What is radioiodine therapy?
Radioiodine therapy is the most common form of nuclear medicine therapy. During the procedure, the patient swallows radioactive iodine in the form of sodium iodide – either as an aqueous solution or in capsule form. It is then transported via the bloodstream to the thyroid gland, which absorbs and stores the iodine very quickly. Once the iodine has reached the thyroid cells, its radioactivity can damage the pathologically altered cells from the inside and ultimately destroy them.
Why does the thyroid gland store iodine in the first place?
The butterfly-shaped thyroid gland located under the larynx is an important organ for the human hormone balance. It stores iodine, which is normally absorbed through food. It needs this iodine to produce hormones (called T3 and T4), which have an activating effect on the body’s energy metabolism. The activity of the thyroid gland is controlled by the pituitary gland (hypophysis) and its messenger substance TSH.
When is radioiodine therapy carried out?
In certain diseases, it may be necessary to eliminate abnormal thyroid tissue. For example, if the tissue proliferates uncontrollably or produces too much thyroid hormone.
Radioiodine therapy is carried out:
- as a follow-up treatment for thyroid cancer and its metastases (only for differentiated thyroid carcinoma)
- for inflammatory immune diseases (Graves’ disease)
in the case of goitre formation. The goitre usually has no effect on the metabolism, but is an aesthetic problem due to the strong growth of thyroid tissue and can lead to swallowing difficulties.
Radioiodine therapy can be used to remove the diseased thyroid tissue very safely and with little risk. Prior surgery is not necessary, except for the treatment of thyroid cancer.
In this type of cancer, radioiodine therapy is used to treat the thyroid gland or thyroid gland remnants and any metastases. However, the treatment only helps if the cancer cells store iodine. This is the case with so-called differentiated thyroid cancer. If the cancer cells no longer store iodine or if the cancer is located in the C-cells (medullary thyroid carcinoma), the therapy is of no use.
Benign thyroid nodules or inflammatory immune diseases can cause the thyroid gland to secrete too many hormones. Its cells then produce the hormones “autonomously”, i.e. independently of the body’s needs and the control signals from the pituitary gland. Radioiodine therapy destroys the cells and stops the overproduction.
What is done during radioiodine therapy?
The procedure and aim of the therapy are always the same, regardless of the underlying disease: The patient is examined and their laboratory values are determined, followed by a radioiodine test and then the radioiodine therapy begins. It usually lasts a few days.
The patient is admitted as an inpatient because although the radiation from the iodine used only reaches a few millimeters, there is a theoretical possibility of harming other people. This is because the radioactive decay of the iodine used not only releases the therapeutic beta radiation, but also a small amount of gamma radiation, which has a much greater range. For this reason, the patient is not allowed to receive visitors during the radioiodine therapy period and the waste water from the toilet, shower and other service water is collected in special facilities until the radiation has subsided.
On the first day of the hospital stay, the patient will have a consultation, an ultrasound examination of the thyroid gland and a final determination of the relevant laboratory values. A scintigraphy is often carried out beforehand to determine the metabolic activity of various tissues in the body.
How long does radioiodine therapy take?
Once the patient has swallowed the therapy capsule or liquid, an inpatient stay of at least 48 hours is required by law, and the daily residual radiation of the thyroid gland must not exceed a certain maximum level. It may therefore sometimes be necessary to spend several weeks in hospital. This period varies from person to person. However, this is offset by the very high chances of recovery from hyperthyroidism and the minimal side effects of radioiodine therapy. After discharge, the patient can immediately resume their normal everyday life and go to work.
The effect of the therapy is delayed. Only after a few months is it possible to say whether it has been successful. In most patients with hyperthyroidism, the metabolic situation normalizes as a result of radioiodine therapy.
What are the risks of radioiodine therapy?
Like almost every therapy, radioiodine therapy also has side effects. Two weeks after the end of treatment, up to 70 percent of patients experience temporary changes in their blood count. In 10 to 40 percent of patients, the thyroid gland swells painfully and becomes inflamed.
To protect the child, radioiodine therapy must not be carried out during pregnancy and breastfeeding. In addition, contraception should be used for six to twelve months afterwards.
Some patients develop hypothyroidism after radioiodine therapy. However, this is not dangerous, as the missing hormones can be easily replaced with thyroid hormones in tablet form without any side effects.
What do I need to consider before and after radioiodine therapy?
In the weeks before radioiodine therapy, no iodine-containing thyroid hormones or other iodine-containing medication (in the case of the heart medication amiodarone, a break of at least 12 months) and contrast media may be taken. Otherwise they would inhibit the absorption of the radioactive, therapeutic iodine and thus the effectiveness of radioiodine therapy. For this reason, experts also recommend a low-iodine diet in the two weeks before treatment begins.
Depending on the disease, doctors also influence the TSH level. In the case of thyroid autonomy, for example, they aim to reduce the TSH level so that areas of the thyroid that are not healthy absorb the iodine.
Pregnancy must be ruled out at the time of treatment. Ideally, affected mothers should stop breastfeeding eight weeks before radioiodine therapy.
Follow-up treatment
The success of radioiodine therapy is checked after three to six months by means of a whole-body scintigraphy. Sometimes it may be necessary to carry out a second radioiodine therapy. If the laboratory check after the therapy shows signs of hypothyroidism, it may be necessary to take thyroid hormones in tablet form.
If there is a desire to have children, it is important that those affected use contraception after radioiodine therapy. The duration depends on the dose used. Experts usually advise both men and women with benign thyroid disease to use contraception for four months. After radioiodine therapy for thyroid cancer, women should use contraception for six to 12 months and men for four months.
In the case of particularly intensive and/or repeated radioiodine therapy, your doctor will also advise you on cryopreservation, i.e. the freezing of sperm or eggs.
