Arm I: Patients receive treatment as in induction therapy, plus G-CSF SC beginning on day 16 and continuing until blood counts recover. If CSF is clear by day 10 of induction, patients receive cytarabine IT on days 0, 10, and 35. If CSF is not clear, patients receive triple intrathecal therapy (TIT; cytarabine, hydrocortisone, methotrexate) on days 0 and 10.