• Age ≥18 years

• Written informed consent

• Eastern Cooperative Oncology Group (ECOG) 0-1

• Presence of histologically confirmed, advanced, well-differentiated, inoperable neuroendocrine tumors (NET) of any primary tumor origin and any grade, except for pheochromocytoma and paraganglioma.

• Somatostatine receptor (SSTR)-expression in tumor lesions \> basal liver uptake on 68Ga-DOTA-PET

• Radiologically progressive disease within the last 1-24 months according to common clinical criteria and confirmed by the institutional multidisciplinary conference for the treatment of NETs. The CT/MRI that shows tumor progression compared to screening/baseline must have been performed 1-24 months earlier.

• All previous anti-tumor treatment except SSA must be terminated at least 4 weeks before start of treatment within the trial.

• Measurable disease according to RECIST v 1.1

• Given the available, approved anti-tumor treatments and the specific characteristics of the patient and the tumor, the investigator judges peptide receptor radionuclide therapy (PRRT) to be the treatment of choice

• GFR \> 50 ml/min/1.73 m2 as determined by iohexol- or 51Cr-EDTA clearance, calculated according to a combination of LMR18 and CAPA formulas, or equally accurate method

• Hemoglobin \> 90 g/L, platelets \>100 x109/L, leukocytes \> 3.0x109/L, neutrophils \> 1.5 x109/L, aspartate transaminase (ASAT)/alanine aminotransferase (ALAT) \< 3 x ULN, bilirubin \< 2 x upper limit of normal (ULN), albumin \> 25 g/L

• For women of child-bearing potential, highly effective contraception should be used from the time of inclusion up to at least six months after the end of treatment (EOT) visit.