Background/Aim: We retrospectively investigated the effect of a biologically effective dose (BED) of Low-dose rate brachytherapy (LDR-BT) and its possible interaction with androgen deprivation therapy (ADT) during LDR-BT treatment for intermediate-risk prostate cancer (PCa). Patients and Methods: A total of 693 patients with localized, intermediate-risk PCa, who underwent LDR-BT with or without supplemental external beam radiotherapy, were included in this study. We stratified patients into two groups according to BED (<180 Gy2, lower BED group; ≥180 Gy2, higher BED group) and evaluated the effect of ADT duration on the oncological outcomes of each group. Results: In total, 431 patients received BED ≥180 Gy2. Significant differences in biochemical recurrence-free survival (BCRFS) and clinical progression-free survival (CPFS) were observed among the non-ADT, ADT ≤3 months, and ADT >3 months subgroups of the lower BED group (p=0.005 and 0.049, respectively). However, no significant differences in BCRFS or CPFS were detected in the higher BED group (p=0. 63 and 0.76, respectively). Multivariate analysis of BCR and CP in the lower BED group revealed a significant decreasing trend in the BCRFS (p for trend=0.001) and CPFS rates (p for trend=0.015) as ADT duration increased, which was associated with favorable outcomes. However, no significant trend was observed in the BCRFS or CPFS rate in the higher BED group. Conclusion: An adequate local radiation dose provides favorable oncological outcomes and could potentially reduce the need for long-term ADT.It has been approximately two decades since low-dose-rate brachytherapy (LDR-BT) was introduced as a treatment for prostate cancer (PCa) in Japan. LDR-BT is currently considered a curative treatment option for patients with lowand intermediate-risk PCa (1). Previous research has shown that a biologically effective dose (BED) is crucial for achieving optimal oncological outcomes after LDR-BT (2-7). Notably, Tanaka et al. have repeatedly reported that a higher BED (>178-180 Gy2) is associated with lower recurrence-free survival in localized PCa patients (5-7). Additionally, we previously suggested that a higher BED may shorten the duration of androgen deprivation therapy (ADT) in patients with intermediate PCa. However, due to a small sample size and short follow-up, we were unable to obtain significant results (8). Moreover, the optimal ADT protocol for localized PCa treated with LDR-BT remains controversial and is currently being investigated in randomized controlled trials (9, 10).Thus, we hypothesized that an adequate local radiation dose would help prevent long-term ADT in intermediate-risk PCa patients. Therefore, we evaluated the effect of BED on the oncological outcomes of intermediate-risk PCa patients, and its possible interaction with ADT during LDR-BT treatment.
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