To Evaluate the Safety and Efficacy of Thoracic Radiotherapy for?ES-SCLC After First Line Treatment with Immune Checkpoint Inhibitors.

Inclusion Criteria:

• Age at least 18 years.
• ECOG PS 0-1.
• Histological or cytological syndrome of small cell lung cancer, imaging evaluation staging is extensive
• Life expectancy >= 3 months.
• Patients are non-progressed after 4 dosed of immunotherapy plus platinum based chemotherapy, with residual thoracic lesions
• Palliative radiotherapy were allowed except for TRT, the interval > 4 weeks
• Adequate organ function prior to enrollment:
• Adequate bone marrow function: white blood cell (WBC) count ≥ 3.0 * 10 ^ 9/L or neutrophil count ≥ 1.5 * 10 ^ 9/L, platelet count ≥ 100 * 10 ^ 9/L and hemoglobin ≥90g/L,;
• Adequate hepatic function: total bilirubin, urea nitrogen and serum creatinine≤ 1.5 x upper limit of normal (ULN). Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) ≤2.0 ULN;
• Sufficient heart and lung function, EF>55%FEV1>50%
• Ability to understand and willingness to provide the informed consent.
• Women of childbearing age and men must agree to use effective contraception during the trial.

Exclusion Criteria:

• History of another malignancy or concurrent malignancy;
• Mixed small cell with non-small cell lung cancer histology;
• History of thoracic radiotherapy;
• Malignant pleural or ascites;
• Patients with leptomeningeal metastasis or uncontrolled brain;
• Severe autoimmune disease: inflammatory bowel disease (including Crohn's disease and ulcerative colitis), rheumatoid arthritis, scleroderma, systemic lupus erythematosus, Wegener's granulomatosis and related vasculitides.
• Symptomatic interstitial lung disease or clinically active infectious/non-infectious pneumonitis.
• Active infection, congestive heart failure, or any evidence of myocardial infarction, unstable angina pectoris or cardiac arrhythmia within 6 months prior to enrollment.
• The patient is pregnant (confirmed by serum b-HCG if applicable) or is breastfeeding.
• Mental disorders, drug abuse, and social condition that may negatively impact compliance in the investigator's opinion.