131I SPECT/CT in the Follow-Up of Patients With Differentiated Thyroid Carcinoma

Purpose: I-131 SPECT/Spiral-CT has been shown to be superior to planar imaging in staging of differentiated thyroid carcinoma (DTC) at first radio-ablation. The purpose of this study was to investigate whether this is also true in the further follow-up of patients with DTC. Methods: From our clinical database, all patients with DTC who underwent planar scintigraphy as well as SPECT/low-dose spiral CT during follow-up between June 2005 and August 2010 were selected. Iodine-positive foci on the planar images as well as on the SPECT/CT data sets were classified as benign or equivocal/malignant. The criterion standard was provided by histology, other imaging modalities, and clinical and serological follow-up of at least 6 months. Results: A total of 123 patients with altogether 139 studies met the selection criteria. Whereas the sensitivities of SPECT/CT and planar imaging did not differ significantly (both 62%), the specificity of SPECT/CT was significantly higher than that of planar imaging (98 vs 78%, P < 0.01). SPECT/CT yielded a gain in diagnostic information in 20 (16.3%) of 123 patients (95% confidence interval, 10.8%-23.8%). Hybrid imaging led to a change of diagnosis in none of the patients in whom planar imaging result was normal, in 16% of patients with foci in the neck, and in 26% of patients with extracervical foci. Conclusions: In the follow-up of patients with DTC, SPECT/CT significantly improves specificity compared with planar imaging. Incremental diagnostic value is higher in lesions outside the neck than in those in the neck and absent in patients without iodine-positive foci on planar imaging.