Initial Ablation Ratio Predicts Volume Reduction and Retreatment After 5 Years From Radiofrequency Ablation of Benign Thyroid Nodules

Abstract

BackgroundRadiofrequency ablation (RFA) has gained ground as an effective and well-tolerated technique to treat benign thyroid nodules. Most of the available studies have described the short-term outcomes of RFA, whereas there is a limited number of studies evaluating long-term issues, such as regrowth and the likelihood of retreatments. In addition, risk markers of regrowth and retreatment remain to be defined. The initial ablation ratio (IAR) is an index that measures the amount of ablation after RFA, which has been associated with technique efficacy (i.e. volume reduction >50% after 1 year from the procedure). This study aimed at evaluating i) IAR reproducibility and ii) IAR predictive value for RFA 5-year outcomes.Materials and MethodsThis is a retrospective single center study on patients with benign thyroid nodules treated with RFA and followed for 5 years after initial treatment. IAR interobserver reproducibility was evaluated with Bland-Altman method and Lin’s concordance correlation coefficient (ρc). IAR predictive value for RFA 5-year outcomes was evaluated with linear and logistic regression models, as well as with Cox models, while receiver operating characteristic (ROC) analyses were used for cut-offs.ResultsWe selected 78 patients with 82 benign thyroid nodules. The procedure significantly reduced nodule volume and this reduction was generally maintained over time. Technique efficacy was achieved in 92% of patients, while 23% of nodules regrew and 12% of nodules were retreated. Median IAR was 83%. Lin’s concordance and Pearson’s correlation coefficients suggested a good interobserver reproducibility of this index, consistent with the limits of agreement of the Bland-Altman plot. IAR was significantly associated with technique efficacy, 1- and 5-year volume reduction ratio, and with the likelihood of a retreatment, but not with nodule regrowth. ROC analyses showed that IAR cut-off was 49% for technique efficacy and 73% for retreatment.ConclusionsOur results show for the first time that IAR is reproducible and that it predicts the volume reduction and the likelihood of a retreatment after 5 years from RFA.

Current Status and Challenges of US-Guided Radiofrequency Ablation of Thyroid Nodules in the Long Term: A Systematic Review

“…As opposed to the first long-term follow-up studies that focused primarily on the efficacy and safety of the technique, the most recent ones have brought up the issue of retreatment and regrowth [ 21 , 22 , 29 ], as defined by a recent proposal for standardization of terminology and reporting criteria [ 35 ]. Based on this proposal, nodule regrowth should be defined as a ≥50% increase compared to the minimum recorded volume measured at a given follow-up time point [ 35 ].…”

“…Given that in the aforementioned work, we could not identify predictors of regrowth, we evaluated if the initial ablation ratio (IAR), which is a semiquantitative index that measures the amount of the ablated area, could predict regrowth [ 22 ]. For this reason, we analysed RFA outcomes on 78 patients (82 nodules) that were followed for 5 years after the procedure.…”

“…Median IAR was 83%. IAR was significantly associated with technique efficacy, VRR, and with the likelihood of retreatment, but not with nodule regrowth [ 22 ]. In particular, an IAR > 49% was a good predictor of technique efficacy and an IAR > 73% was a good predictor of no retreatment in the five years following the procedure [ 22 ].…”

“…Recent studies have shown that also the initial ablation ratio (IAR) [ 46 ] or the residual vital ratio (RVR) [ 47 ] might help predict volume reduction and/or retreatment after RFA [ 22 , 33 , 46 , 47 ]. The IAR is a semiquantitative index that measures the amount of ablation after 1–3 months from RFA and it is calculated as follows: IAR = (ablated volume/total volume) × 100 [ 46 ].…”

“…Last year, one of the main focuses of the original articles that were published on thyroid RFA were its long-term outcomes [ 3 , 16 , 17 , 20 , 21 , 22 , 23 ], namely the volume reduction ratio and/or regrowths in patients with benign nodules and the recurrence rates in patients with malignant ones. Based on this, the aim of this systematic review was to provide an overview on these long-term outcomes of US-guided RFA in patients with either benign or malignant thyroid nodules, as well as to discuss its strengths and limitations.…”