36.25 Gy versus 40 Gy in five fractions of curative stereotactic body radiotherapy for prostate cancer: a propensity score-matched analysis

This study aimed to determine whether 36.25 Gy was inferior to 40 Gy in terms of prostate-specific antigen (PSA) recurrence following stereotactic body radiation therapy (SBRT) for prostate cancer. We retrospectively reviewed the medical records of 863 consecutive patients with prostate cancer treated at a single institution between 2016 and 2025. Propensity score (PS) matching based on age, pre-treatment PSA level, biopsy Gleason score, clinical T-stage, National Comprehensive Cancer Network (NCCN) risk classification, and concomitant androgen-deprivation therapy (ADT) yielded 530 patients for analysis. Patients received SBRT at a total dose of 36.25 or 40 Gy in five fractions administered every other day. The prespecified non-inferiority margin was a hazard ratio of 1.40. After PS matching, no significant differences remained in baseline characteristics that had differed significantly between the two groups before matching. In the 36.25-Gy and 40-Gy groups, respectively, 16 and 10 PSA recurrences and 18 and 10 deaths occurred. Four PSA recurrences (15%) occurred over 5 years. The 5-year event-free survival (EFS) rates were 90% with 36.25 Gy and 88% with 40 Gy (p = 0.37). The hazard ratio for EFS with 36.25 Gy versus 40 Gy was 0.76 (95% confidence interval [CI], 0.42-1.39; p = 0.37). The 5-year PSA recurrence-free rates were 95% and 93%, respectively (p = 0.76). Among the 298 patients receiving 36.25 Gy, grade 3 gastrointestinal (GI) and genitourinary (GU) toxicities occurred in 2.3% and 1.3%, respectively. Among the 565 patients receiving 40 Gy, grade 3 or GI toxicity occurred in 1.9%, and grade ≥ 3 GU toxicity occurred in 0.8%. No grade 5 toxicity occurred. Urinary and bowel quality of life (QOL) scores decreased at 1 month and returned to near-baseline levels by 3 months. In this retrospective study, the findings suggest that the 36.25-Gy regimen may be non-inferior to 40 Gy for EFS and may be associated with fewer grade 4 toxicities and better urinary QOL. Given the retrospective design, these findings should be considered hypothesis-generating.