Indications for Radioactive Iodine Therapy in Thyroid Cancer

There are three main indications for postoperative iodine-131 (131I) use:
- To treat any known (or unknown) residual disease
- To reduce the risk of recurrence
- To destroy remaining noncancerous thyroid cells:
  - This last indication:
    - Called remnant ablation, improves the sensitivity of serum Tg and may also be used as a staging tool to identify previously undiagnosed tumors
The use of RAI therapy is a contentious issue with conflicting findings regarding recurrence and survival benefit:
- Largely stemming from the lack of prospective, randomized, and controlled trials
The patients for whom RAI may be beneficial can be clarified based on the initial risk stratification of the individual tumor (Table) and the postoperative disease status

Studies have consistently shown that patients with American Thyroid Association (ATA) low-risk tumors measuring 1 cm lacking nodal and distant metastases:
- Do not benefit from RAI therapy, and its use is not recommended
Additionally, low-risk tumors measuring 1 to 4 cm lacking local or distant metastases with complete tumor resection and no tumor invasion into the locoregional tissues or structures:
- Do not derive mortality benefit from adjuvant RAI therapy:
  - As such, RAI therapy should not be routinely used in this group unless there is an aggressive histology or evidence of vascular invasion
In contrast, RAI does appear to be beneficial in terms of mortality and disease-free survival for those patients with a high-risk tumor:
- Its use is routinely recommended in the postoperative management of these patients
For the remaining patients, including those with intermediate risk for recurrence:
- There is conflicting data regarding the benefits of therapy:
  - Use of RAI in this cohort of patients should be considered on a case-by-case basis

Published by Rodrigo Arrangoiz MS, MD, FACS, FSSO