Prostate and pelvic SABR with or without a focal boost: results from a multicenter phase II prospective clinical trial

Purpose: Given the complexity of SABR to the pelvis in prostate cancer (PCa), it was important to establish the safety and feasibility in a multicentric setting. We report the outcomes of a multicenter, phase II study of SABR with elective nodal irradiation (ENI) and an optional prostate focal boost. Methods: Patients had unfavorable-intermediate or high-risk PCa. All patients received 5 fractions SABR weekly delivering 25Gy ENI and 40Gy to prostate simultaneously, with an optional 50Gy focal prostate boost. All patients had ADT. Primary endpoint was acute GI and GU adverse events (AE). Results: 76 patients were accrued at 4 hospitals with a median follow-up of 62.8 months. 63% of patients had high-risk PCa. 41% of patients had a focal boost. Acute grade ≥ 2 GI and GU AE was 4.1% and 18%. At 5 years, 2.9% and 4.3% of patients had grade 2 GI and GU AE, and no grade 3+ GI/GU AE was observed at the last follow-up. 5-year cumulative biochemical failure was 10.5%. The median PSA nadir was 0.2 ng/mL. 84% of patients recovered their testosterone level, with a median time of 14.3 months. 2.9%, 5.9% and 4.6% of patients had a large change in QOL (SD*2) in the EPIC urinary, bowel, and sexual domains. Conclusions: 5-fraction SABR to prostate and pelvis for unfavorable-risk PCa was safe and feasible in a multicentric setting with or without a focal boost. There were few significant AE, encouraging PSA kinetics and biochemical control. The results are currently being validated in randomized trials.