Low-grade toxicity after conformal radiation therapy for prostate cancer-impact of bladder volume

Purpose: To assess the impact of dose-volume histogram parameters on low-grade toxicity after radiotherapy for prostate cancer. Methods and Materials: Eighty patients have been surveyed prospectively before (time A), at the last day (B), 2 months after (C), and 16 months (median) after (D) radiotherapy (70.2 Gy) using a validated questionnaire (Expanded Prostate Cancer Index Composite). Dose-volume histograms were correlated with urinary and bowel function/bother scores. Results: The initial bladder volume and the percentage of the bladder volume receiving 10%-90% of the prescription dose significantly correlated with urinary function/bother scores (significant cutoff levels found for all dose levels). Pain with urination proved to be mainly an acute problem, subsiding faster for patients with larger bladder volumes and smaller volumes inside particular isodose lines. At time D, persisting problems with smaller initial bladder volumes were a weak stream and an increased frequency of urination. Though bladder volume and planning target volume both independently have an influence on dose-volume histogram parameters for the bladder, bladder volume plays the decisive role for urinary toxicity. Conclusions: The patient's ability to fill the bladder has a major impact on the dose-volume histogram and both acute and late urinary toxicity.