Answer to Question #14902 Submitted to "Ask the Experts"
Category: Medical and Dental Equipment and Shielding — Shielding
The following question was answered by an expert in the appropriate field:
We were discussing radiation exposure in fluoroscopy cases. One of our x-ray techs mentioned she closes her eyes and turns her head when she is close to the patient during a fluoro case. She claimed that this would help reduce the exposure to her eyes. I understand the part about turning your head, but can the tissue thickness of your eye lids reduce x-ray exposure?
Your question is interesting. The answer is that the eyelids will reduce the x-ray exposure by less than about 5% (i.e., >95% of the x rays will pass through the eyelids). Allow me to elaborate a bit.
The x-ray exposure through the eyelids (and any other part of the body) is based on the number and energy of the x rays impinging on the eyes. Higher x-ray energies are more penetrating and will result in higher exposures through soft tissue (i.e., the eyelids). When fluoroscopy is performed, the x-ray energy and other parameters are typically modulated by the fluoroscope, depending upon the type of procedure and body part being imaged. However, if the x-ray energy impinging on the patient is say 100 keV, the exposure to the fluoroscopist and other staff near the patient primarily is radiation that has been "scattered" from the patient. This scattered radiation is a spectrum of energies that will be lower than the x-ray energy impinging on the patient and as a result, less penetrating than the primary x-ray beam. Actually, the primary x-ray beam is a spectrum of energies as well, with the highest energy being displayed by the fluoroscope.
A quick search on the internet disclosed that the skin thickness of the eyelids varies, depending on the part of the eyelid one is considering. The upper eyelid is apparently thicker, while the lower eyelid is slightly thinner. Regardless, it seemed that the consensus of several websites I reviewed is that the general eyelid thickness is less than 1 millimeter (mm).
So, taking that information and considering the different x-ray energies that might comprise the scatter from a patient undergoing fluoroscopy, I calculated the attenuation characteristics for "soft tissue" at x-ray energies ranging from 100 keV down to 30 keV. It turns out that at 100 keV, about 98.2% of the x rays would pass right through the eyelid (1.8% would be stopped by the eyelid). At 30 keV, about 96.1% would pass through the eyelid (3.9% would be stopped by the eyelid). The calculated percentages at other energies fell between those percentages. Thus, the answer to the primary question is that closed eyelids do provide a slight reduction in eye exposure, but not very much.
As you mentioned, turning the head away from the exposure source (i.e., the patient) may reduce the eye exposure, simply because it may increase the distance from the source and x rays may even have to pass through the skull to reach the eye. However, that could be a problem if the individual turned their head in such a way as to decrease the distance from or inadvertently turn toward the source. If the potential eye exposure is significant, closing the eyes and turning the head would not be very effective at reducing the eye exposure.
For staff who are very close to the patient during fluoroscopy procedures, the best way to protect the eyes would be to wear some type of eye shielding (e.g., leaded glasses that wrap around the sides of the eyes) in addition to the whole-body shielding (e.g., leaded apron) that should be worn to protect most of the body.
Mack L. Richard, MS, CHP