[68Ga]-DOTASOM targeting somatostatin receptors: In vivo biodistribution and dosimetry

1511 Objectives [68Ga]-DOTASOM is a new somatostatin analogue with high affinity towards somatostatin receptor subtypes sst 1,2,3, and 5 for PET imaging in patients with neuroendocrine tumors. We present the in vivo distribution in a pig model as a basis for human dosimetry. Methods All procedures involving animals were performed under a Danish Ministry of Justice license. [68Ga]-DOTASOM was produced in an E&Z Modular lab Pharmtracer system by reacting 35 nM DOTASOM precursor with 68Ga in sodium acetate buffer (pH4.4) at 95°C. In vivo biodistribution and dosimetry studies were performed in anesthetized Danish Landrace pigs (3 female, 2 male, age: 3 - 4 month, average weight: 36.5kg) applying a series of 10 whole body PET/CT scans (Siemens Biograph 64). The physiological parameters were monitored and, if necessary, corrected during the scans. 10 arterial blood samples were taken for metabolite analysis. Time-activity curves and residence times were assessed for organs showing visible uptake. Based on these data a dose assessment was performed using OLINDA. Results The applied radiochemical procedure yielded sufficient amounts of [68Ga]-DOTASOM (RCP>95%). After injection (mean activity: 136 MBq), clearance of [68Ga]-DOTASOM from the body was characterized by fast renal excretion (t½ = 1.5 min), followed by slow clearance with t½ ≈ t½ of 68Ga. There was no visible uptake in the spleen. The highest organ residence times were observed in the bladder, liver and kidneys. The effective dose was estimated to 4.1*10-2mSv/MBq; organs with the highest absorbed doses were bladder, kidneys, testes and liver. Conclusions In vivo distributions and absorbed doses are generally comparable to those obtained for other somatostatin receptor ligands and should be no hindrance for human applications