Inclusion Criteria:

          1. Histologically or cytologically confirmed non-small cell lung cancer (NSCLC)

          2. Stage IV metastatic disease with intra-cranial progressive disease documented by MRI
             evidence

          3. Patient with 1 to 4 brain metastases (< 3.5 cm on T1 post-gadolinium sequence) all
             amenable to hFSRT, with at least 1 metastasis ≥ 1 cm (RANO-BM criteria evaluation)

          4. Patient with no evidence of extra-cranial progressive disease on 18-FDG PET-CT

          5. Patient with wild type EGFR and ALK

          6. Age ≥ 18 years at time of study entry

          7. ECOG performance status < 2 i.e. 0 or 1

          8. Body weight >30kg

          9. Life expectancy of at least 3 months

         10. Previously treated patients even with immunotherapy are accepted

         11. Patients who have received prior anti-PD-1, anti PD-L1 or anti CTLA-4 are accepted, if
             the following conditions are completed:

               -  All AEs while receiving prior immunotherapy must have completely resolved or
                  resolved to baseline prior to screening for this study

               -  Must not have experienced a ≥Grade 3 immune related AE or an immune related
                  neurologic or ocular AE of any grade while receiving prior immunotherapy. NOTE:
                  Patients with endocrine AE of ≤Grade 2 are permitted to enroll if they are stably
                  maintained on appropriate replacement therapy and are asymptomatic Must not have
                  required the use of additional immunosuppression other than corticosteroids for
                  the management of an AE, not have experienced recurrence of an AE if
                  re-challenged, and not currently require maintenance doses of > 10 mg prednisone
                  or equivalent per day.

         12. Adequate Hematology laboratory data within 6 weeks prior to start of treatment:
             Absolute neutrophils> 1.5 x 109/L, Platelets ≥ 100 x 109/L, Hemoglobin ≥ 9 g/dL

         13. Adequate Biochemistry laboratory data within 6 weeks prior to start of treatment:
             Total bilirubin ≤ 1.5 x ULN (except patient with confirmed Gilbert's syndrome or liver
             metastasis: Total bilirubin ≤ 3 X ULN), Transaminases ≤ 2.5 x ULN, Alkalin
             phosphatases ≤ 5 x ULN, Creatinine clearance > 40 mL/min (Cockcroft)

         14. Women should be post-menopaused or willing to accept the use an effective
             contraceptive regimen during the treatment period and at least 3 months after the end
             of the study treatment. All nonmenopaused women should have a negative pregnancy test
             within 72 hours prior to registration. Men should accept to use an effective
             contraception during treatment period and at least 3 months after the end of the study
             treatment

         15. 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

         16. Signed written informed consent

         17. Patient affiliated to a Social Health Insurance in France

        Exclusion Criteria:

          1. Central nervous system complications for whom urgent neurosurgical intervention is
             indicated (e.g., resection, shunt placement)

          2. Brain metastases in the brainstem

          3. Known leptomeningeal metastases

          4. All other cancer histology other than NSCLC

          5. Prior history of brain radiotherapy

          6. Patient with associated extra-cranial progressive disease documented by 18-FDG PET-CT

          7. Patient unable to have MRI for any reason (e.g., due to pacemaker, ferromagnetic
             implants, claustrophobia, extreme obesity)

          8. Any unresolved toxicity NCI CTCAE Grade ≥2 from previous anticancer therapy with the
             exception of alopecia, vitiligo, and the laboratory values defined in the inclusion
             criteria

               1. Patients with Grade ≥2 neuropathy will be evaluated on a case-by-case basis after
                  consultation with the Study Physician

               2. Patients with irreversible toxicity not reasonably expected to be exacerbated by
                  treatment with durvalumab may be included only after consultation with the Study
                  Physician

          9. Participation in another therapeutic trial within the 30 days prior to entering this
             study (participation in a survival follow-up period of a clinical study is not an
             exclusion criterion)

         10. Any concurrent chemotherapy, IP, biologic, or hormonal therapy for cancer treatment.
             Concurrent use of hormonal therapy for non-cancer-related conditions (e.g., hormone
             replacement therapy) is acceptable.

         11. Current or prior use of immunosuppressive medication within 14 days before the first
             fraction of RT (exception: systemic corticosteroids at physiologic doses not exceeding
             10 mg/day of prednisone or equivalent are allowed as well as steroids as premedication
             for hypersensitivity reactions (eg, CT scan premedication) - Topical, inhaled, nasal
             and ophthalmic steroids are not prohibited)

         12. Active suspected or prior documented autoimmune disease (including inflammatory bowel
             disease, celiac disease, diverticulitis with the exception of diverticulosis, systemic
             lupus erythematosus, sarcoidosis syndrome, or Wegener syndrome [granulomatosis with
             polyangiitis, Graves' disease, rheumatoid arthritis, hypophysitis, uveitis, etc]).
             Note: participants with vitiligo or alopecia, residual hypothyroidism due to
             autoimmune condition only requiring hormone replacement, patients with celiac disease
             controlled by diet alone, psoriasis not requiring systemic treatment, or conditions
             not expected to recur in the absence of an external trigger, are permitted to enroll

         13. Known primary immunodeficiency or active HIV (positive HIV 1/2 antibodies)

         14. Known active or chronic viral hepatitis or history of any type of hepatitis within the
             last 6 months indicated by positive test for hepatitis B surface antigen (HBV sAG) or
             hepatitis C virus ribonucleic acid (HCV antibody)

         15. History of active tuberculosis (clinical evaluation that includes clinical history,
             physical examination and radiographic findings, and TB testing in line with local
             practice)

         16. Uncontrolled intercurrent illness, including but not limited to, ongoing or active
             infection, symptomatic congestive heart failure, uncontrolled hypertension, unstable
             angina pectoris, cardiac arrhythmia, interstitial lung disease, serious chronic
             gastrointestinal conditions associated with diarrhea, or psychiatric illness/social
             situations that would limit compliance with study requirement, substantially increase
             risk of incurring AEs or compromise the ability of the patient to give written
             informed consent

         17. History of another primary malignancy except for:

               1. Malignancy treated with curative intent and with no known active disease ≥5 years
                  before the first dose of IP and of low potential risk for recurrence

               2. Adequately treated non-melanoma skin cancer or lentigo maligna without evidence
                  of disease

               3. Adequately treated carcinoma in situ without evidence of disease

         18. History of severe allergic reactions to any unknown allergens or any components of the
             study drug

         19. Major surgical procedure (as defined by the Investigator) within 28 days prior to the
             first dose of IP. Note: Local surgery of isolated lesions for palliative intent is
             acceptable.

         20. History of allogenic organ transplantation

         21. Receipt of live attenuated vaccine within 30 days prior to the first dose of IP. Note:
             Patients, if enrolled, should not receive live vaccine whilst receiving IP and up to
             30 days after the last dose of IP

         22. Female patients who are pregnant or breastfeeding or male or female patients of
             reproductive potential who are not willing to employ effective birth control from
             screening to 90 days after the last dose of durvalumab

         23. Patient who has forfeited his/her freedom or who is under legal protection
             (curatorship and guardianship, protection of justice)