The nature and extent of urinary morbidity in relation to prostate brachytherapy urethral dosimetry

PURPOSE: This study investigates whether the location and dose of urethral radiation received during transperineal interstitial permanent prostate brachytherapy determine the degree and type of urinary symptoms experienced subsequently. METHODS AND MATERIALS: Data from a prospectively acquired database of 219 men treated with transperineal interstitial permanent prostate brachytherapy using (125)I (prescribed dose 145Gy) between May 2001 and June 2003 were reviewed. To assess the effect of regional urethral dosimetry, the prostate was divided into equal thirds (proximal, mid, and apical) with doses beyond this considered distal. Mean and peak doses for each region were correlated with total International Prostate Symptom Score (IPSS) and the irritative and obstructive components of the score. IPSS values at 1 month postimplant, time to resolution of IPSS, and the need for catheterization were used as outcome variables and analyzed with respect to dose using logistic and linear regression. RESULTS: Peak and average doses with standard deviations to the proximal urethra were 168 (24) and 147 (24)Gy, mid prostatic urethra 192 (24) and 181 (21)Gy, and apical urethra 201 (28) and 192 (26)Gy. Catheterization was required for 28 men and was predicted by larger pretreatment transrectal ultrasound (TRUS) volume (OR 1.06 per unit change; 95% CI 1.03-1.10; p<0.001) and lower UV(150) (OR 0.30; 95% CI 0.13-0.68; p=0.004) in multivariate analysis. Greater IPSS at baseline (p<0.001) and preoperative TRUS volume (p=0.012) but conversely smaller D(30) doses (p=0.003) were predictive of IPSS outcomes at 1 month. IPSS returned to within two points of baseline for 72.2% of men by 1 year and 83.3% by 24 months. This was predicted by higher IPSS at baseline (OR 6.0; 95% CI 2.72-13.22; p<0.001), higher D(30) (OR 1.17; 95% CI 1.01-1.36; p=0.031), and lower V(100) (OR 0.39; 95% CI 0.22-0.70; p=0.002). Prostatic urethral segmental dosimetry failed to predict the need for catheterization, the nature of the urinary symptoms, or their time to resolution. CONCLUSIONS: Previously identified factors of importance for urinary morbidity such as pretreatment prostate volume and baseline urinary function were reemphasized in this study. Regional urethral dosimetry within contemporary practice does not seem to influence the nature or extent of urinary symptoms after prostate brachytherapy. Consequently, region sparing dosimetric modifications are not warranted to alter symptomatic outcomes.