RATIONALE: Radiation therapy uses high energy x-rays to damage tumor cells.

PURPOSE: Randomized phase III trial to compare the effectiveness of conventional radiation therapy with high-dose radiation therapy in treating men with stage I or stage II prostate cancer.

OBJECTIVES: I. Determine whether high-dose radiotherapy using conformal photons with a proton boost produces a 20% increase in the proportion of Stage I/II prostate cancer free from local failure and biochemical relapse at 5 years when compared to results of conventional-dose radiotherapy. II. Determine whether high-dose radiotherapy produces a 33% reduction in the cumulative incidence of a rising PSA (second hormone failure) following hormone therapy given at the time of first PSA/clinical failure when compared with conventional-dose radiotherapy. IV. Assess the relative rectal, bladder, and sexual morbidity of conformal photon doses of 70.2 and 79.2 Gy in these patients. V. Collect, in a prospective manner, paraffin biopsy blocks for subsequent analysis of emerging molecular pathologic predictors of outcome in three patients.

OUTLINE: Randomized study. Arm I: Radiotherapy. Boost to the prostate using high-LET protons followed by irradiation of the prostate, periprostatic tissues, and seminal vesicles using conformal photons with energies greater than 6 MV. Conventional dose. Arm II: Radiotherapy. As in Arm I. High dose.

PROJECTED ACCRUAL: There will be 390 patients accrued into this study over 3 years. An additional 3.5 years will be required for follow-up.

DISEASE CHARACTERISTICS: Histologically confirmed adenocarcinoma of the prostate Primary tumor confined to prostate TNM clinical Stages T1b-c or T2a-b No T1a No T1b-c tumor with Gleason grade 1-2/5 No Gleason grade 1-2/5 and PSA less than 4 ng/mL Nodes negative on imaging (Nx) or by surgical sampling (N0) PSA no greater than 15 ng/mL Treatment must begin within 28 days after randomization

PATIENT CHARACTERISTICS: Age: Any age Performance status: Karnofsky 70%-100% Life expectancy: Greater than 10 years Other: No major medical or psychiatric illness that precludes protocol entry No prior or concurrent second malignancy within 5 years except basal cell skin cancer

PRIOR CONCURRENT THERAPY: No prior treatment for prostate cancer