The purpose of this study is to evaluate the incidence of urinary and gastrointestinal acute and late side effects in patients treated with stereotactic body radiotherapy (SBRT) to the prostate. Stereotactic radiation therapy is given as five treatments over a 2-3 week period. The prostate is localized and the plan is reoptimized as needed prior to each treatment.
Inclusion Criteria: * Histologically confirmed diagnosis of adenocarcinoma of the prostate within 365 days of study enrollment * History/physical examination with digital rectal examination of the prostate within 8 weeks prior to study enrollment * Gleason score less than or equal to 7 * Clinical Stage T1-T2c * PSA * less than or = 15 ng/ml prior to start of therapy if Gleason \< or = 6 or * less than or = 10 ng/ml prior to start of therapy if Gleason = 7 * Zubrod Performance Status 0-1 * Age \> 40 Exclusion Criteria: * Prior or concurrent invasive malignancy (except non-melanomatous skin cancer) or lymphomatous/hematogenous malignancy unless continually disease free for a minimum of 5 years. (Carcinoma in situ of the bladder or oral cavity is permissible) * Evidence of distant metastases * Regional lymph node involvement * Significant urinary obstruction * Estimated prostate gland \> 100 grams * Previous radical surgery (prostatectomy) or cryosurgery for prostate cancer * Previous pelvic irradiation, prostate brachytherapy, or bilateral orchiectomy * Previous hormonal therapy, such as LHRH agonists (e.g. goserelin, leuprolide), anti-androgens (e.g., flutamide, bicalutamide), estrogens (e.g., DES), or surgical castration (bilateral orchiectomy) or planned concurrent androgen deprivation therapy * Previous or concurrent cytotoxic chemotherapy for prostate cancer * Prosthetic implants in the pelvic region that contain metal or conductive materials (e.g., an artificial hip). * Severe, active comorbidity