Positron emission tomography in the detection of iodine-negative recurrences and metastases in patients with differentiated thyroid cancer

Solodyannikova O.I.1, Kmetyuk Y.V.2, Danilenko V.V. 1, Sukach G.G.1, Makulyak L.Ya.1

Summary. Introduction. According to foreign authors, the appearance of iodine-negative metastases is observed in 7–25% of cases of differentiated thyroid cancer. As a result, radioiodine therapy becomes ineffective, which, according to the European Consensus on the Management of Patients with Differentiated Thyroid Carcinoma «European consensus for the management of patients with differentiated thyroid carcinoma of the follicular epithelium» (2010) is a mandatory step in complex treatment of differentiated thyroid cancer. The aim is to study the possibilities of positron emission tomography (PET)/computed tomography (CT) with 18F-fluorodeoxyglucose (FDG) in postoperative management of patients with iodine-negative metastases of differentiated thyroid cancer. Materials and methods of research. The study group consisted of 30 patients with iodine-negative metastases of the thyroid gland, who after 131I-NaI negative scan, underwent PET with 18F-FDG. The comparison group consisted of 25 patients who underwent X-ray CT. Results. It was found that signs of possible prolongation of the disease were indicators of thyroglobulin and thyroid-stimulating hormone, as well as ultrasound and CT. On average, the examined patients before the appearance of signs of iodine resistance, were conducted from 5 to 8 courses of radioiodine therapy. In 42% of them there was no accumulation of radioiodine in the lymph nodes of the neck, in 10% — in the lungs, in 8% — in the bones. In all patients, the absence of iodine accumulation was established on the last two post-treatment scans. In order to confirm the presence or absence of foci detected by other diagnostic methods, patients underwent PET/CT with 18F-FDG. Comparative analysis of the effectiveness of PET and X-ray CT in iodine-refractory forms of differentiated thyroid cancer revealed the following results — the highest sensitivity is characteristic of PET with 18F-FDG (p <0.05), with X-ray CT this figure is much lower (p >0.05). Conclusions. PET with 18F-FDG is a highly informative method for detecting iodine-negative metastases of the thyroid gland during the prolongation of the process in the lymph nodes and lungs. Comparative evaluation of CT and PET with 18F-FDG revealed the highest sensitivity characteristic of PET with 18F-FDG (p <0.05). X-ray CT is characterized by significantly lower values of both sensitivity and specificity and accuracy (p >0.05). The use of PET with 18F-FDG will allow timely detection of recurrences and metastases of iodine-negative differentiated thyroid cancer and appropriate treatment, namely surgery, radiation and targeted.Keywords: Iodine-negative metastases of differentiated thyroid cancer; positron emission tomography with 18F-FDG; comparative analysis of diagnostic possibilities of PET with 18F-FDG and X-ray CT.

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