Stereotactic Body Radiotherapy (SBRT) for Prostate Cancer

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