Evaluating Local Doses for Prostate Cancer Treatment Using Low‐Dose‐Rate Brachytherapy Considering Oncological Control and Toxicity

Background This study evaluated factors associated with clinical failure and toxicity in patients with low‐, intermediate‐, and high‐risk prostate cancer treated with low‐dose‐rate brachytherapy (LDR‐BT) alone or combined with external beam radiation therapy (EBRT). Methods Seven hundred thirteen patients (low risk: n = 323; intermediate‐risk: n = 390) underwent LDR‐BT alone, whereas 534 patients (intermediate‐risk: n = 225; high risk: n = 309) underwent LDR‐BT combined with EBRT. The Fine‐Gray hazard model was used to identify factors associated with clinical failure, and the Youden index was employed to determine BED cut‐off values for Grade 3 or higher toxicity. Results In patients treated with LDR‐BT alone, BED thresholds of ≥ 180 Gy2 (low‐risk; hazard ratio [HR]: 0.38; 95% confidence interval [95% CI], 0.15–0.98, intermediate‐risk; HR: 0.29; 95% CI, 0.12–0.70) was significantly associated with better clinical outcomes. Patients with Grade 3 or higher toxicity had significantly higher BEDs than those without toxicity ( p = 0.008). A BED threshold of 200 Gy2 was identified as a cut‐off value for toxicity risk. In patients treated with LDR‐BT combined with EBRT, BED was not significantly associated with improved clinical failure‐free rates. Patients experiencing Grade 3 or higher toxicity exhibited significantly higher BEDs than those without toxicity ( p = 0.04). A BED cut‐off of 220 Gy2 was determined for toxicity. Conclusion For patients undergoing LDR‐BT alone, a BED of 180–200 Gy2 is optimal. For patients undergoing LDR‐BT combined with EBRT, a BED of 200–220 Gy2 may be more appropriate.