Thyroid Research Thyroid Research Archive Thyroid Cancer

The efficacy of iodine-131 therapy in patients with thyroid carcinoma is increased by a low iodine diet

(July 2003)

The background of the study. Patients with thyroid carcinoma are often treated with radioactive iodine (I-131) after surgery to destroy any remaining normal thyroid tissue and thyroid carcinoma. The effect of I-131 to destroy thyroid remnants may be increased by dietary iodine restriction. In this study the ability of I-131 to destroy thyroid remnants was compared in patients who ate a low-iodine diet or their usual diet before treatment.

How the study was done. The study subjects were 120 patients with papillary or follicular carcinoma who underwent thyroidectomy between 1986 and 1998. Four weeks after surgery 24-hour I-131 uptake was measured. The patients were then treated with a high dose of I-131 (mean, 76 mCi). Those patients treated from 1986 to 1991 ate their usual diet, whereas those treated from 1992 to 1998 ate a diet that reduced their lower urinary iodine excretion to ≤49 µg/day for four days before I-131 therapy. The patients were then treated with thyroxine for six months, at which time it was stopped, and thyroid uptake of I-131 scan was again measured.

The results of the study. There were 59 patients in the low-iodine diet group and 61 patients in the usual diet group. The characteristics of the patients, including tumor type, in each group were similar. The thyroid uptake of I-131 was higher in the low-iodine diet group before I-131 therapy, and they had more severe hypothyroidism and were more likely to have no detectable thyroid I-131 uptake and a low serum thyroglobulin concentration at the time of the second study.

The conclusions of the study. The efficacy of I-131 in destroying thyroid remnants in patients with thyroid carcinoma is increased if the patients eat a low iodine diet before I-131 administration.

The original article. Pluijmen MJ, Eustatia-Rutten C, Goslings BM, Stokkel MP, Arias AM, Diamant M, Romijn JA, Smit JW. Effects of low-iodide diet on postsurgical radioiodide ablation therapy in patients with differentiated thyroid carcinoma. Clin Endocrinol 2003;58:428-35.