Durvalumab (MEDI4736) and Radiosurgery (fSRT Vs. PULSAR) for the Treatment of Non-Small Cell Lung Cancer Brain Metastases

Inclusion Criteria: * Biopsy-proven NSCLC primary with PD-L1 expression ≥ 1% * At least one previously untreated, asymptomatic brain metastases (\<=10 total) with at least one measurable (0.5 cm diameter or larger) as assessed by MRI * No prior systemic treatment for metastatic NSCLC. * age ≥ 18 years * Eastern Cooperative Oncology Group (ECOG) performance status 0 to 2 * Life expectancy greater than six (6) months * Adequate normal organ and marrow function * Body weight greater than 30 kg * Ability to understand and willingness to sign written informed consent Exclusion Criteria: * Brain metastases that are symptomatic and/or with recent (\<10 days) steroid use * Active or prior documented autoimmune or inflammatory disorders (including inflammatory bowel disease \[e.g., colitis or Crohn's disease\], diverticulitis \[with the exception of diverticulosis\], systemic lupus erythematosus, Sarcoidosis syndrome, or Wegener syndrome \[granulomatosis with polyangiitis, Graves' disease, rheumatoid arthritis, hypophysitis, uveitis, etc\]). * Subjects may not be receiving any other investigational agents for the treatment of the cancer under study. * 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, in the opinion of the investigator, would limit compliance with study requirements, substantially increase risk of incurring AEs or compromise the ability of the patient to give written informed consent. * Subjects must not be pregnant or nursing due to the potential for congenital abnormalities and the potential of this regimen to harm nursing infants. * Administration of one or more lines of systemic therapy for the diagnosis of metastatic non-small cell lung cancer * Prior receipt of systemic therapy for the management of high-risk early stage or locally advanced non-small cell lung cancer, prior to the development of metastatic disease, would not count towards the number of receipt of systemic therapy * History of allergic reactions attributed to compounds of similar chemical or biologic composition to durvalumab or other agents used in study * 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 monotherapy * Participation in another clinical study with an investigational product during the last 1 month * Concurrent enrolment in another clinical study, unless it is an observational (non-interventional) clinical study or during the follow-up period of an interventional study * Receipt of the last dose of anticancer therapy (chemotherapy, immunotherapy, endocrine therapy, targeted therapy, biologic therapy, tumor embolization, monoclonal antibodies) ≤ 7 days prior to the first dose of study drug If sufficient wash-out time has not occurred due to the schedule or PK properties of an agent, a longer wash-out period will be required, as agreed by AstraZeneca and the investigator * Any unresolved toxicity NCI CTCAE Grade ≥2 from previous anticancer therapy with the exception of alopecia, vitiligo, nausea, anorexia/weight loss, and the laboratory values defined in the inclusion criteria: * Patients with Grade ≥2 neuropathy will be evaluated on a case-by-case basis after consultation with the Study Physician. * Patients with irreversible toxicity not reasonably expected to be exacerbated by treatment with durvalumab may be included only after consultation with the Study Physician. * Any other concurrent immunotherapy, biologic, or hormonal therapy for cancer treatment. Concurrent use of hormonal therapy for non-cancer-related conditions (e.g., hormone replacement therapy) is acceptable. * Major surgical procedure (as defined by the Investigator) within 14 days prior to the first dose of immunotherapy. * History of allogenic organ transplantation * History of another primary malignancy except for: * Malignancy treated with curative intent and with no known active disease ≥5 years before the first dose of immunotherapy 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 * History of leptomeningeal carcinomatosis * History of active primary immunodeficiency * Active infection including tuberculosis (clinical evaluation that includes clinical history, physical examination and radiographic findings, and TB testing in line with local practice), hepatitis B (known positive HBV surface antigen (HBsAg) result), hepatitis C * Current or prior use of immunosuppressive medication within 14 days before the first dose of durvalumab * Receipt of live attenuated vaccine within 30 days prior to the first dose of immunotherapy * Receipt of any prohibited medication