 ARM IV: Patients receive vincristine sulfate, dexamethasone, doxorubicin hydrochloride, pegaspargase, methotrexate IT, nelarabine, cyclophosphamide, cytarabine, and thioguanine as in arm II. Patients with intermediate- or high-risk disease CNS 1 or CNS2 disease undergo prophylactic CRT on days 50-54 and 57-59. 