Treatment and Outcomes in Differentiated Thyroid Cancer: A Retrospective Exploration in Three UK Centres That Provide Different Advice on Low Iodine Diets

Background International guidelines on the treatment of differentiated thyroid cancers promote low iodine diets (LID) before radioiodine remnant ablation. Evidence that the LID ultimately improves treatment success is inconsistent. This study aimed to determine if there is a difference in ablation success rates according to provision of advice to follow a LID.Methods Retrospective study of patients with differentiated thyroid cancer treated with total thyroidectomy and radioiodine remnant ablation between 01/01/2015 and 31/12/2016 in 3 centres advising: no LID (C1: n=108); LID for 1-week before (C2: n=50); LID for 2-weeks before and 48 hours (C3: n=59) after RRA. Response to treatment was determined by adapted American Thyroid Association Dynamic Risk Stratification Score, stratified as excellent, indeterminate, or incomplete response.Results In total, 217 patients were included in the analysis. We found differences in preparation for radioiodine remnant ablation and in the assessment of outcomes between centres. Furthermore, although there was little difference in staging between centres there was a difference in the percentage of patients receiving 1.1GBq vs higher administered activities (15% in C1, 22% in C2 and 44% in C3, p<0.001). An excellent response was recorded for 49% in C1, 48% in C2 and 36% in C3 (p=0.61). With C1 as reference group, the odds ratios (OR) for an excellent response were C2 OR: 0.96 (95% CI 0.46,2.00) and C3 OR: 0.62 (95% CI 0.29,1.30), p=0.40.Conclusions We found no evidence that advice to follow a low iodine diet for 1 or 2 weeks before radioiodine remnant ablation impacts on ablation success but differences between centres means the results should be regarded as exploratory. There is no immediate need to change practice regarding the LID, but a prospective multi-centre study with a more homogenous approach to patient management or a randomised controlled trial will provide more definitive recommendations.

A pre-ablative thyroid-stimulating hormone with 30–70 mIU/L achieves better response to initial radioiodine remnant ablation in differentiated thyroid carcinoma patients

Our aim was to clarify the optimum pre-ablative thyroid-stimulating hormone (TSH) level for initial radioiodine remnant ablation (RRA) in patients with differentiated thyroid carcinoma (DTC). From December 2015 to May 2019, 689 patients undergone RRA at Nuclear Medicine Department, Second Hospital of Shandong University were included in the study. Patients were categorized by their pre-ablative TSH level grouping of < 30, 30–70 and ≥ 70 mIU/L. Response to RRA were evaluated as complete response (including excellent and indeterminate response) and incomplete response (including biochemical and structural incomplete response) after a follow-up of 6–8 months. Multivariable binary logistic regression model was used to explore the optimum pre-ablative TSH level range and independent factors associated with response to RRA. Rates of complete response to RRA were 63.04%, 74.59% and 66.41% in TSH level groups of < 30, 30–70 and ≥ 70 mIU/L, separately. With multivariate analysis, the study found that pre-ablative TSH levels, gender and lymph node dissection were independent predictors of response to RRA. TSH between 30 and 70 mIU/L had a higher rate of complete response compared with TSH < 30 mIU/L, OR 0.451 (95% CI 0.215–0.958, P = 0.036). A pre-ablative TSH level of 30–70 mIU/L was appropriate for patients with DTC to achieve a better response to RRA.