Inclusion Criteria:

          -  1. Age ≥18 years, of both sexes, of any ethnicity;

          -  2. Cyto-histological and immunohistochemical diagnosis of NET;

          -  3. Evaluation of the cell proliferation index by studying Ki-67 and / or E3
             ubiquitin-protein ligase (MIB-1).

          -  4. Illness measurable according to RECIST 1.1 criteria by imaging conventional (CT
             with contrast medium or MRI with contrast medium) not earlier than two months with
             respect to enrollment;

          -  5. Elevated expression of somatostatin receptors documented by PET-CT with
             68Ga-DOTATOC in the target lesion (s). It is defined as "high expression of
             somatostatin receptors "a ratio of Maximum standardized uptake value (SUVmax) lesion /
             Mean standardized uptake value (SUVmean) muscle ≥ 4: 1 calculated with
             semi-quantitative analysis on examination PET-CT with 68Ga-DOTATOC;

          -  6. Dosage of Chromogranin A (and any other specific markers) not prior to two months
             of enrollment;

          -  7. Evaluation of glucose metabolism in the target lesion (s) by PET-CT with 18F-FDG;

          -  8. Preserved haematological, hepatic and renal parameters, in particular: white blood
             cells ≥2500 / μL; platelets ≥ 90000 / μL; hemoglobin ≥ 9 gr / dL; creatinine ≤ 2 mg /
             dL; bilirubin ≤ 2.5 mg / dL

          -  9. Eastern Cooperative Oncology Group (ECOG) performance status ≤2;

          -  10. Life expectancy ≥ 6 months;

          -  11. Stable or progressive disease, at any stage, both in operated patients that
             inoperable;

          -  12. Absence of standard treatments already documented and of equal effectiveness;

          -  13. Absence of surgical, chemotherapy and / or radiotherapy treatments for at least 30
             days. On the other hand, patients in therapy with somatostatin analogues or biologics,
             such as mechanistic target of rapamycin (m-TOR) inhibitors;

          -  14. Voluntary participation in the study by signing the consent form informed, after
             reading and complete understanding of the information notes.

        Exclusion Criteria:

          -  1. Lack of the requirements listed above;

          -  2. State of pregnancy;

          -  3. Breastfeeding and relative refusal to suspend breastfeeding;

          -  4. Participation in another therapeutic experimental clinical protocol in the four
             weeks prior to the PRRT;

          -  5. Bone marrow invasion of disease> 25% confirmed;

          -  6. Previous extensive radiotherapy treatments.