Time to achieve a prostate-specific antigen nadir of ≤0.2 ng/mL and related factors after permanent prostate brachytherapy

Purpose: The purpose of this study was to identify the time to achieve a prostate-specific antigen (PSA) nadir of ≤0.2 ng/mL and the related factors to achieve this goal. Materials and Methods: We retrospectively reviewed 2218 Japanese prostate cancer patients who received ¹²⁵I brachytherapy with or without external beam radiotherapy between 2003 and 2013 at one institution. Among them, patients followed up for ≥72 months and without luteinizing hormone–releasing hormone (LH-RH) agonist/antagonist were included (total of 1089 patients). The time to a PSA nadir of ≤0.2 ng/mL (months) was defined as the time between the date of implantation and the first time the lowest PSA value reached ≤0.2 ng/mL. Biochemical recurrence (BCR) was determined using the Phoenix definition. Multivariate linear regression analysis was performed to detect the related factors to achieve this nadir. Results: We assigned 409, 592, and 88 patients to the low-, intermediate-risk, and high-risk groups, respectively. The median followup time was 9.5 years. The median time to achieve a PSA nadir of ≤0.2 ng/mL was 44.0 (95% confidence interval: 42.3–45.7) months. The percentage of patients that achieved the nadir was 89.1%. BCR was noted in 107 (9.8%) patients. In the multivariate analysis of patients without BCR, younger age, larger prostate volume at implantation, higher initial PSA level, and monotherapy were significantly associated with longer time to achieve the PSA nadir. Conclusion: The median time to achieve a PSA nadir of ≤0.2 ng/mL was 44.0 months. Some patients, however, may require a lengthy period of time to do so.