This trial is a prospective, single-arm, multi-center clinical trial designed to assess whether adaptive radiotherapy with urethral sparing for low to intermediate risk localized prostate cancer will translate into a decreased rate of patient reported acute urinary side effects, as measured by the patient reported EPIC-26 questionnaire, compared with the historically reported rate for non-adaptive, non-urethral sparing prostate SBRT.

Inclusion Criteria:

1. Patient has NCCN low or intermediate risk prostate cancer that is biopsy proven.
2. Prostate volume is ≤80cc as assessed by MRI prior to radiotherapy.
3. AUA/IPSS score is ≤ 15.
4. ECOG performance status is ≤2 (or Karnofsky score is ≥60%).
5. Patient has no PIRADS 4 or 5 lesion on prostate MRI contacting the urethra (determined at physician discretion).
6. Patient has the ability to complete required patient questionnaires.
7. Patient age ≥ 18 years (or greater than the local age of majority).
8. Patient has the ability to understand and the willingness to sign a written informed consent document.

Exclusion Criteria:

1. Patient has baseline grade ≥3 GI or GU toxicity
2. Patient has had prior overlapping pelvic radiotherapy.
3. Patient has had prior transurethral resection of the prostate, prostate HIFU, or cryoablation.
4. Patient has node positive prostate cancer.
5. Patient has extracapsular extension (capsular abutment is permitted).
6. Patient has active inflammatory bowel disease or active collagen vascular disease.
7. Patient cannot undergo prostate MRI.
8. Patient cannot undergo prostate fiducial marker placement.
9. Patient has ongoing receipt of cytotoxic chemotherapy (androgen deprivation therapy is allowed).