Radiation Therapy to the Brain or Observation in Preventing Brain Metastases in Patients With Advanced Non-Small Cell Lung Cancer

DISEASE CHARACTERISTICS:

* Histologically confirmed non-small cell lung cancer

  * Stage IIIB or IV disease
  * Must have had ≥ 8 weeks of gefitinib or erlotinib hydrochloride therapy
* At least 12 weeks of complete response or partial response since starting gefitinib or erlotinib hydrochloride

  * Stable disease allowed provided 1 of the following criteria is met:

    * EGFR mutation (exon 19 or 21)
    * Having ≥ 2 of the following 3 factors:

      * Female
      * Never smoked
      * Histologically confirmed adenocarcinoma of the lung
* No evidence of brain metastases by CT scan or MRI within the past 4 weeks

PATIENT CHARACTERISTICS:

* ECOG performance status 0-2
* ANC ≥ 1,500/mm\^3
* Platelet count ≥ 150,000/mm\^3
* Bilirubin \< 1.5 mg/dL
* Serum creatinine \< 1.5 times upper limit of normal

PRIOR CONCURRENT THERAPY:

* See Disease Characteristics
* Received 1 or 2 prior systemic chemotherapy regimens