Management of Thyroid Cancer: Radioiodine Ablation, “Stunning,” and Treatment of Thyroglobulin-Positive, 131I Scan-Negative Patients

Abstract

To present an overview of three controversial issues in the management of thyroid cancerradioiodine ablation, "stunning," and treatment of thyroglobulin-positive, (131)I scan-negative patients. Pertinent studies from the literature and personal experience are reviewed. Radioiodine is commonly administered after thyroidectomy to destroy residual normal thyroid cells, a procedure known as thyroid ablation. Currently, use of radioiodine for ablation has been shown to decrease the risk of recurrence, increase the sensitivity of postablation whole-body scanning with radioiodine, and increase the sensitivity of serum thyroglobulin testing. With use of conventional criteria, administration of 30,000 rad to the thyroid remnant will successfully ablate approximately 95% of remnants that are 2 g or less, but the success rate is lower in patients with larger remnants. The same degree of success can be achieved by administration of 50 mCi of (131)I. The use of larger amounts of radioiodine does not increase the number of patients with successful thyroid ablation. If recurrence is used as the endpoint, no difference has been observed between patients who were given 29 to 50 mCi and those given 50 to 100 mCi for ablation. Stunning occurs when (131)I administered for preablation imaging causes a decrease in uptake of radioiodine subsequently given for ablation. Scanning doses of 2 mCi or less have not been shown to cause stunning, but the risk increases progressively with larger amounts. Therapeutic radioiodine is being given to patients with detectable thyroglobulin but negative (131)I whole-body scans with increasing frequency. Although posttherapy scans show abnormal uptake in most cases, no available evidence indicates that these patients benefit from treatment. Radioiodine ablation after thyroidectomy decreases the risk of recurrent thyroid cancer and facilitates subsequent radioiodine treatment. Stunning can be avoided by use of a maximal scanning dose of 2 mCi. It seems reasonable to treat patients who have progressively increasing thyroglobulin levels but to continue careful observation in those with stable or decreasing thyroglobulin concentrations.