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24 May 2012

Answer to Question #7194 Submitted to "Ask the Experts"

Category: Pregnancy and Radiation — Proximity to radioactive persons

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

I have a couple of questions about nuclear medicine and radiation exposure. I work in a hospital and I'm about 14 weeks pregnant. I was in the corridor and they happened to wheel in a patient who had just had the injection for a nuclear medicine bone scan. I passed by the stretcher—so contact was minimal and limited to the few minutes that I was walking past the stretcher in the corridor. However, I'm a little concerned in view of the fact that this is a fairly frequent occurrence in the hospital. Also, I had to examine patients who have had PET scans 48 hours before. Please let me know what the dose of radiation exposure is likely to be for the fetus.

Thank you for your question. According to NCRP Report 124, the radiation dose from a patient receiving 20 mCi of technetium-99m (hydroxymethylene disphosphonate) (for a bone scan) within five minutes of the injection is under one one-hundreth of a millirad/hour or 9 microrad/hour (rad is a unit of radiation absorbed dose; natural background radiation exposes us to about 1 mrad each day). With that in mind, you received no measurable radiation dose and neither did the fetus.

For most PET radiopharmaceuticals, the radioactivity is gone within a few hours because they have such short half-lives. The exception is fluorine-18, which would be gone in about 10 hours (half-life of about 110 minutes). At 48 hours post-injection, the radioactivity remaining in the patient would be negligible.

Kelly Classic
Certified Medical Health Physicist

National Council on Radiation Protection and Measurements. Sources and magnitude of occupational and public exposures from nuclear medicine procedures. Bethesda, MD: NCRP; NCRP Report No. 124; 1996. Available at www.ncrponline.org.

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