Barrigel® PPRT (Post-Prostatectomy Radiation Therapy) Trial

Inclusion Criteria: 1. Age ≥ 18 years 2. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 3. Prostatectomy surgeon notes specifying successful bilateral nerve Sparing procedure 4. Documentation of an intra or interfascial radical prostatectomy 5. Confirmed diagnosis of adenocarcinoma of the prostate treated primarily with radical prostatectomy with pN0 or pNX pathologic stage 6. No radiographic evidence of local, regional, or distant metastatic disease via PSMA PET or Axumin fluciclovine F18 scan 7. Prostate specific antigen (PSA) 0.1 ng/mL or higher 8. Intent to receive definitive radiation therapy to the prostate bed 9. Written informed consent for study participation prior to study enrollment Exclusion Criteria: 1. Known allergy to hyaluronic acid 2. Pathologic T4 disease 3. Prior local prostate cancer therapy including cryotherapy or brachytherapy. 4. Prior post-prostatectomy or pelvic radiation therapy 5. Planned elective pelvic lymph node radiation therapy 6. Prior anorectal surgery (e.g. low anterior resection, abdominoperineal resection, absence of a rectum) 7. Inflammatory bowel disease requiring treatment with steroids (e.g. Crohn's disease, ulcerative colitis) 8. Active connective tissue disorder including lupus or scleroderma 9. Any urogenital abnormality that could limit the ability to access the Barrigel injection site 10. White blood cell count \<4000/uL or \>12,000/uL. 11. Hemoglobin \<10 g/dL (transfusion or other intervention to achieve this is acceptable). 12. Active bleeding disorder or clinically significant coagulopathy defined as PTT \>35 seconds or INR \>1.4 or platelet count \<100,000/mm3. 13. Serum AST/ALT \>2.5 times the institutional upper limit of normal 14. Creatinine \>2.0 mg/dL 15. Bilirubin \>2.0 mg/dL 16. History of chronic renal failure. 17. History of uncontrolled diabetes (e.g. symptomatic hyperglycemia that is not controlled with medical management; fasting blood glucose \>300 mg/dL). 18. History of acquired immunodeficiency syndrome (AIDS). Patients with controlled HIV infection (CD4+ T-cell counts ≥ 350 cells/µL) and no history of AIDS-defining opportunistic infections may be included. 19. Contraindication to having an MRI or PSMA/PET scan (e.g. non-MRI compatible device). 20. Presence of bilateral hip implants, although unilateral hip implant may be permissible if the implant is MRI compatible and does not produce artifact that interferes with any requirements of the study protocol 21. Subject unable or unwilling to comply with study requirements 22. Any condition that in the investigator's opinion would prevent administration or completion of study therapy