Tumor-to-Blood Ratio for Assessment of Somatostatin Receptor Density in Neuroendocrine Tumors Using ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE.

Abstract

PET/CT with ⁶⁸Ga-DOTA-somatostatin analogs has been tested for therapy monitoring in patients with neuroendocrine tumors (NETs). However, SUVs in tumors do not correlate with the net influx rate (K_i), as a representation of the somatostatin receptor expression. In this study, tumor-to-blood ratio (TBR) was evaluated as an alternative tool for semiquantitative assessment of ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE tumor uptake and as a therapy monitoring tool for patients with NETs. <b>Methods:</b> Twenty-two NET patients underwent a 45-min dynamic PET/CT scan after injection of ⁶⁸Ga-DOTATOC or ⁶⁸Ga-DOTATATE. K_i was determined using the Patlak method, and TBR was calculated for the 40- to 45-min interval. <b>Results:</b> A linear relation was found between K_i and TBR, with a square of Pearson correlation of 0.98 and 0.93 for ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE, respectively. <b>Conclusion:</b> A high correlation was found between K_i and TBR. Hence, TBR reflects somatostatin receptor density more accurately than SUV and is suggested as the preferred metric for semiquantitative assessment of ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE tumor uptake.