131I SPECT/CT in the follow-up of patients with differentiated thyroid carcinoma

131I SPECT/Spiral-CT has been shown to be superior to planar imaging in staging of differentiated thyroid carcinoma (DTC) at first radioablation. The purpose of this study was to investigate whether this is also true in the further follow-up of patients with DTC.

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.

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.

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.