Inclusion Criteria:

• Histologically confirmed prostate adenocarcinoma at the time of surgery
• Pathologic stages T2-T3b, N0-Nx-N1, M0-1 as staged by the pathology report (American Joint Committee on Cancer [AJCC] criteria 8th edition [Ed.])
• One or more high risk features including: seminal vesicle invasion, extracapsular extension, positive margins, or a PSA post surgery between 0.2 and < 2.0
• PSA values < 2 ng/ml within 90 days prior to enrollment. Obtained at least 6 weeks after surgery
• Eastern Cooperative Oncology Group (ECOG) performance status 0-2 assessed within 90 days of enrollment
• Patients must sign Institutional Review Board (IRB) approved study specific informed consent
• Patients must complete all required pre-entry tests within the specified time frames
• Patients must be able to start treatment (androgen suppression [AS] or radiation) within 120 days of study registration
• Members of all races and ethnic groups are eligible for this trial
• Patients from outside of the United States may participate in the study

Exclusion Criteria:

• Previous pelvic radiation
• Prior androgen suppression therapy for prostate cancer for more than 6 months
• Active rectal diverticulitis, Crohn?s disease affecting the rectum or ulcerative colitis (non-active diverticulitis and Crohn?s disease not affecting the rectum are allowed)
• Prior systemic chemotherapy for prostate cancer
• History of proximal urethral stricture requiring dilatation
• Current and continuing anticoagulation with warfarin sodium (coumadin), heparin, low- molecular weight heparin, Clopidogrel bisulfate (plavix), or equivalent (unless it can be stopped to manage treatment related toxicity, to have a biopsy if needed, or place markers)
• Major medical, addictive or psychiatric illness which in the investigator?s opinion, will prevent the consent process, completion of the treatment and/or interfere with follow-up. (Consent by legal authorized representative is not permitted for this study)
• Evidence of any other cancer within the past 5 years and < 50% probability of a 5 year survival. (Prior or concurrent diagnosis of basal cell or non-invasive squamous cell cancer of the skin is allowed)
• History of myocardial infarction or decompensated congestive heart failure (CHF) within the last 6 months