How Radioactive Iodine Therapy Works
Thyroid cells are unique in the body because they naturally absorb iodine from the bloodstream. This property is exploited in radioactive iodine (RAI) therapy. When a patient swallows a capsule or liquid containing radioactive iodine (I-131), the iodine is absorbed by thyroid cells, including any remaining thyroid cancer cells after surgery. The radiation destroys these cells from within.
RAI therapy is effective for differentiated thyroid cancers, which include papillary and follicular types. These are the most common forms of thyroid cancer and generally retain the ability to absorb iodine. Medullary and anaplastic thyroid cancers do not respond to RAI because they do not take up iodine.
When RAI Therapy Is Recommended
RAI therapy is most commonly used after thyroid surgery (thyroidectomy). Even after a skilled surgeon removes the thyroid gland, microscopic thyroid tissue may remain. RAI therapy destroys this remnant tissue and any microscopic cancer deposits that might be present elsewhere.
It may also be used if thyroid cancer has spread to lymph nodes or other parts of the body, as long as the cancer cells still take up iodine. A diagnostic thyroid scan or post-therapy scan helps confirm iodine uptake and guides treatment decisions.
Preparing for RAI Therapy
Low iodine diet: In the weeks before treatment, patients are typically asked to follow a low iodine diet. This reduces the amount of stable (non-radioactive) iodine in the body, making the thyroid cells more receptive to the radioactive iodine when it is administered.
Thyroid hormone adjustment: To increase the uptake of RAI, thyroid-stimulating hormone (TSH) levels need to be elevated. This can be achieved by stopping thyroid hormone replacement medication for several weeks before treatment, or by receiving injections of recombinant TSH (Thyrogen). Your doctor will advise which approach is appropriate for your situation.
Other medications: Inform your doctor about all medications and supplements you are taking, as some can interfere with iodine uptake.
What Happens During Treatment
RAI therapy is usually given as a single dose, either as a capsule to swallow or as a liquid. The procedure itself is simple. After taking the dose, you may need to stay in the hospital for a day or two, depending on the dose administered and local regulations regarding radiation safety.
Some patients experience mild side effects in the days following treatment, including nausea, swelling or tenderness in the neck, dry mouth, and changes in taste. These are usually temporary.
Isolation and Radiation Precautions
Because you will be emitting radiation for a period after treatment, you will receive specific instructions about limiting close contact with others, especially children and pregnant women. These precautions typically last a few days to a week, depending on the dose. The nuclear medicine team will provide detailed written guidelines covering sleeping arrangements, bathroom hygiene, and safe distances.
Follow-Up After Treatment
A post-treatment whole-body scan is usually performed a few days after RAI therapy. This scan shows where the radioactive iodine has accumulated, confirming the location of any remaining thyroid tissue or cancer cells. Blood tests for thyroglobulin (a marker for thyroid cancer) and TSH are monitored over time to assess the treatment response.
Thyroid hormone replacement medication is resumed after treatment and adjusted to maintain appropriate levels. Long-term follow-up with your endocrinologist and nuclear medicine team is important to monitor for recurrence.
If you have been diagnosed with differentiated thyroid cancer, discuss with your doctor whether RAI therapy is part of your treatment plan and what preparation steps you need to take.