RATIONALE: Radiation therapy uses high-energy x-rays to damage tumor cells. Radiation therapy may be an effective treatment for prostate cancer.

PURPOSE: Phase I trial to study the effectiveness of radiation therapy in treating patients who have stage II or stage III prostate cancer.

OBJECTIVES: I. Determine the maximum tolerated dose of radiotherapy using 3-dimensional (3D) conformal techniques in patients with stage II or III adenocarcinoma of the prostate. II. Determine the morbidity of high-dose 3D conformal therapy in these patients.

OUTLINE: This is a dose escalation study. Patients undergo 3-dimensional conformal radiotherapy 4-5 days a week for at least 8 weeks. Cohorts of 20-40 patients receive escalating doses of radiotherapy until the maximum tolerated dose (MTD) is determined. The MTD is defined as the dose at which no more than 10% of patients experience dose-limiting toxicity. Patients are followed at 3 months, every 6 months for 5 years, and then annually thereafter.

PROJECTED ACCRUAL: A minimum of 40 patients will be accrued for this study.

DISEASE CHARACTERISTICS: Locally advanced (T2c-T3) adenocarcinoma of the prostate including: Bulky tumors confined to prostate (stage II) Tumors extending beyond capsule (stage III) PSA no greater than 20 ng/mL No regional lymph node involvement (by CT scan or surgical sampling) No distant metastases

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 60-100% Life expectancy: Not specified Hematopoietic: WBC greater than 4,000/mm3 Platelet count greater than 100,000/mm3 Hemoglobin greater than 11 g/dL Hepatic: Not specified Renal: Not specified Other: No major medical or psychiatric illness that would preclude study No metallic pelvic prosthesis

PRIOR CONCURRENT THERAPY: Biologic therapy: No prior biologic therapy Chemotherapy: No prior chemotherapy Endocrine therapy: Prior hormonal therapy allowed Radiotherapy: No prior radiotherapy (including pelvic irradiation) Surgery: No prior radical surgery for carcinoma of the prostate