Ultra-fractionated Radiotherapy for Rectal Cancer

Eligibility Criteria

• 1. At least 18 years of age. Both men and women and members of all races and ethnic groups will be included.
• 2. Willing and able to provide written informed consent
• 3. Pathologic diagnosis of rectal adenocarcinoma
• 4. T3-4 and/or N+ disease per AJCC 8th edition
• 5. No prior treatment for rectal adenocarcinoma
• 6. Eastern Cooperative Group (ECOG) performance status of 0-2.
• 7. Laboratory values supporting acceptable organ and marrow function within 30 days of eligibility confirmation. Defined as follows:
• * WBC ≥ 3,000/mL;
• * ANC WBC ≥ 1,000/mL;
• * PLT ≥ 75,000/mL;
• * T Bili ≤ 1.5 x upper limit of normal (ULN);
• * AST/ALT ≤ 2.5 x ULN;
• * Creatinine not above ULN, or creatinine clearance \>50 mL/min/1.73 m\^2 for participants with creatinine levels above institutional normal.
• 8. All men, as well as women of child-bearing potential must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) starting with the first dose of study therapy through 90 days after the last dose of study drugs. Should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately.
• * Has not undergone a hysterectomy or bilateral oophorectomy; or
• * Has not been naturally postmenopausal for at least 12 consecutive months (i.e., has had menses at any time in the preceding 12 consecutive months).
• 1. Distant nodal disease (retroperitoneal nodes) including inguinal nodes, or any metastatic disease by CT.
• 2. Prior RT to the pelvis.
• 3. Uncontrolled comorbid illness or condition including congestive heart failure, unstable angina, cardiac arrhythmia, or psychiatric illness that would limit compliance with the study requirements.
• 4. Psychiatric illness/social situations that would limit consenting and compliance with study requirements.
• 5. Participants who are pregnant or nursing due to the potential for congenital abnormalities and the potential of this regimen to harm nursing infants