Staging of Differentiated Thyroid Carcinoma Using Diagnostic 131I SPECT/CT

OBJECTIVE. The purpose of this study was to evaluate the feasibility of staging differentiated thyroid carcinoma (DTC) before initial radioiodine therapy using diagnostic radioiodine-131 (I-131) scintigraphy with SPECT/CT and to determine the additional value of SPECT/CT. MATERIALS AND METHODS. Forty-eight patients (12 men and 36 women; age range, 17-82 years) with DTC underwent diagnostic I-131 planar imaging and SPECT/CT scintigraphy reinterpreted by two readers, one of whom was not blinded to patients' clinical details. Staging and scoring of carcinomas was done by use of TNM with three levels of sequential information: histopathologic analysis and chest radiograph data, planar images, and SPECT/CT data. Restaging based on the imaging findings was designated as "iTNM." RESULTS. Diagnostic I-131 scintigraphy allowed TNM staging of DTC before initial radioiodine therapy. Planar images detected previously unsuspected distant disease in four (50%) of eight patients with a score of M1. SPECT/CT changed the planar scan interpretation for 19 (40%) of 48 patients, detecting regional nodal metastases in four patients and clarifying equivocal focal neck uptake in 15 patients. Compared with histopathologic analysis and chest radiograph data, planar images and SPECT/CT changed the postsurgical DTC stage for 10 (21%) of 48 patients. SPECT/CT information changed the proposed I-131 therapeutic dose for 28 (58%) of 48 patients, on the basis of our department protocol. CONCLUSION. Diagnostic I-131 scintigraphy, planar images, and SPECT/CT complete the postsurgical staging of DTC. SPECT/CT reduces the number of equivocal diagnoses on planar imaging and improves the interpretation of I-131 scintigraphy. The consequent changes in TNM scores and staging should influence the I-131 dose prescribed at initial therapy.