Proctitis after conventional external radiation therapy for prostate cancer: importance of minimizing posterior rectal dose

To identify factors associated with the prevalence of radiation proctitis in patients with prostate cancer treated with external radiation therapy and to determine if a dose-response relationship exists.The study included 101 prostate cancer patients treated at the University of Minnesota Hospital and Clinics between 1970 and 1987. Radiation therapy at a daily dose of 175-200 cGy was given for 5 consecutive days per week for 7 weeks with a 10-24-MV linear accelerator. Mean dose to the prostate was 6,795 cGy (range, 5,579-7,417 cGy). Simulation radiographs obtained with rectal barium were analyzed in 51 patients. Doses were calculated at specific points in the boost field.Radiation proctitis developed in 19 patients. No pretreatment or treatment factors were associated with a higher prevalence of proctitis. Statistically significant correlation (P.042) was found between the development of proctitis and dose to the posterior rectum. At chi 2 analysis, proctitis was statistically significantly (P.005) associated with posterior rectal doses of5,000 cGy.A high posterior rectal dose (5,000 cGy) is associated with increased prevalence of proctitis after radiation therapy.