Inclusion Criteria:

- Histologically proven diagnosis of acute lymphoblastic leukemia, non-Hodgkin's
lymphoma, or osteosarcoma

- treatment protocol that includes at least one cycle of methotrexate or exogenous
glucocorticoid

- informed consent to participate in the study, according to institutional guidelines

- fluency in Hebrew, English, or Arabic

- age 6 to 25

Exclusion Criteria:

- Cranial irradiation within the past year

- serious concomitant systemic disorders (including active infections) that would
compromise the safety of the patient or compromise the patient's ability to complete
the study

- active meningitis or seizures occurring less than a month before study enrollment