Tumor Burden of Iodine-Avid Bone Metastatic Thyroid Cancer Identified via ¹⁸F-Sodium Fluoride PET/CT Imaging

Background: Patients with differentiated thyroid cancer (DTC) are referred to radioactive I-131 (RAI) therapy and post-therapy I-131 whole-body scintigraphy (WBS) to identify local and/or remote metastases. Positron emission tomography (PET)/computed tomography (CT) imaging with F-18-fluoro-D-glucose (FDG) or F-18-sodium fluoride (NaF) may also be used with these patients for the evaluation of bone metastases. We compared the role of F-18-NaF PET/CT and F-18-FDG-PET/CT in patients with DTC and documented bone metastases at post-therapy WBS. Methods: Ten consecutive DTC patients with iodine avid bone metastasis at post-therapy WBS referred to F-18-NaF PET/CT and F-18-FDG PET/CT were studied. The findings of the three imaging procedures were compared for abnormal detection rates and concordance. Results: At post-therapy I-131 WBS, all patients had skeletal involvement with a total of 21 bone iodine avid lesions. At F-18-FDG PET/TC, 19 bone lesions demonstrated increased tracer uptake and CT pathological alterations, while 2 lesions did not show any pathological finding. At F-18-NaF PET/CT, the 19 bone lesions detected at F-18-FDG PET/TC also demonstrated abnormal tracer uptake, and the other 2 bone iodine avid foci did not show any pathological finding. Conclusions: In patients with DTC, F-18-NaF PET/CT did not obtain more information on the metastatic skeletal involvement than post-therapy I-131 WBS and F-18-FDG PET/CT.