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Radiation therapy for thyroid cancer
Radiation therapy uses high-energy rays or particles to destroy cancer cells. Many people with thyroid cancer have radiation therapy. Your healthcare team will consider your personal needs to plan the type and amount of radiation, and when and how it is given. You may also receive other treatments.
Radiation therapy is given for different reasons. You could have radiation therapy to:
- destroy the cancer cells in the body
- destroy cancer cells left behind after surgery or chemotherapy to reduce the risk of the cancer coming back, or recurring (called adjuvant therapy)
- destroy any normal thyroid tissue remaining after surgery to reduce the risk of the cancer coming back, or recurring (called thyroid remnant ablation)
- relieve pain or control the symptoms of advanced thyroid cancer (called palliative therapy)
The following types of radiation therapy are most commonly used to treat thyroid cancer.
Radioactive iodine therapy
Radioactive iodine therapy is sometimes called RAI therapy. It is a type of systemic radiation therapy commonly used to treat thyroid cancer. A radioactive material called radioactive iodine, or I-131, is given by mouth and travels throughout the body. Both healthy and cancerous thyroid cells absorb, or take up, the radioactive iodine. The radiation destroys the thyroid tissue and cells.
Radioactive iodine therapy is usually given after surgery for intermediate- or high-risk differentiated thyroid cancer (papillary or follicular carcinoma). It is also given after surgery for most poorly differentiated carcinomas. Radioactive iodine therapy is used to kill any cancer cells and normal thyroid tissue that remain after surgery. This can help prevent the cancer from recurring. It is also used to treat cancer that has spread to lymph nodes or other parts of the body.
Radioactive iodine therapy doesn’t work for all types of thyroid cancer because some cancer cells don’t absorb iodine. You may be given a small test dose of I-131 to see if the cells absorb iodine.
Radioactive iodine therapymay be offered if the:
- tumour is larger than 4 cm
- tumour has grown through the thyroid and spread to nearby tissues and structures
- cancer has spread to many lymph nodes in the neck
- cancer is an aggressive variant of differentiated thyroid cancer, is poorly differentiated carcinoma or has other high-risk features when seen under a microscope
- cancer comes back in the same place or close to where it started (called a local or regional recurrence)
- cancer has spread to other parts of the body (called distant metastasis)
Preparing for treatment
The normal amount of iodine in the body needs to be lowered before radioactive iodine therapy starts. This will help the radioactive iodine to be absorbed. When there is less iodine in the body, the pituitary gland makes more thyroid-stimulating hormone (TSH) and releases it into the bloodstream. High TSH levels will make any thyroid tissue and thyroid cancer cells absorb radioactive iodine.
To lower the iodine in the body, you may be told to follow a low iodine diet for 1–2 weeks before treatment. You should avoid or limit salt and salty foods, milk and milk products and seafood. Ask your healthcare team for a complete list of foods to avoid or limit.
People who have had a thyroidectomy to treat thyroid cancer usually have to take hormone therapy with levothyroxine (Synthroid, Eltroxin). This drug replaces thyroxine, which is a hormone that would normally be made by the thyroid. It also lowers the amount of TSH in the body. To increase TSH levels, you may be asked to stop taking levothyroxine for several weeks before you start radioactive iodine therapy.
Another way to increase TSH levels is to give a drug called recombinant TSH (Thyrogen). It is an artificial form of TSH that is given by injection into muscle usually once daily for 2 days before radioactive iodine therapy.
During and after treatment
Your body gives off small amounts of radiation during and for some time after the treatment. Once the dose of radioactive iodine is given, you will need to stay away from people for a few days. This may be done by staying in a private room in the hospital or treatment centre or by following special precautions at home. Talk to your healthcare team about safety precautions you will need to take while in the hospital or at home to protect others from exposure to radiation.
A radioactive iodine scan is a nuclear medicine imaging test that uses radioactive material to examine the thyroid and look for any abnormal areas or thyroid cancer cells in other parts of the body. It is usually done about 1 week after radioactive iodine therapy. It is also repeated 6–12 months after radioactive iodine therapy to check how the cancer responded to the radioactive iodine therapy and if there are any cancer cells remaining. You may need to have more radioactive iodine therapy if cancer cells are found with the scan.
Blood tests are also done to check if you need more treatment. The healthcare team will measure the levels of thyroglobulin (Tg) and TSH in your blood. Abnormal levels may mean that cancer cells were left behind after radioactive iodine therapy or that the thyroid cancer has recurred. An ultrasound of the neck may be done along with the blood tests.
External beam radiation therapy
During external beam radiation therapy, a machine directs radiation through the skin to the tumour and some of the tissue around it. It is most often used when surgery can’t be done or radioactive iodine therapy won’t work because the thyroid cancer cells do not absorb iodine. This includes medullary carcinoma and anaplastic carcinoma. External beam radiation therapy is also used as a palliative treatment for advanced thyroid cancer that can’t be removed with surgery (it is unresectable) or metastatic thyroid cancer that causes symptoms.
How long and how often external beam radiation therapy is given depends on many factors including the type of thyroid cancer, the size of the area being treated and the goal of treatment. External beam radiation therapy is usually given once a day, 5 days a week. Smaller doses of radiation therapy may be given 2 times a day (called hyperfractionation) for anaplastic carcinoma.
Side effects can happen with any type of treatment for thyroid cancer, but everyone’s experience is different. Some people have many side effects. Other people have few or none at all.
During radiation therapy, the healthcare team will find ways to protect healthy cells in the treatment area as much as possible. But damage to healthy cells can happen and may cause side effects. Side effects can happen any time during, immediately after or a few days or weeks after radiation therapy. Sometimes late side effects develop months or years after radiation therapy. Most side effects go away on their own or can be treated, but some side effects may last a long time or become permanent. Side effects of radiation therapy will depend mainly on the type and dose of radiation therapy used.
Some side effects of radioactive iodine therapy include:
- nausea and vomiting
- taste changes
- dry mouth
- swelling in the neck
- sore throat
- watery eyes
- low sperm counts in men
- changes to menstrual periods in women
Side effects of external beam radiation therapy include:
- skin problems, such as red, irritated and peeling skin
- dry mouth and thick saliva (spit)
- difficulty swallowing, including pain during swallowing
- weight loss
Tell your healthcare team if you have these side effects or others you think might be from radiation therapy. The sooner you tell them of any problems, the sooner they can suggest ways to help you deal with them.
Questions to ask about radiation therapy
A protein produced in the thyroid (a gland that makes and releases hormones involved in growth and metabolism) that is used to make thyroid hormones.
Thyroglobulin can also be used as a tumour marker to look for thyroid cancer or monitor a person’s response to treatment.
I’m extremely grateful to the Canadian Cancer Society for funding my research with an Innovation Grant.
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