High-dose Brachytherapy Boost With Stereostatic Body Radiation Therapy to Intermediate or Higher Risk Prostate Cancer

Inclusion Criteria: 1. Histopathologically proven diagnosis of local unfavorable intermediate or higher risk prostate cancer as defined by NCCN risk group criteria. Biopsies will be confirmed by UNMC pathology review if collected outside our institution. 2. No prior definitive treatment or intervention received. 3. Life expectancy of more than 10 years as estimated by the treating physician. 4. Negative evaluation lymph node involvement or distant metastatic disease on abdominopelvic CT, prostate MRI, and/or PSMA PET. 5. Negative evaluation of osseous metastatic disease via bone scan or PSMA PET scan. 6. Greater than or equal to 15% nodal involvement risk predicated on publicly available MSKCC pre-prostatectomy nomogram. 7. Karnofsky performance status ≥ 80 within 30 days prior to registration. 8. Age ≥ 19 years. 9. Clinically determined to be a candidate for HDR brachytherapy. 10. Patient must be able to provide study-specific informed consent prior to study entry. Exclusion Criteria: 1. American Urological Association Urinary Symptom Score (AUA score) ≥ 15. 2. Large prostate volume relative to pelvic arch width that can hinder proper placement of applicator insertion. To be done by MRI, TRUS, and/or physical exam for size, by CT A/P or MRI for arch interference. Specifically, prostates must be no greater than 75 cc in size as decerned by MRI, TRUS, or physical exam. Potential for pubic arch interference will be decerned by the treating radiation oncologist based on MRI and/or CT imaging. 3. Presence of any psychological, familial, sociological or geographical condition potentially hampering compliance with the study protocol and follow-up schedule. 4. Relative or absolute contraindications to radiation therapy as determined by the treating physician. These include, but not limited to, inflammatory bowel disease, connective tissue disorders (systemic lupus erythematosus, scleroderma, etc.), genetic disorders that risk increase sensitivity to radiation therapy. 5. Medical conditions that, in the opinion of the investigator could compromise patient safety. 6. Prior invasive malignancy other than prostate cancer (except non-melanomatous skin cancer) unless disease free for a minimum of 1 year. 7. History of rectal surgeries. 8. Recent major surgical procedure, open biopsy, or significant traumatic injury within 30 days prior to registration. 9. History of Urolift. 10. Contraindications to general anesthesia. 11. Preexisting rectal fistula.