The present study aimed to assess the impact of chest radiotherapy combined with immunotherapy at different time points in lung injury. This retrospective study analyzed 35 patients with thoracic tumors (29 lung cancer cases and 6 esophageal cancer cases) who received radiotherapy combined with immunotherapy between January 2021 and December 2023 at at Capital Medical University, affiliated with Beijing Luhe Hospital (Beijing, China), with a median follow-up time of 21 months. Patients were divided into two groups: Group A (sequential, n=17), who received immunotherapy 2 weeks to 6 months before or after radiotherapy, and group B (synchronous, n=18), who received immunotherapy within 2 weeks before or after radiotherapy. Furthermore, the incidence and severity of lung injury, especially pneumonitis, were also compared. Moreover, risk factors for lung injury, as well as 3-year overall survival (OS) rates for stage III and IV lung cancer, were evaluated. There were no significant differences in tumor location, stage, age, tumor type, Eastern Cooperative Oncology Group score or sex between groups. The proportion of PD-1 in group A was higher, while the proportion of PD-L1 was lower, compared with that in group B. Furthermore, radiotherapy techniques and dosimetric parameters were also similar. Moreover, there were no significant differences in onset time between esophagitis, anemia or pneumonitis between the two groups. However, incidence of grade 3 or higher pneumonitis was 0.0% in the sequential group and 23.5% in the synchronous group, which was significantly different. Univariate analysis identified lung mean dose and the percentage volume receiving ≥30 Gy (V