Thyroid Cancer Canada
Inform. Support. Empower. Informer. Soutenir. Renforcer.

Radioactive Iodine Treatment

Radioactive Iodine Treatment


Treatments – Radioactive Iodine Treatment

Radioactive Iodine Treatment (RAI)


Radioactive Iodine treatment (RAI) is a common way to treat differentiated forms of thyroid cancer (papillary & follicular). It’s not the type of radiation you may think of when you think of cancer treatment. RAI is taken by pill – once swallowed, the radioactive iodine gets to work by destroying cancer cells.

RAI is usually only considered for those with Stages 2-4 of thyroid cancer, which is considered higher risk. Those at a low risk of recurrence generally do not need RAI. This includes patients:

  • Who have only one cancerous nodule without 'aggressive features'
  • Less than 45 years old
  • With no family history of thyroid cancer
  • With Stage I thyroid cancer

See how RAI works and hear two patients’ stories

How RAI works - A video for patients and families. Courtesy: Jubilant DraxImage

What does RAI do?

RAI treatment destroys any remaining thyroid cells (both normal and cancerous) after surgery, minimizing the risk of the cancer coming back. It is also called ablation therapy.

The initial RAI treatment may be given anytime, but usually 6 weeks to 6 months after surgery. The reason for a delay may be because your doctor wants to see how you’re doing after surgery before deciding if RAI is necessary.

How can I prepare for RAI?

One way to maximize the effects of RAI is by raising your TSH level.  There are 2 ways to do this:

  1. Stop hormone replacement (“Going Hypo”)
  2. Receive Thyrogen®

For either, it is also recommended that you go on a Low Iodine Diet. 

Because you are receiving a radioactive substance, there are some precautions you should be aware of. The resources below can help you prepare:

RAI Frequently Asked Questions

  • Can I isolate myself in a hotel room?  No, this is not recommended as there is potential that the housekeeping staff will come in contact with the RAI you discharge from your body. This may include pregnant women.
  • How do I protect my children? If you have young children, it is best that they stay with a relative for the first few days, or that you stay in hospital isolation. Other alternatives are: a basement apartment, a cottage, or friend’s empty house/rooms.
  • What after-effects can I expect? Most people have few after-effects or they are very temporary. Almost all patients treated with RAI have an altered sense of taste for the first few days or weeks (e.g. food tastes like “Styrofoam”). Infrequently, the effect lasts longer.
    • In some cases, patients experience RAI damage to their salivary glands and/or tear ducts (30%). For most people, the effects are temporary. Those who have lasting effects may experience mild pain in their cheeks, mouth dryness and/or blocked tear ducts. Some may require treatment from specialists in corresponding fields of medicine.
    • Occasionally, months later, patients feel some after-effects of RAI as soreness or swelling in glands (face or neck). This usually lasts less than two weeks.
  • When am I “good to go” (be with other people and go back to work)? If you have a treatment dose of RAI, you will have a Whole Body Scan (WBS) about five to seven days after your treatment. This is usually the time that you are given the “go ahead” to resume your normal activities. Patients should be aware that a tiny amount of radioactivity remains in their body for months afterwards, enough so that is possible to set off alarms at border crossings and airports. Although border security systems have precision and can recognize that you have ingested an innocuous medical isotope (I-131), those who are travelling within two months of treatment may want to have a note from the hospital to explain that they had medical treatment with radiation.

What does "Going Hypo" mean?

Our bodies require thyroid hormone (T4) to function normally. This is why people need to take a synthetic (man-made) form of the hormone, by pill, once the thyroid has been removed. Synthroid® and Eltroxin® are brands of thyroid (T4) pills in Canada.

Without thyroid hormone, the body produces more and more thyroid stimulating hormone (TSH). A high level of TSH is needed for RAI treatment to be effective. This is why your doctor may instruct you to stop taking your thyroid pills 4-6 weeks before starting RAI treatment. Temporarily stopping your thyroid pills may cause symptoms of hypothyroidism (low thyroid levels). Symptoms tend to be more common in the 2 weeks leading up to your RAI treatment.

They include:

  • Tiredness
  • Trouble sleeping
  • Puffiness in the face; bloating
  • Poor concentration
  • Weight gain

Your doctor may prescribe a drug called Cytomel® to help ease these symptoms of hypothyroidism.


As an alternative to ‘going hypo’, patients can receive a drug called Thyrogen® before RAI treatment. Thyrogen® raises TSH levels – so patients can continue taking their daily thyroid pills. So, there is no risk of having the symptoms of hypothyroidism.

You need to visit your healthcare provider twice to receive Thyrogen® injections in the 2 days before starting RAI. Thyrogen® is associated with mild side effects, if any.

Thyrogen® is not covered in all provinces, meaning you may have to pay out of pocket or apply though your private health insurance, if you have it. To learn more, consult the resources below:


Low Iodine Diet (LID)

Another important part of RAI treatment is to reduce your iodine intake by following a Low Iodine Diet (LID). This helps maximize the absorption of the radioactive iodine in your body. It is normally recommended you start on a LID two weeks before RAI.

Quick Facts on the Low Iodine Diet:

  • Designed so you consume less than 50 mcg iodine per day.
  • Foods high in iodine that should be avoided: table salt, dairy products, egg yolks and sea foods of all types. Soy is also restricted because it interferes with RAI.
  • Most patients are advised to stay on a LID for 48 hours after RAI treatment. Since LID meals are usually not available in the hospital, you should bring appropriate foods with you (or have a family member or friend do so).

Download Thyroid Cancer Canada’s Low Iodine Diet Booklet, which contains useful information on the diet, including a shopping list and menu samples.


Our diet has been officially endorsed by the Canadian Association of Nuclear Medicine and is approved by the "Practice-based Evidence in Nutrition" project of the Dietitians of Canada.

Low Iodine Diet Recipes

TCC also has an official Low Iodine Diet compilation of easy and nutritious recipes for those being treated with radioactive iodine. Download the pdf version below.