Answer to Question #9351 Submitted to "Ask the Experts"

Category: Nuclear Medicine Patient Issues — Diagnostic Nuclear Medicine

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

Q

I work in the health care field. I recently was assisting with a patient in the operating room and was closely involved with her for about 20 or 30 minutes, helping to position her for the procedure. I then learned that she had just undergone a 99mTc scan. She was having a mole removed for malignant melanoma and they had done the scan to follow the lymph drainage, as I understand it. The surgeon was using a Geiger counter to help figure out which node to remove.

I am currently 13 weeks pregnant and recall hearing that patients undergoing these types of scans should not interact with small children for some time following the scan. Is that true for pregnant women as well? What's the amount of radiation actually emitted by people who've just had this kind of scan? Is there any risk to my fetus at this dose?

A

There was no risk to your fetus from this exposure. Also, there are no restrictions to patients undergoing diagnostic exams to limit their interaction with children or pregnant women. There is only a restriction for patients having high-dose radioiodine therapy for thyroid cancer and a few other therapeutic injections (in addition to prostate seed implants). The dose to others is extremely low from diagnostic exams, so there are no restrictions on activities or people that the patients can be around following injection.

The injection of 99mTc is for a procedure called lymphoscintigraphy and only a very small tracer dose is used since the probe is very sensitive to the material. The patient is injected with a very small amount of 99mTc and may have multiple injections. Assuming a maximum amount of 18.5 MBq and using some assumptions, I calculate a potential dose of 0.0005 mSv if you were close to her for 30 minutes.

We are all exposed to about 1 millirem per day of radiation just living in the United States, so the potential extra 0.0005 mSv of radiation in addition to the 0.01 mSv (already a very small number) is hardly detectable. It is hundreds of thousands of times lower than the exposure that could potentially affect a fetus. There is no need for worry.

Marcia Hartman, MS

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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