A Randomized Controlled Trial Evaluating of Prophylactic Irradiation in CRT for cT1bN0M0 ESCC

Inclusion criteria: 1. Histologically proven squamous cell carcinoma, adenosquamous carcinoma, or basaloid cell carcinoma. 2. All lesions located in the thoracic esophagus. Secondary lesions with an absolute indication for endoscopic resection (EMR/ESD) may not be confined to the thoracic esophagus. 3. Clinical N0M0 with cervical to abdominal contrast-enhanced CT. 4. The deepest lesion is diagnosed as cT1b (SM1 / SM2 / SM3) with upper gastrointestinal endoscopy. If it is difficult to differentiate cT1a-MM and cT1b-SM1 clinically, the wall depth is diagnosed as cT1b-SM1. 5. Aged 20 years and older. 6. ECOG Performance status 0 or 1. 7. No previous therapy against esophageal cancer except for complete resection by EMR/ESD with either pT1a-LPM (pM2) / pT1a-MM (M3) disease or pT1a-MM (M3) disease without vascular infiltration. 8. No history of radiotherapy for the neck, chest, and upper abdomen for any cancers. No chemotherapy or hormone therapy with less than 3 years of disease-free interval for any cancers. 9. Major organ function is preserved. 1) WBC\<=12,000/mm3 2) ANC\>=1,500/mm3 3) Hb\>=10.0 g /dL 4) PLT\>=10,000/mm3 5) T-bil\<=1.5 mg /dL 6) AST\<=100 IU/L 7) ALT\<=100 IU/L 8) SpO2\>=95% 9) Ccr\>=60 mL/min 10. Patients do not have a preference to receive a surgical resection as an initial therapy after receiving explanations. 11. Written informed consent is obtained. Exclusion criteria: 1. Simultaneous or metachronous (within 5 years) double cancers, except for intramucosal tumor curable with local therapy. 2. Active infection requiring systemic therapy. 3. Fever over 38 degrees Celsius 4. Female during pregnancy, within 28 days of post parturition, or during lactation. Male who wants a partner's pregnancy. 5. Psychological disorder, which is difficult to participate in this clinical study. 6. Receiving continuous systemic corticosteroid or immunosuppressant treatment. 7. Positive for HBs antigen or HIV antigen. 8. Diabetes mellitus, which is uncontrollable with continuous use of insulin or hypoglycemic agents. 9. Uncontrolled arterial hypertension. 10. History of unstable angina pectoris within three weeks or myocardial infarction within six months before registration. 11. Uncontrolled valvular disease, dilated cardiomyopathy, and hypertrophic cardiomyopathy. 12. Severe emphysema, interstitial pneumonia or pulmonary fibrosis based on chest CT. 13. With a history of cerebrovascular disorder within 6 months. 14. Drug allergy for iodic drugs.