Predictive factors of rectal toxicity after permanent iodine-125 seed implantation: Prospective cohort study in 2339 patients

PURPOSE: To evaluate the incidence and the associated factors of rectal toxicity in patients with prostate cancer undergoing permanent seed implantation (PI) with or without external beam radiation therapy (EBRT) in a nationwide prospective cohort study in Japan (J-POPS) during the first 2 years. METHODS AND MATERIALS: A total of 2,339 subjects were available for the analyses. Rectal toxicity was evaluated using the National Cancer Institute Common Terminology Criteria for Adverse Events version 3.0. RESULTS: The 3-year cumulative incidence for grade >= 2 rectal toxicity was 2.88%, 1.76%, and 6.53% in all subjects, PI group and EBRT combination therapy group, respectively. On multivariate analysis, among all subjects, grade >= 2 rectal toxicity was associated with rectal volumes receiving 100% of the prescribed dose (R-100; p < 0.0001) and EBRT combination therapy (p = 0.0066). R-100 in the PI group (p = 0.0254), and R-100 (p = 0.0011) and interactive planning (p = 0.0267) in the EBRT combination therapy group were also associated with grade >= 2 toxicity. The 3-year cumulative incidence of grade >= 2 rectal toxicity was 3.80% and 1.37% for R-100 >= 1 mL and R-100 < 1 mL, respectively, in the PI group (p = 0.0068), and 14.09% and 5.52% for R-100 >= 1 mL and R-100 < 1 mL, respectively, in the EBRT combination therapy group (p = 0.0070). CONCLUSIONS: Rectal toxicity was relatively rare in this study compared with previous reports. For Japanese prostate cancer patients, R-100 < 1 mL in both PI and EBRT combination therapy groups and interactive planning in EBRT combination therapy group may be effective in decreasing the incidence of rectal toxicity. (C) 2016 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.