What is Radioactive Iodine for Thyroid Cancer?

Radioactive iodine therapy is most commonly used to treat thyroid cancer. The thyroid gland normally absorbs all the iodine in the body, so when patients swallow radioactive iodine, it travels through the blood and is concentrated in the thyroid. There, high-energy waves from the radioactive iodine begin to kill the cells of the thyroid, including the cancer cells.

Dosing Schedule for Radioisotope Therapy

Your multidisciplinary treatment team will consult with you to explain the dose of radioactive iodine that will best work for your thyroid cancer. Radioactive iodine is generally given in a capsule form.

Side Effects of Radioisotope Therapy

Because patients have to stop thyroid hormone prior to receiving radioisotope therapy, they may experience temporary side effects such as:

  • Tiredness
  • Muscle aches
  • Weight gain due to water retention
  • Changes in memory retention and concentration

Normal cells that are either rapidly dividing or situated close to the cancer cells being treated are also killed by radioactive iodine. Most often, they are cells of the salivary glands and cells lining the stomach. As a result of this bystander damage to normal cells, patients may experience:

  • Tenderness of the neck
  • Dry mouth and changes in taste due to temporary changes in function of salivary glands
  • Swelling of the salivary glands
  • Nausea, stomach upset and vomiting (rarely) due to radioactive iodine being taken up by cells of stomach

How to Prepare for Your Therapy

Patients may need to be admitted into the hospital if they are receiving a large dose of radioactive iodine. There are a number of measures that be taken that will help the thyroid gland to be ‘hungry’ for iodine and absorb as much of the radioactive iodine as possible. Prior to receiving radioactive iodine treatment you will need to do the following:

  • Stop taking thyroid hormone (L-thyroxine also commonly known by brand names such as Synthroid, Eltroxin or Levoxyl) for at least four and preferably six weeks prior to the radioactive iodine; stop taking liothyronine or T3 for 10-14 prior to therapy.
  • Eat a low iodine diet for one week prior to receiving radioactive iodine therapy.
  • Drink lots of fluids to make sure you have regular bowel movements before and after your therapy.

During Your Therapy

Patients receiving small doses of radioactive iodine may be treated in an outpatient setting, but those patients who need to receive larger doses will need to be admitted to the hospital.

After Your Therapy

  • Drink plenty of fluids to help eliminate radioactive iodine that has not been absorbed by the thyroid (patients cannot be safely discharged until that radioactive iodine that excreted).
  • Upon instructions from your head and neck specialist, patients may start taking thyroid hormone again.
  • Chew gum or suck on hard candies 24 hours after therapy to help decrease the swelling of the salivary glands.
  • Avoid getting pregnant for 6-12 months.
  • Stop breast feeding to prevent transmission of radioactive iodine to infants through breast milk.

Follow-Up Care

You will need to see your radiation oncologist and head and neck specialist about 4-8 weeks after you finish radioisotope therapy. At that visit, they will let you know the outcome of the therapy and discuss the long-term considerations.