High dose-rate brachytherapy boost for intermediate risk prostate cancer: Long-term outcomes of two different treatment schedules and early biochemical predictors of success

Background and purpose: To report long-term cancer control rates following high dose-rate (HDR) brachytherapy boost for intermediate risk prostate cancer and explore early biochemical predictors of success. Material and methods: Results of two sequential phase II trials are updated and compared: (1) Single 15 Gy HDR-boost followed by external beam radiotherapy (EBRT) 37.5 Gy/15fractions, (2) Two HDR fractions of 10 Gy followed by EBRT 45 Gy/25fractions. Patients were followed prospectively for clinical and biochemical outcomes. Nadir PSA (nPSA) and PSA at 3-years were analyzed as continuous variables, and ROC analysis was used to identify the optimal cutoff values. Kaplan–Meier bDFS curves were generated and the log-rank test used to compare different groups Results: 183 patients were accrued; 123 to the single fraction trial and 60 to the standard fractionation trial, with a median follow-up of 74 months and 99 months, respectively. The 5-year biochemical relapse-free survival was 97.4% and 92.7%, respectively (p = 0.995). Median nPSA was 0.08 ng/ml. Failure to achieve a nPSA <0.4 ng/ml was associated with a significantly higher rate of biochemical relapse (5-year bDFS: 100% vs. 72%; p < 0.0001). Conclusion: HDR boost with single fraction 15 Gy provides durable long-term biochemical disease-free survival. PSA nadir <0.4 ng/ml is associated with very low risk of biochemical failure