Radiotherapy in Patients With Metastatic Esophageal Cancer Responding to PD-1 Inhibitor Plus Chemotherapy

Inclusion Criteria: * 1\. ≥18 years, any gender * 2\. Histologically or cytologically confirmed squamous cell carcinoma of esophageal cancer. The initial clinical stage is IVb (2018 AJCC Cancer Staging Manual, 8th Edition) or recurrent patients with recurrence after radical treatment (radical treatment includes surgery and radiotherapy, but the recurrence site cannot be located in the previous radiotherapy field). * 3\. ECOG performance status \<= 1. Patients aged 65 years and over need to complete G8 screening or Comprehensive Geriatric Assessment, and the final evaluation is good; * 4.There was no significant abnormality in laboratory routine indicators such as blood routine and liver and kidney function; * 5.For patients after definitive or preoperative radiotherapy, no recurrence was in the prior radiation filed; * 6.Expected survival is more than 12 weeks; * 7.Informed consent provided; * 8.With response to 2-4 cycles of the first-line chemotherapy combined with immunotherapy. Exclusion Criteria: * 1.Patients with other cancer history except hypopharyngeal carcinoma in situ, non-malignant skin cancer and cervical carcinoma in situ. * 2.Received surgery (except ostomy), chemotherapy or other anti-tumor treatment before enrollment； * 3\. Active infection currently exists . The following conditions occurred within 6 months before randomization: myocardial infarction, cerebrovascular accident, or received gastrointestinal, neurological, cardiopulmonary surgery; * 4\. History of allergy to chemotherapy drugs or autoimmune disease; * 5\. Participate in other clinical trials at present or within 4 weeks before enrollment; * 6.There are factors such as high risk of fistula that radiotherapy cannot be safely carried out as assessed by the radiation oncologist.