OUTLINE: Patients undergo whole-brain radiotherapy 5 days a week for 3 weeks beginning on day 1. Patients also receive pemetrexed disodium IV on day 1, 2, or 3 and day 28 of course 1, and on day 1 of each subsequent course. Treatment with pemetrexed disodium repeats every 21 days for a total of 4 courses in the absence of disease progression or unacceptable toxicity.