Year
2024
Degree Name
Master of Research
Department
School of Physics
Abstract
The purpose of this thesis was to develop a more precise and rigorous technique for performing pre-treatment/daily quality assurance (QA) of high dose rate (HDR) brachytherapy afterloaders, incorporating QA of: dwell position accuracy, dwell time accuracy, transit velocity consistency, relative transit dose, timer linearity and relative Air-Kerma Strength (AKS). A Sharp 5F ProGuide 240 mm catheter was fixed above a 1D monolithic 256-channel epitaxial diode array, the ‘dose magnifying glass’ (DMG256) to track the 192Ir source position within the applicator. The outputted data files from the data acquisition system were analysed to provide positional and temporal localisation of the 192Ir source by tracking the centroid of the detected response. Three dwell positions, each of 5.0 s dwell times, were spaced 13.0 mm apart along the array with the Flexitron HDR afterloader. Measurements were repeated on a weekly basis, for a period of 5 weeks to assess the consistency of the measured parameters over an extended period. Using DMG256 for relative AKS measurements resulted in measured values within 0.6 – 3.0 % of the expected source strength over a 7-week period. The set 10 ms temporal resolution of this device allowed for independent measurements of the transit velocity with an average of (10.88 ± 1.01) cm s−1 for 13.0 mm steps, with it accurately resolving the source movement down to the minimum afterloader step size of 1.0 mm and minimum time-step interval of 10 ms. The dwell position localisation for 1, 2, 5, 10 and 13 mm steps had an accuracy between 0.1 – 0.2 mm (3σ). The DMG allows for clinics to perform rigorous QA of HDR afterloader spatial and temporal accuracy, with greater precision to aid in quantifying and minimising dosimetric errors, all performed within the same time-frame as the current standard methodology using CCTV feed and a stopwatch. Additionally, DMG256 unlocks the ability to perform measurements of relative transit dose, transit velocity and relative AKS, which are not possible using current standard techniques.
Recommended Citation
Hunt, Broady D., High Dose Rate Brachytherapy Quality Assurance Optimisation using CMRP Dose Magnifying Glass, Master of Research thesis, School of Physics, University of Wollongong, 2024. https://ro.uow.edu.au/theses1/1859
FoR codes (2008)
029903 Medical Physics
Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.