AAPM: Shun shielding for CT dose reduction

The American Association of Physicists in Medicine (AAPM) has issued a statement recommending that healthcare facilities avoid the use of bismuth shielding for CT dose reduction.

According to AAPM, “Bismuth shields are easy to use and have been shown to reduce dose to anterior organs in CT scanning. However, there are several disadvantages associated with the use of bismuth shields, especially when used with automatic exposure control or tube current modulation. Other techniques exist that can provide the same level of anterior dose reduction at equivalent or superior image quality that do not have these disadvantages. The AAPM recommends that these alternatives to bismuth shielding be carefully considered, and implemented when possible.”

AAPM said the primary disadvantages of the shields are:

1. Applying bismuth shielding together with automatic exposure controls (AEC) systems, such as tube current modulation (TCM), leads to unpredictable and potentially undesirable levels of dose and image quality.
2. The shields can degrade image quality and accuracy.
3. The shields waste some of the patient’s radiation exposure.

The association recommended alternate methods to achieve dose reduction. Operators can reduce the x-ray tube current by the same percentage as the percentage dose reduction to the anterior surface from bismuth shielding. This method does not require additional materials or workflow steps. “Other methods for reducing dose to specific peripheral organs include adjusting AEC parameters to more aggressively decrease the tube current in regions of lower attenuation (e.g. in the thorax) and use of organ-based tube current modulation techniques,” AAPM wrote. However, changes to AEC parameters can be complex and require consultation with a medical physicist or applications specialist.