High-rate-dose brachytherapy
For brachytherapy alone or after conservative surgery, cannulae were inserted percutaneously through the perineum under general anesthesia with ultrasound guidance. Post-implantation computed tomography (sometimes supplemented by fusion with pre-procedural magnetic resonance imaging (MRI)) was used for 3-dimensional treatment planning with accurate delineation of the clinical target volume (CTV) and the organs at risk (OAR). Following optimisation of treatment plans and quality control, 27.5Gy in 5 fractions were administered over three days using HDR Iridium-192 afterloading via the temporary cannulae[13,14,15].
For this study, the doses are reported based on the day 1 post-implantation CT scan. CTV and OAR were contoured by the oncologist and radiation doses calculated using the Nucletron Oncentra treatment planning system (TG-43 dose calculation method[16]). The doses reported were the D90 (the minimum dose to 90% of the volume) for the CTV, D2cm3 doses (the minimum dose received by the two cubic cm of tissue that receives the highest dose) for the bladder, and D0.1cm3 doses (the minimum dose received by 0.1 cubic cm of tissue that receives the highest dose) for the urethra. All doses were converted to EQD2 doses, taking 2.8Gy as the alpha beta ratio for the CTV and 3Gy for OAR[15].
If the likely proximity of radiation field justified, an oophoropexy was offered to female patients before brachytherapy.