Inclusion Criteria:

          -  Patients must have 1 to 15 newly diagnosed brain metastases, ≤3 cm in the largest
             dimension, with at least one metastasis measuring ≥0.5 cm.

          -  Primary tumor histology must be one confirmed as one of the following:

               -  Squamous NSCLC

               -  Adenocarcinoma NSCLC

               -  Not otherwise specified NSCLC

          -  Patient must be able and willing to undergo a thin cut MRI at Duke, which is required
             for study entry.

          -  Patient must be planned for immunotherapy treatment as their next systemic therapy,
             including monotherapy or in combination with chemotherapy.

          -  Patients previously treated with a tyrosine kinase inhibitor (TKI) may be eligible, if
             a second line (or later) immunotherapy regimen is planned.

          -  Patients must be asymptomatic or minimally symptomatic, requiring the equivalent of ≤2
             mg dexamethasone/day for at least 7 days prior to enrollment.

          -  Female and male subjects of childbearing potential must be willing to use an adequate
             method of contraception as outlined in the Duke Contraception Policy.

          -  Age ≥18 years of age at the time of entry into the study.

          -  Karnofsky Performance Score (KPS) ≥70.

          -  Prothrombin and Partial Thromboplastin Times ≤1.2 x normal

          -  Neutrophil count ≥1000

          -  Hemoglobin ≥9 g/dl

          -  Platelet count ≥100,000/µl

          -  Creatinine ≤1.2 x normal range.

        Exclusion Criteria:

          -  Patients on the equivalent of >2 mg of dexamethasone daily ≤ 7 days before receiving
             study treatment

          -  Patients who have previously receive whole brain radiation therapy (WBRT).

          -  Patients must not have ever received immunotherapy in the stage IV setting. Prior
             immune therapy as part of treatment for stage I-III disease is allowed assuming an
             interval >6 months has passed from the completion of that therapy.

          -  Patients with leptomeningeal disease. However, patients with discrete dural-based
             lesions may be eligible.

          -  Females who are pregnant or breast-feeding.

          -  Patients with an impending, life-threatening cerebral hemorrhage or herniation, based
             on the assessment from a brain MRI of the study neurosurgeons or their designate.

          -  Patients with severe, active co-morbidity, defined as follows:

               -  Patients with an active infection requiring intravenous treatment or having an
                  unexplained febrile illness (Tmax > 99.5°F/37.5°C)

               -  Patients with known immunosuppressive disease or known uncontrolled human
                  immunodeficiency virus infection

               -  Patients with unstable or severe intercurrent medical conditions such as severe
                  heart disease (New York Heart Association Class 3 or 4)

          -  Patients who have not recovered from the toxic effects of prior chemo- and/or
             radiation therapy. Guidelines for this recovery period are dependent upon the specific
             therapeutic agent being used:

          -  Patients with prior, unrelated malignancy requiring current active treatment in the
             last 3 years with the exception of cervical carcinoma in situ and adequately treated
             basal cell or squamous cell carcinoma of the skin

          -  Patients with a known history of hypersensitivity to the physician's choice of immune
             checkpoint inhibitor, or any components of the inhibitor.

          -  Patients who have any contraindications to immunotherapy.

          -  Patients with active autoimmune disease requiring systemic immunomodulatory treatment
             within the past 3 months.

          -  History and/or confirmed pneumonitis, or extensive bilateral lung disease on high
             resolution/spiral CT scan.