Thyroid Cancer Treatment: What to Expect with Radioactive Iodine Therapy

“The first thing we do is we have patients go on a low iodine diet for a couple weeks before the treatment, usually two weeks before the treatment, and typically our nurses will educate patients on what foods they have to avoid to make sure that their body iodine stores are extremely, extremely low,” Dr. Kristen Otto, a head and neck surgeon at Moffitt Cancer Center in Florida, explains.

“The treatment is a kind of process that lasts about three or four days, essentially. [For] the first two days, patients get the thyrogen injections [a protein designed to be identical to the natural thyroid-stimulating hormone, or TSH, our bodies make], and then on the third day, most patients will be given a small dose of radioactive iodine and they’ll have a head to toe scan, and we look for any uptake and that allows us to prepare the treatment dose.”

The treatment dose depends on how much cancer your medical team believes is left over.

“If we see some uptake in just in the neck alone, which we almost always do, even after the best thyroid surgery, we’ll see just a little bit of uptake in the neck, then we know we can treat with a slightly lower dose,” Dr. Otto explains. “If we see uptake outside the neck, for instance, in the lungs, then we assume that the thyroid cancer has already metastasized to the lungs. And for those patients, we give a higher treatment dose.”

Understanding TSH

Thyroid-stimulating hormone, or TSH, generates commands specifically to the thyroid cells to capture iodine in the blood stream and make up thyroid hormones (T3 and T4). Therefore, the presence of TSH makes the thyroid cells capable of performing this work. Technically, the more TSH, the more iodine captured and the more thyroid hormone produced.

Thus, scientists realized that a modified iodine molecule could trick the thyroid cell and promote its death instead of thyroid hormone. When both TSH and iodine are given to a patient, this effect could be enhanced since the presence of TSH would stimulate even more the thyroid cells to absorb this modified iodine (radioactive iodine).

There are two main methods to increase TSH in a patient to stimulate this process: thyroid hormone withdrawal (which will alert the pituitary to release more TSH) or administration of recombinant human TSH.

“Since we often give patients thyroid hormone supplements, especially if they’ve had their thyroid removed completely, they need thyroid hormone for normal health in order to avoid taking away their thyroid hormone and making them hypothyroid [which means they have a low level of thyroid hormones],” Dr. Lisa Orloff, Director of the Endocrine Head & Neck Surgery Program at Stanford Medicine, tells SurvivorNet.

“There has been the development of this recombinant TSH, which is basically a way of injecting a dose or two doses of TSH to artificially or temporarily raise the level of TSH in the blood just long enough to give the person radioactive iodine and … that TSH helps the iodine get into the cells. So, it’s a much more comfortable way in many instances to achieve the treatment with radioactive iodine without having to be deprived of your thyroid hormone.”

Thyroid Hormone Withdrawal

After having your thyroid removed (thyroidectomy) or stopping your usual thyroid hormone medication (like levothyroxine), you allow your body’s TSH level to rise naturally.

This approach requires stopping levothyroxine (T4) for about three to four weeks. However, to make the process easier, one method is to reduce your T4 dose by 50% for four weeks, then stop it completely for one more week. Another method is to switch from levothyroxine (T4) to a shorter-acting form (liothyronine or T3) for a certain period to reduce the time you’re off medication entirely.

“In the past, when we did radioactive iodine therapy, we took patients for about six weeks. We had them stop taking thyroid hormone and allowed them to become profoundly hypothyroid. And in most cases, that’s a very miserable feeling … patients are extremely fatigued. They feel terrible. And so these days don’t have to do that because we can give this injection of TSH recombinant TSH or thyroid,” Dr. Otto explains.

Possible side effects of hypothyroid (low thyroid hormone) include:

• Fatigue, low energy, and muscle aches
• Feeling colder than usual
• Weight gain or fluid retention
• Mood changes (depression, irritability)
• Slowed thinking or forgetfulness

Recombinant Human TSH (rhTSH)

Now, instead of stopping your thyroid hormone medication, doctors can inject you with a man-made form of TSH (called rhTSH). This makes the thyroid cells (or thyroid cancer cells) “hungry” for iodine, without you going through a low-thyroid (hypothyroid) phase.

You stay on your usual dose of levothyroxine (T4) so you don’t develop low-thyroid symptoms. You get two injections of rhTSH on two consecutive days, and on the third day, you receive the radioiodine treatment. This quickly raises TSH levels, allowing the radioiodine to be effective without long periods of medication.

This approach avoids hypothyroid symptoms because you stay on your usual thyroid hormone, you don’t go through the typical low-thyroid side effects (fatigue, weight gain, depression, etc.).

Although very uncommon, rhTSH can also stimulate the rapid growth of any remaining thyroid cancer cells. This is extremely rare.

Which Method Is Right for Me?

Thyroid Hormone Withdrawal is the traditional route. It’s effective but can make people feel quite tired and have other “low-thyroid” symptoms for a few weeks.

Recombinant Human TSH (rhTSH) allows you to avoid feeling hypothyroid but can be more expensive and not always available or covered by insurance.

“This medication [recombinant TSH] was FDA approved for getting rid of normal thyroid tissue after thyroidectomy, and it’s widely used in the treatment of thyroid cancer, but there are instances where more advanced cancers are felt to be best treated through the traditional method of taking somebody off their thyroid hormone and having their natural TSH rise and increase the uptake of iodine,” explains Dr. Orloff.

Certainly, your doctor will help you decide which approach is best based on your overall health, cancer specifics, insurance coverage, and personal preferences.

Questions To Ask Your Doctor

• Which approach to radioiodine therapy makes the most sense for me?
• Will my insurance cover this approach?
• How long will I need to stay in the hospital?
• How should I prepare for radioiodine therapy?
• Do I need to make changes to my diet or other lifestyle factors?

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