Radiation Therapy in Preventing Central Nervous System (CNS) Metastases in Patients With Non-Small Cell Lung Cancer

RATIONALE: Radiation therapy uses high-energy x-rays to damage tumor cells. It is not yet known if giving radiation therapy to the head is effective in preventing CNS metastases in patients who have stage III non-small cell lung cancer. PURPOSE: This randomized phase III trial is studying how well radiation therapy to the head works in preventing CNS metastases in patients who have been previously treated for stage III non-small cell lung cancer.