Predictive factors for acute and late urinary toxicity after permanent interstitial brachytherapy in J apanese patients

Objectives To describe the frequency of and to determine predictive factors associated with R adiation T herapy O ncology G roup urinary toxicity in prostate brachytherapy patients. Methods From J anuary 2004 to A pril 2011, 466 consecutive J apanese patients underwent permanent iodine‐125‐seed brachytherapy (median follow up 48 months). International P rostate S ymptom S core and R adiation T herapy O ncology G roup toxicity data were prospectively collected. Prostate volume, International P rostate S ymptom S core before and after brachytherapy, and postimplant analysis were examined for an association with urinary toxicity, defined as R adiation T herapy O ncology G roup urinary toxicity of G rade 1 or higher. Logistic regression analysis was used to examine the factors associated with urinary toxicity. Results The rate of R adiation T herapy O ncology G roup urinary toxicity grade 1 or higher at 1, 6, 12, 24, 36 and 48 months was 67%, 40%, 21%, 31%, 27% and 28%, respectively. Grade 2 or higher urinary toxicity was less than 1% at each time‐point. International P rostate S ymptom S core was highest at 3 months and returned to normal 12 months after brachytherapy. On univariate analysis, patients with a larger prostate size, greater baseline International P rostate S ymptom S core, higher prostate V 100, higher prostate V 150, higher prostate D 90 and a greater number of seeds had more acute urinary toxicities at 1 month and 12 months after brachytherapy. On multivariate analysis, significant predictors for urinary toxicity at 1 month and 12 months were a greater baseline International P rostate S ymptom S core and prostate V 100. Conclusions Most urinary symptoms are tolerated and resolved within 12 months after prostate brachytherapy. Acute and late urinary toxicity after brachytherapy is strongly related to the baseline International P rostate S ymptom S core and prostate V 100.