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Hypofractionated, accelerated radiotherapy to the prostate bed: Five-year outcomes of a prospective phase I/II study.

7 Background: There have been few studies to date that examine the role of hypofractionated radiotherapy for prostate cancer in the post-operative setting. This study reports on the 5-year outcomes from a single institution, prospective, phase I/II study on hypofractionated prostate bed radiotherapy. Methods: Patients enrolled in this study were all eligible for post-operative radiotherapy and received a prescribed dose of 51Gy in 17 fractions to the prostate bed. On subsequent follow-up, GI/GU toxicity was assessed using the NCI CTCAE v3.0, PSA was evaluated and quality-of-life was assessed using the EPIC questionnaire. Results: A total of 30 patients were enrolled between 2008 and 2011. Median age was 65 [52-75] years. Median pre-treatment PSA was 0.12 ng/ml [0.01-1.42]. Twenty-four (86%) patients had Gleason 7 disease, 13 (43%) had pT3 disease and 20 (67%) had positive margins. Twenty-six (87%) patients underwent radiotherapy as salvage treatment. No patient experienced CTCAE grade 3/4 toxicity. Two (7%) patients experienced at least one CTCAE grade 2 late GI toxicity and 11 (37%) had at least one late grade 2 GU toxicity. At baseline and 5 years post radiotherapy, mean EPIC urinary domain score were 80 (SD: 18) and 82 (17). Mean EPIC bowel domain score were 93 (13) and 93 (15). One (4%) patient had a minimally clinically important change (MCIC) in urinary domain score and 1 (4%) patient had a MCIC in bowel domain score. Nelson-Aalen estimated cumulative incidence of biochemical failure were 31% (nadir+0.2) and 18% (nadir+2.0) at 5 years. Four-year PSA ≥0.4 was highly predictive of subsequent rise to nadir+2.0 at 5 years (Nelson-Aalen cumulative hazard: 1.45; standard error: 0.701; p < 0.0001). Five (17%) patients received hormonal therapy for biochemical failure. Nelson-Aalen estimated cumulative incidence of hormone therapy use was 14% at 5 years. Conclusions: In this phase I/II study, hypofractionated post-operative radiotherapy appears to have good clinical efficacy without significant late toxicity. Phase III studies are warranted. Clinical trial information: 042-2009.