Predictors of retreatment after radiofrequency ablation of benign thyroid nodules: role of pre-treatment growth rate and viable volume

Background: Radiofrequency ablation (RFA) has emerged as a minimally invasive and effective alternative to surgery for benign thyroid nodules, providing a significant volume reduction and symptom relief. However, approximately one in five patients experiences regrowth requiring retreatment. This study aimed to identify robust predictive factors - spanning the pre-, peri-, and post-treatment periods - to guide patient selection and follow-up strategies. Methods: In this retrospective cohort study, 293 patients underwent RFA for benign thyroid nodules at Pitié-Salpêtrière Hospital between 2018 and 2023. Retreatment, defined as a second RFA within five years, was the primary outcome. Twelve clinical and treatment variables were analyzed using univariate and multivariate logistic regression. Predictive performance was assessed with receiver operating characteristic (ROC) curves and corresponding area under the curve (AUC) values. Results: Sixty-one patients (20.8%) required retreatment. Among twelve parameters from three periods (pre-treatment, peri-treatment, and post-treatment), optimal multivariate models identified six significant ones. The pre-treatment growth rate (AUC = 0.808, OR = 1.505, 95% CI: 1.182-1.952, P < 0.001) and six-month viable volume (AUC = 0.886, OR = 1.252, 95% CI: 1.088-1.496, P < 0.001) showed the highest predictive accuracy. Optimal thresholds were 1.75 mm/year for pre-treatment growth rate and 4.45 mL for viable volume. Patients with viable volume ≤ 2.1 mL had a 70% when viable volume exceeded 18.05 mL. Four predictive abacuses were developed to facilitate clinical application. Conclusion: Pre-treatment growth rate and six-month viable volume are strong, independent predictors of retreatment after RFA of benign thyroid nodules. Incorporating these parameters into clinical decision-making may enhance patient selection, tailor treatment intensity, and inform follow-up intervals, thereby reducing the risk of retreatment and improving cost-effectiveness.