Nomograms to predict late urinary toxicity after prostate cancer radiotherapy.

53 Background: Tools are needed to predict toxicity after prostate cancer treatment. The objective of the study was to analyze late urinary toxicity after prostate cancer radiotherapy (RT) by symptom description and identification of patient characteristics or treatment parameters allowing for the generation of nomograms. Methods: 965 patient received a median total dose of 70 Gy (range, 65-80 Gy) for localized prostate cancer, using different fractionations (2 or 2.5 Gy/day) and RT techniques. Medical history was recorded. Late urinary toxicity was assessed, prospectively in half of the patients, using the CTCAE v3 classification: urinary frequency, incontinence, bleeding and retention (dysuria). Patients or treatment related predictors of late urinary toxicity (> grade 2) were identified by Univariate and multivariate Cox regression models. Nomograms were built up and their performance were assessed. Results: The median follow-up was 61 months. The 5-year (≥grade 2) global urinary toxicity, urinary frequency, hematuria, urinary retention and urinary incontinence rates were: 15%, 10%, 5%, 3% and 1%, respectively. The 5-year (≥ grade 3) urinary toxicity rate was 3%. The following parameters significantly increased the 5 year risk of global urinary toxicity (≥ grade 2): anticoagulant treatment (RR=2.35), total dose (RR=1.09), age (RR=1.06), bladder D25 (RR=1.03) and maximum dose (RR=1.1). Urinary frequency was increased by the total dose (RR=1.07) and diabetes (RR=4). Hematuria was increased by anticoagulant treatment (RR=2.9). Urinary retention (dysuria) was increased by the total dose (RR=1.1). Corresponding nomograms and their calibration plots were generated. Conclusions: The first nomograms to predict late urinary toxicity but also specific urinary symptoms after prostate RT were generated, contributing to prostate cancer treatment decision.