RATIONALE: Radiation therapy uses high-energy x-rays to damage tumor cells. Amifostine may protect normal cells from the side effects of radiation therapy.

PURPOSE: Phase II trial to study the effectiveness of radiation therapy plus amifostine in treating patients with primary prostate cancer.

OBJECTIVES: I. Determine the incidence, grade, and time course of acute grade 2 or higher gastrointestinal and genitourinary toxicities in patients with primary prostate adenocarcinoma receiving amifostine plus fractionated radiotherapy. II. Determine the incidence and nature of toxicity associated with amifostine in these patients. III. Assess tumor response to this treatment in these patients. IV. Assess impotency rates following radiotherapy in these patients.

OUTLINE: This is an open label study. Patients receive fractionated radiotherapy five days per week for 7 weeks plus amifostine IV push over 5 minutes, 15 minutes before each radiation treatment. Patients are followed at 1 month after radiotherapy, and then every 3 months for at least 5 years.

PROJECTED ACCRUAL: There will be 25 patients accrued into this study over 2 years.

DISEASE CHARACTERISTICS: Histologically confirmed prostate adenocarcinoma Stage T1a-T3b N0 M0 disease PSA at least 10 ng/mL prior to treatment Must have a risk of seminal vesicle involvement between 10-25% No palpable or radiographic evidence of seminal vesicle involvement

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 60-100% Life expectancy: Greater than 24 months Hematopoietic: Not specified Hepatic: SGOT and SGOT no greater than 2.5 times upper limit of normal Renal: Creatinine no greater than 2.0 mg/dL Cardiovascular: No severe cerebrovascular disease or sustained hypotension not secondary to antihypotensive medication Other: No history of inflammatory bowel disease No history of malignancy other than nonmelanoma skin cancer No underlying medical or psychiatric illness that may impair ability to participate in study

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Not specified Endocrine therapy: Not specified Radiotherapy: No prior radiotherapy to the prostate area Surgery: No prior radical prostatectomy Other: No hypertensive medications if blood pressure less than 120/70