Radiotherapy to the Primary in Metastatic Non-small Cell Lung Cancer Patients

Inclusion Criteria: 1. Confirmed histological diagnosis of NSCLC. 2. Stage IV disease. 3. Patients with P.S ≤ 2. 4. finished at least 4 cycles of platinum-based doublet chemotherapy if patient has no diver mutation, or at least 3 months of anti-EGFR, Anti-ALK according to their driver mutation with SD, PR or CR. Exclusion Criteria: 1. History of prior irradiation to the lung. 2. residual Malignant pleural or pericardial effusion at randomization time. 3. History of prior malignant tumor likely to interfere with the treatment protocol. 4. Severe comorbidities as measured by morbidity index. 5. Disease progression on first line systemic therapy.