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

Aim: To retrospectively investigate the risk factors and time to occurrence of genitourinary (GU) toxicity after radiotherapy for localized prostate cancer. Patients and Methods: 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. Results: 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. Conclusion: A wider radiotherapy margin increased the risk of GU toxicity and led to earlier occurrence.