Preoperative Sequential Short-course Radiation Therapy and FOLFOX for Locally Advanced Rectal Cancer

Inclusion Criteria: * Asian * ECOG (Eastern Cooperative Oncology Group) performance status 0-2 * Pathologically confirmed rectal cancer (rectal cancer located 10 cm or low from the anal verge in pelvis MRI) * Histologic type: adenocarcinoma, mucinous carcinoma, and signet ring cell carcinoma * Locally advanced rectal cancer with one or more of the following factors based on pelvis MRI: cTanyN1-2, cT3-4N0, or presence of extramural vascular invasion * MRI findings such as pelvic lymph node metastasis, anal sphincter invasion, and T4b are not included in the exclusion criteria, which cases will be enrolled by the researcher's discretion * Patients with appropriate organ (bone marrow, kidney, liver) function * A person who understands the study and willing to provide informed consent Exclusion Criteria: (one of the following criteria) * Colon cancer or rectal cancer located more than 10 cm from the anal verge * Stage I rectal cancer (clinical stage cT1-2N0) * Clinically or pathologically diagnosed distant metastasis (cTanyNanyM1) * Familial adenomatous polyposis * Hereditary nonpolyposis colorectal cancer * History of chemotherapy or radiotherapy within 6 months * History of colorectal cancer or other type of malignancy within 5 years (except for cured nonmelanoma skin or in situ cervical cancer) * Comorbidities that make it difficult to undergo chemotherapy or radiotherapy * Bone marrow suppression with neutrophil count \<2 ×109/L or platelet count \<100 ×109/L prior to the first chemotherapy * Peripheral sensory neuropathy with functional impairment (grade 2 or higher) * Severe renal dysfunction (GFR ≤30ml/min by Wright or Cockroft formula) * Severe hepatic dysfunction * Genetic problems such as galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption * Taking tegafur, gimeracil, and oteracil potassium complex and those within 7 days of discontinuation * Taking sorivudine or brivudine * Significant heart disease or myocardial infarction within the last 6 months * Hereditary diseases or history of coagulopathy * Central nervous system disorders with disability or mental disorders * Pregnant or lactating women * Currently participating in other clinical trials or receiving research medication * Unhealed wounds, fractures, peptic ulcer, abscesses in the abdominal cavity * Active gastrointestinal bleeding * Active infections requiring antibiotics for injection * Emergency Surgery * History of hypersensitivity to the drugs in study protocol * Patients with non-malignant tumor diseases * Dihydropyrimidine dehydrogenase deficiency * Not willing to participate