Effect of fluoroscopic X‐ray beam spectrum on air‐kerma measurement accuracy: implications for establishing correction coefficients on interventional fluoroscopes with KAP meters

Abstract

The first goal of this study was to investigate the accuracy of the displayed reference plane air kerma (normalKnormala,normalr) or air kerma‐area product (normalPnormalk,normala) over a broad spectrum of X‐ray beam qualities on clinically used interventional fluoroscopes incorporating air kerma‐area product meters (KAP meters) to measure X‐ray output. The second goal was to investigate the accuracy of a correction coefficient (CC) determined at a single beam quality and applied to the measured normalKnormala,normalr over a broad spectrum of beam qualities. Eleven state‐of‐the‐art interventional fluoroscopes were evaluated, consisting of eight Siemens Artis zee and Artis Q systems and three Philips Allura FD systems. A separate calibrated 60 cc ionization chamber (external chamber) was used to determine the accuracy of the KAP meter over a broad range of clinically used beam qualities. For typical adult beam qualities, applying a single CC determined at 100 kVp with copper (Cu) in the beam resulted in a deviation of <5% due to beam quality variation. This result indicates that applying a CC determined using The American Association of Physicists in Medicine Task Group 190 protocol or a similar protocol provides very good accuracy as compared to the allowed ±35% deviation of the KAP meter in this limited beam quality range. For interventional fluoroscopes dedicated to or routinely used to perform pediatric interventions, using a CC established with a low kVp (∼55−60 kVp) and large amount of Cu filtration (∼0.6−0.9 mm) may result in greater accuracy as compared to using the 100 kVp values. KAP meter responses indicate that fluoroscope vendors are likely normalizing or otherwise influencing the KAP meter output data. Although this may provide improved accuracy in some instances, there is the potential for large discrete errors to occur, and these errors may be difficult to identify.PACS number(s): 87.59.C‐, 87.59.cf, 87.53.Bn

The American College of Radiology Fluoroscopy Dose Index Registry Pilot: Technical Considerations and Dosimetric Performance of the Interventional Fluoroscopes

“…Radiation dose indices were also stable over the course of the pilot for the 28 imaging planes with evaluations available from the 3 time points. These results are similar to those reported previously, including those reported in the RAD-IR study (3,7). The RAD-IR study (3) reported the ratio of the displayed index to the measured index, which is the reciprocal of the correction factors reported in the present study.…”

“…First, using a correction factor established at a single X-ray beam spectrum and applying that correction factor to radiation dose indices measured across a wide range of X-ray beam spectra, as is the case clinically, will result in additional uncertainty. This additional uncertainty was estimated in a previous study (7) to be 5% for beam spectra commonly encountered during adult fluoroscopic imaging, but this uncertainty may vary by as much as 12% for beam spectra commonly encountered during pediatric imaging when using a correction factor derived from the American Association of Physicists in Medicine Task Group 190-recommended beam spectra (90-100 kV without a prescribed amount of additional filtration). Second, there are substantial variations in X-ray beam quality and intensity across the X-ray field because of the anode heel effect; with dependencies on X-ray beam quality and field size, variations at or near the skin entrance can exceed ±20% from central axis measurements (15,16).…”

Percent depth doses and X-ray beam characterizations of a fluoroscopic system incorporating copper filtration

“…Among other considerations, caution should be exercised to ensure adequate accuracy in the K a,r . A calibration factor should be applied to the raw K a,r to account for possible deviations and, if necessary, beam quality dependence . BSFs and PDDs reported in this study can be interpolated between energies.…”

Vendor‐independent skin dose mapping application for interventional radiology and cardiology

“…Additionally, a large range of possible values and allowable tolerance of ± 35% above 100 mGy and 2.5 Gy‐cm 2 for the displayed and , respectively, could lead to very inaccurate skin dose calculations. Wunderle et al 34 . showed that for typical adult beam qualities, applying a single determined at tube voltage of 100 kV with cooper filtration in the beam results in a deviation of less than 5% due to beam quality variation.…”