Answer to Question #10304 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:

Q

When shielding male gonads for abdominal x rays, is there any protection benefit for using direct shielding (directly on patient) vs. shadow shielding (shield closer to the tube)? My exact situation is within a neonatal intensive care unit and we sometimes place our gonadal shields on top of incubator covers which is about halfway between the patient and the tube.

A

It's pretty much a wash. While there might be a little more radiation exposure, one way or another, due to tissue scattering and the geometrical penumbra of the x-ray tube focal spot, these effects are quite small when compared to the overall effect of the shield in the first place. While gonadal shielding will usually reduce the organ dose by about 99%, the scatter and penumbra effects would be less than 1%. The most important thing is to make sure the gonadal shield is positioned correctly to block direct radiation to the protected organs and to not interfere with the region of diagnostic interest.

It's primarily dictated by what type of gonadal shielding you have available. True shadow shields are usually affixed to the x-ray collimator and are not designed to be placed directly on the patient. Flat or shaped contact shields are specifically designed to be placed on the patient and are usually affixed with some tape to make sure they do not move during the exposure.

If you have a choice of shields, it should be dictated by the clinical situation at hand. As an example, specific to your situation, in a Neonatal Intensive Care Unit (NICU), if a neonate is in an incubator with a lot of monitoring and life-support equipment, it might be a better choice to use a shadow shield than to risk entering the incubator and possibly disturbing the monitoring or life-support equipment.

You should also keep in mind that for a neonate, your x-ray exposure techniques are about as low as you can get. The typical dose from a radiograph to a neonate is about 16 µSv. This is equivalent to about two days of exposure from natural background sources of radiation per radiograph. Making sure that you avoid retakes, use the right technical factors, proper collimation and the proper positioning of gonadal shielding are much more important factors than whether the shield is located on the skin or at the collimator.

Michael Bohan

References
Puch-Kapst K, Juran R, Stoever B, Wauer RR. Radiation exposure in 212 very low and extremely low birth weight infants. Pediatrics 124:6; 1556-1564; 2009.

National Council on Radiation Protection and Measurements. Ionizing radiation exposure of the population of the United States. Bethesda, MD: NCRP; NCRP Report No. 160; 2009.

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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