Ultra-fractionated Radiotherapy for Rectal Cancer

To determine the maximal tolerated dose (MTD) of dose-escalated hypofractionated adaptive RT, in patients with locally advanced rectal cancer treated with RT, FOLFOX (5-FU, oxaliplatin, leucovorin) or CAPOX (capecitabine, oxaliplatin) chemotherapy and selective omission of surgery.

Inclusion criteria

• At least 18 years of age. Both men and women and members of all races and ethnic groups will be included.
• Willing and able to provide written informed consent
• Pathologic diagnosis of rectal adenocarcinoma
• T3-4 and/or N+ disease per AJCC 8th edition
• No prior treatment for rectal adenocarcinoma
• Eastern Cooperative Group (ECOG) performance status of 0-2.
• 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.
• 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.

A female of child-bearing potential is any woman (regardless of sexual orientation, marital status, having undergone a tubal ligation, or remaining celibate by choice) who meets the following criteria:

• 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).

Exclusion criteria

• Distant nodal disease (retroperitoneal nodes) including inguinal nodes, or any metastatic disease by CT.
• Prior RT to the pelvis.
• Uncontrolled comorbid illness or condition including congestive heart failure, unstable angina, cardiac arrhythmia, or psychiatric illness that would limit compliance with the study requirements.
• Psychiatric illness/social situations that would limit consenting and compliance with study requirements.
• Participants who are pregnant or nursing due to the potential for congenital abnormalities and the potential of this regimen to harm nursing infants