Magnetic Resonance Guided Focal Stereotactic Body Radiation Therapy for Localized Prostate Cancer

Inclusion Criteria:

* Patients must have a histologically confirmed diagnosis of adenocarcinoma of the prostate
* Patient must have a history/physical examination with digital rectal examination of the prostate within 90 days prior to screening
* Eastern Cooperative Oncology Group (ECOG) performance status must be level 0 or 1 within 60 days prior to registration
* Patient must have a histological evaluation of the prostate biopsy with assignment of a Gleason score to the biopsy material; Gleason scores ≤ 7(3+4)
* Serum creatinine ≤ 1.5 times upper limit of institutional normal (normal: ≤ 1.17 mL/min/1.73 m\^2)
* Clinical stage a ≤ T1-T2a (American Joint Committee on Cancer \[AJCC\] 7th edition)
* Prostate specific antigen (PSA) ≤ 10 ng/mL within 90 days prior to registration; PSA should not be obtained within 10 days after prostate biopsy
* Subjects must have the ability to understand and the willingness to sign a written informed consent document
* Patient willing and able to complete the Expanded Prostate Cancer Index Composite (EPIC) questionnaire (baseline, 6, 12 and 24 months post end of radiation therapy)
* Patients must be able to undergo an MRI with contrast
* Bone scan completed within 90 days

Exclusion Criteria:

* Evidence of distant metastases
* Regional lymph node involvement
* Previous radical surgery (prostatectomy), cryosurgery, or high intensity focused ultrasound (HIFU) for prostate cancer
* Previous pelvic irradiation, prostate brachytherapy, or bilateral orchiectomy
* Previous hormonal therapy, such as luteinizing hormone-releasing hormone (LHRH) agonists (e.g., goserelin, leuprolide) or LHRH antagonists (e.g., degarelix), anti-androgens (e.g., flutamide, bicalutamide), estrogens (e.g., diethylstilbestrol \[DES\]), or surgical castration (orchiectomy)
* Use of finasteride within 30 days prior to registration; PSA should not be obtained prior to 30 days after stopping finasteride
* Use of dutasteride within 90 days prior to registration; PSA should not be obtained prior to 90 days after stopping dutasteride
* Previous or concurrent cytotoxic chemotherapy for prostate cancer
* Severe, active co-morbidity, defined as follows:
* 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; note, however, that laboratory tests for liver function and coagulation parameters are not required for entry into this protocol; (patients on Coumadin or other blood thinning agents are eligible for this study)
* Acquired immune deficiency syndrome (AIDS) based upon current Centers for Disease and Control (CDC) definition; note, however, that human immunodeficiency virus (HIV) testing is not required for entry into this protocol; protocol-specific requirements may also exclude immuno-compromised patients
* Patients unable to undergo an MRI with contrast