Decreasing Utilization of Brachytherapy as a Boost Modality in the Treatment of High-Risk Prostate Cancer: A National Patterns of Care Analysis

Abstract

Purpose/Objective(s): ASCENDE-RT, a recent randomized Phase III study comparing androgen suppression (AS) and external beam radiation therapy (EBRT) with either EBRT boost or low-dose rate brachytherapy (LDR-B) boost for men with intermediate and high-risk prostate cancer (PCa), reported improved biochemical failure for those undergoing LDR-B boost. Here we examine if there is a difference in overall survival (OS) between these treatment groups in the National Cancer Database (NCDB). Materials/Methods: We conducted a retrospective NCDB analysis between 2004 and 2012 of men with intermediate and high-risk PCa (Gleason 7-10, prostate specific antigen [PSA] 10 to <40 ng/mL, or T1c-T3a) treated with AS, defined as administration within 8 months of EBRT followed by LDR-B or EBRT boost (75.6-86.4 Gray [Gy]). Univariate, multivariate and subset survival analyses were completed using logistic regression, log-rank, Kaplan-Meier methods, and Cox-proportional hazards models. Multivariate model covariates were selected based on significance (P < 0.05) on univariate analyses. Propensity score match was completed using significant variables from logistic regression. Results: Among 25,164 patients treated with AS and EBRT, 20,624 (82%) were treated with EBRT boost and 4,540 (18%) with LDR-B boost. Mean follow up was 5 years (59.6 months, standard deviation [SD] Z 29.7). On univariate analysis, LDR boost was associated with improved OS (hazard ratio [HR] Z 0.6, 95% confidence interval [CI] Z 0.6-0.7, P < 0.001) when compared to EBRT boost. The 5 year OS for LDR-B and EBRT groups were 89.6% vs 83.7%, respectively, P < 0.001). On multivariate analysis, after controlling for age, race, insurance type, treatment location, facility type, Charlson comorbidity score, whole pelvis radiation, Gleason score, PSA and clinical T-stage, LDR-B boost remained independently associated with improved OS (HR Z 0.7, 95% CI Z 0.7-0.8, P < 0.001). Propensity score matching identified 6,860 patients and confirmed an OS associated with LDR boost (HR Z 0.6, 95% CI Z 0.5-0.7, P < 0.001). On subset analysis, the OS benefit of LDR-B boost persisted when stratified by favorable intermediate (HR Z 0.7, 95% CI Z 0.5-0.9, P Z 0.002), unfavorable intermediate (HR Z 0.7, 95% CI Z 0.6-0.8, P < 0.001), and high risk groups (HR Z 0.7, 95% CI Z 0.6-0.8, P < 0.001). Conclusion: For men with intermediate and high-risk PCa, treatment with AS and EBRT followed by LDR-B boost is independently associated with improved OS when compared to EBRT boost. These results show that the reported improvement in biochemical failure from the ASCENDE-RT trial may translate into improved OS outcomes.