Biochemical disease control outcomes of stereotactic body radiation therapy (SBRT) or moderate hypo-fractionation (HFRT) for low- and intermediate-risk prostate cancer (PrCa): Retrospective analysis of 12 years of experience at two Canadian cancer centers.

363 Background: SBRT uses highly conformal radiotherapy to deliver high dose per fraction treatment. Advantages of SBRT include short treatment times, decreased costs and limited toxicity. Randomized trial outcomes of 7-fraction SBRT for low or intermediate PrCa were reported but results of studies that compared 5-fraction SBRT with conventional and HFRT are pending. Here, we reviewed the 12-year experience with SBRT and HFRT at the Juravinski and Walker Family Cancer Centers in Ontario. Methods: We reviewed patients with low or intermittent-risk PrCa treated with SBRT alone or HFRT alone in the period of July 2010 and February 2022. Database search criteria included treatments with SBRT 35-40Gy in 5 fractions and HFRT 60-62Gy in 20 fractions. Overall survival (OS), time to biochemical failure (per Phoenix criteria: i.e., 2ng/mL above PSA nadir) and biochemical failure-free survival (bFFS) were reviewed. Kaplan-Meier curves were used to assess OS and bFFS. Results: We identified 314 patients with low or intermediate-risk PrCa who were treated with SBRT and 258 patients who were treated with HFRT. Intermediate-risk category composed 86.0% and 95.7% of the SBRT and HFRT cohorts. ISUP Grade Group (GG) distributions for the SBRT and HFRT patients were: GG1: 19.4% and 9.3%, GG2: 72.9% and 74.0%, and GG3: 7.6% and 16.7%, respectively. OS rates at 5 years were 96.6% for SBRT vs. 95.8% for HFRT-treated patients. The 5-year bFFS rates for SBRT and HFRT were 92.3% and 90.1%, respectively. The 7-year bFFS rate for the SBRT cohort was 90.2%. Mean time to biochemical failure was 40.4 months after SBRT vs. 35.8 months after HFRT. Conclusions: SBRT is an effective treatment option for low to intermediate-risk PrCa with encouraging OS and bFFS rates comparable with HFRT. Pending randomized trial results will determine whether SBRT is the new standard of care for this population.