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

Abstract

PET/CT with 68 Ga-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 68 Ga-DOTATOC and 68 Ga-DOTATATE tumor uptake and as a therapy monitoring tool for patients with NETs. Methods: Twenty-two NET patients underwent a 45-min dynamic PET/CT scan after injection of 68 Ga-DOTATOC or 68 Ga-DOTATATE. K i was determined using the Patlak method, and TBR was calculated for the 40-to 45-min interval. Results: A linear relation was found between K i and TBR, with a square of Pearson correlation of 0.98 and 0.93 for 68 Ga-DOTATOC and 68 Ga-DOTATATE, respectively. Conclusion: 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 68 Ga-DOTATOC and 68 Ga-DOTATATE tumor uptake.

Recent Advances in quantitative dynamic PET imaging of neuroendocrine tumors

“…It was considered by author that high value in SUV (SUV>20-25) may not accurately reflect SSTR density, while Ki might be an available result indicator for SSTR density quantification. Faster blood clearance in patients with higher receptor expression was thought to be the reason for the above result in the subsequent study by Ilan et al 27 between Ki and the tumor-to-blood ratio (TBR) was found in this article. Therefore, TBR was supposed to be a better parameter for reflecting SSTR density than SUV.…”

Dose escalation PET imaging for safety and effective therapy dose optimization of a bispecific antibody

“…Thus, a low radiolabelled dose can be set as a baseline scan, and dose-dependent target engagement can be quantitatively evaluated by Patlak analysis by performing dynamic PET imaging. 31 With this model, the tumor uptake (%ID/g) can be defined as a function of the plasma radioactivity concentration Cp(t) using the following equation: 4 Tumor uptake %ID=g…”

(Radio)Theranostic Patient Management in Oncology Exemplified by Neuroendocrine Neoplasms, Prostate Cancer, and Breast Cancer

“…Non-linear correlation between SUV and Ki indicated that SUV most likely did not reflect SSTR density accurately at higher SUVs [100]. While high correlation found between Ki and TBR indicated that the latter might be more accurate metrics than SUV for semi-quantitative assessment of [ 68 Ga]Ga-SST lesion uptake and treatment response monitoring [101]. Total functional tumor volume (TFTV) measured on [ 68 Ga]Ga-SST PET and computed by summing the volumes of all pathological foci was suggested as prognostic biomarker with cut-off of 13.8 cm 3 [102].…”