Ten-year survival after High-Dose-Rate Brachytherapy combined with External Beam Radiation Therapy in high-risk prostate cancer: A comparison with the Norwegian SPCG-7 cohort

Abstract

Background: The survival benefit of dose-escalation with High-Dose-Rate brachytherapy (HDR-BT) combined with External Beam Radiotherapy (EBRT) for the treatment of high-risk prostate cancer (PCa) remains debatable. We investigated 10-year PCa-specific mortality (PCSM) and overall mortality (OM) in high-risk patients treated with HDR-BT/EBRT compared to EBRT alone. Methods: HDR-BT boosts were given followed by 50 Gy conformal EBRT to the prostate and seminal vesicles. The HDR-BT/EBRT group (N:325) received Androgen Deprivation Therapy for median 2 years. The historical control group (N:296), received a median dose of 70 Gy to the prostate and seminal vesicles with lifelong Anti-Androgen Treatment. For each treatment group, PCSM and OM were calculated using competing-risk and Kaplan-Meier analyses, respectively. Differences were assessed with the logrank test. OM and PCSM were computed using Cox and Fine & Grey regression. Significance level set to p<0.05. Patient-measured (PM) toxicity were assessed by EPIC-26 questionnaire at 5 years. Results: Median follow-up was 104 and 120 months for the HDR-BT/EBRT and the EBRT group respectively. A 3.6-fold decreased risk of PCSM (p<0.01) and a 1.6-fold decreased risk of OM (p=0.02) in the HDR-BT/EBRT cohort compared to the EBRT-only group were revealed. Ten year OM and PCSM rates were 16 % and 2.5% in the HDR-BT/EBRT group versus 23% and 8.2% in the EBRT-only group respectively. Treatment modality (SHR=3.58, 95%CI 1.40-9.14) and Gleason score (SHR=2.58, 95%CI 1.15 5.78) were associated with PCSM. Only treatment modality (HR=1.63, 95%CI=1.08-2.44) was significantly associated with OM. Conclusions: Men with high-risk PCa have a significantly reduced PCSM and OM rates when treated with dose-escalated radiotherapy achieved by HDR-BT/EBRT compared to EBRT alone (70 Gy). PM toxicity scores were acceptable and similar to the ProtecT study. A Gleason score of 8-10 was independently associated with increased risk of PCSM. Randomized studies in men with high-risk disease treated with dose-escalation are warranted.