MR-Adaptive Radiation Therapy for Anal Cancer With EScalated-Treatment in a Risk-Optimized Approach

Inclusion Criteria: * Patients with pathologically proven diagnosis of anal SCC. This may include tumors of non-keratinizing histology such as basoloid or cloacogenic histology. Individuals with squamous cell carcinoma of the anal margin are eligible. * Clinical stage T1-4 N0-1 M0 (the Union for International Cancer Control (UICC) / the American Joint Committee on Cancer (AJCC) 8th Ed) * Patients must be eligible for definitive RT or CRT * Must be ≥ 18 years of age * Must have an Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 Exclusion Criteria: * Previous chemotherapy, RT or curative-intent surgical treatment (i.e. APR) for anal cancer. * Any previous RT to the abdomino-pelvic region that would result in overlap of RT volume for the current study. * Individuals with a history of a different malignancy except if they have been disease-free for at least 2 years and are deemed by the investigator to be at low risk for recurrence. Individuals with the following cancers are eligible if diagnosed and treated within the past 5 years: cervical cancer in situ, and basal cell or squamous cell carcinoma of the skin.