Abstract
PurposeThe aim of this study was to assess the potential role of thyroglobulin (Tg) kinetics in predicting 2-[18F]-FDG-PET/CT results and overall survival (OS) in patients affected by differentiated thyroid carcinoma (DTC) and suspected recurrence.MethodsOn hundred and thirty-nine patients were retrospectively included. All patients underwent 2-[18F]-FDG-PET/CT due to detectable Tg levels and negative [131I] whole-body scan. The last two consecutive serum Tg measurements before PET/CT were used for Tg-doubling time (TgDT) and Tg-velocity (Tg-vel) calculation. Receiver operating characteristic (ROC) curves were used to determine the optimal cutoff points for Tg, TgDT and Tg-vel for predicting PET/CT results.ResultsOne hundred and fifteen (83%) patients had positive PET/CT for DTC recurrence, while the remaining 24 (17%) negative. Stimulated Tg before PET and Tg-vel were significantly higher in patients with a positive PET/CT scan than negative scan (average Tg 190 vs 14 ng/mL, p = 0.006; average Tg-vel 4.2 vs 1.7 ng/mL/y, p < 0.001). Instead, TgDT was significantly shorter in positive scan (average TgDT 1.4 vs 4.4 years, p < 0.001). ROC curve analysis revealed the best Tg, TgDT and Tg-vel cutoff of 18 ng/mL,1.36 years and 1.95 ng/mL/y. In patients with Tg<18 ng/mL, the PET/CT detection rate was significantly lower in patients with low Tg-vel (p = 0.018) and with long TgDT (p = 0.001). ATA class risk, PET/CT results and Tg before PET were confirmed to be independent prognostic variables for OS.ConclusionsTg kinetics may help to predict 2-[18F]-FDG-PET/CT results in DTC patients with negative [131I]WBS and detectable Tg, especially in case of low-moderate Tg.
Highlights
Differentiated thyroid cancer (DTC) is the most diffuse endocrine cancer and it is usually considered a cancer with favorable management and a long-term survival [1], except of the cases with distant metastases and iodine refractory disease [2].Excluding low-risk disease, the baseline treatment of DTC consists of thyroidectomy followed by postoperative risk-adapted sodium iodide ([131I]) therapy if indicated [1, 3]
The aim of this study was to assess the potential usefulness of Tg kinetics (Tg, Tg-doubling time (TgDT), Tg-vel) in predicting 2[18F]-FDG PET/CT results and to compare their relative efficacy for restaging DTC patients with detectable Tg and a negative [131I]WBS
We retrospectively screened 2500 patients who underwent [131I] therapy for DTC after total or nearly total thyroidectomy from December 2006 to December 2020 using our institutional Radiology Information System. They were admitted to our Nuclear Medicine Department for the ablation of thyroid remnant and/or therapy according to EANM (European Association of Nuclear Medicine) guidelines [24]
Summary
Excluding low-risk disease, the baseline treatment of DTC consists of thyroidectomy followed by postoperative risk-adapted sodium iodide ([131I]) therapy if indicated [1, 3]. A long-term active follow-up is mandatory because DTC is a dynamic disease and the possibility to have persistent disease or relapse is not uncommon, especially in intermediate and high risk patients [6]. In this clinical scenario, a serum marker useful to check the DTC disease status and its evolution is fundamental.
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