Answer to Question #12560 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I work in a small veterinary facility. We have an Innovet Select beam producer with a Direct Radiology plate supplied by Idexx. We average about 88 kVp per x ray and about 20 x rays are taken per day. The x-ray machine is in its own room, but the walls are not lead-lined. There are two walls (so four layers of regular plasterboard—NOT cement or plaster) between my workstation and the machine, but only about 2.4–3.0 meters. I am concerned because I am pregnant.
I was told that two layers of drywall should stop most of the scatter. Is this correct? Also, I try to wear a nonlead x-ray apron (tungsten-antimony), but sometimes it gets too hot to wear and I have been caught only about 3.0 meters away when they take x rays. Is tungsten-antimony as good as lead? And finally, they won't give me a dosimeter badge because I don't technically take x rays. Have you heard of the Insta-Dose electronic dosimeter that works like a USB? Does it give accurate readings? And is it safe to hang near my body?
Since there are a number of questions here, I'll try to address them one at a time.
- "I was told that two layers of dry wall should stop most of the scatter. Is this correct?"
Without knowing a little more about the x rays being taken, it isn't possible to actually perform a shielding calculation for your workstation. That said, I assume the x rays taken are generally on smaller animals which would generally indicate low levels of scatter due to small field sizes and low milliampere settings on the machine. Four layers of drywall could be anywhere from 5.1 cm to 6.4 cm and that thickness would do a pretty good job of shielding scattered radiation.
- "I try to wear a nonlead x-ray apron (tungsten-antimony), but sometimes it gets too hot to wear and I have been caught only about 3.0 meters away when they take x rays. Is tungsten-antimony as good as lead?"
It isn't clear if you're wearing this type of apron all the time or when you're in the room when x rays are being taken. These types of aprons are designed to provide adequate protection from scattered x rays. Are they better than lead? Possibly not, but you're talking about a difference of possibly 90% vs. 95%, so they are commonly used throughout the medical community due to their lighter weight (older lead aprons were heavy and some individuals developed back problems when they constantly wore them). If you're three meters away when those x rays are taken, the scattered radiation level would be very low, so that probably isn't a big problem on an occasional basis. However, some states require some type of protective apron for staff inside an x-ray room, so be mindful of that requirement.
- "Have you heard of the Insta-Dose electronic dosimeter that works like a USB? Does it give accurate readings? And is it safe to hang near my body?"
Use of the Insta-Dose dosimeter is becoming more common throughout the medical community. The processor (Mirion) of these devices has been accredited by the National Voluntary Laboratory Accreditation Program (NVLAP) which means their process and dosimeters have been tested and meet specific dosimetry standards. Most if not all medical facilities use NVLAP accredited dosimeter processors. The National Institute for Standards and Technology (NIST) has a NVLAP website that provides more information about NVLAP accreditation. Regulations typically require personnel monitoring be provided for individuals likely to receive in excess of 10% of the occupational dose limits (usually 10% of 50 mSv or 5 mSv) in one year. Some regulations reduce the limit to 5 mSv for pregnant employees over the gestation period, so 10% of that would be 0.5 mSv. Based upon the description of what you do, you're probably not likely to exceed 10% of that limit which I assume is why your employer doesn't provide you a personnel monitoring device. However, that doesn't prevent them from providing such a device for your piece of mind—you might ask them again and even consider sharing the cost with them.
You can contact your state regulator if you have concerns that your facility is in violation of regulations.
Mack L. Richard, MS, CHP