Inclusion Criteria:

        Inclusion Criteria for All Patients:

          -  Age >1 year and able to cooperate with radiation safety restrictions during therapy
             period.

          -  Minimum life expectancy of eight weeks as determined by consenting professional

          -  Signed informed consent indicating awareness of the investigational nature of this
             program

          -  Prior to intraperitoneal catheter placement

               -  At least 2 weeks must have elapsed since prior chemotherapy, radiotherapy or
                  biologic therapy

               -  Toxicities of prior therapy must have resolved to grade 1 or less

        At the completion of surgery, patients must fulfill all of the additional following
        criteria:

        Group A patients:

          -  Have the diagnosis of DSRCT with peritoneal involvement, confirmed at MSK

          -  Have undergone GTR of abdomino-pelvic disease, as per surgeon's report

          -  Have no definitive radiological evidence of disease active in liver or outside the
             abdomen/pelvic

          -  Should not have had prior WA-IMRT

          -  Stem cells: Patients must have an autologous hematopoietic stem cell product
             cryopreserved and available for re-infusion after 131 I-omburtamab treatment. The
             minimum dose for hematopoietic stem cells is 2 x 10^6 CD34+ cells/kg

        Group B patients:

          -  Have the diagnosis of DSRCT with peritoneal involvement, confirmed at MSK

          -  Have radiological evidence of disease (does not need to be in the abdomen)

        Group C patients:

          -  Have the diagnosis of tumors other than DSRCT, confirmed at MSK

          -  Have a tumor that involves the peritoneum

          -  Omburtamab reactivity must be confirmed by immunohistochemistry except for tumors with
             a reported incidence of B7H3 expression of >70%: these include neuroblastoma,
             melanoma, Ewing's family of tumors, rhabdomyosarcoma, osteosarcoma, Wilm's tumor,
             hepatoblastoma and rhabdoid tumor (testing for these histologies may be performed if
             desired at the discretion of the investigator and after discussion with the prinicipal
             investigator)

          -  May or may not have radiological evidence of disease

          -  <20% chance of long term disease-free survival

        Exclusion Criteria:

          -  Prior therapy: Less than 3 weeks between any last chemotherapy, radiotherapy or
             biologic therapy and 131I-omburtamab infusion date (ie at least 3 weeks must separate
             prior therapies and ombutamab infusion date).

          -  Severe major organ toxicity. Cardiac, pulmonary, and neurologic toxicity should all be
             grade 1 or less; Renal, gastrointestinal and hepatic, toxicities should all be grade 2
             or less (per NCI CTC version 5)

          -  Platelet count should be >50,000/ul and hemoglobin should be >8gm/dl. Platelet
             transfusions are not permitted within one week for blood count demonstrating platelet
             count >50,000

          -  Patients with clinically suspected dense intraperitoneal adhesions preventing adequate
             IP distribution

          -  History of allergy to mouse proteins

          -  Patients previously treated with murine monoclonal antibodies will be excluded if they
             have a HAMA level of >1000U/ml (defined as positive).

          -  Active serious infections not controlled by antibiotics

          -  Patients with grade 4 hypersensitivity reaction to radiolabeled iodine

          -  Patients who have received live viral vaccines within 30 days before the first dose of
             study treatment (patients are NOT permitted to receive viral vaccines while
             participating in the study)

          -  Pregnant women and women who are breast feeding are excluded for fear of danger to the
             fetus/infant. Therefore, negative pregnancy test is required for all women of
             child-bearing age, and appropriate contraception is used during the study period and
             for 12 months following therapy. Pregnancy testing will be carried out within two
             weeks prior to administration of radioiodinated omburtamb in females of childbearing
             age.

          -  Inability or unwillingness to comply with radiation safety procedures or protocol
             requirements.