Inclusion Criteria:  Diagnosis of diffuse intrinsic pontine glioma based on clinical evidence and radiographic (MRI) imaging. The patient must have undergone prior external beam radiotherapy using standard conformal fractionated or hypo-fractionated techniques to a planned maximal total dose of 54-60 Gy to the brain stem of which the patient must have received ≥ 90% of the planned dose, at least 4 weeks but no more than 14 weeks prior signing of ICF. Lansky or Karnofsky Performance Score of ≥ 70 at study entry. Lansky Performance scale to be used for patients ≤16 years of age. Age ≥ 3 years old and less than 21 years old. Written informed consent from legal guardian(s) and/or child obtained in accordance with local regulations. Pediatric patients must provide assent as required by local regulations.  Exclusion Criteria:  Clinical and/or radiographic (MRI) progression of tumor in the period between external beam radiation therapy and signing of ICF. If pseudoprogression is suspected rescreening is allowed Metastatic or disseminated disease. Tumor size larger than 20cm3. Untreated symptomatic hydrocephalus as determined by the investigator Increasing dose of steroids for 1 week prior to first IMP treatment AST or ALT > 3x the upper limit of normal. Total bilirubin > 3x the upper limit of normal. In case either AST or ALT ≥3 x ULN, bilirubin must be ≤ 2 x the upper limit of normal. Hemoglobin less than 8 g/dL. White blood cell (WBC) count less than 1000/μL. ANC count less than 500/μL. Platelet count less than 100,000/μL. INR (international normalized ratio) higher than 1.5 (calculated from the prothrombin time). Glomerular filtration rate (eGFR) of ≤ 60 ml/min/1.73m2 calculated by 2009 revised Bedside Schwartz Equation. Weight less than 8kg. Life expectancy less than six weeks as judged by the investigator. Tumor whose origin is outside the pons. Patients must not have an uncontrolled life-threatening infection. Patients must not have severe non-hematologic organ or neurological toxicity; specifically, any neurological, cardiac, hepatic, pulmonary, and gastrointestinal system toxicity must be below Grade 3 prior to signing the ICF. Females of childbearing potential who are pregnant, breast feeding, intend to become pregnant, or are not using highly effective contraceptive methods while included in the trial and for 12 months after the last dose of 131I-omburtamab. Fertile male patients who do not agree to the use of condoms during treatment and for a period of 12 months after the last dose of 131I-omburtamab. For a male patient to be exempt from the requirement to use contraception after 131I-omburtamab treatment, he must have undergone surgical sterilization (vasectomy).