6-Deoxy-6-[¹⁸F]fluoro-L-ascorbic acid PET/CT in postoperative metastatic differentiated thyroid cancer: a comparative...

To evaluate the diagnostic performance of ¹⁸F-fluoro-L-ascorbic acid ([¹⁸F]FAA) positron emission tomography-computed tomography (PET/CT) in detecting metastatic differentiated thyroid cancer (DTC) and compare it with ¹⁸F-fluorodeoxyglucose ([¹⁸F]FDG) PET/CT.

Data were retrospectively collected from patients who were clinically suspected or diagnosed with postoperative metastatic DTC between September 2023 and May 2024. Quantification was performed using the maximum standardized uptake value (SUVmax) and target-to-background ratio (TBR). Histopathological outcomes and clinical follow-up served as the reference standard for final diagnosis. Diagnostic accuracy was compared using McNemar's test, and tracer uptake was analyzed via the Wilcoxon signed-rank test.

A total of 85 participants (median age, 51 years; IQR, 38-61 years; 45 women) were evaluated. For cervical lymph nodes (LNs), [¹⁸F]FAA showed superior sensitivity (88% vs. 67%), accuracy (82% vs. 69%), and negative predictive value (78% vs. 57%) (all p < 0.001), with comparable specificity (72% vs. 74%, p = 0.64) and positive predictive value (84% vs. 81%; p = 0.44) than [¹⁸F]FDG. For distant metastases, [¹⁸F]FAA PET/CT demonstrated higher sensitivity than [¹⁸F]FDG for pulmonary metastases (53% vs. 27%), and bone metastases (72% vs. 21%) (all p < 0.001). Semiquantitatively, [¹⁸F]FAA had higher SUVmax in the cervical LN metastasis (10.3 vs. 5.4), pulmonary metastasis (4.7 vs. 2.8), and bone metastasis (16.1 vs. 3.0), as well as higher TBR in cervical LN (18.1 vs. 6.8) and bone metastasis (6.9 vs. 1.9) (all p < 0.01).

[¹⁸F]FAA PET/CT outperforms [¹⁸F]FDG PET/CT in the depiction of metastatic thyroid cancer, particularly in neck LNs, pulmonary, and bone metastases.

Question Is 6-Deoxy-6-[¹⁸F]fluoro-L-ascorbic acid PET/CT ([¹⁸F]FAA) PET/CT an imaging method that can identify metastatic lesions after thyroid cancer surgery, and is it superior to [¹⁸F]FDG PET/CT? Findings [¹⁸F]FAA exhibited higher sensitivity and elevated SUVmax values compared to [¹⁸F]FDG in the detection of lymph node, lung, and bone metastases of metastatic thyroid cancer. Clinical relevance [¹⁸F]FAA is a reliable diagnostic tool that can accurately locate metastatic sites after thyroid cancer surgery. This helps tailor treatment plans and predict prognosis based on different metastatic scenarios.