Purpose: The purpose of this study was to evaluate acute and late genitourinary (GU) toxicity and to elucidate factors associated with GU toxicity in patients with prostate cancer treated with permanent seed implantation (PI) enrolled in a nationwide prospective cohort study in Japan. Methods and Materials: Of 2,354 patients enrolled in this study, GU toxicity was evaluated in 2,339 patients at 3, 12, 24, and 36 months after PI. To elucidate independent factors predictive of acute and late Common Terminology Criteria for Adverse Events Grade 2 or higher (Grade ≥2) GU toxicity, multivariate logistic regression analyses were carried out. Regarding acute urinary retention (AUR), the incidence rate and the recovery rate for AUR were estimated using the Kaplan–Meier curve. Results: Approximately 53% of the patients treated with PI alone and 42% of those treated with combination therapy with PI therapy and external beam radiation therapy showed urinary frequency/urgency at 3 months. The multivariate analysis revealed that age, prostate volume, pretreatment international prostate symptom score, drinking status, and PI were independent predictors of acute GU toxicity Grade ≥2. Of all patients, 53 (2.3%) suffered from AUR, and 49 (92.5%) recovered from AUR with a median time of 4.3 months during the followup period. Conclusions: The results of GU toxicity in Japanese patients who underwent low-dose-rate brachytherapy were acceptable and comparable to those previously reported in U.S. patients. The patients treated with PI alone showed a significantly higher incidence rate of GU toxicity than did those undergoing combination therapy with PI and external beam radiation therapy in the acute phase.
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