Treatment with Iodine-131 (I-131) for Benign Thyroid Diseases

Patient Experience

  • Reference Number: HEY1059/2019
  • Departments: Nuclear Medicine
  • Last Updated: 18 July 2019


This leaflet has been produced to give you general information about your treatment.  Most of your questions should be answered by this leaflet.  It is not intended to replace the discussion between you and your doctor, but may act as a starting point for discussion.  If after reading it you have any concerns or require further explanation, please discuss this with a member of the healthcare team.

What is Iodine-131 (I-131)?

Iodine-131 (also known as I-131) is a radioactive form of the iodine we normally eat in our diets.  I-131 is used to treat some of the thyroid gland in patients who have an overactive thyroid (thyrotoxicosis) or other similar disorders.

Why do I need I-131?

The thyroid gland in your neck is overactive and is producing more thyroid hormone than your body needs.  If it is not properly treated, your health may be adversely affected in the future.

When I-131 is administered to patients, it concentrates in the thyroid gland where it is stored.  Whilst the I-131 is stored there, it kills off the cells within your gland over a period of several weeks.

Can there be any complications or risks?

Radioiodine is a very safe treatment but like everything in life, there may be a small degree of risk.  Your doctor will only prescribe this treatment if the benefits to you outweigh any potential risks.

Your thyroid gland may become underactive after your treatment.  This could happen within a few months or some years after treatment.  This is why the blood tests to check the function of your thyroid are important and should be performed regularly for the rest of your life.  If your thyroid becomes underactive you will be asked to start taking thyroxine tablets.  Once you are on the correct dosage these have no side effects and need only be taken once a day.  If you do not take thyroxine, you could start to put on weight and feel tired. Most patients only need one treatment to cure their thyroid disease.

Occasionally, some patients may need to have additional treatment. This could be repeat radioiodine treatment or surgery.  Your doctor will inform you if this is necessary following your regular blood tests and discuss your options.

Whilst there is no evidence of people being harmed from the radiation associated with this treatment, some people believe there is no such thing as a safe dose of radiation, no matter how small. Therefore, we use the minimum amount of radiation needed to treat your thyroid. However, the radiation could be harmful to an unborn baby so the treatment must not be given to patients who are pregnant. Radioiodine can also pass into breast milk, therefore the treatment is unsuitable for patients who are breast-feeding.

If you believe that there is any chance that you may be pregnant, it is very important that you let us know before your treatment.

How do I prepare for the treatment?

Share the information in this leaflet with your partner and family (if you wish) so that they can be of help and support.  There may be information they need to know, especially if they are taking care of you following this treatment.

There are certain drugs that you may need to stop taking for several days or weeks before your appointment. Your appointment letter will give further details.

If you have thyroid eye disease, please discuss this with your doctor before your appointment date. The treatment may worsen the eye disease, unless steroids are taken.

You will need to follow a low iodine diet and avoid medications containing iodine for 2 weeks prior to the therapy. See the separate leaflet  “Thyroid Tests and Treatments: The Recommended Low Iodine Diet” for advice.

On the day of the treatment, please only have a light lunch (such as a sandwich) before you attend.

There is some information which we need in advance.  This is so we can plan your treatment.  Please call the Nuclear Medicine Department before your appointment if any of the following applies to you:

  1. You have any problems with controlling your bladder, for example, if you wear pads or have a catheter.
  1. You have had any x-ray procedures involving the use of contrast in the 8 weeks prior to your appointment date.
  1. You look after young children. (You will be asked to avoid close contact with children and pregnant women for up to 27 days after your treatment, so young children may need a different carer.)
  1. Your home is not connected to the mains drainage/sewer system (for example if you have a septic tank).
  1. For female patient:
  1. if you are breast feeding or have been breast feeding anytime in the 8 weeks before your appointment date
  2. whether there is any chance that you might be pregnant.

There are some radiation protection precautions you will need to follow for a period of time after your treatment.  These are detailed in the section below.  It is very important that, before you attend, you read these precautions, understand them and discuss them with anyone who may be affected by your treatment.  If you are unsure about any of the instructions, or if you have any questions, please contact the Nuclear Medicine Department to discuss them with a member of staff.

What precautions do I need to follow after the treatment?

Other people who come into contact with you will receive some radiation dose from being near to you or if they become contaminated with any of your bodily fluids. This can be minimised by following the precautions detailed below.

When you attend, you will receive a treatment record sheet giving the exact time period that you need to follow the precautions for.  We will ask you to carry this record sheet with you for up to 8 weeks.

The exact length of time for which you need to follow the precautions depends upon the amount of radioiodine prescribed for you.

For up to 27 days, we will ask you to

Stay at least 1 metre from children under 5 and pregnant women.

It is not necessary to send young children to stay elsewhere providing you can keep your distance from them, perhaps by having a partner or other relative help with looking after them.

For up to 16 days, we will ask you to:

Stay at least 1 metre from adults and children over 5

This does NOT mean that you have to avoid completely other people; only to restrict the time you spend close to individuals.  This may require you not to sit next to someone (e.g. whilst watching television) for more than one hour per day.  You should not share the same bed with other people, including children.

Avoid non-essential medical or dental treatments

This means that non-urgent visits (such as a routine blood test or dental check-up) should be postponed.

Avoid public places of entertainment (such as pubs, restaurants or the cinema)

The purpose of this is to avoid long periods of contact with another person, for example when sitting next to the same person for a few hours at the cinema or in a restaurant.

For 7 days, we will ask you to take extra care with hygiene. For example:

Try to avoid any spill of urine when using the toilet. If any urine is spilt, wipe it up with a tissue immediately and flush it down the toilet. (Male patients  should sit on the toilet rather than standing)

Flush the toilet twice after each use and wash your hands thoroughly

Most of the radioiodine leaves your body in urine. Good toilet hygiene minimises the risk of other people becoming contaminated with this iodine.

Rinse the bathroom sink, and bath or shower thoroughly after use

Small quantities of radioiodine may leave your body in sweat. Washing this away before other people use the bathroom minimises the risk of other people becoming contaminated with iodine.

Avoid food preparation that involves a lot of handling of food (e.g. baking).  Wash your hands before preparing food for others

This is to remove any radioiodine that that could be on your hands due to sweat, and avoid the risk of this radioiodine entering the bodies of other people from eating food contaminated with radioiodine.

Do not share crockery, cutlery, toothbrushes, towels, or facecloths

Small quantities of radioiodine may be present in your saliva. These precautions minimise the risk of this being passed on to other people.

What about my children – can I see them after the treatment?

If you can follow the precautions detailed above, it will be safe to see your children after your treatment. Providing you follow these precautions, there is no need to be concerned.

Can I bring someone with me to the appointment?

You are welcome to bring someone with you when you come for your treatment, but it is very important that you do not bring anyone under the age of 18, or anyone who is or might be pregnant.  Please do not bring more than one person with you if you are travelling by car. This is because we do not want you to spend time in close contact with other people in the car on the way home. We will ask the person who is not driving to sit in the back, behind the passenger seat, to maximise the distance between you and the other person in the car.

What will happen on the day of the treatment?

The treatment will be given in the Nuclear Medicine Department at Castle Hill Hospital.

Before we can give you the treatment, a member of staff (a Medical Physicist) will discuss the procedure with you.  The physicist will ask questions about you, your lifestyle and your family.  This is to make sure that it will be safe for you to have the treatment and so that we can give you the right advice about radiation protection after your treatment.  The physicist will also explain the protection advice and can answer any questions you may have about the treatment.

Female patients under the age of 55, will be asked for a sample of urine so that we can perform a pregnancy test.  The results of this test will be known straight away and we will tell you the outcome in private.

Once you and the physicist are happy that the treatment is right for you, you will be given the I-131 capsule to swallow with a drink of water.  This capsule is similar in size and shape to an antibiotic capsule or a paracetamol tablet and has no taste.  It is important that you swallow the capsule whole and do not chew it.  Once you have taken the capsule you will be able to go home.

Can I drive myself home or travel by public transport?

You will be able to drive yourself to and from the appointment but there should be no more than one other person in the car with you.

You can travel home by public transport if you wish, but if you think you will spend more than 3 hours on a bus or train, please let us know in advance so that we can discuss this with you.

Do I need to take time off work after the treatment?

This depends on how much radioiodine has been prescribed for you and the type of work you do.

  • If you work with children or pregnant women, you may need to take up to 27 days off work.
  • If your work involves handling food, you will need to take 2 weeks off work.
  • If you do not work with children or pregnant women, and do not handle food, you can return to work the day after the treatment providing your work allows you to keep your distance from other people (at least 2 metres). If you regularly work in close contact (closer than 2 metres) with other adults, you may need to take up to 8 days off work.

Please contact the Nuclear Medicine Department if you need more specific advice about when you can return to work.

Please note that the Nuclear Medicine Department are unable to issue fit notes (previously known as sick notes). If you require one of these, please contact your doctor.

What happens afterwards?

The thyroid responds slowly to the radioiodine and it will be several weeks before you feel the results.  Occasionally, after having the treatment your symptoms may become worse before you start to feel better.  This is temporary; but if the symptoms you previously experienced return and are very bad you should contact your doctor for advice about how to relieve them.

We will give you a treatment record sheet which will contain details of what treatment you had and the radiation precautions you need to follow.  Please carry this sheet with you until the date given to you by the physicist and show it to any healthcare professional you visit.

Very occasionally, patients who have had radioactive iodine treatments have triggered radiation detectors at airports and ferry terminals up to three months after treatment.  In all of the cases that we have heard of, the patient has been allowed to travel once the authorities have been made aware of the therapy.  If you are planning to travel abroad in the next three months, we advise that you keep your treatment record sheet and take it with you.

Five weeks after your treatment you need to have a blood test, (usually done at your GP’s surgery).  You should see your hospital consultant approximately six weeks after your treatment.  If you have not already received an appointment please call the consultant’s secretary.

Should you require further advice on the issues contained in this leaflet, please do not hesitate to contact the Nuclear Medicine Department on telephone number: (01482) 622125

General Advice and Consent

Most of your questions should have been answered by this leaflet, but remember that this is only a starting point for discussion with the healthcare team.

Consent to treatment

Before any doctor, nurse or therapist examines or treats you, they must seek your consent or permission. In order to make a decision, you need to have information from health professionals about the treatment or investigation which is being offered to you. You should always ask them more questions if you do not understand or if you want more information.

The information you receive should be about your condition, the alternatives available to you, and whether it carries risks as well as the benefits. What is important is that your consent is genuine or valid. That means:

  • you must be able to give your consent
  • you must be given enough information to enable you to make a decision
  • you must be acting under your own free will and not under the strong influence of another person

Information about you

We collect and use your information to provide you with care and treatment. As part of your care, information about you will be shared between members of a healthcare team, some of whom you may not meet. Your information may also be used to help train staff, to check the quality of our care, to manage and plan the health service, and to help with research. Wherever possible we use anonymous data.

We may pass on relevant information to other health organisations that provide you with care. All information is treated as strictly confidential and is not given to anyone who does not need it. If you have any concerns please ask your doctor, or the person caring for you.

Under the General Data Protection Regulation and the Data Protection Act 2018 we are responsible for maintaining the confidentiality of any information we hold about you. For further information visit the following page: Confidential Information about You.

If you or your carer needs information about your health and wellbeing and about your care and treatment in a different format, such as large print, braille or audio, due to disability, impairment or sensory loss, please advise a member of staff and this can be arranged.

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