The prognosis of NSCLC patients with asymptomatic brain metastasis, who are not treated with SRS or WBRT has not been fully investigated yet. This randomized phase III trial is conducted to determine the exact role of SRS in NSCLC patients with asymptomatic oligo brain metastases whether early treatment with SRS would improve survival even in patients with asymptomatic brain metastasis.

Inclusion Criteria:

• Histologically confirmed non-small cell lung cancer with synchronous brain metastases (diagnosis of brain lesion before or within 2 months from diagnosis of the primary site tumor)

  • One to 4 intraparenchymal brain metastases by contrast-enhanced MRI, meeting the following criteria:

    1. Well circumscribed tumor(s) with brain edema Grade 0-1

    2. Maximum diameter ≤ 3.0 cm

       • No prior complete resection of all known brain metastases or RT ④ No leptomeningeal metastases by MRI or cerebrospinal fluid evaluation

         • Patients without any symptoms or signs from brain metastases (RTOG neurologic functions status of 0) ⑥ Age, 18 and over ⑦ ECOG performance status 0-1 ⑧ Written informed consent

       Exclusion Criteria:

• severe co-morbid illness and/or active infections ② pregnant or lactating women

  • RTOG neurologic function status of 1~4 ④ Uncontrollable extracranial metastases