Effect of a low iodine diet vs. restricted iodine diet on postsurgical preparation for radioiodine ablation therapy in patients with differentiated thyroid carcinoma

Abstract

Background and Objective: When treating differentiated thyroid carcinoma, radioiodine ablation therapy with iodine-131 (131I) is performed in patients who have undergone a total thyroidectomy. For effective radioiodine ablation therapy, L-thyroxine (L-T4) thyroid stimulating hormone (TSH) suppressive therapy as well as a restricted iodine diet for a certain period of time are recommended. Recommendations presented by the American Thyroid Association (ATA) in 2006 advocate a restricted diet for 1~2 weeks before radioiodine ablation therapy. However, because Korea is surrounded by sea on three sides, the average amount of iodine consumption per person is relatively high compared to people in other nations. Accordingly, a restricted diet for patients as a type of treatment may not be feasible and may greatly reduce their quality of life. Through a comparative review of a low iodine diet (LID) and a restricted iodine diet (RID) as postsurgical preparation for radioiodine ablation therapy in patients with differentiated thyroid carcinoma, this study aims to suggest standardized protocol and guidelines that are suitable for the conditions of Korea. Objects and Methodologies: From March of 2009 to May of 2010, this study was conducted with 101 patients who had undergone a total thyroidectomy for differentiated thyroid carcinoma at the Thyroid Cancer Center at Yonsei Severance Hospital. Excluded were patients with progressive thyroid carcinoma or relapsing thyroid carcinoma. For the study, the Research Institute of Food and Nutritional Science at Yonsei University provided meal plans for LID and RID, and the nutrition team at Shinchon Severance Hospital educated the patients about the diet. With 24-hour urine samples from the patients accumulated after a four-week restricted diet as well asa two-week restricted diet, the amount of iodine in the urine was estimated.

With the cooperation of the Department of Nuclear Medicine, the consumed radioiodine amounts for 2 hours and 24 hours were calculated, and a gap was identified. The amount of consumption (%) was calculated by comparing the amount of consumption at the neck based on the consumption amount at the thigh. Outcomes: This study was conducted with 47 patients on a LID composed of a male:female ratio of 1:6.8, with an average age of 53 (23~72), and 54 patients on a RID composed of a male:female ratio of 1:6.7, with an average age of 51.5 (24~72). The analysis of the clinical data and staging between the two groups did not show any statistical differences. The amount of iodine in the urine was measured at two and four weeks and compared between the groups. In the LID group, the average amount of iodine in the urine measured at the 2nd and the 4th week were 28.6 ug/gCr (3.7~107) and 35.0 ug/gCr (3.5~185.9), respectively,with rather less iodine in the urine after the 2-week restrictive diet, having no statistical meaning. In the case of the RID group, the average amount of iodine in urine measured at the 2nd and the 4th weeks were 35.8 ug/gCr (3.7~142.3) and 35.0 ug/gCr (1.9~152.6) respectively, with a slightly lower average amount of iodine in the urine after the 4-week restrictive diet, having no statistical meaning. For the amount of iodine in the urine between the two groups, LID was lower compared to RID for the 2-week diet, and the 4-week diet showed the same figures. However, both groups were included in the range of <50 ug/gCr, the criteria for radioiodine ablation therapy. Also, the radioiodine consumption checked at 2 hours and 24 hours after the 4-week restrictive diet did not show any statistical difference between two groups. Conclusion: The study confirmed that there were no differences in the amounts of urine iodine for a 2-week and 4-week restricted diet in each group, and a comparison between the two groups did not show a difference. In the amounts of radioiodine consumption for a 4-week restricted diet, the two groups did not show any difference. Against this backdrop, a 2-week RID can be considered a type of radioiodine ablation therapy after patients undergo a total thyroidectomy if they receive proper education. Furthermore, through RID, it is anticipated that patients will be able to enjoy a better quality of life.