Is supplemental external beam radiation therapy essential to maximize brachytherapy outcomes in patients with unfavorable intermediate-risk disease?

Purpose: To evaluate whether supplemental external beam radiotherapy (EBRT) is essential to maximize Pd-103 brachytherapy outcomes in patients with unfavorable intermediate-risk (IR) disease.
Methods and Materials: A total of 630 patients were assessed from two prospective randomized brachytherapy trials evaluating the role of supplemental EBRT in patients with higher risk features. Patients were stratified into unfavorable IR (primary Gleason pattern 4, ≥50% positive biopsies, or ≥2 IR features), favorable IR, and high-risk (HR) cohorts. Median follow-up was 7.5 years. The brachytherapy prescription dose was prescribed to the prostate gland with generous periprostatic margins. Biochemical failure (BF) was defined as a prostate-specific antigen >0.40 ng/mL after nadir. Patients with metastatic prostate cancer or nonmetastatic castrate-resistant disease who died of any cause were classified as dead of prostate cancer. Multiple parameters were evaluated for effect on outcomes.
Results: The 10-year BF for favorable IR, unfavorable IR, and HR was 1.7%, 6.6%, and 15.5% (p < 0.001). At 10 years, prostate cancer-specific mortality (PCSM) and overall mortality (OM) were 0% and 20.4%, 2.1% and 23.2%, and 4.3% and 42.4% for favorable IR, unfavorable IR, and HR. Although unfavorable IR patients had a greater incidence of BF, PCSM, and OM when compared with favorable IR, neither the addition nor dose of supplemental EBRT influenced outcome.
Conclusions: Outcomes for favorable IR were superior to those with unfavorable IR. Within the confines of this study, neither the addition nor dose of supplemental EBRT influenced BF, PCSM, or OM in patients with IR disease.
(Copyright © 2016 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)