20-40% of patients with NSCLC will develop brain metastases at some point during their course of the disease. Osimertinib has demonstrated intracranial activity in EFGR mutated NSCLC with leptomeningeal disease in the phase 1 BLOOM study. Stereotactic radiosurgery (SRS) is one of the standard local treatment for patients with limited number of brain metastases. Currently, it is unclear whether adding SRS to Osimertinib will result in superior intracranial disease control in patients with EGFR mutated NSCLC with brain metastases diagnosed de novo or developed while on first line EGFR tyrosine kinase inhibitors (TKIs) such as Erlotinib and Gefinitib. The aim of this study is to compare the effects of Osimertinib alone versus Osimertinib plus SRS on intra-cranial disease control in EGFR mutated NSCLC with brain metastases diagnosed or developed while on first line EGFR tyrosine kinase inhibitors.