Risk Factors and Time to Occurrence of Genitourinary Toxicity After External Beam Radiotherapy for Prostate Cancer

To retrospectively investigate the risk factors and time to occurrence of genitourinary (GU) toxicity after radiotherapy for localized prostate cancer.The study included 320 patients. The radiotherapy planning target volume encompassed the prostate with a 1-cm margin in the transverse plane and a 1-cm margin (Group A) or a 1.5-cm margin (Group B) in the longitudinal plane. Incidence rates, risk factors and time to occurrence of GU toxicity were evaluated.After a median follow-up of 38.2 months, the rate of late grade 2-3 GU toxicity was 5.9% and the median interval was 18.3 months. The wider longitudinal margin was the single significant independent factor. The 2-year cumulative incidence rates of late grade ≥2 GU toxicity were 2.8% and 7.5% in Group A and B patients.A wider radiotherapy margin increased the risk of GU toxicity and led to earlier occurrence.