Decision Making About Participating in Pharmacokinetic Studies in Patients Enrolled in a Phase I Treatment Clinical Trial

brain and central nervous system tumors, leukemia, unspecified adult solid tumor, protocol specific, unspecified childhood solid tumor, protocol specific, recurrent childhood brain stem glioma, recurrent childhood cerebellar astrocytoma, recurrent childhood cerebral astrocytoma, recurrent childhood medulloblastoma, recurrent childhood supratentorial primitive neuroectodermal tumor, recurrent childhood ependymoma, recurrent childhood pineoblastoma, recurrent childhood subependymal giant cell astrocytoma