RecruitingDrug trialAbsorbed Tumor Dose in Peptide Receptor Radionuclide Therapy with Long-acting Somatostatin Analogues - ATSA TrialAccording to current guidelines, patients have to withhalt long-acting somatostatin analogues (LA-SSA) for 4-6 weeks prior to every 177Lutetium-DOTATATE administration. The primary objective of the study is to investigate the effect of LA-SSA on the absorbed dose in tumor lesions during PRRT.