The experimental drug, mafosfamide, will be injected into the spinal fluid. This will be given through either a spinal tap, the Ommaya reservoir, or both. Alternating mafosfamide between the spinal tap and the Ommaya reservoir may improve how well the drug works by making sure it spreads throughout the spinal fluid. If the patient has a VP or VA shunt ( specialized devices that relieve the pressure inside the head that comes from a block in the normal flow of spinal fluid), then the patient will not receive an Ommaya reservoir, and all doses of mafosfamide will be given through a spinal tap only.