Dietary Iodine Restriction in Preparation for Radioactive Iodine Treatment or Scanning in Well-Differentiated Thyroid Cancer: A Systematic Review

Background: Dietary iodine is often restricted before radioactive iodine (RAI) scanning or treatment of welldifferentiated thyroid cancer. Our objective was to examine the impact of a low-iodine diet (LID) before RAI treatment or scanning on the following outcomes: (i) the efficacy of thyroid remnant ablation (or residual disease elimination), (ii) urinary iodine measurements, (iii) RAI kinetics, and (iv) long-term thyroid cancer outcomes. Methods: We performed a systematic review of the English literature. We searched four electronic databases and conducted a hand search. Two reviewers independently screened citations and reviewed full-text articles and reached consensus on included articles. Two reviewers independently abstracted data. Results: We reviewed 76 abstracts or citations and 26 full-text articles. Eight studies were included in the review. The most commonly studied diets allowed <= 50 mu g/day of iodine for 1-2 weeks. In one study, 6-month successful remnant ablation rates were higher in patients following an LID than in controls. However, in another study, there was no significant benefit of an LID. LIDs reduce urinary iodine measurements and appear to increase I-131 uptake or lesional radiation compared to regular diets. No studies have examined long-term recurrence or mortality rates. Conclusions: Given that LIDs reduce urinary iodine measurements, increase I-131 uptake, and possibly improve efficacy of I-131 treatment, we currently favor the use of a 1-2-week LID before I-131 therapy or scanning. However, more research is needed to clarify the role of this dietary intervention.