Comparison of FDG PET/CT and Ga-68 PSMA PET/CT imaging in radioactive iodine-refractory differentiated thyroid cancer

Aim: We aim to compare the lesion detection rates of routinely used FDG PET/CT with those of Ga-68 PSMA PET/CT in radioactive iodine-refractory differentiated thyroid cancer (RAIRDTC). Additionally, the study aims to evaluate the theranostic potential of PSMA using Ga-68 PSMA PET/CT. Materials and Methods: Patients with RAIR-DTC followed in our department between 2022- 2024 were included in the study. FDG PET/CT and Ga-68 PSMA PET/CT imaging were performed. Areas with higher uptake than the background were considered positive, excluding physiological uptake and benign foci on CT. Lesion detection rates were calculated and the tumor-to-background ratio (TBR) was determined by dividing the SUVmax values of the lesions by the SUVmean values of the blood pool (aorta). Results: FDG PET/CT detected a significantly higher number of lesions than Ga-68 PSMA PET/CT, including in the thyroid bed, lymph nodes, lungs, and other regions; while Ga-68 PSMA PET/CT detected more lesions in the bones. The SUVmax and TBR values on FDG PET/CT were found to be significantly higher compared to Ga-68 PSMA PET/CT. Additionally, in 10 patients, Ga-68 PSMA PET/CT detected lesions with SUVmax values higher than the liver SUVmax, suggesting that these patients might be candidates for PSMA-based radionuclide therapy. Conclusion: Although FDG PET/CT demonstrated higher lesion detection compared to Ga-68 PSMA PET/CT, PSMA PET detected more bone lesions. Additionally, PSMA PET may be beneficial in predicting the potential for radionuclide therapy in this patient group with limited treatment options. Further studies with larger cohorts are necessary.