3. Patients with clinical evidence of obstructive hydrocephalus or compartmentalization of the CSF flow as documented by radioisotope Indium-(111) (Technetium(99) -DTPA when Indium-(111) unavailable) flow study are not eligible for this protocol. CSF obstruction will be determined by routine nuclear medicine CSF flow study parameters. If patients have evidence of block that is subsequently proven to be relieved after focal XRT, these patients can enroll immediately after repeat flow study shows block to be relieved.