Stereotactic Body Radiation Therapy or Intensity-Modulated Radiation Therapy in Treating Patients With Stage IIA-B Prostate Cancer

Inclusion Criteria: * Previously untreated (no local therapy such as surgery, radiation cryotherapy, high-intensity focused ultrasound \[HIFU\], etc.) localized adenocarcinoma of the prostate with the following clinical findings: * Clinical stage by digital rectal exam of either T1c or T2a/b (limited to one side of the gland); (American Joint Committee on Cancer \[AJCC\], version 7) or cT1a-c or 2a or 2b * Stages T1a-T1b are eligible if patient underwent transurethral prostatic resection (TURP) * The patient must meet one of the following 3 criteria: 1) Gleason score must be Gleason 7(3+4) with a PSA \< 20 ng/mL, or 2) Gleason 6 (3+3) with a PSA \> 10 ng/mL and \< 20 ng/mL which is considered intermediate risk and eligible for the study (AJCC, version 7), or 3) Group Grade 1 with a PSA \> 10 ng/mL and \< 20 ng/mL or 2 with a PSA \< 20 ng/mL * If patient is receiving a 5-alpha reductase inhibitor at the time of enrollment, the baseline PSA value may be double the initial value and the medication should be discontinued but a washout period is not required; to be eligible, a PSA drawn while still on the medicine must be: * \< 10 ng/mL if Gleason 7(3+4) (note this patient would be on stratification level 1 if PSA \< 5 ng/mL and stratification level 2 if less than 10 ng/mL) * \> 5 ng/mL and less than 10 ng/mL for Gleason 6(3+3) (note this patient would be on stratification level 3) * The prostate volume must be \< 70 cc as reported at time of biopsy or …