Purpose/Objective(s): This study aims to evaluate predictors for the prostate-specific antigen (PSA) bounce in patients treated with ¹²⁵I-brachytherapy only for prostate cancer and to assess the correlation between testosterone and the PSA bounce.

Materials/Methods: Between 2004 and 2012, 252 patients with prostate cancer were treated with ¹²⁵I-brachytherapy with ≥1-year follow-up. The patients were followed-up with PSA and testosterone before and after 1, 3, 6, 12, 18, 24, 30, 36, 42, 48, 54, and 60 months of treatment with ¹²⁵I-brachytherapy. After a 5-year follow-up, the PSA and testosterone levels were examined once every year. In the present study, the PSA bounce was defined as a ≥0.2-ng/mL increase above the interval PSA followed by a decline to nadir or below. The mean follow-up [±standard deviation (SD)] was 84.1 (±30.4) months.

Results: After receiving ¹²⁵I-brachytherapy, PSA bounce was reported in 74 patients (29.3%; 91 cases) with a mean (±SD) of 20.4 (±10.1) months. Among age, the prostate volume, %D90, D90, V100, V150, R100, %UD90, UD90, T stage, PSA before treatment, Gleason score, and testosterone before treatment, age was the only predictor for the PSA bounce (60–70 years: P = 0.23, 95% Confidence Interval (CI) 0.25–1.39, ≥70 years: P = 0.005, 95% CI: 0.11–0.69; reference to <60 years). In 86 cases of 91 cases with PSA bounce, the testosterone value was evaluated at nadir before the PSA bounce and at PSA bounce. The testosterone value was significantly higher at the PSA bounce than that at nadir before the PSA bounce (P = 0.007, Wilcoxon signed-rank test).

Conclusion: This study suggests that younger patients tend to receive the PSA bounce, which is possibly caused by elevated testosterone levels.