This trial is a multicenter, perspective, non-blinded, randomized controlled phase 3 trial. In order to establish whether the SIB technique can improve the results of twice-daily chemo-RT for patients with LS-SCLC, the investigators will primarily compare survival of patients treated with standard chemotherapy (cisplatin and etoposide) and either SIB twice-daily RT or standard dose twice-daily RT.

Three hundred and twenty-six patients with a histological or cytological proven diagnosis of SCLC will be recruited from 35 centers in 14 areas including provinces, municipalities and autonomous region, from May 2017 to May 2020.

Inclusion Criteria:

• Read the patient information and Sign the informed consent before enrollment
• Either sex, age ≥18 and ≤70
• Histologically or cytologically confirmed SLCL
• Limited stage disease(AJCC, 2009 version 7), stage I-III(T any, N any, M0) that can be safely treated with definitive radiation doses, excludes T3-4 due to multiple lung nodules that are too extensive or have tumor/nodal volume that is too large to be encompassed in a tolerable radiation plan, clinical nonmalignant diagnosis by investigator when the pleural is too few to obtain cytological evidence.
• measurable lesion according RECIST 1.1
• PS ECOG 0-1
• having zero to two cycles of systemic chemotherapy with etoposide and cisplatin (cisplatin 60-80 mg/m2 at day1 or divided into two to three days, etoposide 100-120 mg/m2 at day 1 to 3, Q21d, and the treatment delay between two cycles shouldn't be more than 14days).
• patients especially female patients must satisfy the investigator that they are not pregnant, or are not of childbearing potential, or are using adequate contraception. Man must also use adequate contraception
• adequate haematological function: white blood cell ≥3.0×109/L , neutrophils ≥1.5×109/L, platelet ≥100×109/L, hemoglobin ≥90g/L.
• adequate liver and renal function: total bilirubin ≤1.5 ×upper limit normal , alanine transaminase and aspartate aminotransferase ≤1.5 ×upper limit normal, normal serum creatinine and/or calculated creatinine clearance ≥60ml/min.

Exclusion Criteria:

• prior surgical resection of the primary tumor or prior RT for lung cancer
• mixed small-cell and non-small-cell histological features
• contemporaneous immunotherapy or target therapy
• pregnancy or lactation
• physical or mental disease that could impact treatment plan
• unable to understand the trial, or could not follow the process
• to refuse the sign the informed consent.
• no history of previous malignancy in the past 5 years (except non-melanomatous skin or in situ servix carcinoma)
• be allergic to any known protocol in this trail
• be enrolled in other clinical trial in past 30days

undecided