Answer to Question #4955 Submitted to "Ask the Experts"

Category: Radiation Workers — Pregnant Workers

The following question was answered by an expert in the appropriate field:

I am a nuclear medicine technologist working in an institution that performs iodine-131 therapies. Every week, six patients are administered with iodine-131 anywhere between 100 mCi and 350 mCi. When performing this rotation we are expected to receive the iodine package, administer the dose, release the patient, and immediately decommission the patient room. I am currently trying to conceive a child and will be starting fertility medications. I am concerned about my radiation exposure and the chance that I might be pregnant while performing this rotation.

Since you are a nuclear medicine technologist who administers iodine-131, you are most likely wearing a radiation dosimeter and are probably also undergoing thyroid monitoring to see if you inhaled radioiodine (if the radioiodine is in liquid form). This is the information you should look at to determine your previous exposures relative to what exposures you might get if you do get pregnant.

While you are looking at your exposure history, keep in mind that the regulatory limit to the fetus of a "declared" occupationally exposed worker is 500 mrem during the gestation period. (You probably know this, but mrem or millirem is a unit of radiation dose and "declared" means you have identified yourself in writing to your organization [usually to the radiation safety officer or chief nuclear medical technician].)

Once you have declared your pregnancy, you have the right to ask for an exposure history assessment and to ask for assistance to minimize radiation exposure the fetus might receive. If the exposure history assessment suggests you/your fetus might receive 500 mrem or more, then additional precautions must be taken to assure the limit is not exceeded.

The part that holds the greatest exposure hazard to your fetus after its thyroid is formed (usually between week 10 and 13) is inhalation of the iodine if you are administering it in liquid form. The fetal thyroid is quite sensitive to radiation and, being so small, is certainly at risk of biological effect if you inhale iodine-131. If you are administering it in pill form, this is not an issue.

So, here is what you can do before you get pregnant: Review your exposure history—both external and internal. If your radiation badge readings accumulate to less than 500 mrem in a year and you have had no thyroid burden of iodine-131, then there is no worry.

If your radiation badge readings accumulate to more than 500 mrem in a year or if you have routinely had thyroid burdens of iodine-131, then you need to work with your radiation safety office or chief nuclear medical technician in advance of your pregnancy to look for ways to reduce the external exposure and eliminate the internal burdens.

Kelly Classic
Certified Medical Health Physicist

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