The purpose of this prospective study was to determine the incremental diagnostic value of single photon emission computed tomography/computed tomography with iodine-131 over planar whole body scan in the staging of patients with differentiated thyroid carcinoma. A total of 365 patients (270 female, 95 male) with differentiated thyroid carcinoma were treated with radioiodine therapy for thyroid remnant ablation with radical intent after thyroidectomy between January 2013 and November 2014. In addition to planar whole body scan, single photon emission computed tomography/computed tomography of neck and chest were performed. Each radioactive focus at whole body scan was classified as positive or equivocal with respect of specific territories: thyroid bed, cervical lymph nodes and distant metastases.Whole-body scan detected focal uptake in 353 patients and no uptake in 12. The location was considered equivocal in 100. Single photon emission computed tomography/computed tomography detected focal uptake in 356 patients and no uptake in nine. In three patients with negative wholebody scan, single photon emission computed tomography/computed tomography provided information about residual activity in the thyroid bed. By single photon emission computed tomography/computed tomography the location was equivocal in 18 patients only. Single photon emission computed tomography/computed tomography was helpful in 82 out of 100 patients with equivocal findings by whole body scan allowing a correct identification of the uptake sites. In a great number of equivocal whole body scan, due to high remnant activity, single photon emission computed tomography/computed tomography was able to differentiate between thyroid remnant and lymph nodes uptake. In 22 out of 100 patients with doubtful whole body scan, single photon emission computed tomography/computed tomography correctly identified nodal or distant metastases, and in 2/100 patients, focal uptake classified as metastatic by whole body scan was reclassified as para-physiological by single photon emission computed tomography/computed tomography. The TNM classification changed in 13 out of 22 patients. Single photon emission computed tomography/computed tomography improves detection and localization of the iodine-131 uptake after thyroidectomy in patients with differentiated thyroid carcinoma and it is more accurate than whole body scan to evaluate lymph nodes and to identify and characterize distant metastases. Single photon emission computed tomography/computed tomography aids assessment of lower/upper stage in a significant number of patients with differentiated thyroid carcinoma and it can affect therapy decision-making and patient management.
Keywords: 131-I; Differentiated Thyroid cancer; SPECT/CT; Staging; Whole body scan.