Safety of Dose Escalation in Definitive Hypofractionated Radiation Therapy and Hormone Therapy With SpaceOAR TM for Patients With High - Risk Localized Prostate Cancer (DESAR-H)

This trial tests whether a higher dose of radiation therapy (hypofractionated radiotherapy — meaning fewer, larger doses) is safe for men with high-risk localized prostate cancer, using a gel spacer (SpaceOAR) to protect the rectum from radiation damage. **You may be eligible if...** - You are a man aged 20 or older with prostate cancer confirmed by biopsy within the past 6 months - Your cancer is classified as high-risk (stage T3a–T4, Gleason Grade Group 4–5, or PSA over 20) - You have received or are planned to receive hormone therapy for your prostate cancer - You have had or are willing to have the SpaceOAR gel spacer procedure - You are in good general health (ECOG 0–1) **You may NOT be eligible if...** - You have had previous prostate removal surgery or other lower pelvic surgery (including rectal cancer surgery) - You have already had pelvic radiation therapy - You have lymph node or distant metastases - You have a bleeding disorder or other condition preventing the gel spacer infusion Talk to your doctor to see if this trial is right for you.