Inclusion Criteria:  Age greater than or equal to 18 years Histological diagnosis of well-differentiated neuroendocrine tumor (NET) (typical and atypical lung carcinoids and NET of all gastroenteropancreatic sites according to World Health Organization (WHO) 2019 classification); metastatic/unresectable, with no possibility of curative treatment. MIBG-I131 positive scan in at least one lesion with uptake compatible with therapeutic effectiveness. Disease with radiological progression (at least 10 percent tumor volume growth) in the last 12 months before day 1 cycle 1. Intolerance due to toxicities or lack of access to standard treatments - [private context (somatostatin analog, everolimus) and public health system (somatostatin analog)]. Measurable disease Eastern Cooperative Oncology Group (ECOG) performance scale 0 to 2.  Adequate organic function as defined by the following criteria:  serum aspartate aminotransferase (AST), serum alanine aminotransferase (ALT) ≤ 2.5 times the upper limit of normal of the local laboratory (ULN-LL); Total serum bilirubin ≤ 2.0 x ULN-LL; Absolute neutrophil count ≥ 1,500 / mm^3; Platelet count ≥ 100,000 / mm^3; Hemoglobin ≥ 9.0 g / dL; Estimated creatinine clearance by the Modification of Diet in Renal Disease (MDRD) equation ≥ 60ml / min Term of free and informed consent signed by the patient or legal representative.  Exclusion Criteria:  Patients already treated with MIBG-I131. A history of serious clinical or psychiatric illness that, by clinical judgment, may involve participation risk in this study. Patients participating in other protocols with experimental drugs. Patients who underwent major recent surgery less than 4 weeks previously. Patients receiving chemotherapy or other oncologic therapy for less than 3 weeks. Pregnant or lactating patients. Another synchronous neoplasm that requires systemic treatment.