Retreatment for Local Recurrence of Prostatic Carcinoma after Prior Therapeutic Irradiation: Efficacy and Toxicity of HDR-Like SBRT.

Purpose: We evaluated the use of high dose-rate-like stereotactic body radiation therapy (SBRT) retreatment for biopsy-proven local persistence in prostate postradiation therapy, evaluating efficacy and toxicity. Methods and Materials: From 2009 to 2018, 50 patients with biopsy-proven recurrent prostate cancer >2 years after prior treatment were retreated with a high dose-rate-like dose of 3400 cGy over 5 fractions. Previous radiation therapy dose measured 75.6 Gy (64.8-81.0) and median salvage interval was 8.1 years (32-241 mo.). Eighty-three percent of patients had Gleason score 7 or higher disease at retreatment. Those with preexisting toxicity >grade 1 from their prior course were excluded. The planning target volume was comprised of the clinical target volume (prostate + any contiguous extension only) with no additional expansion. Toxicity assessment used CTCAE v.3.0 criteria. Results: Median follow-up was 44 months (3-110). Median pre-SBRT salvage baseline prostate specific antigen (PSA) of 3.97 ng/mL decreased to 0.6 ng/mL and 0.16 ng/mL at 1 and 5 years in nonrelapsed patients, respectively. Actuarial 5-year biochemical disease-free survival (DFS) measured 60%, with corresponding 5-year actuarial local, distant, and salvage androgen deprivation therapy free rates of 94%, 89%, and 69%, respectively. Actuarial 5-year biochemical DFS measured 78% if PSA at salvage was <6.92 ng/mL versus 12% with >= 6.92 ng/mL (P = .0001). Toxicity was primarily in the GU domain, with an 8% 5-year actuarial rate of grade 3+, 3% when limited to salvage of "conventional external beam only" local relapse. No gastrointestinal (GI) toxicity >grade 1 occurred. Of the 30% sexually potent at the time of salvage, 82% subsequently lost potency. Conclusions: SBRT salvage of local prostate recurrence in previously irradiated patients appears clinically feasible in this challenging group. It demonstrates favorable PSA and DFS response, typically deferring the need for salvage androgen deprivation therapy or other treatment by over 5 years, with low GU and GI toxicity. (C) 2019 The Authors. Published by Elsevier Inc.