Objective:To investigate the effect and adverse reactions of radiotherapy combined with targeted drugs for the treatment of multiple brain metastases (MBM) in patients with non-small cell lung cancer (NSCLC) and the changes in serum tumor marker levels.Methods:A retrospective cohort study was conducted. Eighty-six patients with NSCLC-MBM who were admitted to the Fifth People's Hospital of Datong from June 2019 to June 2022 were selected, and the patients were divided into the study group and the control group according to different treatment methods, with 43 cases in each group. The study group was given radiotherapy to the tumor primary focus combined with erlotinib or gefitinib targeted therapy, and the control group was given radiotherapy to the tumor primary focus based on conventional chemotherapy with pemetrexed combined with platinum-based drugs. The efficacy, overall survival rate and incidence of adverse reactions were compared between the two groups at 1 month after treatment; the levels of serum tumor markers S100-β, carcinoembryonic antigen (CEA), squamous cell carcinoma antigen (SCCA) were compared between the two groups before and after treatment.Results:The study group was aged (55±5) years old, ranging from 39 to 75 years old, including 15 (34.88%) males and 28 (65.12%) females; the control group was aged (54±5) years old, ranging from 38 to 72 years old, including 17 (39.53%) males and 26 (60.47%) females. The general data such as age and gender of patients were compared between the two groups, and the differences were not statistically significant (all P>0.05). The objective remission rate [53.49% (23/43) vs. 32.56% (14/43)] and disease control rate [93.02% (40/43) vs. 69.77% (30/43)] at 1 month after treatment, and 1-year overall survival rate [58.14% (25/43) vs. 46.51% (20/43)] of the study group were higher than those of the control group, and the differences were statistically significant ( χ2 values were 10.91, 5.76 and 11.02, respectively; P values were 0.001, 0.016 and 0.001, respectively). Before treatment, the differences in serum S100-β, CEA and SCCA levels between the two groups of patients were not statistically significant (all P > 0.05). At 1 month after treatment, the serum S100-β, CEA and SCCA levels of the study group were lower than those of the control group, and the differences were statistically significant (all P < 0.05). The proportion of patients with adverse reactions in the study group was lower than that in the control group [13.95% (6/43) vs. 39.53% (17/43)], and the difference was statistically significant ( χ2 = 8.35, P < 0.05). Conclusions:Radiotherapy combined with targeted drugs therapy may prolong the survival of NSCLC-MBM patients, reduce the occurrence of adverse reactions and decrease the levels of serum tumor markers, which is worthy of clinical promotion.