• The subject voluntarily joins the study, signs the informed consent form, and has good compliance;

• Age: 18\

⁃ 75 years old (when signing the informed consent form); ECOG PS score: 0-1 points; Expected survival beyond 6 months; body weight\> 40 kg;

• Patients with pathologically confirmed limited-stage small cell lung cancer (according to the Veterans Administration Lung Study Group (VALG stage);

• Through the neck, chest, abdomen, pelvic enhanced CT and brain plain scan + enhanced MRI examination with diagnostic quality, there is no evidence of metastatic disease (PET-CT examination is recommended before starting radiotherapy and chemotherapy, if not performed before radiotherapy and chemotherapy PET-CT examination, bone scan examination should be performed; PET-CT examination must be performed during the screening period after chemoradiotherapy to exclude metastasis);

• It is expected that no tumor resection will be required during the study (patients who are not suitable for surgery or those who are unwilling to undergo surgery are acceptable);

• Radiotherapy technology adopts three-dimensional conformal radiotherapy, conformal intensity-modulated radiotherapy, tomographic radiation therapy and other precision radiotherapy technologies;

• Patients must achieve CR, PR or SD after receiving radical platinum-based CRT and cannot develop disease progression;

• Patients with at least one measurable lesion confirmed according to RECIST 1.1 criteria prior to chemoradiotherapy;