This randomized controlled non-inferior trial prospectively enrolled patients with limited-stage small cell lung cancer (LS-SCLC). Patients in the experimental group would receive radiotherapy with omission of the clinical target volume (CTV) for the primary tumor, while those in the control group would receive radiotherapy including CTV. The efficacy and toxicity of the two groups are compared to provide evidence for the radiotherapy of LS-SCLC. The target volume of LS-SCLC may be reduced by omitting CTV without increasing local recurrence but potentially reducing the dose to organs at risk and the side effects.

Inclusion Criteria:

1. Small cell lung cancer confirmed by histology or cytology; TNM stage IA-IIIC (AJCC 8th edition, 2017; limited-stage) without intrapulmonary metastasis;
2. Aged 18-75 years, KPS score ≥ 80, ≤ 10% weight loss within the past 6 months;
3. Have measurable lesions per RECIST 1.1 criteria;
4. Have no disease progression after 2-4 cycles of etoposide/carboplatin or etoposide/cisplatin;
5. Lung function test: FEV1 ≥ 1 L (Optional);
6. Complete blood count: neutrophil count ≥ 1.5 x 10^9/L, hemoglobin ≥ 100 g/L, platelet count ≥ 100 x 10^9/L;
7. Renal function: serum creatinine ≤ 1.5 x upper limit of normal (ULN);
8. Liver function: AST and ALT ≤ 2.5 x ULN, bilirubin ≤ 1.5 x ULN;
9. Fully understand the study, able to complete treatment and follow-up, and voluntarily sign the informed consent.

Exclusion Criteria:

1. Other malignant tumors (prior or concurrent), except those that have been curatively treated with disease-free survival ≥ 5 years, such as non-melanoma skin cancer, cervical carcinoma in situ, or early-stage papillary thyroid cancer;
2. Uncontrolled heart disease or myocardial infarction within the past 6 months;
3. Patients with a history of mental illness;
4. Pregnant and lactating patients;
5. Poorly controlled diabetes and hypertension;
6. Interstitial pneumonia or active pulmonary fibrosis;
7. Active infection;
8. Other conditions unsuitable for enrollment (per investigator judgment).