Whole-Brain Radiation Therapy and Pemetrexed in Treating Patients With Brain Metastases From Non-Small Cell Lung Cancer

RATIONALE: Radiation therapy uses high-energy x-rays to kill tumor cells. Pemetrexed may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Giving radiation therapy together with pemetrexed may kill more tumor cells. PURPOSE: This phase II trial is studying how well giving whole-brain radiation therapy together with pemetrexed works in treating patients with brain metastases from non-small cell lung cancer.