Normal tissue tolerance of the rectum limits the dose of radiation that can be delivered to the prostate for curative treatment of prostate cancer. Amifostine is a radioprotector, an agent that reduces tissue damage incurred by ionizing radiation. It has been well studied in humans and is approved for intravenous use. Rectal administration results in a preferential accumulation of Amifostine in the rectal mucosa, and neither free parent compound nor free active metabolite have been detected in systemic circulation. This trial proposes to observe the rate of early and late bowel toxicity in a group of patients with prostate cancer receiving standard high dose, 3D conformal external beam radiotherapy and concurrent intra-rectal applications of Amifostine. Primary measures of rectal toxicity (RTOG radiation morbidity scoring) will also be compared with self-assessment measures of quality of life, and rectal radiation dose as assessed by dose-volume histograms.