PURPOSE: This study aims to evaluate the outcomes of patients treated for low-risk (LR) and favorable intermediate risk (FIR) prostate cancer with brachytherapy (BT) in monotherapy with LDR or HDR and its relationship with nadir PSA (nPSA). MATERIALS AND METHODS: We retrospectively analyzed 139 patients (2005-2019) with exclusive LDR (46%. 145/160 Gy) /HDR (54%. 2 implants of 13.5 Gy each separated 10 days). 69% LR and 31% FIR. PSA nadir was grouped into two categories: ≤ 0.2 ng/mL and >
0.2 ng/mL. RESULTS: Median patient age was 69 years (46-84). Seventy-six patients (55%) received androgen deprivation therapy, and 37% received neoadjuvant therapy. Median follow-up period was 90 months. Actuarial biochemical failure-free survival (BFFS), local control (LC), overall survival (OS), and cause-specific survival (CSS) rates for the total cohort were 78%, 87%, 68%, and 98% at 10 years, respectively. BFFS, LC, OS and CSS in nPSA ≤ 0,2 ng/ml was 90%, 96%, 67%, 100% at 10 years respectively, whereas, those with a nPSA >
0.2 ng/ml had a BFFS, LC, OS and CSS of was 37%, 51%, 72%, 90% at 10 years respectively Statistical significance between both groups was reached in BFFS (p=0,000), LC (p=0,000) and CSS (p=0,007)). In the univariate analysis, there was no difference between risk stratification, BT technique, ADT, or the development of bouncing. CONCLUSIONS: Prostate brachytherapy as monotherapy (LDR and HDR) is an effective treatment option for patients with LR and FIR prostate cancer. nPSA ≤0,2 ng/ml is a representative value that provides prognostic information for favorable outcomes in this group of patients.