Predicting late fecal incontinence risk after RT for prostate cancer: External independent validation.

116Background: To validating a predictive model for late fecal incontinence (FI) on a recent population (pop) of prostate cancer patients (pts) treated with radical radiotherapy. NTCP model was derived from literature. Methods: Pop included 267 pts treated with IMRT in 2010-2014. Prescribed dose was between 68 and 80 Gy with conventional and hypo-fractionated (HF, from 2.2 to 2.8 Gy) treatment. Rectal toxicity was scored using the LENT/SOMA. Follow-up (FU) was considered up to 2 years. We chose to validate a model for prediction of chronic FI through multiple measures during FU. Mean FI was defined as the average score during the FU period after RT (Mean incontinence > 1). Literature based multivariate model included: mean rectal dose (Dmean), previous diseases of colon (COLO) and previous abdominal surgery (SURG). Dose distributions were corrected EQD in 2 Gy fractions. Results: 186 pts were available. Mean grade > 1 FI was scored in 18 patients (〜10%). Univariate logistic analysis confirmed the risk fac...