Combined Beta- Plus Auger Electron Therapy Using a Novel Somatostatin Receptor Subtype 2 Antagonist Labelled With Terbium-161 (161Tb-DOTA-LM3)

The goal of this phase 0 proof-of concept study is to measure the therapeutic index (tumour to dose-limiting-organ dose ratios) of 161Tb-DOTA-LM3 in comparison to the current standard 177Lu-DOTATOC in the same gastroenteropancreatic neuroendocrine tumour (GEP-NET) patients in a randomized, cross-over design, in all patients. Population to be studied are patients with diagnosed and metastasized secreting and non-secreting GEP-NEN (grade 1 and 2). The number of participants will be limited to 4 - 8 patients (phase 0a) and 4 - 8 patients (phase 0b). All patients will get the same treatment in a balanced cross-over order. The study will be divided into a phase 0a and phase 0b. Beforehand the selected patients will be randomised into two groups. In phase 0a one test injection with 161Tb-DOTA-LM3 and 177Lu-DOTATOC will administered in both randomised groups in a different order followed by \~ 3 cycles PRRT with 177Lu-DOTATOC in both groups. In phase 0b two test injections with 161Tb-DOTA-LM3 (with different peptide amounts) will administered in both randomised groups in a different order followed by \~2 cycles PRRT with 161Tb-DOTA-LM3 in both groups.