RAD 1801: Pilot Study of Intra-Urethral Radiotransponder Beacon Guided Focal Prostate Stereotactic Body Radiotherapy

Inclusion Criteria: * All patients must have histologically confirmed adenocarcinoma of the prostate, with biopsies obtained within 12 months of registration * Gleason score 3+3 or 3+4 * PSA \<10 ng/mL within 3 months of enrollment * Clinical stage T1a-T2a by digital rectal exam * Up to 2 intraprostatic nodules visible on MRI, with combined volume \<50% of the total prostate volume * Karnofsky Performance Status (KPS) \>70%. * Life expectancy \>10 years * Age ≥ 19 years * Subjects given written informed consent Exclusion Criteria: * \>2 MRI defined nodules representing prostate cancer * Total volume of MRI nodules exceeding 50% of total prostate volume * Positive biopsy core in sextant region without MRI defined nodule (i.e. biopsy proven MRI occult prostate cancer) * American Urological Association (AUA) urinary score ≥ 18. * History of inflammatory bowel disease. * Prior pelvic surgery * Prior treatment for prostate cancer * Patients using immunosuppressive medications or other medications that may increase radiation toxicity such as methotrexate, sirolimus, tacrolimus, or colchicine that are unable to discontinue these medications during SBRT course. Use of corticosteroids is not considered an exclusion criteria. * Platelet count \< 70,000/µL * Patients unable to discontinue anti-platelet or anti-coagulant medicine such as clopidogrel, dabigatran, warfarin, or low molecular weight heparin. Use of aspirin is not an exclusion criteria. * Contraindication to MRI such as implanted devices. * Metallic pelvic implants resulting in imaging artifact within the prostate on MRI or CT