Utility of ^99m Tc-Hynic-TOC in 131I Whole-Body Scan Negative Thyroid Cancer Patients with Elevated Serum Thyroglobulin Levels

Several studies have reported on the expression of somatostatin receptors (SSTRs) in patients with differentiated thyroid cancer (DTC). The aim of this study was to evaluate the imaging abilities of a recently developed Technetium-99m labeled somatostatin analog, ^99m Tc-Hynic-TOC, in terms of precise localization of the disease. The study population consisted of 28 patients (16 men, 12 women; age range: 39-72 years) with histologically confirmed DTC, who presented with recurrent or persistent disease as indicated by elevated serum thyroglobulin (Tg) levels after initial treatment (serum Tg > 10 ng/ml off T4 suppression for 4-6 weeks). All patients were negative on the Iodine-131 posttherapy whole-body scans. Fluorine-18 fluorodeoxyglucose positron emission tomography ( ¹⁸ F-FDG PET) was performed in all patients. SSTR scintigraphy was true positive in 23 cases (82.1%), true negative in two cases (7.1%) and false negative in three cases (10.7%) which resulted in a sensitivity of 88.46%, specificity of 100% and an accuracy of 89.2%. Sensitivity of ^99m Tc-Hynic-TOC scan was higher (93.7%) for patients with advanced stages, that is stages III and IV. ¹⁸ F-FDG showed a sensitivity of 93.7%, a specificity of 50% and an accuracy of 89.3%. ¹⁸ F-FDG PET was found to be more sensitive, with lower specificity due to false positive results in 2 patients. Analysis on a lesion basis demonstrated substantial agreement between the two imaging techniques with a Cohen′s kappa of 0.66. Scintigraphy with ^99m Tc-Hynic-TOC might be a promising tool for treatment planning; it is easy to perform and showed sufficient accuracy for localization diagnostics in thyroid cancer patients with recurrent or metastatic disease.

Keywords

Fluorodeoxyglucose positron emission tomography - Hynic-TOC - single-photon emission computed tomography - thyroglobulin elevated - thyroid cancer - whole-body scan negative

Publication History

Article published online:
21 May 2022