The value of elective pelvic lymph node radiotherapy in high risk prostate cancer

Abstract

High risk prostate cancer patients carry a high risk of microscopic pelvic lymph node (PLN) disease; however, the clinical benefit elective PLN radiotherapy remains unproven due to conflicting results from clinical trials. This thesis investigates methods of improving the PLN control achieved with IMRT, while maintaining acceptable levels of toxicity. My first aim was to determine the rates of disease controls for patients treated in the RMH Phase I/II IMRT trial. A similar anatomical pattern of disease relapse was seen in all trial cohorts with a low rate (6%) of PLN relapse. The majority of PLN relapses occurred at the proximal common iliac nodes. 50% of relapses occurred within the radiation field and no clear dose gradient or favoured site was seen. My second aim was to determine the coverage provided by the PIVOTAL trial PLN contouring guidelines. The contours covered 66% of choline PET-CT identified PLN. The common iliac nodal group was the site most poorly covered and I considered the implications on bowel dosimetry of modifying the standard PLN to improve coverage. My third aim was to determine if the dose-volume constraints developed in the IMRT trial and used in the PIVOTAL trial could be refined any further to improve the toxicity profile of pelvic IMRT. Using the bowel dose cube data and late toxicity results for the PIVOTAL trial cohorts, I found no clear correlation between radiation dose to any part of the bowel and late RTOG toxicity that suggested modification of dose constraints. In conclusion, the current target volumes and planning constraints are associated with a favourable late toxicity profile. Further PLN control might be achieved by covering the upper common iliac nodes. However, the impact of PLN IMRT needs to be evaluated in the context of recent developments in treatment intensification using systemic therapies which may treat microscopic nodal disease.