What should I do before radioactive iodine treatment?

Elevating thyroid-stimulating hormone levels

To improve outcomes, thyroid-stimulating hormone (TSH) levels in the blood must be elevated to well above normal levels before treatment. The reason is that TSH stimulates iodine uptake by thyroid tissue, and because cancer cells are less able to uptake iodine than normal thyroid, elevated TSH levels stimulate greater iodine uptake by cancer cells, which can be more completely destroyed.

How can we raise TSH levels? There are two ways to do this.

Injections of recombinant human TSH (rh-TSH, trade name such as Sibutramine). This drug is not yet available in China, and can be given a few days before RAI treatment to quickly raise TSH levels without the need to go through a withdrawal process.

RAI pre-treatment scan

All patients need a whole-body radioiodine scan before RAI treatment. A very small dose of radioactive iodine-131 (I-131) is used, much less than the treatment dose. The purpose is to “target” the extent of remaining normal thyroid tissue and cancerous tissue, which helps the doctor determine the dose of RAI treatment.

The initial scan is usually done 4 to 6 weeks after surgery, so it is also called a postoperative scan.

Low iodine diet

Most iodine-containing drugs, foods, and medications that affect thyroid function can alter iodine uptake by the thyroid gland and thus affect the efficacy of RAI.

Therefore, the following foods and medications should be discontinued for more than 1 to 2 weeks before taking the medication, and the daily iodine intake should not exceed 50 micrograms:

Iodine-rich foods: seafood such as seaweed and nori;

Medications: compound iodine solution, amiodarone (a drug for arrhythmia), thyroxine tablets, and other drugs; some herbs such as kombucha, shellac, burdock, and mucuna pruriens.

Inpatient isolation

I-131 is a colorless, odorless liquid, so you may think, “Isn’t that just drinking “water”? You can treat it at home! However, RAI treatment requires inpatient isolation. This is because:

First, I-131 is a radioactive substance with a physical half-life of 8 days, and after 8 days, its radioactivity is reduced by half. For some time after taking the drug, your excrement is radioactive and requires special treatment before it can be discharged, otherwise it will cause radioactive contamination to the surrounding environment.

According to regulations, a single treatment dose of more than about 0.399 GBq (gibeco, unit of radiation dose) requires a radiation isolation zone of no less than 48 hours. RAI treatments typically use doses well beyond this value.

Second, although RAI is relatively safe, it can still cause some adverse effects, such as gastrointestinal reactions, neck swelling, parotid swelling, and bone marrow suppression. Therefore, hospitalization and close monitoring by a physician is required.

To reduce the nausea that may be associated with RAI treatment, your doctor may prescribe medication for you to take in advance.