Hypofractionated Stereotactic Body Radiation Therapy for Patients With Prostate Cancer That Was Removed by Surgery

PRIMARY OBJECTIVES: I. To determine maximum tolerated dose-per-fraction for SBRT to the prostate fossa following prostatectomy based on acute toxicity (\< 90 days). SECONDARY OBJECTIVES: I. To describe the acute (\< 90 days) toxicities and adverse events associated with hypofractionated SBRT when administered to the prostate bed in the post-prostatectomy setting. II. To describe the late (\> 90 days from treatment) toxicities and adverse events associated with hypofractionated SBRT when administered to the prostate bed in the post-prostatectomy setting. TERTIARY OBJECTIVES: I. To describe the patient-reported toxicity/quality of life (QOL) following hypofractionated SBRT treatment. OUTLINE: This is a dose-escalation study. Patients undergo 5, 10, or 15 fractions of hypofractionated SBRT daily over 1-3 weeks. After completion of study treatment, patients are followed up at 2, 6, and 13 weeks and then at 6, 9, 12, 18, 24, 30 and 36 months.