Two sequential applications of high-intensity focused ultrasound (HIFU) ablation for large benign thyroid nodules.

High-intensity focused ultrasound (HIFU) ablation is a promising treatment for benign thyroid nodules but single application is less effective in larger-sized nodules. We aimed to assess the efficacy and safety of two sequential applications in larger-sized nodules.Fifty patients underwent ablation of a large-sized nodule (baseline volume ≥ 20 mL and diameter ≤ 50 mm). Thirty-one (62.0%) patients underwent single application (group I) while 19 (38.0%) underwent two sequential applications (group II). Nodule shrinkage (by volume reduction ratio or VRR), pain scores during and after ablation, and rate of vocal cord palsy (VCP), skin burn, and nausea/vomiting were compared between the two groups. t test or the Mann-Whitney U test was used for continuous variables while chi-square test was used for categorical variables. To determine factors for VRR, multivariate analysis was done by logistic regression analysis.Total energy delivered and treatment time were significantly more in group II (p < 0.001 and p = 0.001, respectively). Total energy per nodule volume (kJ/mL) was also significantly greater in group II (1.01 kJ/mL vs. 0.57 kJ/mL, p < 0.001). The 6-month VRR was significantly greater in group II (56.74 ± 11.47% vs. 43.49 ± 12.03%, p = 0.004). Pain severity and rates of VCP, skin burn, and nausea/vomiting were comparable between the two groups (p > 0.05). Sequential application was an independent determinant of 6-month VRR (OR = 13.936, 95% CI = 1.738-197.399, p = 0.036).Sequential application led to better 6-month treatment efficacy than single application in large-sized nodules. Patients undergoing sequential application are not at greater risks of treatment-related side effects afterwards.• Sequential application produces better 6-month efficacy over single application for large-sized nodules. • Sequential HIFU application is well-tolerated and safe in patients with large-sized nodules. • Sequential application takes longer and requires larger amount of pethidine and diazepam.