Ryan Brown
St George Cancer Care Centre
Medical Physics Registrar

Andrew Howie
Senior Medical Physicist
St George Cancer Care Centre

Komiti Enari
Senior Medical Physicist
St George Cancer Care Centre

Iliana Peters
PhD student
University of Wollongong

Dean Cutajar
Research Physicist
St George Cancer Care Centre

Joseph Bucci
Radiation Oncologist
St George Cancer Care Centre

Background & Purpose The aim of this project was to implement real-time HDR prostate brachytherapy at St George Cancer Care Centre using the treatment planning system (TPS) Oncentra Prostate (OCP) v4.2.2 (Elekta AB, Stockholm, Sweden). There is currently no published literature specifically discussing commissioning of real-time HDR planning systems. AAPM TG53 and IAEA TRS430 include recommendations for the commissioning of brachytherapy TPS that were utilised in the formation of a commissioning plan tailored for real-time HDR. Methods Extensive commissioning testing was performed on OCP as well as the associated sub-systems (stepper, encoder, template). The tests were designed based on recommendations in IAEA TRS430 and AAPM TG53, with some additional testing added to cover thorough testing of OCP-specific features. Peripheral testing was also carried out on the brachytherapy module of RadCalc v6.3.2 (LifeLine Software Inc, USA) for plan verification. The heavy reliance of OCP on ultrasound imaging required extensive quality assurance (QA) testing to be performed, and implemented at a higher frequency within the department, to maintain confidence. Finally, an end-to-end test was carried out and real time dose verification measurements obtained in a prostate phantom using MOSkin dosimeters, placed in 3 locations along the rectal wall. Before clinical release, a detailed multidisciplinary risk assessment was performed and extensive documentation formulated, including workflow guidelines and QA checklists. Results Initial geometric accuracy tests within OCP revealed a 10% discrepancy, requiring the ultrasound to be recalibrated within the software. Isodose distribution differences were noted in OCP when compared to the current brachytherapy TPS Oncentra Brachy (OCB). Analysis of the Flexisource data within OCP revealed some minor differences with the source data when compared to source data from published literature. Final end-to-end testing of the real-time HDR system with OCP on a prostate phantom with in vivo dosimetry yielded point measurements in agreement with OCP by less than 3.7%, and validation of the plan in RadCalc exhibited maximum point dose differences of 0.1%. Conclusions Accuracy of ultrasound calibration in the ultrasound system and in OCP is essential for providing accurate patient treatment. Additional extrapolated source data in OCP relative to the published source data can lead to small inconsistencies when compared to OCB. End-to-end testing verified, through in vivo measurement and TPS comparisons, that the set up was correct, including all calibrations, sub-systems and hardware, and that the technique was safe for clinical use.


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