Description of the study: The aim of the study is to develop an algorithm for the treatment of GEP-NET patients using ItraPol and LutaPol isotope mixtures (177Lu-DOTATATE and 90Y-DOTATATE) based on personalized dosimetry. The specific goal is to assess the effectiveness and safety of personalized treatment of GEP-NET patients using 177Lu-DOTATATE and 90Y-Lu-DOTATATE mixtures compared to standard treatment of NEN patients using 177Lu-DOTATATE