University of Kansas Medical Center

Subjects must meet the following criteria to be eligible for participation in the study: 1. Age ≥18 years old 2. Subjects must have had pathologically confirmed (by routine hematoxylin and eosin [H&E] staining) invasive adenocarcinoma of the prostate and planning to undergo EBRT 3. Subjects must meet ALL of the following: 1. Clinical stage T1-T2c (AJCC Ver. 8) tumor AND 2. Gleason Score 7 or less as determined from a biopsy taken within 12 months of the Baseline visit AND 3. Demonstrated blood prostate specific antigen (PSA) levels ≤20 ng/ml as measured within 6 months of the Baseline visit and prior to commencing androgen deprivation therapy (ADT) 4. Subject is able to provide written informed consent, approved by the appropriate Institutional Review Board/Ethics Committee/Research Ethics Board (IRB/EC/REB) of the respective clinical site

1. Prostate > 80 cc 2. Subjects who are planning to undergo brachytherapy or focal boost 3. Subjects who have magnetic resonance imaging (MRI) evidence of gross posterior extracapsular extension (ECE) of the prostate cancer Note: MRI must be taken within 6 months prior to the Baseline visit 4. Subjects who have metastatic disease, other ongoing cancers which are being treated during the study or subjects for whom pelvic lymph node radiotherapy is planned 5. Subjects with any prior invasive solid tumor malignancy or hematologic malignancy (except non-melanomatous skin cancer) unless the subject has been disease free and treatment free for a minimum of 3 years 6. History of radical prostatectomy, other ablative anti-prostate cancer therapy (e.g., cryotherapy, high intensity focused ultrasound, irreversible electroporation) or previous pelvic irradiation (including prior prostate brachytherapy) at any time prior to screening 7. History of transurethral prostate surgery (e.g., Transurethral Needle Ablation (TUNA), Transurethral Microwave Therapy (TUMT), Transurethral Resection of the Prostate (TURP)) if performed within 1 year prior to screening 8. History of prior pelvic surgery requiring low anterior or abdominoperineal resections or rectal surgery 9. History of or current perirectal disease that may interfere with interpretation of study outcomes, including anal or perianal diseases such as fistula 10. Bleeding hemorrhoids requiring medical intervention within the prior three months 11. Diagnosed active bleeding disorder or a clinically significant coagulopathy, defined as PTT > 70s or aPTT>35s or INR > 1.4, or platelet count < 100,000 per mm3 Note: Subjects on anticoagulants may be included if the anticoagulant medication can be held for index procedure 12. Active inflammatory or infectious process involving the perineum, GI or urinary tract based on positive diagnosis or suspected diagnosis in the presence of fever >38⁰ C, WBC > 12,000/uL 13. Inability to undergo pelvic MRI or presence of implants causing severe artifact (e.g. bilateral arthroplasty) that interferes with imaging interpretation for this study at Investigator discretion 14. If a subject was enrolled in another investigational drug or device trial that had not completed the primary endpoint or that clinically interfered with this study 15. Unable to comply with the study requirements or follow-up schedule 16. Any condition the Investigator believed would interfere with the intent of the study or would make participation not in the best interest of the patient 17. Known PEG (polyethylene glycol) sensitivity or allergy 18. Known iodine sensitivity or allergy 19. ADT, if applicable, cannot or was not started 15-60 days prior to the pre-index procedure RT planning imaging and is planned to continue for a total planned duration greater than 6 months