Are bismuth shields, for eyes, breasts, and/or thyroid, a good idea?
The flexible, disposable, commercially available shields are placed over the breasts, thyroid, or eyes to reduce the organ dose to the specific region. Whether or not they are effective vs. simply reducing the mAs per rotation is still being debated. Of course there is a degradation in image quality, as will always be the case when radiation dose is reduced. Some researchers claim that the image quality degradation is acceptable and a worthwhile tradeoff when dose reduction is considered. Other researchers point out that although the shields attenuate the primary beam when the tube is in the anterior position, when the tube is in the posterior position, the shields attenuate radiation that has already contributed to patient dose and contains useful image information. Therefore it might be better and less expensive to reduce dose by reducing the technique or using tube current modulation. The AAPM is currently working on a position statement on the use of these shields, and NPC will post it as soon as it becomes available.
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