15-Year BPFS, OS, and DMFS Outcomes of High-Dose-Rate Salvage Therapy for Locally Recurrent Prostate Cancer

Abstract

HDR brachytherapy has been used extensively as a boost after external beam radiation therapy or as monotherapy in select patients, but is increasingly being tested as salvage treatment for locally recurrent prostate cancer. We report long-term results for salvage HDR brachytherapy in patients in a cohort of patients with recurrent disease. 34 patients (median age of 71 years at time of recurrence) treated between 1991 and 2014 were analyzed. Median recurrent PSA was 7.1 ng/mL, and there were 11, 12, and 11 patients in low-, intermediate-, and high-risk NCCN risk groups, respectively. The majority of patients (79.4%) were treated with radiation therapy (RT group) for their initial disease (median dose 68.2 Gy), while the rest received primary prostatectomy or cryotherapy (non-RT group). Median salvage HDR brachytherapy dose was 36 Gy (range 15-46) in 6 fractions (range 1-8). Sustained PSA nadir+2 (Phoenix definition) was used to define biochemical failure. Kaplan-Meier analyses were performed to determine 5-15 year rates of overall survival (OS), biochemical progression free survival (BPFS), distant metastasis free survival (DMFS), and cause specific survival. Results were also stratified according RT vs. non-RT as primary treatment. Median follow-up was 7.1 years (range 0.62-16.65). 20 patients (59%) were still living at the time of analysis. The 5-, 10- and 15-year OS rates were 89%, 59% and 17%, respectively. 12 patients (35%) developed distant metastases. The 5-, 10- and 15-year DMFS rates were 65%, 52% and 18%, respectively. Cause specific survival was 93.1% and 71.4% at 5 and 10 years, respectively. 13 patients (38%) developed biochemical failure at a median time to failure of 1.89 years. The 5- and 10-year BPFS rates were 56.1% and 28.1%. Outcomes were comparable between the primary RT and non-RT groups. Rates of G2 and G3 GU and GI toxicity were minimal and mainly based upon the baseline toxicity with which the patient presented for salvage brachytherapy. Our long-term data validates HDR salvage brachytherapy in recurrent prostate cancer patients as standard treatment option with excellent rates of disease control and overall survival with acceptable toxicity rates.