This study is expected to enroll 182 patients with partial response or stable disease after first-line immunochemotherapy for extensive-stage small cell lung cancer and eligible for thoracic consolidation radiotherapy within 2 years. Patients were randomized 2:1 to immune single-agent maintenance therapy in combination with hyperfractionated high-dose radiotherapy and immune single-agent maintenance therapy after being assessed by the investigator as otherwise eligible for enrollment. Patients in both arms received maintenance therapy with the PD-L1 inhibitor, atezolizumab or dulvedolizumab, until disease progression, unacceptable toxicity, or loss of clinical benefit. Patients in the combined radiotherapy arm required hyperfractionated high-dose (54 Gy) radiotherapy twice daily for residual disease in the chest. Each patient will be followed for approximately 2 years.