5-Year Outcomes of a Prospective Phase I/II Study of Accelerated Hypofractionated Radiotherapy to the Prostate Bed

Abstract Purpose To report the 5-year outcomes from a single institution, prospective, phase I/II study on hypofractionated, accelerated radiotherapy to the prostate bed after radical prostatectomy. Materials and 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-six (93%) 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. After a median follow-up of 6.4 (2.1-8.1) years, no patient experienced CTCAE grade 3/4 toxicity. Eleven (37%) patients had grade 2 GU and 2 (7%) had grade 2 GI toxicity. At baseline and 5 years post radiotherapy, mean EPIC urinary domain score was 80 (SD: 18)% and 82 (17)%. Mean EPIC bowel domain score was 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 predictive of subsequent ADT use (Nelson-Aalen cumulative incidence: 1.45; p 0.4 at 4 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.