Answer to Question #1346 Submitted to "Ask the Experts"

Q

I'm a dental hygienist and I am 4½ months pregnant. I routinely perform dental x rays at work. Is my baby at risk for a birth defect even though I practice safe radiation protection procedures such as wearing a dosimetry badge and standing behind a lead-lined wall during exposures? How dangerous is scatter radiation to the fetus?

A

A fetus is considered to be at higher risk from radiation effects than an adult because of the rapid differentiation and growth of cells during development. For that reason, radiation protection guidelines are stricter for the fetus than for others. Guidelines for radiation dose limits have been developed by the National Council on Radiation Protection and Measurements (NCRP) for various classes of people, including those exposed during their occupational duties and members of the general public. Separate guidelines are available for the fetus. The occupational effective dose limit, which applies to you in your work as a dental hygienist, is 50 mSv/year relative to stochastic effects such as cancer. For the fetus the dose limit is 0.5 mSv per month (500 µSv per month) after pregnancy is known. Although these dose levels are thought to present minimal risk, it is recommended that the principles of ALARA (As Low As Reasonably Achievable) be followed.

Protection for the user of dental radiographic equipment can be obtained by two methods: standing behind a barrier or, if that is not possible, standing at least 2 m away from the x-ray machine, at an angle of 90-135 degrees from the beam, during the exposure. According to your statement, you are already standing behind a lead-lined wall, which provides a safe environment for you. The wall will absorb the small amount of radiation that scatters from the patient's face.

To put some doses into perspective for you, when a pregnant woman receives a full-mouth series of dental radiographs while wearing a leaded apron, the dose to the fetus is approximately 0.25 Gy. This entire dose is a result of scattered radiation since the abdomen is not in the direct beam. Since scattered radiation decreases in intensity with increasing distance, the dose to the operator, who is either 2 m away or behind a barrier, is significantly less than what the patient receives. The average effective dose from background radiation in the United States is 3.6 mSv/yr (3600 Sv) or approximately 10 Sv/day. From this it can be seen that the radiation exposure of an operator of dental x-ray equipment is far less than the normal background radiation exposure. Because you are wearing a dosimetry badge, you can track the amount of radiation you are receiving. The reported exposures to dental personnel are extremely small and can be zero if appropriate precautions are observed. My analysis of the situation that you presented is that you are working in an environment that will not put you or your fetus at risk from radiation exposure.

Sharon L. Brooks, DDS, MS
Diplomat, American Board of Oral and Maxillofacial Radiology
President, American Academy of Oral and Maxillofacial Radiology