Inclusion Criteria:  Experimental group:  18 years old ≤ age ≤ 75 years old, no gender limitation; NSCLC who have received radiotherapy for brain lesions + PD-1/PD-L1 immunotherapy; Histologically confirmed as NSCLC; Imaging confirmed brain metastasis (CT or MRI); The presence of imaging-evaluable lesions can be evaluated in accordance with RECIST 1.1  Control group:  1 18 years old ≤ age ≤ 75 years old, no gender limitation; 2 NSCLC who has received radiotherapy for brain lesions; 3 Histologically confirmed as non-small cell lung cancer; 4 Imaging confirmed brain metastasis (CT or MRI); 5 The presence of imaging-evaluable lesions can be evaluated in accordance with RECIST 1.1  -  Exclusion Criteria:  1 The age is less than 18 years old, regardless of gender; 2 Histologically confirmed as NSCLC 3 Imaging confirmed the absence of brain metastases 4 NSCLC with brain metastasis only received chemotherapy or targeted therapy, and did not receive radiotherapy or immunotherapy  -