PurposeThe 44/20 and 20/0 randomized trials evaluated whether different external beam radiation therapy (EBRT) dosing regimens prior to brachytherapy impacted biochemical failure (BF). We report long-term outcomes of both trials, and evaluate whether biological equivalent dose (BED) was associated with reduced BF in the combined trial cohort. Materials/methodsBoth trials enrolled patients with clinical T1c-T2b, Gleason score 7-9 and/or a pre-treatment prostate-specific antigen (PSA) 10-20 ng/ml disease. The 44/20 trial randomized patients to 44Gy EBRT with 90Gy palladium (Pd)-103 versus 20Gy EBRT with 115Gy Pd-103. The subsequent 20/0 trial randomized patients to the 20Gy arm versus monotherapeutic 125Gy Pd-103. For each trial, univariate Fine-Gray analysis evaluated whether treatment arm was associated with BF for the entire cohort and the unfavorable intermediate risk (UIR) subgroup. For the combined trial cohort, multivariate Fine-Gray analysis evaluated whether BED was associated with BF, while adjusting for clinical factors. ResultsThere were 247 analyzable patients in the 44/20 trial. At a median follow-up of 13.7 years, there were no differences in BF for the entire cohort (sub-distribution hazard ratio (sHR) 0.99; 95% CI: 0.43, 2.276; p = 0.97) or the UIR subgroup (sHR 0.72; 95% CI: 0.25, 2.08; p = 0.55). There were 383 analyzable patients in the 20/0 trial. At a median follow-up of 10.4 years, there were no differences in BF for the entire cohort (sHR 0.42; 95% CI: 0.13-1.80; p = 0.15) or the UIR subgroup (sHR 0.81; 95% CI: 0.16-4.03; p = 0.80). For the combined cohort (630 patients), BED was not associated with BF (1.00; 95% CI: 0.98-1.02; p = 0.88) on multivariate analyses, while adjusting for androgen deprivation therapy utilization, 4-tiered National Comprehensive Cancer Network category, and year of treatment. ConclusionsBrachytherapy monotherapy should be a standard-of-care treatment for clinically localized, intermediate risk prostate cancer, including UIR disease.