Comparison of 18F-FDG PET and Bone Scintigraphy in Detection of Bone Metastases of Thyroid Cancer

Abstract

We compared the efficacies of (18)F-FDG PET and (99m)Tc-bone scintigraphy for the detection of bone metastases in patients with differentiated thyroid carcinoma (DTC). We examined 47 patients (32 women, 15 men; mean age +/- SD, 57.0 +/- 10.7 y) with DTC who had undergone total thyroidectomy and were hospitalized to be given (131)I therapy. All patients underwent both whole-body (18)F-FDG PET and (99m)Tc-bone scintigraphy. The skeletal system was classified into 11 anatomic segments and assessed for the presence of bone metastases. Bone metastases were verified either when positive findings were obtained on >2 imaging modalities--(201)Tl scintigraphy, (131)I scintigraphy, and CT--or when MRI findings were positive if vertebral MRI was performed. Bone metastases were confirmed in 59 of 517 (11%) segments in 18 (38%) of the 47 study patients. The sensitivities (visualization rate) for bone metastases on a segment basis using (18)F-FDG PET and (99m)Tc-bone scintigraphy were 50 of 59 (84.7%) and 46 of 59 (78.0%), respectively; the difference between these values was not statistically significant. There were only 2 (0.4%) false-positive cases in a total of 451 bone segments without bone metastases when examined by (18)F-FDG PET, whereas 39 (8.6%) were false-positive when examined by (99m)Tc-bone scintigraphy. Therefore, the specificities of (18)F-FDG PET and (99m)Tc-bone scintigraphy were 449 of 451 (99.6%) and 412 of 451 (91.4%), respectively; the difference between these values was statistically significant (P < 0.001). The overall accuracies of (18)F-FDG PET and (99m)Tc-bone scintigraphy were 499 of 510 (97.8%) and 458 of 510 (89.8%), respectively; the difference between these was also statistically significant (P < 0.001). The specificity and the overall accuracy of (18)F-FDG PET for the diagnosis of bone metastases in patients with DTC are higher than those of (99m)Tc-bone scintigraphy, whereas the difference in the sensitivities of both modalities is not statistically significant. In comparison with (99m)Tc-bone scintigraphy, (18)F-FDG PET is superior because of its lower incidence of false-positive results in the detection of bone metastases of DTC.