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.