination with multi-channel analysis, is appropriate for applicator, treatment unit and planning system commissioning measurements as well as practical routine QC to confirm agreement of planned and delivered complex HDR brachytherapy dose distributions. © 2013 Institute of Physics and Engineering in Medicine.
Fathi K (2017) Optimisation of a novel micro-calorimeter
through Monte Carlo simulations and thermal
analysis for use in particle therapy.,
The high uncertainty in the Relative Biological Effectiveness (RBE) values of particle
therapy beams, which are used in combination with the quantity absorbed dose in
radiotherapy, together with the increase in the number of particle therapy centres
worldwide necessitate a better understating of the biological effect of such modalities.
The present novel study is part of performance testing and development of a microcalorimeter
based on Superconducting QUantum Interference Devices (SQUIDs). Unlike
other microdosimetric detectors that are used for investigating the energy distribution,
this detector provides a direct measurement of energy deposition at the micrometer
scale, that can be used to improve our understanding of biological effects in particle
therapy application, radiation protection and environmental dosimetry. Temperature
rises of less than 1 ¼K are detectable and when combined with the low specific heat
capacity of the absorber at cryogenic temperature, extremely high energy deposition
sensitivity of approximately 0.4 eV can be achieved.
The detector consists of three layers: a Tissue Equivalent (TE) absorber, a SuperConducting
(SC) absorber and a silicon substrate. Ideally all energy would be deposited in
the TE absorber and the heat rise in the SC layer would arise due to heat conduction
from the TE layer. However, in practice direct particle absorption occurs in all three
layers and must be corrected for.
To investigate the thermal behavior within the detector, and quantify any possible
correction, particle tracks were simulated employing Geant4 (v9.6) Monte Carlo simulations.
The track information was then passed to the COMSOL Multiphysics (Finite
Element Method) software. The 3D heat transfer within each layer was then evaluated
in a time-dependent model. For a statistically reliable outcome, the simulations had to
be repeated for a large number of particles. An automated system has been developed
that couples Geant4 Monte Carlo output to COMSOL for determining the expected
distribution of proton tracks and their thermal contribution within the detector.
The percentage heat contribution from the TE absorber into the SC absorber was
determined for mono-energetic proton pencil beams of 3.8, 10, 62 and 230 MeV. The
corrected energy distribution is compared to the ideal energy distribution, exhibiting
good agreement.
Jafari S, Jordan T, Hussein M, Bradley DA, Clark C, Nisbet A, Spyrou NM (2014) Energy response of glass bead TLDs irradiated with radiation therapy beams, RADIATION PHYSICS AND CHEMISTRY 104 pp. 208-211 PERGAMON-ELSEVIER SCIENCE LTD
Glass beads are a novel TL dosimeter in radiotherapy. An important characteristic of TL dosimeters is
their energy response, especially when intended for use in radiotherapy applications over a wide range
of energies (typically from X-rays generated at 80 kVp up to 25 MV photon and MeV electron beams). In
this paper, the energy response of glass beads (Mill Hill, Japan) is investigated for their TL response to kV
X-rays from an orthovoltage radiotherapy unit and also for MV photon and MeV electron beams from a
medical linear accelerator. The experimental findings show that for photon and electron beams, the TL
response of this particular glass bead, normalised to unity for 6 MV X-rays (TPR20/10¼0.670), decreases
to 0.9670.02 for 15 MV X-rays (TPR20/10¼0.761) and to 0.9570.01 for 20 MeV electron beams
(R50,D¼8.35 cm). This compares favourably with other TLD materials such as LiF and also alanine
dosimeters that are readout with an EPR system. For kV X-rays, the response increases to 4.5270.05 for
80 kV X-rays (HVL¼2.4 mm Al) which approaches 3 times that of LiF TLDs and 5 times that of alanine.
In conclusion, the particular glass beads, when used as a dosimeter material, show a relatively small
energy dependence over the megavoltage range of clinically relevant radiation qualities, being clearly
advantageous for accurate dosimetry. Conversely, the energy response is significant for photon beam
energies covering the kV range. In both circumstances, in dosimetric evaluations the energy response
needs to be taken into account.
Bradley DA, Abdul Sani S, Alalawi A, Jafari S, Nisbet A, Noor N, Hairul Azhar A, Mahdiraji G, Tamchek N, Ghosh S, Paul M, Alzimami K, Maah M (2014) Development of tailor-made silica fibres for TL dosimetry, Radiation Physics and Chemistry 104 pp. 3-9
The Ge dopant in commercially available silica optical fibres gives rise to appreciable thermoluminscence (TL), weight-for-weight offering sensitivity to MV X-rays several times that of the LiF dosimeter TLD100. The response of these fibres to UV radiation, X-rays, electrons, protons, neutrons and alpha particles, with doses from a fraction of 1Gy up to 10kGy, have stimulated further investigation of the magnitude of the TL signal for intrinsic and doped SiO fibres. We represent a consortium effort between Malaysian partners and the University of Surrey, aimed at production of silica fibres with specific TL dosimetry applications, utilizing modified chemical vapour deposition (MCVD) doped silica-glass production and fibre-pulling facilities. The work is informed by defect and dopant concentration and various production dependences including pulling parameters such as temperature, speed and tension; the fibres also provide for spatial resolutions down to
Issa F, Abdul Rahman A, Hugtenburg R, Bradley DA, Nisbet A (2012) Establishment of Ge-doped optical fibres as thermoluminescence dosimeters for brachytherapy, Applied Radiation and Isotopes 70 (7) pp. 1158-1161 Elsevier
This study aims to establish the sensitive, ~120¼m high spatial resolution, high dynamic range Ge-doped optical fibres as thermoluminescence (TL) dosimeters for brachytherapy dose distribution. This requires investigation to accommodate sensitivity of detection, both for the possibility of short range dose deposition from beta components as well as gamma/x-mediated dose. In-air measurements are made at distances close to radionuclide sources, evaluating the fall off in dose along the transverse axis of Ba and Co radioactive sources, at distances from 2mm up to 20mm from their midpoints. Measurements have been compared with Monte Carlo code DOSRZnrc simulations for photon-mediated dose only, agreement being obtained to within 3% and 1% for the Ba and Co sources, respectively. As such, in both cases it is determined that as intended, beta dose has been filtered out by source encapsulation. © 2012 Elsevier Ltd.
Dimitriadis A, Palmer A, Thomas R, Nisbet A, Clark C (2017) Adaptation and validation of a commercial head phantom for cranial radiosurgery dosimetry end-to-end audit, British Journal of Radiology 90 (1074) British Institute of Radiology
Objectives: To adapt and validate an anthropomorphic head phantom for use in a cranial radiosurgery audit. Methods: Two bespoke inserts were produced for the phantom: one for providing the target and organ at risk for delineation, and one for performing dose measurements. The inserts were tested to assess their positional accuracy. A basic treatment plan dose verification with an ionisation chamber was performed to establish a baseline accuracy for the phantom and beam model. The phantom and inserts were then used to perform dose verification measurements of a radiosurgery plan. The dose was measured with alanine pellets, EBT-XD film and a plastic scintillation detector (PSD). Results: Both inserts showed reproducible positioning (±0.5 mm) and good positional agreement between them (±0.6 mm). The basic treatment plan measurements showed agreement to the Treatment Planning System (TPS) within 0.5%. Repeated film measurements showed consistent gamma passing rates with good agreement to the TPS. For 2%-2mm global gamma, the mean passing rate was 96.7% and the variation in passing rates did not exceed 2.1%. The alanine pellets and PSD showed good agreement with the TPS (-0.1 and 0.3% dose difference in the target) and good agreement with each other (within 1%). Conclusions: The adaptations to the phantom showed acceptable accuracies. The presence of alanine and PSD do not affect film measurements significantly, enabling simultaneous measurements by all three detectors. Advancements in knowledge: A novel method for thorough end-to-end test of radiosurgery, with capability to incorporate all steps of the clinical pathway in a time-efficient and reproducible manner, suitable for a national audit.
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.
Mohd Noor N, Nisbet A, Hussein M, Sarene Chu S, Kadni T, Abdullah N, Bradley DA (2017) Dosimetry Audits and Intercomparisons in Radiotherapy: a Malaysian Profile, Radiation Physics and Chemistry 140 pp. 207-212 Elsevier
Quality audits and intercomparisons are important in ensuring control of processes in any system of endeavour. Present interest is in control of dosimetry in teletherapy, there being a need to assess the extent to which there is consistent radiation dose delivery to the patient. In this study we review significant factors that impact upon radiotherapy dosimetry, focusing upon the example situation of radiotherapy delivery in Malaysia, examining existing literature in support of such efforts. A number of recommendations are made to provide for increased quality assurance and control. In addition to this study, the first level of intercomparison audit i.e. measuring beam output under reference conditions at eight selected Malaysian radiotherapy centres is checked; use being made of 9 µm core diameter Ge-doped silica fibres (Ge-9 µm). The results of Malaysian Secondary Standard Dosimetry Laboratory (SSDL) participation in the IAEA/WHO TLD postal dose audit services during the period between 2011 and 2015 will also been discussed. In conclusion, following review of the development of dosimetry audits and the conduct of one such exercise in Malaysia, it is apparent that regular periodic radiotherapy audits and intercomparison programmes should be strongly supported and implemented worldwide. The programmes to-date demonstrate these to be a good indicator of errors and of consistency between centres. A total of ei+ght beams have been checked in eight Malaysian radiotherapy centres. One out of the eight beams checked produced an unacceptable deviation; this was found to be due to unfamiliarity with the irradiation procedures. Prior to a repeat measurement, the mean ratio of measured to quoted dose was found to be 0.99 with standard deviation of 3%. Subsequent to the repeat measurement, the mean distribution was 1.00, and the standard deviation was 1.3%.
Hussein M, South C, Barry M, Adams E, Jordan T, Stewart A, Nisbet A (2016) Clinical validation and benchmarking of knowledge-based IMRT and VMAT treatment planning in pelvic anatomy, Radiotherapy and Oncology 120 (3) pp. 473-479 Elsevier
Purpose: The aim of this work was to determine whether a commercial knowledge-based treatment planning (KBP) module can efficiently produce IMRT and VMAT plans in the pelvic region (prostate & cervical cancer), and to assess sensitivity of plan quality to training data and model parameters. Methods: Initial benchmarking of KBP was performed using prostate cancer cases. Structures and dose distributions from 40 patients previously treated using a 5-field IMRT technique were used for model training. Two types of model were created: one excluded statistical outliers (as identified by RapidPlan guidelines) and the other had no exclusions. A separate model for cervix uteri cancer cases was subsequently developed using 37 clinical patients treated for cervical cancer using RapidArcTM VMAT, with no exclusions. The resulting models were then used to generate plans for ten patients from each patient group who had not been included in the modelling process. Comparisons of generated RapidPlans with the corresponding clinical plans were carried out to indicate the required modifications to the models. Model parameters were then iteratively adjusted until plan quality converged with that obtained by experienced planners without KBP. Results: Initial automated model generation settings led to poor conformity, coverage and efficiency compared to clinical plans. Therefore a number of changes to the initial KBP models were required. Before model optimisation, it was found that the PTV coverage was slightly reduced in the superior and inferior directions for RapidPlan compared with clinical plans and therefore PTV parameters were adjusted to improve coverage. OAR doses were similar for both RapidPlan and clinical plans (p > 0.05). Excluding outliers had little effect on plan quality (p 0.05). Manually fixing key optimisation objectives enabled production of clinically acceptable treatment plans without further planner intervention for 9 of 10 prostate test patients and all 10 cervix test patients. Conclusions: The Varian RapidPlanTM system was able to produce IMRT & VMAT treatment plans in the pelvis, in a single optimisation, that had comparable sparing and comparable or better conformity than the original clinically acceptable plans. The system allows for better consistency and efficiency in the treatment planning process and has therefore been adopted clinically within our institute with over 100 patients treated.
Abdul Sani S, Alalawi A, Nisbet A, Bradley DA, Azhar A R H, Amouzad Mahdiraji G, Tamchek N, Maah M (2014) High sensitivity flat SiO fibres for medical dosimetry, Radiation Physics and Chemistry 104 pp. 134-138
We describe investigation of a novel undoped flat fibre fabricated for medical radiation dosimetry. Using high energy X-ray beams generated at a potential of 6MV, comparison has been made of the TL yield of silica flat fibres, TLD-100 chips and Ge-doped silica fibres. The flat fibres provide competitive TL yield to that of TLD-100 chips, being some 100 times that of the Ge-doped fibres. Pt-coated flat fibres have then been used to increase photoelectron production and hence local dose deposition, obtaining significant increase in dose sensitivity over that of undoped flat fibres. Using 250kVp X-ray beams, the TL yield reveals a progressive linear increase in dose for Pt thicknesses from 20nm up to 80nm. The dose enhancement factor (DEF) of (0.0150±0.0003)nm Pt is comparable to that obtained using gold, agreeing at the 1% level with the value expected on the basis of photoelectron generation. Finally, X-ray photoelectron spectroscopy (XPS) has been employed to characterize the surface oxidation state of the fibre medium. The charge state of Si2p was found to lie on 103.86eV of binding energy and the atomic percentage obtained from the XPS analysis is 22.41%. © 2014 Elsevier Ltd.
Hussein M, Clark C, Nisbet A (2017) Challenges in calculation of the gamma index in radiotherapy - towards good practice, Physica Medica: European Journal of Medical Physics 36 pp. 1-11 Elsevier
The gamma index (c) is one of the most commonly used metrics for the verification of complex modulated radiotherapy. The mathematical definition of the c is computationally expensive and various techniques have been reported to speed up the calculation either by mathematically refining the c or employing various computational techniques. These techniques can cause variation in output with different software implementations. The c has traditionally been used to compare a 2D measured plane against a 2D or 3D dose distribution. Recently, software algorithm and hardware improvements have led to the possibility of using measured 2D data from commercial detector arrays to reconstruct a 3D-dose distribution and perform a volumetric comparison against the treatment planning system (TPS). A limitation in this approach is that commercial detector arrays have so far been limited by their spatial resolution which may affect the accuracy of the reconstructed 3D volume and subsequently the c calculation. Additionally, 3D versus 3D c comparison adds a layer of complication in the calculation of the c given the increase in the number of calculation points and the result cannot be as easily interpreted in the same way as 2D comparison. This review summarises and highlights the computational challenges of the c calculation and sheds light on some of these issues by means of a bespoke MATLAB software to demonstrate the impact of interpolation, c search distance, resolution and 2D and 3D calculations. Finally, a recommendation is made on the minimum information that should be reported when publishing c results.
Scuffham J, Yip-Braidley M, Shutt A, Hinton P, Nisbet A, Bradley DA (2016) Adapting clinical gamma cameras for body monitoring in the event of a large-scale radiological incident, JOURNAL OF RADIOLOGICAL PROTECTION 36 (2) pp. 363-381 IOP PUBLISHING LTD
After a release of radionuclides, accidental or otherwise, there will be an urgent need to identify members of the general public who have received a significant intake of radioactive material, sufficient to require medical treatment or further investigation. A large number of people could be contaminated in such an incident. For gamma-ray emitting radionuclides this screening could be carried out using gamma camera medical imaging systems, such as those that are present in many large UK hospital sites. By making a number of simple reversible changes such as removal of collimators, these cameras could be employed as useful additional screening instruments as well as an aid in contamination control. A study was carried out to investigate which systems were present in sufficient number to offer wide scale coverage of UK population centres. Nine gamma cameras (eight dual head and one single head) were assessed using point source and bottle mannequin (BOMAB) phantom measurements so that a mathematical model could be developed for use with the MCNPX Monte Carlo radiation transport code. The gamma camera models were assessed for practical seated and supine geometries to give calibration factors for a list of target radionuclides that could be released in a radiological incident. The minimum detectable activities (MDAs) that were achieved for a five minute measurement demonstrated that these systems are sufficiently sensitive to be used for screening of the general public and are comparable to other body monitoring facilities. While gamma cameras have on-board software that are designed for imaging and provide for a gamma-ray energy range suitable for radionuclides for diagnostic imaging (such as 99mTc), they are not as versatile as custom-built body monitoring systems.
Davis A, Palmer A, Nisbet A (2017) Can CT scan protocols used for radiotherapy treatment planning be adjusted to optimise image quality and patient dose? A systematic review, British Journal of Radiology 90 (1076) British Institute of Radiology
This article reviews publications related to the use of CT scans for radiotherapy treatment planning, specifically the impact of scan protocol changes on CT number and treatment planning dosimetry and on CT image quality. A search on PubMed and EMBASE and a subsequent review of references yielded 53 relevant articles. CT scan parameters significantly affect image quality. Some will also affect Hounsfield unit (HU) values, though this is not comprehensively reported on. Changes in tube kilovoltage and, on some scanners, field of view and reconstruction algorithms have been found to produce notable HU changes. The degree of HU change which can be tolerated without changing planning dose by >1% depends on the body region and size, planning algorithms, treatment beam energy and type of plan. A change in soft-tissue HU value has a greater impact than changes in HU for bone and air. The use of anthropomorphic phantoms is recommended when assessing HU changes. There is limited published work on CT scan protocol optimization in radiotherapy. Publications suggest that HU tolerances of ±20 HU for soft tissue and of ±50 HU for the lung and bone would restrict dose changes in the treatment plan to
Bradley DA, Hugtenburg R, Nisbet A, Abdul Rahman A, Issa F, Mohd Noor N, Alalawi A (2012) Review of doped silica glass optical fibre: Their TL properties and potential applications in radiation therapy dosimetry, Applied Radiation and Isotopes 71 (SUPPL.) pp. 2-11 Elsevier
Review is made of dosimetric studies of Ge-doped SiO telecommunication fibre as a 1-D thermoluminescence (TL) system for therapeutic applications. To-date, the response of these fibres has been investigated for UV sources, superficial X-ray beam therapy facilities, a synchrotron microbeam facility, electron linear accelerators, protons, neutrons and alpha particles, covering the energy range from a few eV to several MeV. Dosimetric characteristics include, reproducibility, fading, dose response, reciprocity between TL yield and dose-rate and energy dependence. The fibres produce a flat response to fixed photon and electron doses to within better than 3% of the mean TL distribution. Irradiated Ge-doped SiO optical fibres show limited signal fading, with an average loss of TL signal of ~0.4% per day. In terms of dose response, Ge-doped SiO optical fibres have been shown to provide linearity to x and electron doses, from a fraction of 1Gy up to 2kGy. The dosimeters have also been used in measuring photoelectron generation from iodinated contrast media; TL yields being some 60% greater in the presence of iodine than in its absence. The review is accompanied by previously unpublished data. © 2012 Elsevier Ltd.
Thomas R, Bolt MA, Bass G, Nutbrown R, Chen T, Nisbet A, Clark C (2017) Radiotherapy reference dose audit in the United Kingdom by the National Physical Laboratory: 20 years of consistency and improvements., Physics & Imaging in Radiation Oncology 3 pp. 21-27 Elsevier
Background and Purpose
Audit is imperative in delivering consistent and safe radiotherapy and the UK has a strong history of radiotherapy audit. The National Physical Laboratory (NPL) has undertaken audit measurements since 1994 and this work examines results from these audits.
Materials and Methods
This paper reviews audit results from 209 separate beams from 82 on-site visits to National Health Service (NHS) radiotherapy departments conducted between June 1994 and February 2015. Measurements were undertaken following the relevant UK code of practice. The accuracy of the implementation of absorbed dose calibration across the UK is quantified for MV photon, MeV electron and kV x-ray radiotherapy beams.
Results
Over the measurement period the standard deviation of MV photon beam output has reduced from 0.8 % to 0.4 %. The switch from air kerma- to absorbed dose-based electron code of practice contributed to a reduction in the difference of electron beam output of 0.6 % (p Conclusions
The introduction of the 2003 electron code of practice based on absorbed dose to water decreased the difference between absolute dose measurements by the centre and NPL. The use of a single photon code of practice over the period of measurements has contributed to a reduction in measurement variation. Within the clinical setting, on-site audit visits have been shown to identify areas of improvement for determining and implementing absolute dose calibrations.
Al-Ahbabi S, Bradley DA, Nisbet A (2013) Tomotherapy evaluation for head and neck cases using two types of phantoms, Radiation Physics and Chemistry 95 pp. 323-325 Elsevier
The use of rotational therapy as an important method of treatment delivery is expected to increase due in a large part to the development and utilisation of tomotherapy. Rotational therapy minimises the occurrence of hotspots and the irradiation of critical organs, providing more uniform dosing while sparing critical organs. Two important characteristics of rotational radiation are its dynamic nature and dosimetric variability in radiation delivery, both of which present a considerable challenge for clinical physicists seeking appropriate tools to meet the demands of quality assurance.In this paper 15 Delivery Quality Assurance (DQA) plans of head and neck patients were assessed for the Hi-Art tomotherapy system using Kodak X-Omat V film and an A1SL Ref F92722 ion chamber versus MapCheck. Absolute dose measurement showed average differences of 3.42. cGy and 98% Gamma (³) factor for the Cheese phantom technique. For the MapCheck technique the average difference and Gamma factor were 0.74. cGy and 96%, respectively. Gamma (³) matrix distribution was used to evaluate the difference between measured and calculated dose distribution. © 2013 Elsevier Ltd.
Jafari S, Distefano G, Lee J, Gouldstone C, Mayles H, Jupp T, Nisbet A, Clark C (2017) Feasibility study of silica bead thermoluminescence detectors (TLDs) in an external radiotherapy dosimetry audit programme, Radiation Physics and Chemistry 141 pp. 251-256 Elsevier
Purpose:
Investigating the feasibility of using low-cost commercially available silica beads as novel thermo-luminescence dosimeters (TLD) for postal dosimetry audit.

Methods:
A mail-based dosimetry audit was designed to assess the positional and dosimetric accuracy of SABR-lung treatment delivery using alanine and EBT3-film, placed in a CIRS-anthropomorphic thorax phantom. In conjunction, the silica beads were dosimetrically characterised as TLDs and cross-calibrated against the alanine. A CT-scan of the phantom with pre-delineated volumes was sent to 20 RT centres and used to create a SABR plan using local current protocols and techniques. The silica beads were held in an insert, designed to match that of the alanine holder and ionisation chamber to give the same measurement length. The doses determined by the silica beads were compared to those measured by alanine, the local ionisation chamber, film and the TPS calculation.

Results:
The mean percentage difference between the doses measured by the silica beads and the calculated doses by the TPS was found to be 0.7% and differed by 0.6%, 0.7%, and 1.3% from the alanine, film and local ionisation chamber measurements respectively.

Conclusions:
Results obtained with the silica beads agree well with those obtained from conventional detectors including alanine, film and ionisation chambers. This together with the waterproof and inert characteristics and minimal dose fading associated with silica bead TLDs confirm their potential as a postal dosimetry audit tool in both water and plastic phantoms which could withstand challenges of temperature and humidity variation, as well as postal service delays.

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.
Galer SE, Shipley D, Palmans H, Kirkby KJ, Nisbet A (2017) Monte Carlo simulation of a TEPC for microdosimetry of carbon ions, Radiation Physics and Chemistry 140 pp. 412-418 Elsevier
The increase in the number of therapeutic proton and ion beam centres worldwide has prompted renewed interest in measuring and simulating microdosimetric spectra in order to help understand the complexity underlying the Relative Biological Effectiveness (RBE) of these treatment modalities. In this context we have studied the capability of the Geant4 toolkit to simulate microdosimetric spectra measured with a Tissue Equivalent Proportional Counter (TEPC) in a clinical carbon ion beam. The simulated spectra were compared with published experimental data obtained along the depth dose curve of a 194 MeV/u carbon beam at the GSI, Darmstadt (Gerlach et al., 2002). The initial beam energy and energy spread employed in the simulation were tuned to match the calculated and measured depth dose distributions. A good agreement was found at all depths after a shift of 4.025 mm was taken into account with agreement for the microdosimetric derived RBE values to within 0.4% and 11.9% for depths 40 and 66 mm in PMMA (Perspex). This work demonstrates that the Geant4 toolkit can accurately reproduce experimental microdosimetric data and can thus be used for independent calculation of lineal energy spectra from which RBE estimates can be derived using the equation of Pihet et al. (1990). The work highlights the difficulty in using experimental work to benchmark Monte Carlo simulations and the need for detailed descriptions of experimental setups used.
Dimitriadis A, Silvestre Patallob I, Billas I, Duane S, Nisbet A, Clark C (2017) Characterisation of a plastic scintillation detector to be used in a multicentre stereotactic radiosurgery dosimetry audit, Radiation Physics and Chemistry 140 pp. 373-378 Elsevier
Scintillation detectors are considered highly suitable for dosimetric measurement of small fields in radiotherapy due to their near-tissue equivalence and their small size. A commercially available scintillation detector, the Exradin W1 (Standard Imaging, Middleton, USA), has been previously characterised by two independent studies (Beierholm et al., 2014; Carrasco et al., 2015a ; Carrasco et al., 2015b) but the results from these publications differed in some aspects (e.g. energy dependence, long term stability). The respective authors highlighted the need for more studies to be published (Beierholm et al., 2015; Carrasco et al., 2015a ; Carrasco et al., 2015b). In this work, the Exradin W1 was characterised in terms of dose response, dependence on dose rate, energy, temperature and angle of irradiation, and long-term stability. The observed dose linearity, short-term repeatability and temperature dependence were in good agreement with previously published data. Appropriate corrections should therefore be applied, where possible, in order to achieve measurements with low-uncertainty. The angular dependence was characterised along both the symmetrical and polar axis of the detector for the first time in this work and a dose variation of up to 1% was observed. The response of the detector was observed to decrease at a rate of approximately 1.6% kGy?1 for the first 5 kGy delivered, and then stabilised to 0.2% kGy?1 in the subsequent 20 kGy. The main goal of this work was to assess the suitability of the Exradin W1 for use in dose verification measurements for stereotactic radiosurgery. The results obtained confirm that the detector is suitable for use in such situations. The detector is now utilised in a multi-centre stereotactic radiosurgery dosimetric audit, with the application of appropriate correction factors.
Wevrett JL, Fenwick A, Scuffham J, Nisbet A (2017) Development of a calibration protocol for quantitative imaging for molecular radiotherapy dosimetry, Radiation Physics and Chemistry 140 pp. 355-360 Elsevier
Within the field of molecular radiotherapy, there is a significant need for standardisation in dosimetry, in both quantitative imaging and dosimetry calculations. Currently, there are a wide range of techniques used by different clinical centres and as a result there is no means to compare patient doses between centres. To help address this need, a 3 year project was funded by the European Metrology Research Programme, and a number of clinical centres were involved in the project. One of the required outcomes of the project was to develop a calibration protocol for three dimensional quantitative imaging of volumes of interest. Two radionuclides were selected as being of particular interest: iodine-131 (131I, used to treat thyroid disorders) and lutetium-177 (177Lu, used to treat neuroendocrine tumours). A small volume of activity within a scatter medium (water), representing a lesion within a patient body, was chosen as the calibration method. To ensure ease of use in clinical centres, an ?off-the-shelf? solution was proposed ? to avoid the need for in-house manufacturing. The BIODEX elliptical Jaszczak phantom and 16 ml fillable sphere were selected. The protocol was developed for use on SPECT/CT gamma cameras only, where the CT dataset would be used to correct the imaging data for attenuation of the emitted photons within the phantom. The protocol corrects for scatter of emitted photons using the triple energy window correction technique utilised by most clinical systems. A number of clinical systems were tested in the development of this protocol, covering the major manufacturers of gamma camera generally used in Europe. Initial imaging was performed with 131I and 177Lu at a number of clinical centres, but due to time constraints in the project, some acquisitions were performed with 177Lu only. The protocol is relatively simplistic, and does not account for the effects of dead-time in high activity patients, the presence of background activity surrounding volumes of interest or the partial volume effect of imaging lesions smaller than 16 ml. The development of this simple protocol demonstrates that it is possible to produce a standardised quantitative imaging protocol for molecular radiotherapy dosimetry. However, the protocol needs further development to expand it to incorporate other radionuclides, and to account for the effects that have been disregarded in this initial version
Kamali-Zonouzi P, Shutt A, Nisbet A, Bradley D (2017) Feasibility of employing thick microbeams from superficial and orthovoltage kVp x-ray tubes for radiotherapy of superficial cancers, Radiation Physics and Chemistry 140 pp. 237-241 Elsevier
Preclinical investigations of thick microbeams show these to be feasible for use in radiotherapeutic dose delivery. To create the beams we access a radiotherapy x-ray tube that is familiarly used within a conventional clinical environment, coupling this with beam-defining grids. Beam characterisation, both single and in the form of arrays, has been by use of both MCNP simulation and direct Gafchromic EBT film dosimetry. As a first step in defining optimal exit-beam profiles over a range of beam energies, simulation has been made of the x-ray tube and numbers of beam-defining parallel geometry grids, the latter being made to vary in thickness, slit separation and material composition. For a grid positioned after the treatment applicator, and of similar design to those used in the first part of the study, MCNP simulation and Gafchromic EBT film were then applied in examining the resultant radiation profiles. MCNP simulations and direct dosimetry both show useful thick microbeams to be produced from the x-ray tube, with peak-to-valley dose ratios (PVDRs) in the approximate range 8.8?13.9. Although the potential to create thick microbeams using radiotherapy x-ray tubes and a grid has been demonstrated, Microbeam Radiation Therapy (MRT) would still need to be approved outside of the preclinical setting, a viable treatment technique of clinical interest needing to benefit for instance from substantially improved x-ray tube dose rates.
Fathi K, Galer SE, Kirkby KJ, Palmans H, Nisbet A (2017) Coupling Monte Carlo simulations with thermal analysis for correcting microdosimetric spectra from a novel micro-calorimeter, Radiation Physics and Chemistry 140 pp. 406-411 Elsevier
The high uncertainty in the Relative Biological Effectiveness (RBE) values of particle therapy beam, which are used in combination with the quantity absorbed dose in radiotherapy, together with the increase in the number of particle therapy centres worldwide necessitate a better understating of the biological effect of such modalities. The present novel study is part of performance testing and development of a micro-calorimeter based on Superconducting QUantum Interference Devices (SQUIDs). Unlike other microdosimetric detectors that are used for investigating the energy distribution, this detector provides a direct measurement of energy deposition at the micrometre scale, that can be used to improve our understanding of biological effects in particle therapy application, radiation protection and environmental dosimetry. Temperature rises of less than 1¼K are detectable and when combined with the low specific heat capacity of the absorber at cryogenic temperature, extremely high energy deposition sensitivity of approximately 0.4 eV can be achieved. The detector consists of 3 layers: tissue equivalent (TE) absorber, superconducting (SC) absorber and silicon substrate. Ideally all energy would be absorbed in the TE absorber and heat rise in the superconducting layer would arise due to heat conduction from the TE layer. However, in practice direct particle absorption occurs in all 3 layers and must be corrected for. To investigate the thermal behaviour within the detector, and quantify any possible correction, particle tracks were simulated employing Geant4 (v9.6) Monte Carlo simulations. The track information was then passed to the COMSOL Multiphysics (Finite Element Method) software. The 3D heat transfer within each layer was then evaluated in a time-dependent model. For a statistically reliable outcome, the simulations had to be repeated for a large number of particles. An automated system has been developed that couples Geant4 Monte Carlo output to COMSOL for determining the expected distribution of proton tracks and their thermal contribution within the detector. The correction factor for a 3.8 MeV proton pencil beam was determined and applied to the expected spectra. The corrected microdosimetric spectra was shown to have a good agreement with the ideal spectra.
Bolt M, Clark C, Chen T, Nisbet A (2017) A multi-centre analysis of radiotherapy beam output measurement, Physics & Imaging in Radiation Oncology 4 pp. 39-43 Elsevier
Background and Purpose

Radiotherapy requires tight control of the delivered dose. This should include the variation in beam output as this may directly affect treatment outcomes. This work provides results from a multi-centre analysis of routine beam output measurements.

Materials and Methods

A request for 6MV beam output data was submitted to all radiotherapy centres in the UK, covering the period January 2015 ? July 2015. An analysis of the received data was performed, grouping the data by manufacturer, machine age, and recording method to quantify any observed differences. Trends in beam output drift over time were assessed as well as inter-centre variability. Annual trends were calculated by linear extrapolation of the fitted data.

Results

Data was received from 204 treatment machines across 52 centres. Results were normally distributed with mean of 0.0% (percentage deviation from initial calibration) and a 0.8% standard deviation, with 98.1% of results within ±2%. There were eight centres relying solely on paper records. Annual trends varied greatly between machines with a mean drift of +0.9%/year with 95th percentiles of +5.1%/year and -2.2%/year. For the machines of known age 25% were over ten years old, however there was no significant differences observed with machine age.

Conclusions

Machine beam output measurements were largely within ±2% of 1.00cGy/MU. Clear trends in measured output over time were seen, with some machines having large drifts which would result in additional burden to maintain within acceptable tolerances. This work may act as a baseline for future comparison of beam output measurements.

Davis A, Palmer A, Pani S, Nisbet A (2017) Assessment of the variation in CT scanner performance (image quality and Hounsfield Units) with scan parameters, for image optimisation in radiotherapy treatment planning, Physica Medica: European Journal of Medical Physics 45 pp. 59-64 Elsevier, for Associazione Italiana di Fisica Medica and European Federation of Organisations for Medical Physics
Purpose:

To define a method and investigate how the adjustment of scan parameters affected the image quality and Hounsfield units (HUs) on a CT scanner used for radiotherapy treatment planning. A lack of similar investigations in the literature may be a contributing factor in the apparent reluctance to optimise radiotherapy CT protocols.

Method:

A Catphan phantom was used to assess how image quality on a Toshiba Aquilion LB scanner changed with scan parameters. Acquisition and reconstruction field-of-view (FOV), collimation, image slice thickness, effective mAs per rotation and reconstruction algorithm were varied. Changes were assessed for HUs of different materials, high contrast spatial resolution (HCSR), contrast-noise ratio (CNR), HU uniformity, scan direction low contrast and CT dose-index.

Results:

CNR and HCSR varied most with reconstruction algorithm, reconstruction FOV and effective mAs. Collimation, but not image slice width, had a significant effect on CT dose-index with narrower collimation giving higher doses. Dose increased with effective mAs. Highest HU differences were seen when changing reconstruction algorithm: 56 HU for densities close to water and 117 HU for bone-like materials. Acquisition FOV affected the HUs but reconstruction FOV and effective mAs did not.

Conclusions:

All the scan parameters investigated affected the image quality metrics. Reconstruction algorithm, reconstruction FOV, collimation and effective mAs were most important. Reconstruction algorithm and acquisition FOV had significant effect on HU. The methodology is applicable to radiotherapy CT scanners when investigating image quality optimisation, prior to assessing the impact of scan protocol changes on clinical CT images and treatment plans.

Bolt M, Clark C, Chen T, Nisbet A (2017) A multi-centre analysis of radiotherapy beam output measurement, Physics and Imaging in Radiation Oncology 4 pp. 39-43 Elsevier
Background and purpose:

Radiotherapy requires tight control of the delivered dose. This should include the
variation in beam output as this may directly affect treatment outcomes. This work provides results from a multicentre
analysis of routine beam output measurements.

Materials and methods:

A request for 6MV beam output data was submitted to all radiotherapy centres in the UK,
covering the period January 2015?July 2015. An analysis of the received data was performed, grouping the data
by manufacturer, machine age, and recording method to quantify any observed differences. Trends in beam
output drift over time were assessed as well as inter-centre variability. Annual trends were calculated by linear
extrapolation of the fitted data.

Results:

Data was received from 204 treatment machines across 52 centres. Results were normally distributed
with mean of 0.0% (percentage deviation from initial calibration) and a 0.8% standard deviation, with 98.1% of
results within ± 2%. There were eight centres relying solely on paper records. Annual trends varied greatly
between machines with a mean drift of +0.9%/year with 95th percentiles of +5.1%/year and ?2.2%/year. For
the machines of known age 25% were over ten years old, however there was no significant differences observed
with machine age.

Conclusions:

Machine beam output measurements were largely within ± 2% of 1.00 cGy/MU. Clear trends in
measured output over time were seen, with some machines having large drifts which would result in additional
burden to maintain within acceptable tolerances. This work may act as a baseline for future comparison of beam
output measurements.

Li B, Godfrey T, Cox D, Li T, Gallop J, Galer S, Nisbet A, Romans E, Hao L (2018) Investigation of properties of nanobridge Josephson junctions and superconducting tracks fabricated by FIB, Journal of Physics: Conference Series 964 012004 Institute of Physics
An important requirement across a range of sensitive detectors is to determine accurately the energy deposited by the impact of a particle in a small volume. The particle may be anything from a visible photon through to an X-ray or massive charged particle. We have been developing nanobridge Josephson junctions based SQUIDs and nanoSQUID devices covering the entire range of particle detection energies from 1eV to MeV. In this paper we discuss some developments in nanobridge Josephson junctions fabrication using focussed ion beam (FIB) and how these developments impact future applications. We focus on tuning of the transition temperature of a superconducting thin-film absorber, with the aim to match the absorber Tc to the working temperature range of the SQUID and also on using a new Xe FIB to improve Josephson junction and superconducting film quality.
Wevrett J, Fenwick A, Scuffham J, Johansson L, Gear J, Schlögl S, Segbers M, Sjögreen-Gleisner K, Solný P, Lassman M, Tipping J, Nisbet A (2018) Inter-comparison of quantitative imaging of lutetium-177 (177Lu) in European hospitals, EJNMMI Physics SpringerOpen
Purpose

This inter-comparison exercise was performed to demonstrate the variability of
quantitative SPECT/CT imaging for lutetium-177 (177Lu) in current clinical practice.
Our aim was to assess the feasibility of using international inter-comparison exercises
as a means to ensure consistency between clinical sites whilst enabling the sites to
use their own choice of quantitative imaging protocols, specific to their systems.

Methods

Dual-compartment concentric spherical sources of accurately known activity
concentrations were prepared and sent to seven European clinical sites. The site staff
were not aware of the true volumes or activity within the sources - they performed
SPECT/CT imaging of the source, positioned within a water-filled phantom, using their
own choice of parameters and reported their estimate of the activities within the
source.

Results

The volumes reported by the participants for the inner section of the source were all
within 29% of the true value, and within 60% of the true value for the outer section. The
activities reported by the participants for the inner section of the source were all within
20% of the true value, whilst those reported for the outer section were up to 83%
different to the true value.

Conclusions

A variety of calibration and segmentation methods were used by the participants for
this exercise which demonstrated the variability of quantitative imaging across clinical
sites. . This paper presents a method to assess consistency between sites using
different calibration and segmentation methods.

Jafari S, Gouldstone C, Sharpe P, Alalawi A, Bradley D, Clark C, Nisbet A, Spyrou N (2013) Low-cost commercial glass beads as dosimeters in radiotherapy,
Jafari S, Gouldstone C, Sharpe P, Bradley D, Clark C, Nisbet A, Spyrou N (2013) Characterisation of Glass Beads for Radiotherapy Dosimetry, Proceedings of the 7th United Kingdom & Republic of Ireland Postgraduate Conference in Biomedical Engineering and Medical Physics pp. p15-15
Examinations have been made of a low cost commercially available material which is potentially useful as a dosimeter in radiotherapy. An investigation of the thermoluminescent (TL) yield and electron paramagnetic resonance (EPR) signal was performed by irradiating acid-washed glass jewellery beads to MV photons using a medical linear-accelerator and 60Co gamma rays. For
comparison, irradiation exposures were also carried
out on 5 mm length of Ge-doped optical fibres that
have been widely investigated for their TL properties
[1].
The dose response was linear for the investigated
dose range of 1 to 2500 cGy, with an R2 correlation
coefficient of > 0.999 and reproducibility of 1.7%.
The results suggest the potential for use of glass
beads as TL dosimeters in radiotherapy.
Jafari S, Bates N, Jupp T, Abdul Sani S, Nisbet A, Bradley D (2016) Characterisation of commercial glass beads as TLDs in radiotherapy, Radiation Physics and Chemistry 137 pp. pp181-186 Elsevier
Jafari S, Bates N, Jupp T, Abdul Sani S, Nisbet A, Bradley D (2016) Commercial glass beads as TLDs in radiotherapy produced by different manufacturers, Radiation Physics and Chemistry 137 pp. pp181-186 www.elsevier.com
While commercial jewellery glass beads offer the basis of novel radiotherapy TL dosimetry (Jafari et al.
2014a,b,c, 2015a,b), detailed study of TL variation is required for the products from various manufacturers.
Investigation is made for glass beads from four manufacturers from four countries: China (Rocaille), Japan (Mill Hill), Indonesia (TOHO") and Czech Republic (Czech). Sample composition was determined using an energy-dispersive X-ray unit coupled to a scanning electron microscope. Values of mass attenuation coefficient, ¼/Á, as a function of photon energy were then calculated for photons of energy 1 keV to 10 MeV, using the National Institute of Standards and Technology XCOM program. Radiation and energy response were determined using X-rays generated at accelerating potentials from 80 kVp to 6 MV (TPR20/10¼0.670).
All bead types showed TL to be linear with dose (R240.999). Glow curve dosimetric peaks reached a
maximum value at 300 °C for the Toho and 290 °C for the Czech and Mill Hill products but was between
200?250 °C for the Rocaille product. Radiation sensitivity following mass normalisation varied within an
order of magnitude; Toho samples showed the greatest and Rocaille the least sensitivity. For the Toho,
Czech, Rocaille and Mill Hill samples the energy responses at 80 kVp were 5.0, 4.0, 3.6 and 3.3 times that
obtained at 6 MV. All four glass bead types offer potential use as TL dosimeters over doses commonly
applied in radiotherapy. Energy response variation was o1% at 6 MV but significant variation was found
for photon beam energies covering the kV range; careful characterisation is required if use at this range is
intended.
Bradley D, Siti Shafiqah A, Siti Rozaila Z, Sabtu S, Abdul Sani S, Alanazi A, Jafari S, Amouzad Mahdiraji G, Mahamd Adikan F, Maah M, Nisbet A, Tamchek N, Abdul Rashid H, Alkhorayef M, Alzimami K (2016) Developments in production of silica-based thermoluminescence dosimeters, Radiation Physics and Chemistry 137 pp. 37-44 http://www.elsevier.com/
This work addresses purpose-made thermoluminescence dosimeters (TLD) based on doped silica fibres and sol?gel nanoparticles, produced via Modified Chemical Vapour Deposition (MCVD) and wet chemistry techniques respectively. These seek to improve upon the versatility offered by conventional phosphor-based TLD forms such as that of doped LiF. Fabrication and irradiation-dependent factors are seen to produce defects of differing origin, influencing the luminescence of the media. In coming to a close, we illustrate the utility of Ge-doped silica media for ionizing radiation dosimetry, first showing results from gamma-irradiated Ag-decorated nanoparticles, in the particular instance pointing to an extended dynamic range of dose. For the fibres, at radiotherapy dose levels, we show high spatial resolution (0.1 mm) depth-dose results for proton irradiations. For novel microstructured fibres (photonic crystal fibres, PCFs) we show first results from a study of undisturbed and technologically modified naturally occurring radioactivity environments, measuring doses of some 10 s of ¼Gy over a period of several months.
Davis A, Earley J, Edyvean S, Findlay U, Lindsay R, Nisbet A, Palmer A, Plaistow R, Williams M, Wood T (2018) IPEM topical report 2: the first UK survey of dose indices from radiotherapy treatment planning computed tomography scans for adult patients, Physics in Medicine and Biology IOP Publishing
CT scans are an integral component of modern radiotherapy treatments, enabling the accurate localisation of the treatment target and organs-at-risk, and providing the tissue density information required for dose calculations in the treatment planning system. For these reasons, it is important to ensure exposures are optimised to give the required clinical image quality with doses that are as low as reasonably achievable. However, there is little guidance on dose levels in radiotherapy CT imaging either within the UK or internationally. This IPEM topical report presents the results of the first UK wide survey of dose indices in radiotherapy CT planning scans. Patient dose indices were collected for prostate, gynaecological, breast, 3D-lung, 4D-lung, brain and head/neck scans. Median values per scanner and examination type were calculated and national dose reference levels and 'achievable levels' of CT dose index (CTDIvol), dose-length-product (DLP) and scan length are proposed based on the third quartile and median values of these distributions, respectively. A total of 68 radiotherapy CT scanners were included in this audit. The proposed dose reference levels for CTDIvol and DLP are; prostate 16 mGy and 570 mGy.cm, gynaecological 16 mGy and 610 mGy.cm, breast 10 mGy and 390 mGy.cm, 3D-lung 14 mGy and 550 mGy.cm, 4D-lung 63 mGy and 1750 mGy.cm, brain 50 mGy and 1500 mGy.cm and head/neck 49 mGy and 2150 mGy.cm. Significant variations in dose indices were noted, with head/neck and 4D-lung yielding a factor of eighteen difference between the lowest and highest dose scanners. There was also evidence of some clustering in the data by scanner manufacturer, which may be indicative of a lack of local optimisation of individual systems to the clinical task. It is anticipated that providing this data to the UK and wider radiotherapy community will aid the optimisation of treatment planning CT scan protocols.