Radioactive Iodine Therapy

Radioactive iodine therapy is a treatment that uses a radioactive form of iodine to destroy overactive or cancerous thyroid tissue from the inside.

The thyroid gland — the butterfly-shaped gland in the front of your neck — naturally absorbs almost all the iodine you consume. When you swallow a capsule or liquid containing radioactive iodine (called iodine-131), the thyroid pulls it in just like regular iodine. Once inside, the radiation damages or destroys the thyroid cells while causing very little harm to surrounding tissues. The effect builds over several weeks as treated cells gradually stop working.

Radioactive iodine therapy is used when the thyroid gland is producing too much hormone or when thyroid cancer cells need to be eliminated. A specialist in nuclear medicine or an endocrinologist (a hormone specialist) decides whether this treatment is the right fit based on the patient's diagnosis, age, and overall health.

• Hyperthyroidism (an overactive thyroid) caused by Graves' disease — an autoimmune condition that makes the thyroid produce excess hormone
• Toxic nodular goitre — one or more lumps in the thyroid that produce too much hormone on their own
• Differentiated thyroid cancer — the most common types of thyroid cancer, including papillary and follicular thyroid cancer, especially after surgical removal of the thyroid
• Remnant ablation — destroying small amounts of thyroid tissue left behind after surgery for thyroid cancer
• Metastatic thyroid cancer — cancer that has spread from the thyroid to other parts of the body, such as the lungs or bones, when those cells still absorb iodine

There are situations where radioactive iodine therapy is not suitable. A doctor will consider avoiding or postponing it in these cases:

• Pregnancy — radiation can seriously harm a developing baby
• Breastfeeding — radioactive iodine passes into breast milk
• Thyroid cancer types that do not absorb iodine, such as medullary or anaplastic thyroid cancer
• Severe eye disease related to Graves' disease (called thyroid eye disease or Graves' ophthalmopathy), where the treatment may worsen eye symptoms
• Patients who cannot follow the radiation safety isolation instructions required after treatment

Radioactive iodine therapy is generally well tolerated, but like any treatment, it carries possible side effects and risks that your care team will discuss with you beforehand.

• Hypothyroidism (an underactive thyroid) — the most common long-term outcome; the thyroid produces too little hormone and lifelong thyroid hormone replacement tablets are usually needed
• Neck tenderness or swelling — mild soreness in the neck area in the days after treatment as thyroid cells break down
• Nausea — some patients feel sick to their stomach shortly after swallowing the iodine, usually mild and brief
• Dry mouth and reduced saliva — the salivary glands (glands that make saliva) can absorb a small amount of radioactive iodine, causing temporary or, rarely, longer-lasting dryness
• Changes in taste or smell — usually temporary, resolving within weeks to months
• Radiation sialadenitis (inflammation of the salivary glands) — causing jaw pain or swelling, more common with higher doses used for thyroid cancer
• Worsening of thyroid eye disease — in patients who already have eye problems related to Graves' disease, symptoms may temporarily increase
• Temporary reduction in sperm count in men — usually recovers over several months
• Radiation safety precautions — for a period after treatment, patients must limit close contact with others, especially children and pregnant women, to prevent exposing them to radiation; the care team gives specific instructions
• Very rarely, a small increase in the risk of certain other cancers over many years, particularly with higher doses — your doctor weighs this against the benefit of treating thyroid cancer

Preparation for radioactive iodine therapy usually begins several weeks before the treatment day. The goal is to make the thyroid cells as hungry for iodine as possible, so they absorb the maximum amount of the radioactive dose.

Your care team will usually ask you to follow a low-iodine diet for one to two weeks before treatment. This means avoiding iodised salt, seafood, dairy products, and certain breads that contain iodine. The team will provide a detailed food list. You may also be asked to stop certain thyroid medications for a period beforehand — never stop any medication without the instruction of your doctor. Smoking and alcohol are generally discouraged in the period leading up to treatment. Women of childbearing age are usually asked to take a pregnancy test, and to use reliable contraception; pregnancy must be avoided for several months after treatment.

To boost iodine absorption, doctors sometimes use one of two approaches: stopping thyroid hormone tablets for several weeks (allowing a natural hormone called TSH — thyroid-stimulating hormone — to rise), or giving injections of a synthetic TSH called recombinant TSH. Your specialist will decide which is appropriate for your situation.

Tests that are commonly arranged before the treatment include:

• Blood tests to measure thyroid hormone levels and TSH
• A pregnancy test for women who could be pregnant
• Thyroid uptake scan — a small tracer dose of radioactive iodine is given first to check how much the thyroid absorbs, helping the doctor calculate the right treatment dose
• Imaging such as ultrasound (USG) or a whole-body scan, depending on the reason for treatment

On the treatment day, here is what typically happens, though the exact steps may differ between hospitals:

• 1. You arrive at the nuclear medicine department, usually having fasted for a few hours as directed.
• 2. The nuclear medicine team reviews your file and confirms your identity and dose.
• 3. You are given the radioactive iodine as a capsule or a small amount of liquid to swallow — this takes only a moment.
• 4. You are asked to drink extra water to help move the iodine through your stomach quickly and to protect other organs.
• 5. Depending on the dose and your hospital's facilities, you may be admitted to an isolation room for one to several days, or allowed to go home with strict safety instructions — your team will tell you in advance which applies to you.
• 6. Staff monitor you during your stay; radiation levels are checked before you are cleared to leave.

Recovery after radioactive iodine therapy does not usually involve wound care or physical limitations in the way surgery does, but radiation safety precautions and close medical follow-up are essential. Most patients feel well enough to manage day-to-day activities relatively quickly, though the full effect on the thyroid takes several weeks to months to become clear.

• Radiation isolation: For a period that your nuclear medicine team will specify — typically ranging from a few days to about a week depending on the dose — you will need to stay away from pregnant women, young children, and infants, sleep in a separate bed, use separate toiletries, and maintain distance from others in public. Detailed written instructions are given before you leave the hospital.
• Hydration: Drinking plenty of fluids in the days after treatment helps flush radioactive iodine from the body more quickly and protects the kidneys and bladder.
• Sour candies or lemon juice: Sucking on sour sweets or lemon slices several times a day for a few days may help stimulate saliva flow and reduce the risk of salivary gland problems — your care team will advise whether this is recommended for your dose.
• Thyroid hormone monitoring: Blood tests are usually arranged at regular intervals — often at six to eight weeks after treatment, then periodically — to check thyroid function. Many patients, especially those treated for cancer or high-dose hyperthyroidism, will need to start thyroid hormone replacement tablets.
• Contraception: Women are usually advised to avoid pregnancy for at least six months after treatment; men are also typically advised to use contraception for several months. Your doctor will give specific guidance.
• Follow-up imaging: Patients treated for thyroid cancer usually need a whole-body scan several months after treatment to assess how well the therapy worked and whether any thyroid tissue or spread of cancer remains.
• Ongoing cancer surveillance: For thyroid cancer patients, regular blood tests measuring thyroglobulin (a protein made by thyroid cells) and periodic imaging are part of long-term follow-up.
• Lifestyle: No specific dietary restrictions apply after the radiation isolation period ends. A balanced diet and avoiding smoking support general recovery. Your doctor will advise when it is safe to return to work or travel.