Single Arm Trial of Preoperative Stereotactic Body Radiation Therapy (SBRT) for T3a or Gleason Grade Group 4 Prostate Cancer

* Histologically proven prostate adenocarcinoma. * Clinical stage ≤T3a based on digital rectal exam (DRE) and ≤T3a based on MRI (within 3 months); N0-Nx; M0-Mx, or Gleason score 4 + 4. No more than 1 lymph node \>1 cm. * PSA ≤ 50 ng/ml, obtained within 3 months * Prostate volume: ≤60 cc. * IPSS score ≤15. * No previous radiotherapy to the prostate or lower pelvis. * Lymph node risk of \<35% using https://www.mskcc.org/nomograms/prostate/pre\_op. * No prior radical prostatectomy or cryotherapy of the prostate (prior transurethral resection or laser ablation are permitted). * No implanted hardware or other material that would prohibit appropriate treatment planning or treatment delivery, in the investigator's opinion. * No history of an invasive malignancy (other than this prostate cancer, or non-metastatic basal or squamous skin cancers) in the last 3 years. * No androgen deprivation therapy (ADT) can be prescribed prior to or during radiation therapy. * Participant must be able to have gold fiducial markers placed in the prostate. Note: patients can be enrolled after fiducial markers have been placed, as long as the procedure was done in accordance with the protocol (Section 4.2.2). * Eastern Cooperative Oncology Group (ECOG) performance status ≤2 * Ability to understand and the willingness to sign a written informed consent document. * Willing to fill out quality of life questionnaires.