AbstractID: 8079 Title: Problems in Determining Lead Equivalence of Aprons
Specifying the lead equivalence of an apron involves more than just providing a thickness and a
kVp. This is particularly true of aprons made from lead-free and lead-composite materials. Xray generator type and HVL affect the results as well as measurement methods. Manufacturers
of aprons often image both the apron material and a lead step wedge on a screen-film cassette
and determine lead equivalency by comparing film densities. We find that this gives misleading
results when the attenuating material in the apron is other than just lead.
Measurements using an ion chamber to determine the x-ray transmission can be made in narrow
beam or variations of broad beam geometry. Both Compton and coherent scatter affect results.
Also the emissions of characteristic radiation complicate the measurement. While low energy
characteristic radiation (L-characteristic) should probably be excluded from transmission
measurements, higher energy characteristic (K-characteristic) should not. Backscatter has been
included in some papers, but should probably also be omitted.
We explore the effects of these different measurement techniques on transmission and lead
equivalency results. The greatest variations are generally found with aprons using lead-free and
lead-composite materials. We also relate the measurement techniques to realistic considerations
of patient radiation exposure using these aprons.
One result of these investigations is the discovery of an unusual property of lead free and lead
composite materials: a lack of strict additivity of lead equivalence. Thus, two materials of 0.25
mm lead equivalence do not yield a material with 0.5 mm of lead equivalence.