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Radiotherapy| treats cancer by using high-energy x-rays to destroy the cancer cells, while doing as little harm as possible to normal cells.
Radiotherapy for thyroid cancer can be given either as radioactive iodine treatment or external beam radiotherapy. The type of radiotherapy given will depend on the type of thyroid cancer and, in most cases, the stage| of the disease. Sometimes both radioactive iodine and external radiotherapy will be used.
Radioactive iodine treatment is a type of internal radiotherapy that is targeted at thyroid cells. It’s usually given to treat papillary or follicular thyroid cancer:
It’s not used as a treatment for medullary thyroid cancer or anaplastic thyroid cancer.
The radioactive substance used for treatment is called iodine-131. It’s mainly taken as capsules, but it can also be taken as a drink or injected into a vein in your arm (intravenously).
The thyroid cells absorb the iodine and receive a very high dose of radiation. This will help to destroy them and any cancer cells that might still remain after surgery. Radioactive iodine has very little effect on other parts of the body, as other cells don’t absorb iodine as much as the thyroid cells. The treatment is sometimes known as thyroid remnant ablation.
If, after radioactive iodine treatment, tests show that some thyroid cells remain, the treatment can be repeated.
Before radioactive iodine treatment you may be asked to start eating a low iodine diet. If you’re taking thyroid hormones, you’ll be asked to stop taking them.
You’ll usually be asked to take a low iodine diet for about 2-3 weeks before your treatment. This is because having too much iodine in your body will make the treatment less effective.
Foods to avoid can include:
You should also try to cut down on the amount of dairy products that you eat, as these also contain some iodine.
This includes milk and milk products such as milk chocolate and cheese. Dark chocolates and cocoa powder are allowed.
If you’ve been taking thyroid hormones (T3 or T4), these will usually be stopped for 2-4 weeks before the treatment.
You’ll probably find that you feel very tired during this time. But it’s important that you stop taking thyroid hormones or the radioactive iodine treatment won’t work.
Alternatively, it may be possible to be treated with recombinant human thyroid-stimulating hormone (rhTSH), also known as thyrotropin alfa (Thyrogen®). This man-made drug is similar to the TSH produced in your body. Having this allows you to carry on taking your hormone replacement tablets (see above) and avoid the symptoms of thyroid hormone withdrawal. rhTSH is given as two injections 24 hours apart into the buttock (intramuscularly).
rhTSH has very few side effects. Possible side effects include feeling sick (nausea), being sick (vomiting), headaches and fatigue. rhTSH is not suitable for everyone, and your doctor can tell you if you’re able to have this treatment.
Because of the possibility of unnecessary radiation exposure to the hospital staff, your relatives and friends, certain safety measures are taken while the radioactive iodine is still in your body.
The staff looking after you will explain these restrictions in detail before you start your treatment. Each hospital has different routines, and it’s worth visiting beforehand to discuss the procedure with the nursing and medical staff.
This is a good time to ask questions and it may help to make a list of them beforehand.
Radioactive iodine treatment makes you slightly radioactive for about 4-5 days. During this time, the radioactivity will gradually leave your body in your urine, bowel motions (stools), blood (in women have a period), saliva and sweat. You’ll need to be looked after in hospital until the radioactivity has reduced to a safe level.
Very rarely, you may have pain or feel sick (nausea), tired and/or breathless, and have a sore throat after having radioactive iodine treatment. If these side effects occur, let your nurse or doctor know as medicines can be prescribed to help.
A rare, long-term side effect of radioactive treatment is a dry mouth. This can happen if the radioactive iodine is absorbed by the salivary glands. Let your doctor know if you develop a dry mouth|.
You should not become pregnant or father a child while being treated for thyroid cancer, and for 6-12 months afterwards. If you’re pregnant, you can’t be given radioactive iodine treatment. For this reason, you must tell your doctor if you’re pregnant or think you might be. Your fertility shouldn’t be affected by radioactive iodine treatment, although there is a very small risk if you need to have repeated treatments.
Your doctor or nurse can give you more information and support about this.
If you’re breastfeeding, you must stop at least four weeks before you’re treated with radioactive iodine. Although it isn’t safe to start breastfeeding again after your treatment, it will be safe for you to do so after future pregnancies.
This type of treatment is used less commonly than internal radiotherapy for treating thyroid cancer. It’s more commonly used to treat anaplastic thyroid cancer and some cases of medullary thyroid cancer, as they don’t respond to radioactive iodine treatment.
External radiotherapy doesn’t make you radioactive and it’s perfectly safe for you to be with other people, including children, throughout your treatment.
It may be used:
External radiotherapy is sometimes used for papillary or follicular thyroid cancer if the cancer is difficult to remove with surgery. It can be given before or after radioactive iodine treatment.
This treatment is given in the hospital radiotherapy department. The course is usually given every Monday–Friday, with a rest at the weekend. The length of your treatment will depend on the type and size of the cancer. Your doctor will discuss your treatment with you in more detail beforehand.
To make sure that your radiotherapy is as effective as possible, it has to be carefully planned. Planning ensures that radiotherapy rays are aimed precisely at the cancer and cause as little damage to the surrounding healthy tissue as possible.
The treatment is planned by a specialist doctor known as a clinical oncologist. Planning is important and may take a few visits.
On your first visit to the radiotherapy department, you’ll have a CT (computerised tomography) scan| taken of the area to be treated. Radiographers (experts in giving radiotherapy) will also take measurements from you to tailor the treatment to you. This session will usually take about 45-60 minutes.
Some people also have an MRI scan| as part of their radiotherapy planning.
The radiographer’s measurements and the information from the scans are fed into the radiotherapy planning computer.
This helps your doctors plan your treatment precisely.
Occasionally, marks may be drawn on your skin. These help the radiographer position you accurately before each treatment. The marks must stay visible throughout your treatment, but they can be washed off once your course of treatment is over.
It’s important that you’re able to lie still, in exactly the same position, for each treatment. To help you do this, you’ll wear a see-through plastic mask (sometimes called an immobilisation shell) for each session of radiotherapy. The mask holds your head and neck as still as possible. It’s designed so that you can see and breathe normally while wearing it. You’ll have it on for up to about 15 minutes at a time. It may feel unusual at first, but most people soon get used to it.
Your mask will be made on one of your first visits to the radiotherapy department. The radiographer or the mask room technician will explain the whole process to you.
We have more information in our section on how radiotherapy masks| are made.
Before each treatment session, the radiographer will position you on the treatment couch and carefully fit your mask.
The treatment only takes a few minutes. During this time, you will be left alone in the room, but the radiographer will watch you from the next room. If you need assistance you can raise your arm and the radiographer will return to the room.
During the treatment, you’ll be advised not to talk.
Specific side effects of radiotherapy to the neck can include:
These side effects vary depending on the dose of the radiotherapy and the length of your treatment. Your doctor or radiotherapist will discuss any possible side effects with you before you start your treatment. If your throat is sore and you find it painful to eat your normal diet, you can replace meals with nutritious, high-calorie drinks, which are available from most chemists.
Our section on eating problems and cancer| has tips on how to eat when you find swallowing difficult, and what you can do if you have a dry mouth or taste changes.
Your radiographer will give you advice on how to care for the skin on your neck if it becomes sore.
Here are some things that may help:
The side effects should begin to reduce gradually about 3-4 weeks after your treatment is over. It’s important to let your doctor know if they continue for longer than this.
Your ability to become pregnant or father children isn’t affected by external radiotherapy treatment for thyroid cancer, but you’ll probably be advised to wait for at least a year. Women who become pregnant will have their hormone levels carefully monitored throughout the pregnancy.
You may feel very tired during your radiotherapy treatment. Tiredness| (fatigue) can often be made worse by having to travel to hospital each day, or by other treatments such as surgery or chemotherapy. Listen to your body and allow yourself extra time to rest, perhaps by taking a nap. It may help if you spread chores out over the week, sit down to do them wherever possible and accept any offers of help. Tiredness can be a problem for several months after your treatment has finished.
Content last reviewed: 1 December 2012
Next planned review: 2014
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© Macmillan Cancer Support 2013
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