Prospective study on tumor control, survival, toxicity and quality of life after EBRT and an HDR-brachytherapy boost in intermediate to high-risk prostate cancer patients.

[INTRODUCTION] Brachytherapy boost improves biochemical disease-free survival (bDFS) for intermediate/high-risk prostate cancer, but may increase toxicity. We prospectively assessed tumor control, survival, toxicity, and quality of life (QoL) in a large cohort treated with high-dose-rate (HDR) brachytherapy boost after hypo-fractionated external beam radiotherapy (EBRT) and assessed predictors for tumor control and survival.

[METHODS AND MATERIALS] From 2010 to 2020 patients received EBRT (58 Gy in 20 fractions to prostate/seminal vesicles or 62.5 Gy in 25 fractions with 50 Gy to pelvic nodes), followed by a 10 Gy HDR brachytherapy boost, and androgen deprivation therapy (ADT) up to 3 years. Biochemical recurrence was defined by the Phoenix criterion. Toxicity (CTCAE v3.0) and QoL (IPSS, Likert scales for bowel and erectile function) were prospectively recorded. Outcomes were analyzed using Kaplan-Meier analysis and Cox/competing-risk models.

[RESULTS] Among 274 patients (267 high risk), median follow-up was 95 months. Eight-year bDFS and overall survival (OS) were both 76%, and prostate cancer-specific survival (PCASS) 95%. PSA nadir > 0.1 ng/mL was the strongest predictor for biochemical failure and PCASS (8-year bDFS: 88% vs. 31%, p < 0.001). Longer time to PSA nadir improved tumor control and survival. Late Grade 3 genitourinary toxicity occurred in 4.4% and gastrointestinal in 0.7%. Median IPSS increased from 7 to maximum 10 (p < 0.001), minor bowel symptoms from 3% to maximum 13%. Complete erectile dysfunction rose from 18% to maximum 47% (p < 0.001).

[CONCLUSION] EBRT with ADT and HDR brachytherapy boost provides durable tumor control with acceptable long-term toxicity. PSA nadir and time to nadir are strong predictors for outcomes and may support personalized follow-up strategies.