What to Know About Radioactive Iodine Therapy

What to Know About Radioactive Iodine Therapy
Cecille R. dela Paz, MD, FPCP, FPCEDM

Radioactive iodine (RAI) therapy is a commonly ordered endocrine procedure. If you have diffuse toxic goiter or autonomously functioning thyroid nodule, RAI therapy can be used to treat hyperthyroidism. If you have been diagnosed with papillary or follicular thyroid cancer, you may have to undergo radioactive iodine therapy after total thyroidectomy in order to destroy any remaining cancer cells. The procedure strikes fear in a lot of patients because of the word “radioactive” but it is actually safer than it sounds.

First things first: what is iodine and how is it used for treating thyroid disease?
Iodine is an element that is essential to life. It is required for the production of thyroid hormones and is particularly important for healthy brain development in children. The thyroid gland is the only organ of the body that takes up and stores iodine because it has a specialised pump that moves iodine into the cells. The richest sources of iodine come from food derived from the sea. Milk and dairy products are also good sources of iodine. The ASIN law, enacted in 1995, recognises the important role that iodine plays in good health and requires all salt manufacturers here in the Philippines to iodise the salt they produce and distribute.
There are 2 radioactive forms of iodine: 123I which is harmless to thyroid cells and is used for imaging, and 131I which destroys thyroid cells and is used for imaging and treatment of hyperthyroidism and thyroid cancer. Radioactive iodine for therapy are available in capsule and liquid form. RAI only affects the thyroid gland. The thyroid cells are the main cells that can absorb iodine so there is very little radiation exposure to the rest of the body. RAI is an unstable form of iodine and when absorbed, it damages thyroid cells.

What preparations must be taken before undergoing radioactive iodine therapy?
Patients are usually asked to follow a low iodine diet about 2 weeks before RAI therapy. The reason for this is to reduce the amount of iodine in the body before treatment in order to increase uptake of the RAI in the thyroid gland.

The Low Iodine Diet
Low iodine foods you can eat freely
– Fresh/ frozen fruit
– Fresh/ frozen vegetables
– Cooked green vegetables
– Ordinary table salt and sea salt
– Rice
– Dried pasta
– Potatoes
– Fresh bread
– Non – dairy spread such as Vitalite or Pure or Flora non – dairy
– Olive oil, vegetable oils and nut oils
– Water, soft drinks, fruit juices & alcoholic drinks
– Tea without milk
– Coffee without milk
– Milk substitutes such as rice coconut, almond or soya milk (please check labels for ingredients and avoid brands that contain carrageenan which is a seaweed derivative)
– Dark /plain chocolate with a minimum of 70% cocoa
– Crisps

High iodine foods which should be avoided
– Fish, seafood, seaweed, kelp, laverbread
– Dairy produce such as milk, butter, margarine, cheese, yoghurt, ice-cream etc
– Egg and foods that contain egg yolk – for example custard, mayonnaise
– Fresh egg, egg fired rice
– Milky coffee and tea, cappuccino, hot chocolate, malted milk drinks
– Cakes and biscuits containing butter and eggs
– Milk chocolate and white chocolate
– Dried fruit
– Take away – meals and fast foods/ restaurant foods (as ingredients are unknown)
– Iodized salt and pink Himalayan salt
– Vitamins and minerals supplements, nutritional supplements and cough mixtures
– (unless prescribed by your medical team, for example vitamin D)

Foods which should be limited
– Milk – a maximum of 25ml per day which could be used in tea and coffee (i.e. about 5-7 teaspoons of milk per day)
– Butter – limit to a very thin scraping (one teaspoon or 5g) per day
– Cheese – one source or 25g once per week
– Egg – one per week

For hyperthyroid patients receiving antithyroid medications like PTU or methimazole, they are required to discontinue these medications 5 to 7 days before undergoing radioactive iodine therapy in order to increase uptake in thyroid cells.

What are the side effects of radioactive iodine therapy?
RAI is generally safe. Some patients experience a mild pain or discomfort in the neck area after treatment. This is managed by taking paracetamol or any pain relievers. Some patients report loss of taste and dry mouth due to salivary gland damage. These side effects can be lessened by sucking on sour candy.
If you are allergic to shellfish or to radio contrast dye, you may still undergo radioactive iodine treatment. People who have allergies usually react to compounds that contain iodine, not the iodine itself.
The most common (and expected) long term side effect of RAI therapy is hypothyroidism which is easily treated with levothyroxine supplementation.
After receiving radioactive iodine treatment, you will be given instructions to reduce exposure to other people. The duration of action is dependent on the amount of radiation you receive.

Does radioactive iodine cause cancer or infertility?
There are no evidence linking radioactive iodine therapy with cancer or infertility. However, women who are pregnant or breastfeeding should not undergo imaging or treatment with radioactive iodine. Women who have undergone radioactive iodine treatment are also advised not to get pregnant 6 months to a 1 year after to avoid exposure of the foetus to radiation. The delay also ensures adequate time to stabilise thyroid hormone levels. Men who receive higher doses of radioactive iodine for thyroid cancer may experience low sperm counts and temporary infertility for about 2 years.

If you have any questions or concerns regarding radioactive iodine therapy, always consult your endocrinologist for proper advise.

Instructions to reduce exposure to others after I RAI treatment
Action Duration (Days)
Sleep in a separate bed (~6 feet of separation) from another adult 1-11*
Delay return to work 1-5*
Maximize distance from children and pregnant women (6 feet) 1-5* Limit time in public places 1-3* Do not travel by airplane or public transportation 1-3* Do not travel on a prolonged automobile trip with others 2-3 Maintain prudent distances from others (~6 feet) 2-3 Drink plenty of fluids 2-3 Do not prepare food for others 2-3 Do not share utensils with others 2-3 Sit to urinate and flush the toilet 2-3 times after use 2-3 Sleep in a separate bed (~6 feet of separation) from pregnant partner, child or infant 6-23* *duration depends on dose of I-131 given Source: American Thyroid Association
Mr. Michael Barachina underwent radioactive iodine (RAI) treatment following surgery. He shares his thoughts about his last treatment.

I already underwent RAI twice. My second time was easier for me to handle because I already knew what to expect before and after my RAI treatment. Here are my personal experiences.

How did I prepare for my RAI?
– I avoided foods rich in iodine. These included iodized salt, seafood, egg yolk, milk and other dairy products. I also avoided using mouthwash.
– I stopped taking my daily maintenance of levothyroxine a month prior to my treatment.
– Although not required, I kept my exercise plan in order to be physically fit. I also avoided eating fatty foods because of my hypertension.

What were the instructions after receiving RAI in the hospital?
– The first 3 days were challenging. I was admitted to a designated isolation room of the hospital. Nobody was allowed to have close contact with me—even nurses and doctors— without protective covering.
– I drank a lot of water everyday, particularly during the first 3 days following my RAI treatment.
– I was discharged from the hospital on the fourth day. I resumed taking my daily maintenance medications as prescribed by my doctors.

What were the instructions after my discharge from the hospital?
– I avoided close contact with my family and household members for 1 week. I avoided close contact with pregnant women and children for 2 weeks after treatment.
– For the first 10 days after RAI, I had a designated bathroom in our home.
– I kept all the clothes I wore since I was admitted until 10 days after treatment in a bag. After 10 days, I was allowed to have them washed.
– After a few more days from my discharge from the hospital, I underwent a whole body iodine-131 scan.

What did I feel after receiving RAI?
– Physically, I felt sluggish although I had a normal body temperature.
– For the first ten days after my treatment, I lost my appetite. I totally could not taste about 80% of what I ate. It gradually came back after 1 to 2 months.
– I felt tolerable pain under my jaws after the treatment.
– After 10 days, I resumed work and went back to my my daily routine.

Lastly, acceptance and having a positive mindset helped. Despite needing RAI treatment twice, I maintained a positive outlook regarding my condition. I knew that I will be able to overcome it.
Tips from Patients
“Magdala ng libangan para di mainip sa loob. Wala akong naramdamang pagsusuka pagkatapos uminom.” -Nina, 51
“Magdala ng mga damit na luma para diretso tapon.” -Jaime, 55
“Magdala ng babasahin. Magdasal habang nakaadmit.” -Marilyn “Maligo ng madalas. Magbaon ng prutas para mawala ang lasa ng RAI. Magbaon ng tatag ng loob at tiwala sa Diyos.” -Alberto, 59
“Magdala ng maraming tubig at maghanda ng lumang damit na gagamitin sa ospital. Maligo araw-araw.” -Rosalia, 49
“After taking the RAI, take a bath 7 to 8 times a day (during the 3 days of confinement). I took a bath every 2 hours starting 6 AM, para hindi naman masyado maginaw at abutin ng gabi sa pagligo. On the 3rd day, my radiation reading was low and I was discharged early.” -Raquel, 47
“Huwag matakot sa pag-inom ng RAI capsule. Kung may mga side effects, ipagbigay alam agad dahil may naka-standby na gamut.” -Corazon, 58
“Huwag matakot sa RAI. Uminom ng maraming tubig.” -Cristina, 66
“Trust your doctor. Be positive.” -Sonia, 56
“Pray. Let your family know what you will go through. Prepare your family.” – Raquel, 47


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The PCEDM is a sub-specialty society of the Philippine College of Physicians, a founding member of the ASEAN Federation of Endocrine Societies, and a member of the International Society of Endocrinology.

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