Assessing the role of external beam radiation therapy in combination with brachytherapy versus brachytherapy alone for unfavorable intermediate-risk prostate cancer.

ABSTRACT

BACKGROUND: Definitive treatment options for unfavorable intermediate-risk prostate cancer (UIR-PCa) include external beam radiotherapy (EBRT) ± brachytherapy boost ± androgen deprivation therapy (ADT). The role of brachytherapy ± ADT in the absence of EBRT is not well defined. We hypothesized that EBRT+BT±ADT is associated with improved overall survival (OS) relative to BT±ADT for UIR-PCa. METHODS AND MATERIALS Men with UIR-PCa diagnosed between 2004 and 2015 were identified in the National Cancer Database (NCDB). Inverse propensity of treatment weighting was used to balance covariables that influenced treatment allocation and outcomes, and propensity-weighted multivariable analysis (MVA) using Cox regression modeling was used to compare OS hazard ratios. RESULTS: A total of 11,721 men were stratified into four treatment groups (1) BT without ADT (n = 4,535), (2) BT+ADT (n = 1,303), (3) EBRT+BT (n = 3,446), or (4) EBRT+BT+ADT (n = 2,437). Relative to patients treated with BT alone, BT+ADT (Hazard Ratio (HR) 0.86 [95% Confidence Interval (CI) 0.76-0.99], p = 0.03), EBRT+BT (HR 0.79 [0.70-0.88], p = 0.00002), and EBRT+BT+ADT (HR 0.76 [0.67-0.85], p = 0.000003) were associated with improved OS on MVA. Relative to BT alone, EBRT+BT correlated with improved OS on weight-adjusted MVA (HR 0.82 [0.75-0.89], p = 0.000005). 10-year OS for BT vs. EBRT+BT was 62.4% [60.1-64.7] vs. 69.3% [67.5-71.2], respectively (p < 0.0001). CONCLUSIONS: EBRT+BT correlated with improved OS relative to BT alone in men with UIR-PCa, reaffirming current NCCN recommendations recommending EBRT+BT over BT alone. While prior studies reported no benefit to adding EBRT to BT with optimal implant dosimetry, this study suggests men benefit from EBRT in a population of variable implant quality.