Inclusion Criteria:

• Histologically confirmed diagnosis of adenocarcinoma of the rectum;
• Tumors located at mid or low rectum (distal extension less than 10 cm from the anal verge);
• Clinical stage II or III (T3/4 and/or N+; no distant metastasis);
• No prior chemotherapy, radiotherapy or surgery for rectal cancer;
• Age ≥20;
• ECOG 0-1;
• Adequate organ function, including followings:

ANC ≥1,500/μL; Hb ≥8.0 gm/dL; Platelet 100,000/mm3; Total bilirubin ≤1.5x upper normal limit; AST ≤3x upper normal limit; ALT ≤3x upper normal limit; Creatinine ≤1.5x upper normal limit;

• Ability to understand and the willingness to sing a written informed consent.

Exclusion criteria

• Recurrent rectal cancer;
• Patients who have concomitant malignancies, except for adequately treated basal cell carcinoma of the skin or in situ carcinoma of the cervix. Subjects who have prior malignancies and have been disease-free for more than 5 years can be enrolled;
• Patients who have received prior pelvic radiotherapy;
• Patients with active infection requiring intravenous antibiotic treatment;
• Patients with a history of any arterial thrombotic event within the past 6 months, including unstable angina, myocardial infarction (MI) or cerebrovascular accident (CVA), New York Hear Association (NYHA) grade II or greater congestive heart failure, or uncontrolled cardiac arrhythmia;
• Patients with any other concurrent medical or psychiatric condition or disease which, in the investigator's judgement, would make them inappropriate candidates for entry into this study;
• Women who are pregnant or breastfeeding. Women of childbearing potential who are unwilling or unable to use an acceptable method of birth control to avoid pregnancy for the entire study period;
• Patients receiving other anticancer or experimental therapy;
• Known DPD deficiency or hypersensitivity to oxaliplatin;
• Any contraindications to MRI.

History of severe allergic reactions to study medication Currently pregnant or breastfeeding Recent participation in another clinical trial within the last 30 days Presence of uncontrolled medical conditions that could affect safety