Radioactive Iodine


For patients who require surgery for thyroid cancer, there may be residual traces of affected tissues that need to treated. Also known as I-131, radioactive iodine (RAI), which only affects the thyroid gland, may be given to patients in an attempt to destroy any remaining cancer cells. Since thyroid cells absorb most of the iodine that’s in the body, there is very little risk of radiation affecting healthy cells other than those in thyroid glands.

How Does Radioactive Iodine Treatment Work?

When thyroid cells absorb radioactive iodine, those cells are damaged or destroyed. RAI is typically administered in high doses in capsule or liquid form. Nearly all of the iodine will be absorbed by thyroid cells, which will ultimately destroy the thyroid gland and its cells, including ones that are abnormal, or cancerous.

When is Radioactive Iodine Treatment Recommended?

In addition to being recommended for patients who have had surgery but still show traces of cancer in thyroid glands, RAI therapy may be used to treat thyroid cancer that has spread to nearby lymph nodes or other areas. It is not recommended for smaller, solitary tumors less than a centimeter in size. However, radioactive iodine treatment may be effective on larger tumors greater than 4 centimeters.

RAI therapy may be recommended when cancer has spread to distant organs or lymph nodes (distant metastasis) or when a primary a tumor has extended to surrounding structures such as the larynx and trachea (gross extrathyroid extension). RAI treatment may also be effective for tumors that are:

  • Moderate in size and present in lymph nodes (node positive)
  • Multifocal in nature (a primary tumor with nearby “satellite tumors”)
  • Especially aggressive
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What Are the Potential Benefits of RAI Treatment?

For patients with the two most common forms of thyroid cancer (papillary thyroid cancer and follicular thyroid cancer), survival rates often improve. The same is true of patients with thyroid cancer that has spread to other areas adjacent to thyroid glands and elsewhere in the body. RAI treatment is not considered effective for forms of thyroid cancer where the cancerous cells do not absorb iodine. Medullary thyroid cancer (MTC) is an example of this type of thyroid cancer.

When is RAI Therapy Most Effective?

Prior to initiating radioactive iodine treatment, patients will undergo a thorough examination to determine what tissues are still affected by cancer and whether or not RAI therapy is an appropriate option. RAI treatment is considered most effective for patients with higher levels of thyrotropin, a thyroid-stimulating hormone. TSH increases the effectiveness of RAI because it stimulates cancer cells and thyroid tissues to encourage radioactive iodine absorption.

Radioactive iodine treatment is generally considered a safe treatment for most patients since it only affects thyroid cells. Some patients may experience dry mouth, nausea, and salivary gland swelling post-treatment. While there are no reports of issues in babies born to parents who underwent RAI treatment, female patients are urged to avoid pregnancy for six months to a year after treatment since radioactive iodine may remain in tissues after therapy is complete.