Comparison of [68Ga]Ga-DOTA-FAPI-04 PET/CT and [18F]FDG PET/CT for diagnosis of metastasis in differentiated thyroid cancer with negative iodine scintigraphy

Abstract Purpose Evaluation of the potential value of [ 68 Ga]Ga-DOTA-FAPI-04 positron emission tomography/computed tomography (PET/CT) and [ 18 F]FDG PET/CT in detection of differentiated thyroid cancer (DTC) metastases. Methods [ 68 Ga]Ga-DOTA-FAPI-04 and [ 18 F]FDG PET/CT scans were performed on suspected metastatic DTC patients. Maximum standard uptake value (SUVmax) was used to quantify the uptake of positive lesions. Histopathology or follow-up images were used as the standard for final diagnosis. Results A total of 35 DTC patients underwent [ 68 Ga]Ga-DOTA-FAPI-04 and [ 18 F]FDG PET/CT scans in the same time period. Average SUVmax of [ 68 Ga]Ga-DOTA-FAPI-04 uptake by DTC lesions was low (average SUVmax<7). The difference in detection rate of SUVmax of[ 68 Ga]Ga-DOTA-FAPI-04compared with that of[ 18 F]FDG in bone metastases was statistically significant (P=0.000, 0.049). There were differences in the detection rate of other distant and lymph node metastases, and SUVmax, with no statistical significance ( P >0.05). The specificity, accuracy, and positive predictive value of [ 68 Ga]Ga-DOTA-FAPI-04 in the diagnosis of lymph node lesions were higher than those of [ 18 F]FDG PET/CT, and the difference was statistically significant (c 2 =16.583，c 2 =9.910，c 2 =7.548，c 2 =2.781 , P ＜0.05). There were no statistically significant differences in sensitivity, specificity, accuracy, and positive and negative predictive value of the two groups in the diagnosis of distant metastases (c 2 =0.440，c 2 =4.956，c 2 =0.013，c 2 =1.194，c 2 =2.618， P ＞0.05). Conclusion [ 68 Ga]Ga-DOTA-FAPI-04 has certain advantages over [ 18 F]FDG PET/CT in detecting lymph node and bone metastases. It has the same ability to detect other distant metastases and can be used as a supplementary imaging method for DTC.