Objective:To evaluate the safety and tolerance of sequential thoracic radiotherapy combined with PD-1/PD-L1 inhibitors in patients with extensive-stage small cell lung cancer (ES-SCLC) after induction systemic therapy.Methods:ES-SCLC patients from a phase I trial and a real-world study were enrolled for those who received thoracic radiotherapy after induction systemic treatment (chemotherapy/chemotherapy combined with PD-1/PD-L1 inhibitors) and consolidated with PD-1/PD-L1 inhibitors. These two studies were both approved by the Ethics Committee of Chinese Academy of Medical Sciences Cancer Hospital (Clinical Trials.gov number, NCT03971214, NCT04947774).Results:Between January 2019 and March 2021, a total of 11 patients with ES-SCLC were analyzed, aged 52-73 years, with a median age of 62 years. Among them, five patients (45.5%) received induction chemotherapy and six patients (54.5%) received chemotherapy combined with PD-1/PD-L1 inhibitor, and then all received intensity-modulated thoracic radiotherapy after evaluation of systemic treatment efficacy. Two patients developed treatment-related grade G3-5 toxicity (18.2%, 1 treatment-related pneumonitis and 1 radiation esophagitis). G 1-G 2 hematologic toxicity, pneumonia, and anorexia were common mild toxicities. Only one patient (9.1%) terminated immunotherapy due to immune-related pneumonitis. During a median follow-up time of 12.5 months (range: 3.5-16.4 months), the median disease progression-free survival and overall survival was 7.4 months (95% CI: 6.9-8.0 months) and 14.6 months (95% CI: 9.0-20.2 months), respectively. Conclusions:Sequential thoracic radiotherapy followed by PD-1/PD-L1 inhibitor is safe and feasible in patients with ES-SCLC after induction therapy. Given that both thoracic radiotherapy and immunotherapy benefits the ES-SCLC in survival, this comprehensive treatment modality warrants further investigation.