INDUCTION THERAPY 2 (WEEKS 6-10 or 7-11): Once blood counts recover, all patients receive etoposide phosphate IV over = 1 hour and cyclophosphamide IV over 1 hour on days 1-5; high-dose methotrexate IV continuously over 24 hours on day 22; leucovorin calcium IV or PO beginning 42 hours after start of high-dose methotrexate and continuing every 6 hours for at least 3 doses; and methotrexate IT* on days 1 and 22. Patients also receive filgrastim (G-CSF) IV or subcutaneously (SC) beginning on day 6 and continuing until blood counts recover.