Intensity-Modulated Radiation Therapy With or Without Decreased Radiation Dose to Erectile Tissue in Treating Patients With Stage II Prostate Cancer

OBJECTIVES: Primary * Compare erectile dysfunction in patients with stage T1b-T2c adenocarcinoma of the prostate after treatment with intensity-modulated radiotherapy with vs without dose sparing for erectile tissue. Secondary * Compare biochemical freedom from failure rates, as a measure of prostate cancer control, in patients treated with these regimens. * Compare the quality of life of patients treated with these regimens. * Determine the association of molecular markers and biochemical freedom from failure rate and other endpoints in patients treated with these regimens. OUTLINE: This is a randomized, single-blind study. Patients are stratified according to age (≤ 65 vs \> 65), prescription radiotherapy dose (74 Gy vs 76 Gy), and frequency of erection during sexual activity within the past 4 weeks (a few times vs sometimes vs most times to always). Patients are randomized to 1 of 2 treatment arms. * Arm I: Patients undergo conventional intensity-modulated radiotherapy (IMRT) once daily 5 days a week for approximately 7.5 weeks. * Arm II: Patients undergo IMRT with dose restriction to erectile tissue once daily 5 days a week for approximately 7.5 weeks. Treatment in both arms continues in the absence of unacceptable toxicity or disease metastasis. Quality of life is assessed at baseline, at 6 and 12 months, and then annually for 4 years Patients are followed at 3 months and then every 6 months thereafter. PROJECTED ACCRUAL: A total of 200 patients (100 per treatment arm) will be accrued for this study within 2.5 years.