Ultrasound-Elastography for Predicting Response of Hyperfunctional Thyroid Nodules to Radioiodine Therapy: Initial Results

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Radioiodine Therapy (RIT) is an effective and safe treatment for hyperfunctional thyroid nodules. Individual therapy activity is calculated based on the volume of the targeted thyroid nodule and thyroid uptake, which is measured by the radioactive iodine uptake test [1]. During follow-up, treatment response should be evaluated within 6 months and should include thyroid scintigraphy and measurement of serum thyroid-stimulating hormone (TSH) level. RIT failure is observed in approximately 10% of treated patients for whom the estimated therapy activity was applied. It is unclear why some nodules do not respond to RIT. Possible explanations are malfunction of radioiodine absorption resulting in a lower absorbed dose than the calculated one, or a high iodine metabolism of thyroid cells resulting in a shorter retention of iodine in the nodules. Moreover, an inhomogeneous structure of the thyroid nodules could lead to an inhomogeneous distribution of radioiodine with some areas of the nodule remaining untreated or insufficiently treated. To prevent therapy failure and to identify patients at risk for insufficient treatment, a predictive marker of therapy response would be beneficial.

Many studies, including studies by Rago et al. and Vorländer et al., have investigated Ultrasound-Based Real-Time Elastography (USE) for the diagnosis of thyroid nodules. The initial results of those studies were promising for the diagnosis of malignant thyroid nodules. USE measures the stiffness of a tissue, and this characterization provides additional information about the nodule, e.g., a hard nodule is suspicious for malignancy. Although recently published studies were not able to reproduce the initial results of USE, we assumed that the stiffness of nodules can indicate nodule homogeneity and might have a predictive value for RIT.

In this study, 93 hyperfunctional thyroid nodules (52, 14, and 27 nodules of unifocal, bifocal, and multifocal thyroid autonomies, respectively) of 72 patients (52 women, 20 men; age 62.6 years ±12.2) with hyperthyroidism prior to RIT were included. One of the inclusion criteria was the absence of a large calcification or cystic areas, because these reduce the reliability of USE. For the remainder of the manuscript, solitary and bifocal autonomies will be referred to as “focal autonomies”. According to the guidelines of the European Association of Nuclear Medicine, all patients underwent a pretherapeutic assessment, including thyroid scintigraphy, ultrasound and determination of serum TSH. Additionally, a US-elastography of the target nodules was performed to evaluate elasticity prior to RIT. To assess the success of RIT, a follow-up examination was performed approximately 4 months after RIT and included thyroid scintigraphy and determination of TSH level.