Linear Energy Transfer (LET)-Optimized Intensity Modulated Proton Therapy (IMPT) as a Component of Definitive Chemoradiation for Newly Diagnosed Squamous Cell Carcinoma of the Anal Canal: a Feasibility Trial

Inclusion Criteria: * Histologically-proven, non-metastatic invasive primary squamous cell carcinoma of the anal canal (stages I, II, and III) * History/physical examination including documentation of the primary anal lesion size, distance from the anal verge and anal sphincter tone within 60 days prior to registration * Anal examination with biopsy on either colonoscopy, sigmoidoscopy, rigid proctoscopy or anoscopy * Computed tomography (CT) scan of the chest and abdomen with contrast or contrast-enhanced positron emission tomography (PET)/CT scan within 60 days of registration unless the patient has a documented contrast allergy * CT scan of pelvis with contrast or contrast-enhanced PET/CT scan within 60 days of registration unless the patient has a documented contrast allergy * Zubrod performance status of 0-1 within 60 days prior to registration * Absolute neutrophil count (ANC) \>=1.8 K/ul, cannot be achieved through granulocyte-colony stimulating factor (GCSF) (within 30 days prior to study registration) * Platelets \>= 100 K/uL, cannot be achieved through transfusion (within 30 days prior to study registration) * Hemoglobin \>= 8 g/dL, cannot be achieved through transfusion (within 30 days prior to study registration) * Serum creatinine =\< 1.5 mg/dL (within 30 days prior to study registration) * Bilirubin =\< 1.4 mg/dL, except in the case of patients with Gilbert's disease (within 30 days prior to study registration) * White blood cells (WBC) \>= 3000/microliter (wit…