Half of the patients will receive standard high-dose methotrexate on weeks 1 & 2 and high-dose methotrexate with glucarpidase on weeks 4 & 5 (arm A) and half of the patients will first have high-dose methotrexate with glucarpidase on weeks 1 & 2 and then standard high-dose methotrexate on weeks 4 & 5 (arm B).