The changing role of radioiodine in the management of differentiated thyroid cancer.

This article discusses several aspects of the evaluation and management of differentiated thyroid carcinoma that are changing or may change in the near future. Although conventional treatment of this disease is highly effective, some modification may improve the welfare of patients and the overall results. Because the symptoms of hypothyroidism are vexing, there has been great interest in using recombinant human thyroid-stimulating hormone (rhTSH) to prepare patients for iodine 131 imaging. rhTSH has been about as effective as thyroid hormone withdrawal for diagnostic imaging so that approval for this use is expected. Another topic of interest is the administration of 131I therapy to patients whose serum thyroglobulin levels are abnormal but whose diagnostic 131I scans are negative. Because the 131I scans after therapy are often abnormal in these patients and a reduction of serum thyroglobulin can occur, this approach seems effective. The long-term impact of this therapy on recurrence and survival, however, is unknown. A third issue that is currently under review is the amount of 131I that should be used for diagnostic scanning. Although past opinion favored larger doses, "stunning" of thyroid remnant and tumor can occur with diagnostic 131I imaging. Substituting iodine 123 is an alternative for postthyroidectomy scanning, but when administered as 300 uCi it is less accurate than 131I for recurrent disease or distant metastases. Related to these issues, two other topics are reviewed: the use of other radiopharmaceuticals for imaging patients with thyroid cancer, and 131I dosimetry.