- Arm II (weeks 5-24): Patients receive MTX IV over 4 hours on weeks 7, 10, 13, 16, 19, and 22. At 42 hours after the beginning of the MTX infusion, patients receive oral leucovorin calcium as in arm I. Patients also receive mercaptopurine, dexamethasone, vincristine, and IT MTX as in arm I.