How long am I radioactive after radioactive iodine treatment?

Radiation levels fall quickly over the first few days as the unbound iodine is cleared in urine. Standard advice is to avoid intimate contact for the first 24 hours, limit exposure to young children and pregnant women for around five days, and keep about six feet from other people for three to ten days. Your team will give precise timings based on your dose.

What can I eat on a low-iodine diet?

Fresh fruit and vegetables, fresh meat in moderate portions, rice, egg whites, and non-iodised salt are all suitable. You need to avoid iodised salt, seafood and fish, dairy, eggs, milk chocolate, soy products and any iodine-containing supplements, starting one to two weeks before treatment.

Does radioactive iodine therapy hurt?

No. The dose is swallowed as a capsule or liquid and causes no pain. Any discomfort develops later — most commonly swelling and tenderness of the salivary glands, dry mouth, or mild nausea — and is managed with hydration, saliva stimulation and simple medication.

Can I be around my family after treatment?

Yes, with precautions and distance. Sleep alone, keep about six feet away where possible, do not share utensils, towels, razors or toothbrushes, do not cook for others, and wash your laundry separately. Take particular care to avoid close contact with young children and pregnant women for the first several days.

Will I need thyroid tablets after radioactive iodine?

Almost certainly. Because RAI destroys thyroid tissue, most patients become permanently hypothyroid afterwards. This is the expected outcome and is managed with a daily thyroxine tablet, with periodic TSH monitoring to keep the dose correct.

How soon can I get pregnant after RAI?

You will be advised to wait at least six months after treatment before trying to conceive. This allows the radioactivity to clear completely and thyroid hormone levels to stabilise on replacement therapy. Men are usually advised to wait a similar interval, as sperm counts can fall temporarily.

Can radioactive iodine therapy be repeated?

Yes. Where thyroid cancer persists, treatment can be repeated — generally every three months or longer — until there is no evidence of remaining disease. Repeat doses are spaced deliberately to let the bone marrow and salivary glands recover between treatments.

Radioactive Iodine Therapy — Preparation, Procedure &

What Is Radioactive Iodine Therapy?

Radioactive iodine (RAI) therapy I-131, also known as radioiodine therapy, is a treatment that uses radioactive iodine. The material circulates throughout the body and is concentrated in the thyroid gland, where the radioiodine destroys the thyroid cells.

The treatment works because of a quirk of physiology: the thyroid is the only organ in the body that actively traps and concentrates iodine, in order to build thyroid hormone. Given radioactive iodine, it absorbs that too — and the radiation, which travels only a few millimetres, is delivered almost entirely to the tissue you want to treat while sparing everything around it.

It is taken as a drink or a capsule. There is no surgery, no anaesthetic, and no injection.

What Is It Used For?

Radioactive iodine is mainly absorbed by the thyroid cells with little effect on other cells. Hence it can be used as a treatment for thyroid cancer and for hyperthyroidism — an overactive thyroid gland.

This therapy can also be used:

After a thyroidectomy, to destroy any cancer cells that remain after surgery
To treat thyroid cancer that has spread
To treat recurring thyroid cancer

You may need to have the treatment only once but, if needed, it can be repeated every three months until there is no sign of thyroid cancer.

Preparing for Treatment

Before starting on this treatment, you will need to do some preparation. Two things must happen: your body must be depleted of ordinary iodine, and your TSH level must be high.

The low-iodine diet

Following a low-iodine diet for at least two weeks before treatment makes your thyroid more receptive to the medication, increasing the effectiveness of the treatment. When the therapy is given, the iodine-starved thyroid cells absorb the radioactive iodine avidly — and are therefore destroyed.

For a low-iodine diet you will need to eliminate:

Iodised salt
Seafood and fish
Supplements containing iodine
Dairy products
Eggs
Milk chocolate
Soy products

This should be started one to two weeks before beginning the treatment.

Consistency matters more than people expect. A single high-iodine meal can saturate the thyroid's receptors, so that the therapeutic dose is simply excreted instead of absorbed — wasting the treatment. There are no useful "cheat days" on this diet.

Fresh fruit, fresh vegetables, fresh meat in moderate quantity, egg whites, rice and non-iodised salt are all acceptable. Review every medication and supplement with your doctor, since multivitamins, cough preparations and some heart medications contain substantial iodine.

Raising your TSH level

Your thyroid gland absorbs iodine best when there are high levels of thyroid-stimulating hormone (TSH) in your blood.

This is accomplished in one of two ways:

Injections of thyrogen (thyrotropin alfa) — a recombinant form of TSH, given as injections, which raises TSH without you having to stop your thyroxine
Withholding levothyroxine — stopping thyroid hormone replacement for several weeks so that your own pituitary drives TSH up naturally

The second approach works well but makes you temporarily and often profoundly hypothyroid, with fatigue, cold intolerance, weight gain and low mood in the weeks before treatment. Where thyrogen is available and appropriate, it avoids that entirely. Your team will advise which route suits your case.

The Procedure

The procedure takes place in a hospital setting. Radioactive iodine is ingested either as an oral solution or as a capsule, in a single dose.

You will need to refrain from eating so that your body can absorb the iodine. You will be able to eat and drink normally afterward, and you will need to drink plenty of liquids to flush the radioactive iodine out of your system.

That last point is not incidental. Aggressive hydration and frequent urination clear unbound radioactive iodine through the kidneys, reducing the radiation dose to your bladder and surrounding healthy tissue.

Once your body's level of radioactivity falls to a safe level, you will be sent home with post-care instructions. You will need to avoid contact with small children and pregnant or breastfeeding women for a period of time, because the treatment will make you slightly radioactive.

Radiation Safety After Treatment

When you undergo treatment with radioiodine, your body will give off a certain amount of radiation for a while. Because of this, you may expose those around you to the effects of radiation. This radiation can pose a health risk to others, especially small children.

Your healthcare provider will give you specific instructions about limiting the amount of time you spend around other people. It is very important that you follow these instructions carefully.

Distance and contact

Timeframe	Precaution
First 24 hours	Avoid intimate contact
First 5 days or so	Limit exposure to young children and pregnant women. In particular, avoid carrying children in a way that exposes them to your thyroid area
3 to 10 days	Stay at least six feet away from other people — this means avoiding public transport, hotels, carpools and, in some cases, your workplace

Household precautions

To further avoid exposing others to radiation:

Do not share any towels, razors, toothbrushes, cups, spoons, forks or dishes
Do not cook for anyone else
Use disposable dishes and place them in a specially marked plastic bag for disposal
Wash your clothes separately

Practical additions that help: close the lid and flush the toilet twice, wash your hands thoroughly each time, and sleep alone for the first several nights.

Travel and security screening

If you will be travelling by aeroplane or crossing an international border in the period following treatment, you must get a written document from your healthcare provider stating that you have had medical treatment involving radiation.

This is not a formality. Security monitoring devices at airports, ports and government buildings are sensitive enough to detect residual radioactivity for weeks after treatment, and being stopped without documentation is both stressful and difficult to resolve on the spot.

Side Effects

Depending on your age, overall health and the amount of radioactive iodine you received, you may have one or more short-term side effects:

Swelling and inflammation of the salivary glands
Dry mouth and dry eye
Changes in taste and sense of smell
Nausea
Neck swelling
Constipation or diarrhoea

Salivary gland symptoms are the most common complaint. The glands take up a small amount of iodine themselves, and can become swollen and tender. Sucking sour sweets or chewing sugar-free gum stimulates saliva flow and helps clear residual activity — but start this 24 hours after the dose rather than before, and stay well hydrated.

Possible long-term side effects are:

Lower sperm counts in men
Irregular menstrual cycles in women
Reduced level of blood cells produced
Risk of developing leukaemia in the future

The leukaemia risk is small and relates mainly to patients who receive multiple high-dose treatments for metastatic disease. It is a reason for using the lowest effective cumulative dose, not a reason to decline appropriate treatment.

You will be advised to wait at least six months after having radioactive iodine before getting pregnant.

Thyroid Care at THANC

Thyroid cancer and thyroid surgery at THANC are managed through the thyroid and parathyroid surgery service, working alongside our head and neck surgery team.

Radioactive iodine follows surgery in many thyroid cancer pathways, and the preparation — the low-iodine diet, the decision between thyrogen and hormone withdrawal, and planning the practical radiation-safety arrangements around your household and work — is coordinated as part of your overall treatment plan rather than left to you to work out alone.

If you would value another view on a thyroid mass or a proposed treatment plan, we offer a thyroid and parotid tumour second opinion.

Book a consultation to discuss thyroid treatment options.

Radioactive Iodine (RAI) Therapy — What to Expect