My name is Liz. I have been a Nuclear Medicine Technologist for ten years. I would like to present to you the information you need in order to form your own educated decision on whether to go ahead with radio-iodine treatment of your thyroid. I will tell you about:

• how the treatment works,

 

• the potential draw-backs and

 

• the way that we, in Nuclear Medicine, are monitored and regulated to ensure safety and high standards at all times.

First are some things to consider about having radio-iodine treatment, followed by some information aimed at dispelling some of the common fallacies that are found here on the internet.

Radio-iodine treatment has become one of the most common treatments for hyperthyroidism and has been used for over 60 years. It is extremely successful, non-invasive, simple to administer, easy to recover from and cheap.

One of the reasons that radio-iodine treatment is so effective is because the thyroid readily takes up iodine, which is used in thyroid hormone production. To ensure that the treatment is maximised you will be asked to avoid any foods and medicines that contain iodine for up to three weeks before the treatment. This way, when you take the capsule (or drink the liquid) it will all be taken up into the thyroid gland and the effect of the beta radiation will be mostly confined to the thyroid tissue, which is the target of the treatment. The point of the radio-iodine treatment is to destroy the thyroid tissue which is causing the over-production of thyroid hormones. This is especially important for patients with certain types of thyroid cancer who need to have all thyroid cells within their body destroyed in order to cure the cancer and to stop it from spreading. So, yes, radiation can be dangerous when not carefully controlled, but that very fact is the reason why the treatment works. The aim of the treatment is to damage and kill the cells responsible for the hyperthyroidism. Radioactive iodine and some other radioisotopes used in Nuclear Medicine are produced during the production of nuclear energy. They are a by-product or, if you like, a useful waste product. Every batch is rigorously tested to ensure its safety.

Patients who have what is called an ablative dose (usually for treatment of thyroid cancer) are asked to stay in hospital for three days following the treatment. This is to reduce the doses to other members of the public. The I131 will be present in the body for a few weeks but will be reducing all the time due to the half-life and biological half-life. I131 is excreted from the body in all bodily fluids, including urine and sweat, so it is best that the first few days (when the radiation present in the body is highest) are spent in isolation at the hospital where it matters less that things will become contaminated. You should be allowed to have visitors for up to an hour per day, but this will not include children or pregnant women. You may be advised to throw away the clothes and toiletries that you use, so it is advisable to wear old clothes for your stay in hospital. Alternatively, the hospital may offer to store your belongings until they are deemed not to be radioactive and you can collect them.

Patients having treatment for overactive thyroid will not normally be asked to stay in hospital overnight. All patients should be monitored with a radiation monitor (Geiger counter or scintillation monitor) before being allowed to go home, to ensure that the radiation dose to the public is negligible. Much research has been done on the effects of radiation and the levels at which it is considered safe, and the ALARP (explained in detail later on) principles are always applied when considering whether to allow a patient to go home, and thorough advice should always be given.

So, some things to consider when you are offered treatment for hyperthyroidism:

1. It’s permanent; once you take the iodine capsule there is no changing your mind. The permanency can be seen as a benefit as patients condition will become stable and symptoms can be more easily controlled.

2. Since the science is inexact there are two ways of approaching the treatment. Some hospitals carry out a preliminary scan of the patients thyroid to try to calculate a dose of iodine that will reduce the thyroids production of hormones to a normal level. This is rarely successful for two reasons: the dose is too low, meaning it needs repeating; or too high meaning the patient will become hypothyroid and need to take hormone replacement tablets. For this reason it is common for the hospital to skip the scan and automatically give a higher dose of iodine in order to ensure a satisfactory reduction in hormone production, which is then replaced by tablets. These tablets will need to be taken for life but the dose should be closely monitored based on hormone tests carried out on a regular basis. The symptoms of hypothyroidism are tiredness, weight gain, aches, felling cold and possibly depression. This is due to a slowed metabolism. If left untreated it could result in a coma and death.

3. Treatment can cause thyroid storm as the dying gland “dumps” (releases) excess thyroid hormone and thyroid antibodies into the body. However this can also occur as a result of untreated hyperthyroidism and from surgery for the treatment of hyperthyroidism. It is like a more severe case of hyperthyroidism and can result in death if untreated, but is extremely rare.

4. For up to 4-8 weeks after dosage, the patient is exposing those around them to radioiodine. This is demonstrated by patients registering measurable radio-iodine in airport and other screening devices. However, this dose is extremely small and extensive scientific research and testing has determined that the level of radiation given off by patients will have a negligible effect on those around them. Radiation is also given off by the sun, the rock-bed of the earth, the food we eat (eg bananas and brazil nuts) and we exposed when we fly, have x-rays etc, so we are exposed on a daily basis to radiation of many kinds anyway.

5. There is a tiny chance that the exposure to radiation can cause cancer approximately a 1 in 10000 chance. However, when put into context 1 in 3 people will naturally develop cancer at some point in their life. Doctors will always weigh up the pros and cons of treatment and this should all be explained to the patient. We would only treat a patient if it provided a clear benefit we are not allowed to give unnecessary treatments.

6. Patients are advised not to become pregnant for 6 months following radio-iodine treatment. This is because the radiation that is used could potentially affect the DNA in human cells. The chance is extremely low, at around a 1 in 10000 chance of causing cancer, but childrens DNA is more susceptible to change as it is replicating far faster as they are growing. Staff are bound by law to protect people from radiation as much as possible, and so this is a way to prevent a foetus from being exposed to an unnecessary dose.

7. Graves disease is an auto-immune disease, not a disease of the thyroid, so killing the thyroid doesn’t stop the disease process. There is a school of thought that without adequate thyroid tissue, the antibodies that cause hyperthyroidism may go on to affect orbital or dermal tissue, causing Graves’ ophthalmology. For this reason some hospitals avoid using radio-iodine treatment for patients with Graves disease who already have Graves ophthalmology. There is a small but definite chance that radioactive iodine treatment may worsen already existing Graves ophthalmology or cause it. Again, this is rare.

8. Replacement hormone products currently on the market, both synthetic and glandular, are not comparable to our own hormone, and in some cases people, never feel “right”.

9. There are other treatments for hyperthyroidism available. One option is surgery, if the type of hyperthyroidism allows this approach. There is also anti-thyroid medication, which reduces the amount of hormone produced by the thyroid gland. This is usually prescribed in the beginning, for all patients, and approximately half of all patients are successfully treated with this method and can cease taking the medication after six months. Beta blockers can be given to prevent some of the symptoms like racing heart, but do not affect the thyroids production of hormones. These medications come with their own side effects which can include itching, rash and fever and, rarely, liver inflammation or a reduction in white blood cells which can be dangerous. If this is unsuccessful then patients will be advised to consider a permanent treatment such as radio-iodine or surgery.

10. Radioactive iodine is also taken in by the salivary glands which may cause temporary swelling or a sore throat. Iodine can also be expressed in breast milk and breast feeding will not be allowed following administration of the dose. There is also a very rare occurrence of adenoma of one of the parathyroid glands due to their close proximity to the thyroid gland.

In order to understand the treatment it is useful to know how the treatment will work and to dispel the myths of radiation. Nuclear Medicine concerns three types of radiation: Alpha particles, which are made up of two protons and two neutrons (the material that makes up the nucleus of any atom), Beta, which is either an electron or a positron (smaller particles that form part of an atom) and Gamma, which is basically an energy wave. All atoms follow basic rules in structure. Protons have a positive electric charge, and electrons are negative. When the number of protons in an atom is equal to the number of electrons the electric charge is balanced and the atom is stable. Radioactivity occurs when an atom is unstable because it contains too many protons, neutrons or electrons, or the electrons contain too much energy. Unstable atoms are called a radioisotope. These excesses of particles or energy are released from the radioisotope as one of the three types of radiation. Alpha particles are extremely damaging to human tissue because they are large and low energy. This means that as soon as they are released from their radioisotope their energy is deposited in the first cell they encounter and will cause cell death or mutation.

Beta radiation, is much smaller and higher energy and so can pass a short distance through the human body before depositing its energy into a cell. This then causes cell death and this is the property that has been harnessed in order to make the radio-iodine treatment possible. Gamma radiation is higher energy still and these energy waves are capable of passing through the body entirely, without causing any damage at all, and this property enables gamma emitting substances to be used for diagnostic studies in the Nuclear Medicine field.

Certain types of Gamma radiation is deemed so safe (in regulated doses) that Nuclear Medicine staff do not wear lead protection like those in radiology. As I mentioned, I have worked in Nuclear Medicine for ten years, through two pregnancies, and have worn monitors at all times. Staff radiation doses are rarely much higher than those of the general public (approximately 1mSv) even though we wear no protection and spend lots of time within 2 meters of patients, including radio-iodine patients. The exception to this is if the staff are involved in the production of the pharmaceuticals used each day. I did this extra job for the last four years and we are monitored more thoroughly and given health checks, but our doses are still within safe limits. To put the public dose in perspective, the dose a classified worker, like me, is allowed to receive is up to 150mSv.

All Nuclear Medicine staff should work to the ALARP principle it is the first thing I learnt as a student and it is for the protection of not only our patients but also ourselves. The principle means that we should keep radiation doses As Low As Reasonably Practicable at all times. This means that doses for tests and treatments are designed to be as low as possible whilst still maintaining the quality of the outcome, and the advice given is always designed to ensure that other people are not exposed unnecessarily to the radiation contained within our patients.

This principle is laid down by ARSAC: a body who advise the government on matters concerning radiation. If this principle is broken at any time it must be reported and we are accountable to the ARSAC body and can be removed from practice. ALARP is achieved using the three basic rules of time, distance and shielding. For this reason all of our radioactive substances are kept in lead or tungsten shields. The lead captures the emitted radiation, preventing it from resulting in a dose to anybody. It also helps to reduce the amount of time staff spend in contact with radiation, making it possible for us to prepare injections and transport doses without exposing ourselves to an unnecessary dose of radiation. We also try to keep as much distance between us and any source of radiation, including vials of radioactive substances and patients, and to encourage patients to keep a distance from other people, especially pregnant women and children for an amount of time, following a test or treatment, based on what isotope they have been given, and the dose they receive.

The other important factor in radiation treatment is the half-life of a radioisotope.

This is the time it takes for half of the radioactive particles to be released from the radioactive substance. The isotope used is chosen very carefully as it has to be readily available, affordable, non-toxic and have a half-life that is long enough for the effect of the radiation to work, but short enough so that it is not present in the body for too long. The half-life of I131, used in radio-iodine treatment, is 8 days. So after 8 days half of the radiation contained in the original dose will have decayed away (been released), and after another 8 days the residual will be half again.

On top of that is something called biological half-life which is the time it takes for half of the dose to be excreted from the body, which further reduces the time that the radioactive substance is in the body. This happens mainly via the urine. For this reason patients are often told to drink plenty and urinate often, as this helps to get rid of any radiation that is not taken up by the target organ. Eight days is a fairly short half-life.

This is one reason that I131 is kept for only a short time on hospital premises. We have limits as to how much radioactivity we are allowed to hold on site. Therefore we tend to order what we need and have it delivered the day before the patient is due to attend. Because of the nature of radioactive substances – the radioactivity is decaying constantly (by half every 8 days for I131) we have to order more than we need so that at the time of administration it is the correct dose for the patient. In the case of I131, if we were to have it delivered 8 days before the patient attended we would have to order twice as much as we needed.

On top of that all radioactive substances on site have to be accounted for and we are only allowed to dispose of so much radioactive waste. If a patient does not attend an appointment we are left with radioactivity that we cannot use, and must store until it reaches a low level before we can throw it away. These measures are designed to protect the staff and public, and demonstrate just how tightly regulated the industry is. We are regularly inspected by HMRC to check that we comply with the regulations.

I hope that I have given a balanced view of the pros and cons of radioactive iodine treatment, so that you can make your own decision based on facts. I am a firm believer in the treatment, having seen the positive effect on hundreds of patients during my ten years in Nuclear Medicine. This is reinforced by continued study and monitoring within the Nuclear Medicine discipline. However, I would never take away a patients freedom of choice. What I would warn against is reading and listening to personal anecdotes. There are many ill-informed people out there, and some who have had bad experiences. These are a tiny majority of people who are very outspoken. Doctors always have a patients best interest at heart and they are the ones who are most knowledgeable about their specialist subject. Trust them but ask questions if you are unsure. Far better to listen to the experts than the internet! Best wishes and good health. Liz