Radioactive iodine (RAI), also written as I-131 or ¹³¹I, is a targeted treatment that uses the thyroid gland's natural ability to absorb iodine. Because the thyroid is the only tissue in the body that actively takes up iodine, radioactive iodine can selectively damage or destroy thyroid tissue while sparing surrounding structures.

Uses of Radioactive Iodine

  • Hyperthyroidism treatment — To reduce thyroid activity in Graves' disease or toxic nodular goiter
  • Thyroid cancer treatment — After thyroidectomy, to ablate (destroy) remaining thyroid tissue and treat metastases
  • Diagnostic scanning — Low doses used to image the thyroid and detect cancer spread

How RAI Treatment Works

RAI is taken orally as a capsule or liquid. The iodine is absorbed into the bloodstream and concentrated in thyroid tissue, where it emits beta radiation that destroys the cells. The radioactivity dissipates within days to weeks as iodine is eliminated through urine. Because the radiation is locally delivered and beta particles travel only a few millimeters, damage to nearby tissues is minimal.

RAI for Hyperthyroidism

For hyperthyroidism, a single oral dose of RAI typically produces a permanent reduction in thyroid function within 3–6 months. Most patients become hypothyroid and require lifelong levothyroxine — this is expected and manageable. Antithyroid medications are usually stopped 5–7 days before RAI treatment.

🚫 Contraindications: RAI is absolutely contraindicated during pregnancy and breastfeeding. Women of childbearing age must have a negative pregnancy test before treatment and must use reliable contraception for at least 6 months after RAI. Men should also avoid fathering a child for at least 6 months.

RAI After Thyroid Cancer Surgery

After total thyroidectomy for thyroid cancer, RAI ablation destroys any remaining thyroid tissue and can treat lymph node or distant metastases. For RAI to work optimally, TSH must be elevated to stimulate iodine uptake — achieved either by stopping levothyroxine (thyroid hormone withdrawal) or by injecting recombinant TSH (Thyrogen injections), which avoids the symptoms of hypothyroidism.

Radiation Safety Precautions

After RAI treatment, patients should follow temporary isolation precautions to protect others from radiation exposure. Common recommendations include:

  • Sleep alone for 5–7 days
  • Avoid close contact with pregnant women and young children for 5–14 days
  • Stay home from work (especially if working near pregnant women or children) for several days
  • Drink plenty of fluids and void frequently to flush iodine from the body
  • Avoid sharing utensils and towels for a few days

The specific duration of precautions depends on the dose received and will be outlined by your endocrinologist and nuclear medicine team.

Key Takeaways

  • RAI is a targeted, effective treatment for hyperthyroidism and thyroid cancer
  • It works by concentrating in thyroid tissue and delivering local radiation
  • Most patients treated for hyperthyroidism become hypothyroid and need levothyroxine long-term
  • RAI is absolutely contraindicated in pregnancy
  • Temporary radiation safety precautions protect family and close contacts
Medical Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider before making any changes to your treatment plan. Individual medical decisions should be made in partnership with your physician based on your specific circumstances.