Inclusion Criteria:

1. Adenocarcinoma of the prostate treated primarily with radical prostatectomy, pathologically proven to be lymph node negative by pelvic lymphadenectomy (N0) or lymph node status pathologically unknown (undissected pelvic lymph nodes \[Nx\]), i.e. lymph node dissection is not required;

• Any type of radical prostatectomy will be permitted, including retropubic, perineal, laparoscopic or robotically assisted. There is no time limit for the date of radical prostatectomy.
2. A post-radical prostatectomy entry prostate-specific antigen (PSA) of ≥ 0.1 and \< 2.0 ng/mL at least 6 weeks (45 days) after prostatectomy and within 30 days of registration;
3. One of the following pathologic classifications:

* T3N0/Nx disease with or without a positive prostatectomy surgical margin; or
* T2N0/Nx disease with or without a positive prostatectomy surgical margin;
4. Prostatectomy Gleason score of 9 or less;
5. Zubrod Performance Status of 0-1;
6. Age ≥ 18;
7. No distant metastases, based upon the following minimum diagnostic workup:

* History/physical examination (including digital rectal exam) within 8 weeks (60 days) prior to registration;
* A computerized tomography (CT) scan of the pelvis (with contrast if renal function is acceptable; a noncontrast CT is permitted if the patient is not a candidate for contrast) or magnetic resonance imaging (MRI) of the pelvis within 120 days prior to registration;
* Bone scan within 120 days prior to registration; if the bone scan is suspicious, a plain x-ray and/or MRI must be obtained to rule out metastasis.
8. Adequate bone marrow function, within 90 days prior to registration, defined as follows:

* Platelets ≥ 100,000 cells/mm\^3 based upon compete blood count (CBC);
* Hemoglobin ≥ 10.0 g/dl based upon CBC (Note: The use of transfusion or other intervention to achieve Hgb ≥ 10.0 g/dl is recommended).
9. Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \< 2 x the upper limit of normal within 90 days prior to registration;
10. Serum total testosterone must be ≥ 40% of the lower limit of normal (LLN) of the assay used (testosterone ÷ LLN must be ≥ 0.40) within 90 days prior to registration (Note: Patients who have had a unilateral orchiectomy are eligible as long as this requirement is met);
11. Patients must sign a study-specific informed consent prior to study entry.

Exclusion Criteria:

1. A palpable prostatic fossa abnormality/mass suggestive of recurrence, unless shown by biopsy under ultrasound guidance not to contain cancer;
2. N1 patients are ineligible, as are those with pelvic lymph node enlargement ≥ 1.5 cm in greatest dimension by CT scan or MRI of the pelvis, unless the enlarged lymph node is sampled and is negative;
3. Androgen deprivation therapy started prior to prostatectomy for \> 6 months (180 days) duration. Note: The use of finasteride or dutasteride (±tamsulosin) for longer periods prior to prostatectomy is acceptable;
4. Androgen deprivation therapy started after prostatectomy and prior to registration (Note: The use of finasteride or dutasteride (±tamsulosin) after prostatectomy is not acceptable - must be stopped within 3 months after prostatectomy. Androgen deprivation therapy must be stopped within 3 months after prostatectomy);
5. Neoadjuvant chemotherapy before or after prostatectomy;
6. Prior chemotherapy for any other disease site if given within 5 years prior to registration;
7. Prior cryosurgery or brachytherapy of the prostate; prostatectomy should be the primary treatment and not a salvage procedure;
8. Prior pelvic radiotherapy;
9. Prior invasive malignancy (except non-melanomatous skin cancer) or superficial bladder cancer unless disease free for a minimum of 5 years \[for example, carcinoma in situ of the oral cavity is permissible\];
10. Severe, active co-morbidity, defined as follows:

* History of inflammatory bowel disease;
* History of hepatitis B or C; Blood tests are not required to determine if the patient has had hepatitis B or C, unless the patient reports a history of hepatitis.
* Unstable angina and/or congestive heart failure requiring hospitalization within the last 6 months;
* Transmural myocardial infarction within the last 6 months;
* Acute bacterial or fungal infection requiring intravenous antibiotics at the time of registration;
* Chronic Obstructive Pulmonary Disease exacerbation or other respiratory illness requiring hospitalization or precluding study therapy at the time of registration;
* Hepatic insufficiency resulting in clinical jaundice and/or coagulation defects; AST or ALT are required; note, however, that laboratory tests for coagulation parameters are not required for entry into this protocol.
* Acquired Immune Deficiency Syndrome (AIDS) based upon current Centers for Disease Control and Prevention (CDC) definition; Note, however, that human immunodeficiency viruses (HIV) testing is not required for entry into this protocol. The need to exclude patients with acquired immunodeficiency syndrome (AIDS) from this protocol is necessary because the treatments involved in this protocol may result in increased toxicity and immunosuppression.
11. Prior allergic reaction to the study drug(s) involved in this protocol.