Dosimetric predictors of diarrhea during radiotherapy for prostate cancer

Purpose: To investigate dosimetric predictors of diarrhea during radiotherapy (RT) for prostate cancer. Patients and Methods: All patients who underwent external-beam radiotherapy as part of treatment for localized prostate cancer at the University of Texas Medical Branch, Galveston, TX, USA, from May 2002 to November 2006 were extracted from the own database. From the cumulative dose-volume histogram (DVH), the absolute volumes (V-value) of intestinal cavity (IC) receiving 15, 30, and 45 Gy were extracted for each patient. Acute gastrointestinal toxicity was prospectively scored at each weekly treatment visit according to CTC (Common Toxicity Criteria) v2.0. The endpoint was the development of peak grade > 2 diarrhea during RT. Various patient, tumor, and treatment characteristics were evaluated using logistic regression. Results: 149 patients were included in the analysis, 112 (75.2%) treated with whole-pelvis intensity-modulated radiotherapy (WP-IMRT) and 37 (24.8%) with prostate-only RT, including or not including, the seminal vesicles (PORT ± SV). 45 patients (30.2%) developed peak grade > 2 diarrhea during treatment. At univariate analysis, IC-V₁₅ and IC-V₃₀, but not IC-V₄₅, were correlated to the endpoint; at multivariate analysis, only IC-V₁₅ (p = 0.047) along with peak acute proctitis (p = 0.041) was independently correlated with the endpoint. Conclusion: These data provide a novel and prostate treatment-specific "upper limit" DVH for IC.