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Matt Bolt


Postgraduate Research Student
MPhys, MSc, dipIPEM, CSci
+44 (0)1483 684601
34 BC 02

My research project

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Research

Research interests

My publications

Publications

Russell A.S. Thomas, Matthew A. Bolt, Graham Bass, Rebecca Nutbrown, Tao Chen, Andrew Nisbet, Catharine H. Clark (2017). Radiotherapy reference dose audit in the United Kingdom by the National Physical Laboratory: 20 years of consistency and improvements
View abstract

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 < 0.01). The mean difference in NPL to local measurement for radiation output calibration was less than 0.25% for all beam modalities.

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.
Matthew A. Bolt, Catharine H. Clark, Tao Chen, Andrew Nisbet (2017). A multi-centre analysis of radiotherapy beam output measurement
View abstract

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 1.00 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.
M. Cunningham, M. Bolt, A. Franklin, A. Stewart (2015). PO-1019: Improving service efficiency by reducing the volume of bowel contoured when performing IGBT of the cervix?
View abstract
Purpose/Objective: Contouring the bowel is one of the most time consuming aspects of planning a HDR treatment of the cervix. This investigates the possibility of reducing the volume of bowel to be contoured for planning purposes when treating the Cervix with HDR using a Tandem and Ovoid Applicator with CT simulation. It is hoped that the service efficiency can be improved by reducing the volume of bowel contoured prior to planning. Materials and Methods: Additional contours were constructed on previous patient plans which were clinically accepted. Using Oncentra Brachy (Version 4.3), 3D margins of 0.5cm, 1.0cm, 1.5cm and 2.0cm were grown around the HRCTV. The overlap of the original (complete) bowel volume and the newly created volumes was extracted to produce a bowel contour which was limited to within a given distance from the HR-CTV. For example, taking the intersection of the ‘Bowel’ and the ‘HRCTV + 1.0cm’ to give a bowel contour which only extends to 1.0cm beyond the HR-CTV (referred to as ‘HR-CTV + 1.0cm & Bowel’) This produced a set of bowel outlines which were limited to within a given margin of the HR-CTV. The dosimetric parameters (D2cc, D1cc, D0.1cc) reported by Oncentra were recorded for the original bowel volume, as well as the limited bowel volumes produced to enable comparison. Results: A total of 10 plans were contoured and assessed, with comparison of the dosimetric parameters performed for the limited bowel volumes. A summary of the results is given in the table. The mean doses for the fully contoured bowel were 3.99Gy, 4.39Gy and 5.37Gy for the D2cc, D1cc and D0.1cc respectively . When the bowel was limited to within 1.5cm or less of the HR-CTV there was at least one contour which did not give sufficient volume to produce complete dose statistics. When considering contouring within a 2.0cm margin of the HR-CTV the mean change in the D0.1cc was less than 0.1Gy (with D2cc and D1cc being less than 0.05Gy). The reduction in volume contoured however was large, with a reduction of around 65% in volume when restricting contouring to within 2.0cm of the HR-CTV. Conclusions: Restricting the bowel contouring for planning of treatments of the Cervix using Tandem and Ovoid applicators with CT simulation to within 2.0cm of the HR-CTV has the potential to reduce the volume contoured by 65%. This results in a change in reported dose statistics of less than 0.1Gy for the D0.1cc and less than 0.05Gy for the D1cc and D2cc. These small changes would not have an effect on the clinical decision to treat using the produced plans. By producing a an expanded HR-CTV contour, the bowel contouring could be easily limited to within this region, thus reducing the time taken to contour, ultimately leading to a more efficient treatment delivery. Applying this to other organs at risk may also be possible.