Bipolar radiofrequency ablation for nodular thyroid disease--ex vivo and in vivo evaluation of a dose-response relationship.

Background: The prevalence of thyroid nodules ranges between 2% and 60% depending on the population studied. However, minimally invasive procedures like radiofrequency ablation (rfA) are increasingly used to treat tumors of parenchymatous organs, and seem to be suitable for singular thyroid nodules as well. Their successful clinical application depends on the induction of sufficiently large lesions and a knowledge of the energy parameters required for complete thermal ablation. The aim of this study was to establish a dose-response relationship for rfA of thyroid nodules.

Material And Methods: Thermal lesions were induced in healthy porcine thyroid glands ex vivo (n=110) and in vivo (n=10) using a bipolar radiofrequency system; rf was applied in a power range of 10-20 watts. During the ablation, continuous temperature measurement at a distance of 5 and 10 mm from the applicator was performed. The transversal and axial lesion diameters were measured, and the volume was calculated. Furthermore, enzyme histochemical analysis of the thyroid tissue was performed.

Results: The inducible lesion volumes were between 0.91±0.71 cm(3) at 20W and 2.80±0.85 cm(3) at 14W. The maximum temperatures after rf ablation were between 44.0±9.7°C and 61.6±13.9°C at a distance of 5 mm and between 30.0±8.6°C and 53.5±8.6°C at a distance of 10 mm from the applicator. The histochemical analysis demonstrates a complete loss of nicotinamide adenine dinucleotide phosphate-oxidase (NADPH) dehydrogenase activity in thermal lesions as a sign of irreversible cell damage.

Conclusion: This study is the first to demonstrate a dose-response relationship for rfA of thyroid tissue. rfA is suitable for singular thyroid nodules and induces reproducible, clinically relevant lesions with irreversible cell damage in an appropriate application time.