SBRT standard of care radiotherapy treatment

The goal of this clinical trial is to measure the toxicity and effectiveness of the following treatments for cFIR/cgUIR prostate cancer patients. Stereotactic body radiotherapy (SBRT) alone or Stereotactic body radiotherapy (SBRT) combined with Ultrashort GNRH Antagonist called Relugolix (an oral drug). Treatments will be randomly assigned to study patients. The main questions it aims to answer are the following: 1. Whether the proportion of men who undergo SUGAR have superior rate of attaining PSA nadir of \<= 0.2 compared to SBRT alone, and 2. Whether SUGAR is superior to historical rates of minimal clinically important decline (MCID) in sexual and hormonal function at 6 months for patients undergoing 6 months of androgen deprivation therapy (ADT) Men aged 18+ with cFIR/cgUIR will be enrolled. Specifically, patients must meet one of the following 2 criteria: 1) Gleason score must be Gleason 3+4 with a PSA \< 20 ng/mL, or 2) Gleason 6 (3+3) and PSA \> 10 ng/mL and \< 20 ng mL.