Equivalent uniform dose (eud) is a predictor of acute rectal toxicity in patients with prostate cancer treated with intensity modulated radiotherapy

Purpose: To apply the concept of equivalent uniform dose (EUD) to predict acute rectal and bladder toxicity for prostate cancer patients treated with intensity modulated radiotherapy (1MRT). Methods and Materials: 398 consecutive prostate cancer patients treated with IMRT from October 1998 to November 2001 were evaluated. Acute rectal and bladder toxicities were prospectively evaluated. The results were correlated with EUD values of the rectum and bladder using logistic regression analysis. RTOG scores were used as a measure of toxicity. Scores were grouped as either 0 or 0 for both acute rectal and acute bladder toxicity. EUD values were calculated using the formula: EUD = [(X fnuJ.D,')"" from t = 1 to N], where [nu], and D, are the fractional volume and absolute dose in the ilh volume element of the structure of interest, N is the number of bins, and a is the model parameter. The model parameter of a = 6 was used for bladder and rectum. Results: The median acute Gl score was 1 (range: 0-2). Scores of 0,1, and 2 were found in 37%, 51%, and 12% of patients, respectively. The median acute GU score was 1 (range: 0-4). GU scores of 0, 1, 2, 3, and 4 were found in 17%, 63%, 18%, 1.3% and < 1%, . respectively. The median EUD value for the rectum was 53.63 Gy (range: 44.71 to 61.29 Gy). The median EUD value for the bladder was 50.63 Gy (range: 36.43 to 63.21 Gy). High rectal EUD scores were found to predict acute GI toxicity that were 0 (P = 0.0005; OR = 1.22, 95% CI = 1.06-1.22). Acute rectal toxicity was not seen with rectal EUD values = 46.78 Gy. Bladder EUD scores were not associated with acute GU toxicity (P = 0.33). Conclusion: With higher rectal EUD values, the odds of acute GI toxicity increased for prostate cancer patients treated with IMRT. Because of its ability to predict clinical outcome, EUD scores may be useful in optimizing IMRT plans for prostate cancer patients to hopefully reduce acute GI toxicity.