Head-to-head comparison of [68Ga]Ga-DOTA.SA.FAPi with [18F]F-FDG PET/CT in radioiodine-resistant follicular-cell derived thyroid cancers

Abstract

Abstract Purpose [18F]F-FDG is a standard and valuable diagnostic imaging modality for radioiodine-resistant follicular-cell derived thyroid cancers (RAI-R FCTC). Recently, molecular imaging probes targeting cancer-associated fibroblasts (CAFs) have gained prominence and have proved to be a potential alternative to [18F]F-FDG PET/CT in oncological imaging. This study aimed to compare the diagnostic efficacy of [68Ga]Ga-DOTA.SA.FAPi and [18F]-FDG PET/CT in RAI-R FCTC patients. Methods The retrospective study included 117 RAI-R FCTC patients [68 females, 49 males; mean age: 53.2 ± 11.7 years]. Qualitative assessment parameters included comparing patient-based and lesion-based visual interpretation of both scans. The quantitative assessment included comparing standardized uptake values corrected for lean body mass (SULpeak and SULavg). The findings on both scans were validated with the morphological findings of the diagnostic computed tomography. Results 60 had single remnants, and 9 had bilateral remnant lesions with a complete concordance in the detection rate on both PET scans. [68Ga]Ga-DOTA.SA.FAPi showed a higher detection efficiency rate for lymph nodes (sensitivity 95.4% vs 86.6%, p < 0.0001), liver metastases (100% vs. 81.3%; p < 0.0001), brain metastasis (100% vs. 43.4%; p-0.0003). Except for brain metastasis (SULpeak [68Ga]Ga-DOTA.SA.FAPi vs. [18F]-FDG: 13.9 vs. 6.7) and muscle metastasis (SULpeak FAPI vs. FDG: 9.56 vs. 5.62), there was no significant difference in the median SUL uptake values between the radiotracers. Conclusion [68Ga]Ga-DOTA.SA.FAPi showed a superior detection efficiency for lymph nodes, liver, bowel, and brain metastasis. Unlike [18F]F-FDG, [68Ga]Ga-DOTA.SA.FAPi can be used as theranostic probes in RAI-R FCTC. [68Ga]Ga-DOTA.SA.FAPi provided a complimentary benefit to the [18F]F-FDG-PET/CT scan in the imaging of RAI-R FCTC.