http://www.thyca.org/rai.htm#diet
ThyCa: Thyroid Cancer Survivors' Association, Inc.
In preparation for a radioactive iodine (RAI) scan or a RAI treatment, patients are usually asked to go on a low-iodine diet. The purpose of a low-iodine diet is to deplete the body of its natural stores of iodine to help make the radioactive iodine treatment more effective.