Purpose: The objective of this study is to analyze the in vivo behavior of the (177)Lu-labeled peptides DOTATATE, DOTANOC, and DOTATOC used for peptide receptor radionuclide therapy (PRRNT) of neuroendocrine tumors (NETs), by measuring organ and tumor kinetics and by performing dosimetric calculations.
Methods: Two hundred fifty-three patients (group 1) with metastasized NET who underwent PRRNT were examined. Out of these, 185 patients received (177)Lu-DOTATATE, 9 were treated with (177)Lu-DOTANOC, and 59 with (177)Lu-DOTATOC. Additionally, 25 patients receiving, in consecutive PRRNT cycles, DOTATATE followed by DOTATOC (group 2) and 3 patients receiving DOTATATE and DOTANOC (group 3) were analyzed. Dosimetric calculations (according to MIRD scheme) were performed using OLINDA software.
Results: In group 1, DOTATOC exhibited the lowest and DOTANOC the highest uptake and therefore mean absorbed dose in normal organs (whole body, kidney, and spleen). In group 2, there was a significant difference between DOTATATE and DOTATOC concerning kinetics and normal organ doses. (177)Lu-DOTATOC had the lowest uptake/dose delivered to normal organs and highest tumor-to-kidney ratio. There were no significant differences between the three peptides concerning tumor kinetics and mean absorbed tumor dose.
Conclusions: The study demonstrates a correlation between high affinity of DOTANOC in vitro and high uptake in normal organs/whole body in vivo, resulting in a higher whole-body dose. DOTATOC exhibited the lowest uptake and dose delivered to normal tissues and the best tumor-to-kidney ratio. Due to large interpatient variability, individual dosimetry should be performed for each therapy cycle.