Microwave Ablation of Symptomatic Benign Thyroid Nodules: Energy Requirement per ml Volume Reduction

Purpose: Microwave ablation (MWA) represents a novel thermal ablative treatment of benign thyroid nodules. The aim was to determine the energy required per ml volume reduction in order to match the required energy to the volume-of-interest (VOI). Materials and Methods: 25 patients with 25 nodules (6 solid, 13 complex and 6 cystic) were treated by microwave ablation (MWA). The transmitted energy (E) was correlated with the volume change (Delta V) after 3 months. The energy required per ml volume reduction after 3 months was calculated by E/Delta V. Results: MWA resulted in a significant (p < 0.0001) volume reduction (Delta V) with a mean of 12.4 +/- 13.0 ml (range: 1.5 - 63.2 ml) and relative reduction of 52 +/- 16 % (range: 22 - 77 %). There was a positive correlation between E and Delta V (r = 0.82; p < 0.05). The mean E/Delta V was 1.52 +/- 1.08 (range: 0.4 - 4.6) kJ/ml for all nodules and 2.30 +/- 1.5 (0.9 - 4.6), 1.5 +/- 0.9 (0.4 - 3.6), 0.75 +/- 0.25 (0.4 - 1.2) kJ/ml, respectively, for solid, complex and cystic nodules with a significant difference in E/Delta V for solid and cystic (p < 0.03). Conclusion: The energy required per volume depends on the nodule consistency. Solid nodules require more energy than cystic ones. The estimation of the energy needed per volume-of-interest as an additional parameter should help to avoid under-or overtreatment.