Radioactive iodine (RAI) is a therapy used in the treatment of some thyroid cancers, specifically papillary and follicular thyroid cancer. For the thyroid gland to make thyroid hormone, the first step in the process is for the thyroid cells to "take up" iodide from the bloodstream. Iodide is one of the building blocks used to produce thyroid hormone. By making the iodine radioactive (in the form of I-131), it becomes toxic to cells that accumulate iodine from the bloodstream, in turn killing these cells. This therapy can be used for several purposes:
- The most common use of RAI is to destroy (called "ablate") the small amount of normal thyroid that remains (called the "remnant") after you have had thyroid surgery (near-total or total thyroidectomy). This use of RAI is called remnant ablation.
- Sometimes, but not always, thyroid cancer cells are also able to "take up" iodine, which means that the cancer cells are "iodine-avid". If there are any remaining thyroid cancer cells after surgery or if thyroid cancer returns AND if the cells have this ability to concentrate iodine, then the RAI may kill these cells and act as a treatment.
- RAI treatment includes a follow up scan, known as a "post-therapy scan" performed 7-10 days after treatment, which can also allow your treatment team to see that the RAI targeted the thyroid "remnant" and to detect if there are any remaining cancer cells that "took up" the I-131 but were not visible on other scans.
- RAI treatment can also be repeated for persistent, recurrent, or metastatic thyroid cancer (cancer that has spread outside the thyroid gland, to lymph nodes or other areas of the body).
Given the potential benefits of RAI, it may seem like something all patients with thyroid cancer should receive. However, RAI does have potential side effects to consider. In addition, patients with larger, more aggressive or residual tumor after surgery have been shown to derive a survival benefit with RAI, but those with smaller, less aggressive cancers have not.