Radioisotope therapy
Radioactive iodine is a type of iodine that is radioactive – iodine 131 (I-131). It is also called radio iodine. You usually have radioactive iodine as a capsule or a drink.
Your doctor might ask you to eat a low iodine diet before you have treatment with radioactive iodine. They might also ask you to change your thyroid hormone medicines or other medicines for a while.
You have a scan before treatment. This is so your doctor has a clear picture of your thyroid. This might be on the day of your treatment or a few days or weeks before.
Preparing for radioactive iodine treatment
Radioactive iodine is an effective type of treatment for cancer of the thyroid gland.
This is because your body absorbs the radioactive iodine from the drink or capsule. The thyroid cancer cells pick up the iodine, even if they have spread to other parts of the body. The radiation then destroys the cancer cells.
This is targeted radiotherapy because the treatment goes straight to the cancer. It has very little effect on healthy cells in the body.
During radioactive iodine treatment
Radioactive iodine can be attached to a chemical called MIBG – meta-iodo-benzyl-guanidine. MIBG is taken up by some types of cancer, including:
a rare childhood tumour called neuroblastoma
neuroendocrine tumours (NETs), including phaeochromocytomas
Scans use radioactive iodine attached to MIBG to diagnose these tumours. It is also used to treat these tumour types.
Radioactive iodine treatment can make you radioactive for a few days after treatment. Any radioactive iodine that is not absorbed by the thyroid cancer cells leaves your body in your sweat and urine.
The staff tell you about the radiation safety procedures you need to follow.
You need to drink plenty of fluids during your treatment. This helps to flush the iodine out of your body.
You'll be checked regularly for the amount of radiation in your body. You can go home as soon as it falls to a safe level for the people around you, usually after about 4 to 7 days. In the meantime you stay in a single room at the hospital.
You might be given some safety steps to follow for a while when you get home. For example if you are in contact with children or pregnant women. Your doctor or specialist nurse explain these to you before you leave hospital.
After radioactive iodine treatment
Side effects of radioactive iodine treatment can include:
inflammation of the salivary glands
dry mouth and changes to your taste
a swollen or tender neck
feeling flushed
feeling sick (nausea)
There is a chance of developing an under active thyroid. Speak to your doctor about when they will test for this. You usually have a blood test 4 weeks after the treatment.
Read more about side effects of radioactive iodine treatment
Last reviewed: 19 Dec 2023
Next review due: 19 Dec 2026
Internal radiotherapy means having radiation treatment from inside the body. It is also called brachytherapy. Read more about what it is and how you have it.
You need to follow some safety procedures when you have internal radiotherapy. This is to protect others from being exposed to radiation.
Thyroid cancer is when abnormal cells in the thyroid gland start to divide and grow in an uncontrolled way.
Find out about cancer treatment with radiotherapy, including external radiotherapy, internal radiotherapy, side effects, radiotherapy for symptoms and follow up after treatment.
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