Short Course Radiation Therapy and Combination Chemotherapy for the Treatment of Stage II-III Rectal Cancer

Inclusion Criteria: * Histologically confirmed rectal adenocarcinoma * Patients must have stage II (cT3, cN0) or stage III (cT1-3, cN1-3) tumor as staged by MRI * No evidence of metastatic disease * Resectable primary lesion * Karnofsky performance status (KPS) \>= 70 or Eastern Cooperative Oncology Group (ECOG) 0-2 * Absolute neutrophil count (ANC) \> 1.5 cell/mm\^3 * Hemoglobin (Hgb) \> 8.0 gm/dL * Platelets (PLT) \> 150,000/mm\^3 * Total bilirubin \< or equal to 1.5 x upper limit of normal * Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) \< or equal to three times upper limit of normal * If a woman is of childbearing potential, a negative serum pregnancy test must be documented prior to initiation of radiation therapy Exclusion Criteria: * Active treatment of a separate malignancy * Distant metastatic disease as assessed by staging positron emission tomography (PET)/computed tomography (CT) or CT of the chest and abdomen within 6 weeks of starting radiation therapy * Prior radiotherapy to the region of the study cancer that would result in overlap of radiation therapy fields * Pregnant and/or breastfeeding * Medical/psychological contraindication to MRI