<qa>  What was the mean standard deviation nodule volume?Symptomatic hypocalcaemia was not observed in any patient after HIFU treatments or during follow-up. A prospective monocenter study was performed in Bulgaria for the treatment of benign solid thyroid nodule by US-Guided HIFU. Twenty thyroid nodules were treated during one HIFU session. The mean standard deviation nodule volume was 4.96 mL 2.79 at the start of the study. Nodule volume had decreased to 3.05 mL 1.96 at the 3-month follow-up examination n 20, P .001, and reached 2.91 mL 2.43 by the 6-month follow-up examination n 16, P .001. By then, the mean volume reduction was 48.7 24.3 P .001. Minor transient complications such as subcutaneous edema and mild skin redness were observed in two patients. Another monocenter study was performed in Germany in 2014. Ten patients with one thyroid nodule each were treated by HIFU. Three months after the procedure, thyroid nodule volume was significantly reduced by 48.8 median and a shrinkage up to 75 of the volume was observed. In terms of safety, no serious side effect related to the procedure was reported. 