LAUSR

PURPOSE Urethral strictures are a rare complication of prostate brachytherapy (BXT), with prior studies showing radiation dose to the bulbomembranous urethra as being associated with stricture formation. This retrospective case-control study explored clinical and dosimetric parameters associated with the development of BXT-related urethral strictures. METHODS AND MATERIALS A cohort of 34 patients developed urethral strictures after BXT at our institution for the period of 2008-2014. Each case was matched with two controls (68 controls) that had not developed a urethral stricture according to similar baseline clinical and dosimetric parameters. Stricture development was compared with clinical (i.e., age, smoking status, diabetes, hypertension, vascular disease, International Prostate Symptom Score, hormones) and dosimetric (i.e., prostate, urethra, urethral segments [base, midgland, apex, extraprostatic, and 5 mm margin]) variables. Statistical modeling approaches such as univariate, multivariate, and subset selection methods for risk prediction were applied to identify parameter(s) with best predictive ability of toxicity. The performances of models were ranked according to Akaike information criterion score. RESULTS The results show that the R2 statistic increases from 6%, when only one parameter is included in the model, to almost 33%, when all the parameters are included. The best-fit subset of parameters included pretreatment International Prostate Symptom Score sum, urethra D30 Gy, urethra D5 Gy, and intraprostatic urethra with 5-mm margin V200 at the apex having the highest ability to predict the development of urinary strictures. CONCLUSIONS This study used statistical modeling, a novel approach in prostate BXT dosimetric studies, to identify a subset of parameters with predictive ability in identifying patients who develop urethral strictures.