Patients receive thiotepa IV over 15 minutes on day 1. Patients also receive methotrexate IV over 4 hours on days 1 (8 hours after thiotepa) and 14. Beginning 24 hours after the start of methotrexate infusion, patients receive leucovorin calcium IV or orally every 6 hours until rescue is achieved. Treatment repeats every 28 days for up to 4 courses in the absence of disease progression or unacceptable toxicity. Patients achieving disappearance of enhancement of disease on MRI receive an additional 28-day course followed by maintenance therapy comprising thiotepa and methotrexate once a month for 11 courses.