Inclusion Criteria:  Patient aged 18 or more, Patient treated for histologically proven non-small cell lung cancer, Stage IIIB or IV, Performance status 0 to 2, Patient treated by immunotherapy (anti PD-1 or anti PD-L1) started for at least 6 months and regardless of the treatment line (in first line, immunotherapy may have been combined with chemotherapy), Response or stable disease on thoraco abdomino pelvic and cerebral CT scan, Maximum 5 residual hypermetabolic lesions measured on the 18F-FDG PET / CT centrally reviewed, including primary tumor and a maximum of 3 asymptomatic brain metastases (even if they are poorly seen in 18F- FDG PET/CT) treatable in stereotactic radiotherapy (extracerebral lesions ≤ 4cm and brain lesions ≤ 3cm measured on CT scanners) Effective contraception used in women of childbearing potential Written informed consent obtained from the patient prior to performing any protocol-related procedures, including screening evaluations, Patient is willing and able to comply with the protocol for the duration of the study including undergoing treatment and scheduled visits and examinations including follow up, Patient has valid health insurance.  Exclusion Criteria:  Persistence of grade 2 or greater adverse effects of immunotherapy, Infection in progress, At least one of the 5 hypermetabolic lesions measured on the 18F-FDG PET / CT centrally reviewed in a previously irradiated area, Uncontrolled severe comorbidity, History of another primary malignancy except for Malignancy treated with curative intent and with no known active disease ≥ 3 years and of low potential risk for recurrence ; Adequately treated non-melanoma skin cancer or lentigo maligna without evidence of disease ; Adequately treated carcinoma in situ without evidence of disease Pregnant or nursing patient Patient deprived of liberty or under guardianship, Patient unable to undergo regular medical check-ups for geographical, social or psychological reasons. Disorder precluding understanding of trial information or informed consent