Association between iodine intake and treatment outcomes dioiodine remnant ablation in patients with papillary thyroid cancer

Objectives To evaluate the association between iodine intake and treatment outcomes of radioiodine remnant ablation in patients with papillary thyroid cancer(PTC), and to investigate the determinants related to the ablation efficacy.

Methods A total of 95 PTC patients without distant metastases were enrolled into the retrospective study. All patients had undergone total thyroidectomy and 2-4 weeks of low iodine diet (LID) before initial ¹³¹I therapy. According to urinary iodine excretion(UIE) of patients, they were divided into 3 groups: moderate-severe iodine deficient (UIE＜50 ug/L, n=30), mild iodine deficient(UIE 50~100ug/L, n=26), adequate iodine (UIE 100~300 ug/L, n=39). Patients were followed up for 3 to 6 months after ablation, successful ablation was defined using the definition: no visible uptake in the thyroid bed on a follow-up scan and stimulated thyroglobulin(sTg) level <2 ug/L. Chi-square test, t-test, Mann Whitney rank-sum test and multivariate binary logistic regression analysis were performed.

Results 84.2%(80/95)of patients were successfully ablated.The successful rates in the three different iodine intake groups were 96.7%(29/30), 84.6%(22/26),74.4%(29/39), respectively, with significant difference among three groups(p<0.05).Besides UIE, univariate analysis revealed that TSH, sTg, remnant thyroid at ablation affected ablation efficacy.Logistic regression showed that stimulated Tg and adequate iodine intake were independent factors of ablation efficacy.

Conclusions Adequate iodine intake during ¹³¹I remnant ablation is one of important factors of treatment outcomes. Thyroid remnant is more successfully ablated if we make reasonable LID protocols according to the iodine nutritional status in PTC patients before treatment.