Objective: The aim of this study was to compare the diagnostic and prognostic values of 99mTc-MDP-planar bone scintigraphy (99mTc-MDP-BS), 131I single-photon emission computed tomography/computed tomography (131I-SPECT/CT) and 18F-fluorodeoxyglucose (18F-FDG)-PET/CT for the detection of bone metastases from differentiated thyroid cancer (DTC).
Methods: Eighty patients with DTC with suspected bone metastases from DTC were retrospectively analysed. All patients were examined with 99mTc-MDP-BS, 131I-SPECT/CT and 18F-FDG-PET/CT, with a maximum interval of 2 months between scans. The diagnostic performances of 99mTc-MDP-BS, 131I-SPECT/CT and 18F-FDG-PET/CT were investigated and compared. Univariate and multivariate analyses were carried out to evaluate the effects of variables on the survival of patients.
Results: Out of the 80 patients with 148 foci, 43 with 106 foci were diagnosed as being true positive for bone metastases from DTC. In patient-based analysis, the sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of 99mTc-MDP-BS were 79.07, 83.78, 85.00, 77.50 and 81.25%, respectively; those of 131I-SPECT/CT were 93.02, 97.30, 97.56, 92.31 and 95.00%, and those of 18F-FDG-PET/CT were 86.05, 94.59, 94.87, 85.36 and 87.80%, respectively. In lesion-based analysis, the sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of 99mTc-MDP-BS were 72.64, 73.81, 87.50, 51.67 and 72.97%, respectively; those of 131I-SPECT/CT were 92.45, 97.62, 98.99, 83.67 and 93.92%, and those of 18F-FDG-PET/CT were 85.85, 88.10, 94.50, 71.15 and 86.49%, respectively. Comparing the receiver-operating characteristic area using the McNemar test, both 131I-SPECT/CT and 18F-FDG-PET/CT were found to be superior to 99mTc-MDP-BS for the detection of bone metastases from DTC in patient-based and lesion-based analyses (P<0.05). Patient-based analysis showed that there were no significant differences between 131I-SPECT/CT and 18F-FDG-PET/CT (P=0.087) but lesion-based analysis revealed that 131I-SPECT/CT was superior to 18F-FDG-PET/CT (P=0.002). For the association between these image patterns and the prognosis of DTC patients, 18F-FDG positivity was the factor predicting a poor prognosis.
Conclusion: 131I-SPECT/CT and 18F-FDG-PET/CT demonstrated high diagnostic performance in detecting bone metastases from DTC. 99mTc-MDP-BS might be completely replaced by 131I-SPECT/CT in combination with 18F-FDG-PET/CT in the management of DTC patients with bone metastases. 18F-FDG-PET/CT positivity was an independent factor associated with poor prognosis.