Effect of gut retention on the effective whole body half-time of iodine-131 in thyroid cancer patients

The whole body radiation dose resulting from iodine-131 (131I) therapy in patients with thyroid cancer is directly related to the effective whole body half-time of 131I in those patients. In 101 studied on 64 patients referred for quantitative whole body radioiodine scans for thyroid cancer, the effective whole body half-time was found to be significantly greater when gut retention was maximal. These results indicate that gut retention is a significant contributor to the whole body half-time of 131I. The routine use of non-iodine-containing laxatives at the time of 131I studies and therapy may be useful in decreasing whole body 131I retention times and, therefore, in decreasing whole body radiation doses, and should be considered in such patients