Tumor Detection Using Iodine-131-Labeled Monoclonal Antibody 8H9

Inclusion Criteria: * Diagnosis of pediatric/adolescent solid tumor (including neuroblastoma, rhabdomyosarcoma, Ewing's/PNET, osteosarcoma, brain tumors, desmoplastic small round cell tumor (DSRT) and other tumors that are 8H9-positive) confirmed by the MSKCC Department of Pathology. * Patient must have either recurrent disease or have \<20% chance of long term disease-free survival. * Patient must be at least 1 year old. Age can range from 1-50 years of age. * Patients should have measurable or evaluable disease. For tumor types that are known to be 8H9-positive, patients can be imaged after the diagnosis is made, prior to definitive surgery or surgery to confirm tumor recurrence. * Tumor tissue is or will be available for 8H9 immunostaining. For patients with tumor-types known to be 8H9-positive, surgical samples obtained after 131I- 8H9 imaging will be immunostained to confirm 8H9-reactivity. These tumor types include: neuroblastoma, rhabdomyosarcoma, osteosarcoma, DSRT, Ewing's Sarcoma/PNET), brain tumors (glioblastoma multiforme, mixed glioma, astrocytoma, ependymoma, medulloblastoma, schwannoma., meningioma). * If frozen tumor tissue is unavailable, and if bone marrow involvement is demonstrated by histology, 8H9 immunostaining by immunofluorescence will be carried out on patient's bone marrow. In this case, patients will be eligible for study if bone marrow 8H9 immunostaining is positive. Exclusion Criteria: * Severe major organ toxicity. Specifically, renal, cardiac, hepatic, pulmonary, gastrointestinal, and neurologic system toxicity should all be less than grade 2. Patients with stable neurological deficits (because of their brain tumor) are not excluded. Patients with \<= 3 hearing loss are not excluded. * Clinically apparent infections. * History of allergy to iodine or mouse proteins. * Patients previously treated with mouse monoclonal antibodies are not eligible unless they have no circulating HAMA. * Pregnant women are excluded for fear of danger to the fetus. Therefore negative pregnancy test is required for all women of child-bearing age, and appropriate contraception is used during the study period. * Patient's own tumor is negative by 8H9 immunostaining.