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Effect of X-Ray Beam Quality On Fluoroscope Reported Reference Plane Air Kerma When Measured by DAP Meters: TG190 Protocol Implications for Interventional Fluoroscopes


K Wunderle

K Wunderle1*, J Rakowski2 , M Joiner3 , F Dong4 , (1) Cleveland Clinic Foundation, Cleveland, OH & Wayne State University School of Medicine, Detroit, MI (2) Wayne State University School of Medicine, Detroit, MI (3) Wayne State University School of Medicine, Detroit, MI (4) Cleveland Clinic Foundation, Cleveland, OH

Presentations

TH-AB-201-9 (Thursday, July 16, 2015) 7:30 AM - 9:30 AM Room: 201


Purpose:To investigate the accuracy of the correction factor (CF) determined using the AAPM-TG190 protocol and applied to measurements made across a full spectrum of x-ray beam qualities on interventional c-arm fluoroscopes.

Methods:The x-ray beam area was measured to allow for the calculation of the air-kerma-area-product (Pk,a). Air kerma was measured using a calibrated ionization chamber centered in the x-ray beam free-in-air. Manual technique factors were set with vendor service support. Data were collected on 10 fluoroscopic systems at 55 kVp to 125 kVp in 10-kVp increments and also at 100 kVp. At each available combination of kVp and spectral filter (copper) thickness, three measurements were taken. A CF for each beam quality was determined by dividing the measured Pk,a by the Pk,a reported by the fluoroscope. Two normalized correction factors (NCFs) were defined to determine the potential error in using a single CF across a spectrum of beam qualities. The first normalized the CF at a given beam quality to the CF at 100 kVp without filtration (NCF[100,0]) and another normalized to the CF at 100 kVp with 0.1 mm copper (NCF[100,0.1]).

Results:The accuracy of the CF varied depending on whether it was determined using spectral filtration, which was apparent in comparisons of NCF(100,0) with NCF(100,0.1). In general, the CF was dependent on beam quality, an effect that was most pronounced at low kVps with spectral filtration.

Conclusion:For interventional fluoroscopes employing spectral filtration, better accuracy is achieved when copper is used to establish the CF. Additionally, a CF determined at 100 ± 10 kVp may not be optimal for pediatric applications, in which the beam quality typically consists of low kVps and large amounts of copper filtration. The accuracy of the CF can be improved for pediatric applications by using a more clinically relevant beam quality.


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