Degree Name

Master of Research - Medical Radiation Physics


School of Physics


High dose rate brachytherapy allows the delivery of radiation internally, with high-dose gradients creating a conformal distribution. The inherent drawback of this treatment exists within small uncertainties producing a large impact on safety and efficacy. Applicator displacement was ret-rospectively simulated for 29 cervical cancer treatments to determine a critical shift in applicator position. A 2 mm shift in the anterior and posterior directions was detrimental to the bladder and rectum, respectively and a 4 mm shift in all directions caused a critical reduction in HR-CTV cover-age. These findings indicate the importance of quality assurance practices that mitigate applicator displacement. Furthermore, the source localisation accuracy required for cervical brachytherapy was quantified. HDR gynaecological brachytherapy relies on 3D imaging, contouring, precise reconstruc-tion of applicator position and transfer of data to the afterloading device. To evaluate this process an end-to-end phantom was developed, which consists of a component that houses gynaecological applicators and the Magic Plate 987 (MP987), created by the Centre of Medical and Radiation Physics, University of Wollongong. The 21 × 22.5 cm2 silicon diode array facilitates source tracking at clinically relevant depths. A characterisation of the MP987 for HDR source tracking has been performed, producing an error in dwell time and position of 0.1s and 0.25 mm respectively, for dwell times greater than 5 s. Source tracking accuracy is a function of both dwell time and distance from detector to source.

The End-to-end phantom has verified both vaginal and cervical treatments. For a vaginal treat-ment, the mean residual in dwell position is within (0.24 ± 0.01) mm for all directions, with the difference in dwell time being (0.10 ± 0.01) s. Catheter swap, indexer length and activity miscalibration errors were all detected within the vaginal therapy end-to-end test. Validation of the End-to-end phantom for a cervical brachytherapy treatment produced a mean difference of (3.49 ± 0.57) mm,(4.74 ± 0.77) mm, (6.14± 1) mm in the X, Y and Z directions respectively, with a dwell time differ-ence of (0.19 ± 0.03) s. The localisation accuracy achieved is below the critical displacement value established within the treatment planning study. Improvement in co-registration and Z localisation methodologies will provide better outcomes for cervical cases. The End-to-end phantom successfully verifies the procedure for HDR gynaecological brachytherapy treatments, enabling safe and effective patient care.

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.