Patients must be able to undergo MRI of the brain with gadolinium; patients must be maintained on a stable or decreasing dose of corticosteroid regimen (no increase for days) prior to this baseline MRI Patients must be maintained on a stable corticosteroid regimen from the time of their baseline scan until the start of the treatment and/or for at least days before starting treatment Patients must be maintained on a stable corticosteroid regimen for days prior each magnetic resonance (MR)-PET scan Patients must be maintained on a stable corticosteroid regimen from the time of their baseline scan until the start of treatment and/or for at least days before starting treatment Phase I patients must be maintained on a stable corticosteroid regimen (no increase for days) prior to the baseline MRI Patients must be maintained on a stable or decreasing corticosteroid regimen from the time of their baseline scan until registration Patients with corticosteroid requirements to control cerebral edema must be maintained at a stable or decreasing dose for a minimum of two weeks without progression of clinical symptoms Must be maintained on a stable or decreasing corticosteroid regimen (no increase for days) prior to the start of treatment Patients must be maintained on a stable corticosteroid regimen (no increase for days) prior to the baseline MRI Patients must be maintained on a stable corticosteroid regimen (no increase for days) prior to the baseline MRI Patients must be able to undergo MRI of the brain with gadolinium; patients must be maintained on a stable or decreasing dose of corticosteroid regimen (no increase for days) prior to this baseline MRI Patients must be maintained on a stable corticosteroid regimen (no increase for days) prior to the start of treatment Patient must be maintained on a stable or decreasing dose of corticosteroid for at least days before the baseline scan. Patient must be maintained on a stable corticosteroid regimen for days prior to each MR-PET scan Patients on corticosteroids must be maintained on a stable corticosteroid regimen for days prior each magnetic resonance (MR)-PET scan