Postoperative or Salvage Radiotherapy (RT) for Node Negative Prostate Cancer Following Radical Prostatectomy

Inclusion Criteria: * Prostate cancer treated primarily with open, laparoscopic or robotically assisted prostatectomy. * Maximum PSA value of 20 ng/ml. Exclusion Criteria: * Evidence of distant metastasis (M1). * Prior systemic chemotherapy for any reason. * Previous irradiation to the pelvis that would compromise the ability to deliver the prescribed study treatment. * Active inflammatory bowel disease (Crohn's disease, diverticulitis or ulcerative colitis) affecting the rectum. (Non-active diverticulitis and Crohn's disease not affecting the rectum are allowed). * Prior or concurrent cancer, other than non-melanomatous skin cancer, unless disease free for at least 5 years. * Taking Saw Palmetto or methotrexate and unable or unwilling to discontinue its use during radiation.