Clinical and dosimetric predictors of late rectal toxicity after conformal radiation for localized prostate cancer : results of a large multicenter observational study

Purpose: Assessing the predictors of late rectal toxicity after high-dose conformal radiotherapy for prostate cancer. Methods: One thousand one hundred thirty-two patients entered a prospective observational multicentric study; late rectal toxicity was evaluated by a self-reported questionnaire. Results concerning bleeding and faecal incontinence of 718/1132 patients with a complete follow-up at 36 months were analysed. The correlation between a number of clinical-dosimetric parameters and moderate/severe toxicity was investigated by univariate and multivariate logistic analyses. Results: Fifty-two (7.2%) and 57/718 (7.9%) patients were scored as moderate/severe bleeders and faecal incontinents, respectively; 19/57 incontinent patients showed persistent incontinence at 36 months. Bleeding was mainly correlated with V75 Gy while severe bleeding was mainly correlated with the previous abdominal/pelvic surgery; a different rectal dose-volume relationship in the two groups of patients (with/without surgery) was found. Moderate/severe acute toxicity was weakly correlated to late bleeding. The best predictor of faecal incontinence was acute toxicity (OR = 4 and 7 for chronic and actuarial incontinence, respectively). Conclusion: The application of rectal dose-volume constraints limited the incidence of rectal bleeding. The risk of bleeding may be further reduced by limiting V75 Gy < 5% and, in the case of patients previously submitted to abdominal/pelvic surgery, V70 Gy < 15-20%. Faecal incontinence seems to be mainly a consequential effect after acute toxicity.