<qa>  What is the measurable contrast-enhancing disease defined as?- Patients must have measurable contrast-enhancing disease defined as at least 1 cm x 1 cm by magnetic resonance imaging MRI imaging within 21 days of starting treatment patients may have gross total resection, but should have measurable disease post-operatively; patients must be able to undergo MRI of the brain with gadolinium; patients must be maintained on a stable corticosteroid regimen no increase for 5 days prior to this baseline MRI 