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07 November 2009

Answer to Question #5562 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Shielding

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

Can you please tell me the most effective position for lead shielding during a cardiac catheterization? Should the shield be closer to the patient or closer to the investigator? We use a moveable ceiling-suspended shield and have a table-mounted shield that swivels. There is a difference of opinion on where the shields should be placed to have the maximum protection for the staff at the side of the patient. My opinion is that closer to the staff provides more protection.

In order to provide the best protection for the largest area and number of staff, the best location for the movable shield would be close to the patient and here is why. X rays travel in straight lines in the same manner as visible light. They are basically the same physical entity—electromagnetic radiation—but they differ in wavelength and frequency.

Here is an analogy to help illustrate the best position for the shield. If you take an ordinary light bulb and place a square piece of opaque material (for this example, let's use a 12"-square piece of cardboard) between the lightbulb and a wall, you'll see a shadow of the cardboard square produced on the wall. As you move the piece of cardboard closer to the lightbulb, the shadow on the wall gets larger. Conversely, as you move the piece of cardboard farther away from the lightbulb, the shadow that is cast on the wall gets smaller.

Now, comparing this example to your situation in the cardiac catheterization laboratory, the patient is the "lightbulb" (i.e., the scattered radiation from the patient is the radiation source) and your portable shield is your "piece of cardboard." Thus, as you move the portable shield closer to the patient, you cast a larger "shadow" and provide shielding for a wider area and anyone who happens to be standing in that shadowed area. As in the above example, if you move the portable shield farther away from the patient, you limit the shielding benefit to smaller area.

Mack L. Richard, MS, CHP
Radiation Safety Officer

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