Predictors for chronic urinary toxicity after the treatment of prostate cancer with adaptive three-dimensional conformal radiotherapy: dose-volume analysis of a phase II dose-escalation study.

PURPOSE: To identify factors predictive for chronic urinary toxicity secondary to high-dose adaptive three-dimensional conformal radiation. METHODS AND MATERIALS: From 1999 to 2002, 331 consecutive patients with clinical Stage II-III prostate cancer were prospectively treated (median dose, 75.6 Gy). The bladder was contoured, and the bladder wall was defined as the outer 3 mm of the bladder solid volume. Toxicity was quantified according to the National Cancer Institute Common Toxicity Criteria 2.0. Median follow-up was 1.6 years.
RESULTS: The 3-year rates of Grade > or =2 and Grade 3 chronic urinary toxicity were 17.0% and 3.6%, respectively. Prostate volume, confidence-limited patient-specific planning target volume, bladder wall volume, and acute urinary toxicity were all found to be accurate predictors for chronic urinary toxicity. The volume of bladder wall receiving > or =30 Gy (V30) and > or =82 Gy (V82), along with prostate volume, were all clinically useful predictors of Grade > or =2 and Grade 3 chronic urinary toxicity and chronic urinary retention. Both Grade > or =2 (p = 0.001) and Grade 3 (p = 0.03) acute urinary toxicity were predictive for the development of Grade > or =2 (p = 0.001, p = 0.03) and Grade 3 (p = 0.05, p < 0.001) chronic urinary toxicity. On Cox multivariate analysis the development of acute toxicity was independently predictive for the development of both Grade > or =2 and Grade 3 chronic urinary toxicity.
CONCLUSIONS: Acute urinary toxicity and bladder wall dose-volume endpoints are strong predictors for the development of subsequent chronic urinary toxicity. Our recommendation is to attempt to limit the bladder wall V30 to <30 cm(3) and the V82 to <7 cm(3) when possible. If bladder wall information is not available, bladder solid V30 and V82 may be used.