This phase II trial studies how well stereotactic body radiation therapy works in treating patients with prostate cancer that has not spread to other parts of the body and have undergone surgery. Stereotactic body radiation therapy is a specialized radiation therapy that sends x-rays directly to the tumor using smaller doses over several days and may cause less damage to normal tissue.

PRIMARY OBJECTIVES:

I. To determine the efficacy of postoperative stereotactic body radiation therapy (SBRT) at a dose of 34 grays (Gy) in five fractions, as compared with historical control efficacy rates in patients who received conventionally fractionated postoperative radiotherapy.

II. To determine the toxicity of postoperative SBRT at a dose of 34 Gy in five fractions, both via physician-scored and patient-reported metrics.

SECONDARY OBJECTIVES:

I. To determine the proportion of SBRT fractions for which on-line adaptive radiotherapy is required due to changes in organ-at-risk anatomy, in the subset of patients treated with magnetic resonance imaging (MRI)-guided radiotherapy.

II. To gather biomarkers that may elucidate predictors of increased efficacy or increased toxicity.

TERTIARY OBJECTIVES:

I. To compare toxicity profiles (both physician-scored and patient-reported) between patients treated utilizing a linear accelerator versus a tri-60Co teletherapy platform.

OUTLINE:

Patients undergo SBRT every other day (QOD) for 14 days. Patients may also receive androgen deprivation therapy (ADT) comprised of a luteinizing hormone-releasing hormone agonist or a gonadotropin-releasing hormone antagonist, and an oral anti-androgen for 6 months at the discretion of the treating physician.

After completion of study treatment, patients are followed up at 1 month, every 3 months for 1 year, every 6 months for 4 years, and then annually thereafter.

Inclusion Criteria:

• History of histologically confirmed, clinical localized adenocarcinoma of the prostate treated with radical prostatectomy with definitive intent
• Presence of adverse pathologic features at the time of prostatectomy (positive surgical margin, pathologic T-stage 3-4 disease, pathologic Gleason score 8-10 disease, presence of tertiary Gleason grade 5 disease) OR documentation of rising prostate-specific antigen on at least two consecutive draws, with the magnitude of prostate-specific antigen exceeding 0.03 ng/mL
• Computed tomography (CT) scan and MRI of the pelvis within 120 days prior to enrollment (note: [a] if patient has medical contraindication to MRI, an exemption will be granted and enrollment can proceed [b] for patients with PSA < 1.0 ng/mL, the treatment planning CT can substitute for a diagnostic CT scan)
• Bone scan within 120 days prior to enrollment; if the bone scan is suspicious, a plain x-ray and/or MRI must be obtained to rule out metastasis, and advanced imaging (e.g., 18NaF positron emission tomography [PET]/CT) is strongly recommended
• Karnofsky performance score (KPS) >= 70
• Ability to understand, and willingness to sign, the written informed consent

Exclusion Criteria:

• Patients with any evidence of distant metastases
• Patients with pathologically-confirmed N1 prostate cancer
• Patients with neuroendocrine or small cell carcinoma of the prostate
• Prior cryosurgery, high-intensity focused ultrasound ablation (HIFU) or brachytherapy of the prostate
• Prior pelvic radiotherapy
• History of Crohn's disease, ulcerative colitis, or ataxia telangiectasia