We conclude the following: (1) 18 Gy CRT per se was not an independent toxic agent for cognitive outcome; (2) HD-MTX during induction was associated with IQ decline in girls, but only when it was followed by CRT; and (3) impairment of verbal memory and coding was a consistent finding that was independent of CRT, which implicates some component of chemotherapy, possibly prednisone, as a CNS toxin.

This randomized trial revealed only subtle differences 6 years after diagnosis between children who received CNS therapy as CRT plus double IT drug or as intensive triple IT drug. In most situations where comparable therapeutic efficacy can be achieved without CRT, it is preferable to do so. Where therapeutically necessary, however, CRT at lower doses may not add risk for significant neurotoxicity.

HFX provides no benefit in terms of cognitive late effects and may compromise antileukemic efficacy. HFX should not be substituted for conventionally dosed CRT in children who require radiation therapy for treatment of acute lymphoblastic leukemia.