A Study of Stereotactic Radiosurgery (SRS) and Standard Treatment in People With Lung Cancer That Has Spread to the Brain

Participant Inclusion Criteria: Screening * Age ≥ 18 years * Non-small cell lung cancer (NSCLC) with somatic activating mutation in EGFR diagnosis, confirmed at enrolling institution * At least one intact brain metastasis at baseline prior to TKI therapy initiation, visible on MRI brain with contrast (but without a minimum diameter requirement) * Either TKI-naïve or started TKI ≤ 3-months prior (with documented start date and available imaging prior to TKI start) Participant Exclusion Criteria: Screening * Unable to undergo contrast-enhanced MRI brain * Prior brain-directed radiotherapy * Evidence of leptomeningeal disease on MRI total spine and/or lumbar puncture cytology. The latter are not mandated by protocol but are rather at the discretion of the treating medical team as clinically indicated. * Neurologic symptoms or presence of a lesion in the brainstem, motor strip, or other eloquent brain area that is felt to warrant immediate intervention with SRS * Active hematologic malignancy or a second solid tumor histology with known CNS tropism * Patients who have undergone a therapeutic craniotomy for resection of one or more symptomatic brain metastasis are ineligible unless one or more additional intact BM remain unresected, and meets size criteria (e.g., a patient with removal of a 3cm symptomatic brain metastasis, but has an additional visible lesion remaining post-operatively, remains eligible for the study). * Judgment by the investigator that the patient should not…