One of the few treatment options for inoperable neuroendocrine tumors (NET) is peptide receptor radiotherapy with somatostatin analogs. In this study, we compared the dosimetric parameter uptake, half-life (kinetics), and mean absorbed organ and tumor doses of 177Lu DOTA-NOC and 177Lu DOTA-TATE. Methods: Ninety-five (95) post-therapeutic dosimetric assessments using 177Lu DOTA-TATE and 8 using 177Lu DOTA-NOC in 69 patients with neuroendocrine tumors with high somatostatin receptor expression (verified by Ga-68 DOTA-NOC positron emission tomography/computed tomography) were analyzed. Dosimetric calculations were performed according to the Medical Internal Radiation Dose scheme. Results: 177Lu DOTA-NOC showed a significantly (p ≤ 0.05; sign test) higher uptake for whole-body and normal tissue, as compared to 177Lu DOTA-TATE, leading to a significant higher whole-body dose of 0.07mGy/ MBq for DOTA-NOC, as compared to 0.05 mGy/MBq for DOTA-TATE. Renal and spleen uptake and radiation doses were not significantly higher for DOTA-NOC. The uptake in tumor lesions and the mean absorbed tumor dose were higher for DOTA-TATE. The red marrow dose was approximately 0.2 Gy. Conclusions: Our first results demonstrated that the higher in vitro affinity of DOTA-NOC leads to a higher uptake in normal tissues and, therefore, to an increase in the whole-body dose. The high interpatient variability of these results makes an individual patient dosimetry obligatory.
