Maintenance Targeted Therapy With or Without Stereotactic Body Radiation Therapy for Stage IV Non-small Cell Lung Cancer

Inclusion Criteria: 1. Patients must have biopsy proven metastatic NSCLC (Stage IV). 2. Patients must have received first line chemotherapy, from 4-6 cycles, and achieved stable disease or a partial response. 3. Patients receiving first-line erlotinib, gefitinib, or icotinib for EGFR mutant-positive for 3 months and achieved stable disease, partial response or completely response. 4. Age 18 to 75 years old. 5. Patients must have measurable disease at baseline. 6. The amount of metastatic focus \<5. 7. ECOG score 0-2 8. Adequate normal organ and marrow function for TKI treatment and radiotherapy. 9. Patients must has sensitizing EGFR mutation (e.g. exon 19 deletion or exon 21 L858R) 10. Patients must provide written informed consent to participate in the study. Exclusion Criteria: 1. Patients who previously received radiotherapy to the primary site. 2. Patient can't tolerate radiotherapy or targeted therapy; 3. Pregnant or nursing women