Radioactive iodine (RAI), or I131, is given to destroy thyroid tissue in your body.

Radioactive iodine works by preferentially concentrating in thyroid tissue and emitting radiation very slowly (for up to year) to kill thyroid cells. RAI is generally very well tolerated.

Indications for RAI

The are two indications for radioactive iodine therapy

Grave’s disease

  • A small dose of RAI is given
  • Contraindications (RAI therapy is not appropriate): moderate to severe eye disease, suspicious thyroid nodule (s), pregnancy or desire to become pregnant in next 12 months, need for quick control of hyperthyroidism.

Intermediate to high risk differentiated (papillary or follicular) thyroid cancer

  • Dose depends on your individual risk of recurrence and extent of your cancer
  • Definite indications for RAI for cancer: tumors that have spread to the surrounding tissues, distant metastases, and when gross tumor remains at the  end of surgery.
  • Strong indications for RAI for cancer: large tumor size (greater than 4cm), lateral lymph node involvement, aggressive histologic subtypes.
  • Definite indications to NOT give RAI for cancer: small tumors less than 1-2 cm confined to the thyroid gland with no evidence of spread to the lymph nodes or surrounding tissues.

The actual radioiodine treatment - practical matters

When giving RAI for cancer, there are two parts to treatment.

  • Preparing your body for RAI. You will need to a. Go on a low-iodine diet, and b. Increase the level of TSH in your blood (to be most effective).  This can be achieved in two ways:
    • Go off thyroid replacement and become hypothyroid (with all its side effects)
    • Temporarily raise the TSH by artificially stimulating the the TSH levels to increase. This is done by giving a medication called Thyrogen (recombinant human TSH) for two days before I131
  • Administration of the RAI pill (or liquid)

Radiation safety

  • Sometimes this will require hospitalization for up to 24 hours (if you get a high dose and depending on the state you live in)
  • ‘Contact’ precautions for a few days (This includes: separate beds, no close contact with animals, pregnant women, or young children; do not share food, utensils, etc..)

Possible Side Effects of RAI

Because I131 concentrates in the thyroid, there are few side effects throughout the body. However, there are a few, mainly temporary to watch for:

  • Short-term: neck or salivary gland tenderness and swelling, nausea and vomiting, dry mouth, taste changes, dry eyes
  • Long-term: temporary infertility (men and women) for 6 months to a year, irregular menstruation, small increase in leukemia with high doses