Usefulness of SPECT/CT to Detect Residual Thyroid Differentiated Carcinoma after Radioablation

Abstract

In the absence of distant metastasis after total thyroidectomy for differentiated thyroid cancer, ¹³¹I ablation with a dose of 30 mCi is performed. However, a single dose of ¹³¹I is not always sufficient, and re-dosing is becoming increasingly common. Difficulties are associated with using conventional ¹³¹I whole-body scintigraphy to detect residual thyroid tissue (thyroid bed) in the head and neck region and assess treatment efficacy. Post-treatment imaging with whole-body scintigraphy was performed on the present cases after the first administration of ¹³¹I, and with whole-body scintigraphy and single photon emission computed tomography/computed tomography after the second administration. In case 1, ¹³¹I flowed into the gap between a tooth and crown, and non-specific uptake was observed on single photon emission computed tomography/computed tomography. In case 2, saliva containing ¹³¹I adhered to dentures in the oral cavity, and whole-body scintigraphy indicated uptake in the lesion; however, this was confirmed as a false positive by single photon emission computed tomography/computed tomography. In case 3, the uptake of ¹³¹I in the thyroglossal duct pathway was confirmed by single photon emission computed tomography/computed tomography. Therefore, single photon emission computed tomography/computed tomography was useful for detecting non-specific uptake in the head and neck region.