Comparison of EBRT and I-125 seed brachytherapy concerning outcome in intermediate-risk prostate cancer

PURPOSE: This study’s objective was the comparison of external beam radiotherapy (EBRT) and I‑125 seed brachytherapy regarding clinical outcome and development of side effects. PATIENTS AND METHODS: In all, 462 localized intermediate-risk prostate cancer patients treated between 2000 and 2019 at our department using either I‑125 seed brachytherapy or EBRT with a dose of 74 or 78 Gy were included: 297 patients were treated with EBRT and 165 with seeds. Biochemical no evidence of disease (bNED) rates according to Phoenix definition as well as late gastrointestinal and urogenital side effects (EORTC/RTOG) were assessed. RESULTS: Patients were followed up yearly with a median follow-up of 54 (3–192) months. Observed bNED rates for 74 Gy, 78 Gy and seeds were 87, 92, and 88% after 5 years and 71, 85, and 76% after 9 years, respectively. No significant differences were found comparing seeds with 74 Gy (p = 0.81) and 78 Gy (p = 0.19), as well as between 74 and 78 Gy (p = 0.32). Concerning gastrointestinal side effects, EBRT showed significantly higher rates of RTOG grade ≥ 2 toxicity compared to seeds, but at no point of the follow-up more than 10% of all patients. However, genitourinary side effects were significantly more prevalent in patients treated with seeds, with 33% RTOG grade ≥ 2 toxicity 12 months after treatment. Nevertheless, both types of side effects decreased over time. CONCLUSION: Favorable intermediate-risk prostate cancer patients can be treated either by external beam radiotherapy (74/78 Gy) or permanent interstitial seed brachytherapy.