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

Abstract 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.