Trial of the Efficacy and Safety of Short and Long Course Radiation Therapy With/Without BMX-001

This study is testing whether adding a drug called BMX-001 to standard radiation therapy improves treatment for patients with locally advanced rectal cancer receiving total neoadjuvant therapy (chemotherapy and radiation before surgery). BMX-001 is a drug that may protect healthy tissue from radiation damage while potentially making cancer cells more vulnerable. **You may be eligible if...** - You are 18 or older (19 or older in Nebraska) - You have confirmed stage II or III rectal adenocarcinoma (rectal cancer, not yet spread to other organs) - You are scheduled for total neoadjuvant therapy (chemotherapy and radiation before surgery) with curative intent - Your blood counts and organ function meet required levels - You are in reasonably good physical condition (ECOG 0-2) **You may NOT be eligible if...** - Your cancer has already spread to other organs - You have severe blood, liver, or kidney problems - You are pregnant or planning to become pregnant during the study period - You have had prior pelvic radiation Talk to your doctor to see if this trial is right for you.