Table 1.

The risk assessment system for the ablation of benign thyroid nodules

Grade	Location of nodules
Grade 0, low risk	Nodules located in the thyroid parenchyma, and the distance between nodule edge and adjacent important structures was ≥ 2 mm.
Grade 1, median risk	The distance between nodule edge and carotid sheath, anterior cervical muscles or cervical posterior muscles was less than 2 mm.
Grade 2, high risk	The distance between nodule edge and trachea, esophagus, or recurrent laryngeal nerve was less than 2 mm.
Grade 3,Very high risk	Both Grade 1 and Grade 2 were existed.