Late radiation damage in prostate cancer patients treated by high dose external radiotherapy in relation to rectal dose.

A retrospective analysis of the incidence of radiation proctitis was performed in 154 patients with carcinoma of the prostate treated with external radiotherapy assisted by CT-scan planning from 1983 to 1985. An attempt was made to assess a dose-response relationship for proctitis. Multivariate Cox regression analysis showed that previous bowel disease or surgery, anterior rectal dose, and average rectal dose contributed to a higher risk of proctitis. The anterior rectal dose was the most important indicator. No statistically significant correlation was found for the posterior rectal dose. The actuarial 2-year incidence of moderate or severe proctitis was 22% for anterior rectal doses less than 70 Gy and 20% for anterior rectal doses between 70 and 75 Gy, but increased to 60% when the dose was more than 75 Gy. A dose effect relation was evident, with a sharp dose-response gradient around 75 Gy at the anterior rectal wall.