• Voluntary participation and written signed informed consent;

• Age 18-75 years old, gender is not limited;

• Histologically or cytologically confirmed limited-stage small cell lung cancer (2009 AJCC/UICC/IASLC lung cancer TNM staging criteria, limited-stage SCLC is any T stage, any N stage, and M0), and patients with suspected brain or bone metastasis at the time of screening should undergo brain MRI or ECT before study enrollment;

• There are immunohistochemical results;

• Chemotherapy must include either cisplatin or carboplatin, in combination with etoposide;

• Physical status score ECOG 0-1;

• Weight \> 40 kg;

• Expected survival ≥ 6 months;

• According to RECIST 1.1 guidelines, at least one lesion (not previously receiving radiotherapy) with a maximum diameter ≥ 10 mm as accurately measured by computed tomography (CT) or magnetic resonance imaging (MRI) at baseline (except lymph nodes, whose short axis must be ≥ 15 mm); And the lesion is suitable for repeated accurate measurement.;

• No previous immunotherapy;

• no serious abnormalities of haematopoietic, cardiac, pulmonary, hepatic; and renal functions and immunodeficiency (Haematology: white blood cells ≥3.5×109/L; neutrophils ≥1.5×109/L; haemoglobin ≥90g/L; platelets

• ≥100×109/L. Liver and kidney function: total bilirubin ≤1.5 times the upper limit of normal (ULN); AST (SGOT) and ALT (SGPT) ≤2.5 times the upper limit of normal; creatinine ≤1.5 times the upper limit of normal; albumin ≥30 g/L. Coagulation: International Normalised Ratio (INR) or Prothrombin Time (PT) or Activated Partial Thromboplastin Time (APTT)

• ≤ 1.5 times ULN; if the subject is receiving anticoagulation therapy, PT or INR is acceptable as long as the PT or INR is within the range of the anticoagulant drug formulation. Echocardiographic assessment: left ventricular ejection fraction (LVEF) ≥ low limit of normal (50%). Pulmonary function FEV1 ≥70% of % of predicted value and DLCO ≥60% of % of predicted value).

• The female patient has evidence of postmenopausal status, or the urine or serum pregnancy test results of the premenopausal woman are negative. Women who stop menstruating for 12 months without other medical reasons are considered menopausal.