Most local failures after definitive chemoradiation for unresectable esophageal cancer occur in the gross tumor volume (GTV). And the metabolic active areas post-treatment were located in the high FDG uptake areas prior to the radiotherapy. The hypothesis is that selective dose boost to the esophageal GTV could be safely delivered using a simultaneous integrated boost (SIB) technique, and that boosting the high 18F-deoxyglucose (FDG) uptake areas of the esophageal GTV defined prior to treatment may improve local tumor control.

Inclusion Criteria:

1. Histopathologically proven diagnosis of esophageal squamous cell carcinoma.
2. ECOG performance status 0-1.
3. Able to swallow semifluid diet.
4. Patients must not have received either radiotherapy or chemotherapy.
5. Technically unresectable, medically inoperable, or surgery declined by the patient.
6. SUVmax in the pre-treatment FDG-PET scan > 5 for the primary tumor and the length of the primary tumor ≤10cm.
7. Normal liver and renal function and adequate bone marrow reservation.
8. Meet the requirements of the dose limitation to the critical organ: V20≤25%，Dmean≤15Gy for lung; Dmax ≤45Gy for spinal cord，Dmean ≤20Gy for liver.
9. Written, signed informed consent.

Exclusion Criteria:

1. Other malignancy histology.
2. Any evidence of visceral metastases.
3. Prior radiotherapy to the thorax or systemic therapy for esophageal cancer.
4. Evidence of deep esophageal ulcer or esophageal perforation.
5. Weight loss ≥10% within half year or cachexia.
6. Other co-existing malignancies or malignancies diagnosed within the last 5 years with the exception of basal cell carcinoma or cervical cancer in situ.
7. History of cardiac disease: congestive heart failure > NYHA class 2, active CAD, cardiac arrythmias requiring anti-arrhythmic therapy or uncontrolled hypertension within the last 12 months.
8. Concurrent uncontrolled medical conditions.
9. Pregnant or lactating women.
10. Drug addiction, alcoholism or AIDS.
11. Uncontrolled seizures or psychiatric, behavioural disorders.