After the treatment of advanced non-small cell lung cancer with immune checkpoint inhibitor PD-1/PD-L1 monoclonal antibody, if the treatment response of complete response (CR) or partial response (PR) can be achieved in the early stage, the patients are expected to obtain a better long-term survival rate. Radiotherapy can synergistically improve the effect of immunotherapy. Therefore, we propose a hypothesis: in patients with advanced lung cancer, if only stable disease (SD) is achieved after PD-1 antibody immunotherapy in the early stage, by increasing the stereotactic radiotherapy (SBRT) for primary or metastatic lesions, in order to improve the mechanism of tumor antigen release, promote the activation and activation of effector T cells, and increase the sensitivity of immunotherapy, so as to achieve the goal of early improvement of objective remission rate (ORR). It is expected to improve the long-term survival rate of patients.

Inclusion Criteria:

1. Informed consent has been signed, and according to the judgment of the investigator, the patient can comply with the study protocol;
2. Patients with stage IIIB, IIIC and stage IV NSCLC (according to the definition of the 8th edition of the American Joint Commission on cancer), who have not been treated and cannot receive radical surgery or radiotherapy confirmed by histopathology, received 3-4 cycles of PD1 antibody ± chemotherapy in the early stage, and the efficacy was evaluated as SD;
3. Previously, no EGFR sensitive mutation and ALK, ROS1 gene fusion mutation were detected based on tissue examination;
4. There are measurable lesions evaluated by researchers according to RECIST version 1.1;
5. The physical state score (ECOG PS) of the eastern cancer cooperation group was 0-1;
6. Good cardiopulmonary function

Exclusion Criteria:

1. The patient's compliance is poor and violates the test regulations;
2. Patients with positive driver gene are known to carry EGFR mutation or ALK, ROS1 gene translocation;
3. There are dysfunction of important organs of liver and kidney, such as myocardial infarction, angina pectoris, liver transaminase significantly increased;
4. Serious adverse drug reactions occurred during induction;
5. Have suffered from any disease requiring systemic treatment with corticosteroids or other immunosuppressive drugs within 14 days before enrollment;
6. Severe infection occurred within 4 weeks before enrollment, including but not limited to hospitalization due to infection complications, bacteremia or severe pneumonia;
7. Severe chronic or active infection (including tuberculosis infection) requiring systemic (oral or intravenous) antibiotic treatment within 14 days before enrollment;
8. Have a history of interstitial lung disease, non infectious pneumonia or poorly controlled diseases, including pulmonary fibrosis, acute lung disease, etc;
9. Untreated patients with chronic hepatitis B, HBV carriers with hepatitis B virus (HBV) DNA ≥ 500 iu/ml, or patients with active hepatitis C virus (HCV) should be excluded;
10. Known history of HIV infection;
11. Received any other trial drug treatment or participated in other clinical trials within 28 days.

Patients with stage IIIB, IIIC and stage IV NSCLC (according to the definition of the 8th edition of the American Joint Commission on cancer), who have not been treated and cannot receive radical surgery or radiotherapy confirmed by histopathology, received 3-4 cycles of PD1 antibody ± chemotherapy in the early stage, and the efficacy was evaluated as stable disease