Inclusion Criteria:  Patients with esophageal cancer who received definitive radiotherapy (radiotherapy dose ≥50Gy) from 2015 to 2016 Age ≥ 18 The radiation field included primary esophageal tumor with or without lymph node metastasis  Exclusion Criteria:  Radiotherapy dose < 50Gy Palliative radiotherapy The radiation field are metastatic areas, such as bone, brain, adrenal gland, isolated metastatic lymph nodes, etc