Purpose To present procedure-specific radiation dose metric distributions and define quantitative CT utilization factors for CT-guided interventional procedures. Materials and Methods This single-center, retrospective study collected dictation reports and radiation dose data from 9143 consecutive CT-guided interventional procedures in adult patients from 2012 to 2017. Procedures were sorted into four major interventional categories: ablation, aspiration, biopsy, and drainage, each of which was further divided into subcategories. After exclusion, a total of 8213 procedures (4391 in men and 3822 in women) were divided into 21 subcategories. The mean patient age at examination for men was 62 years ± 15 (standard deviation; age range, 19-114 years), and for women it was 61 years ± 15 (age range, 19-113 years). Distributions of dose metrics and CT usage-related parameters were analyzed by category with descriptive statistic outcomes. Quantitative CT utilization factors (which measure average CT usage) for each interventional subcategory were derived by using total scan length, acquisition count, and number of images. Results Interventional CT scans have distinctly different dose metric characteristics from diagnostic CT scans. Wide variations of dose metrics were observed among subcategories, even within the same major category. For the most frequently performed CT-guided interventional procedures within each major category, liver ablation, chest aspiration, liver biopsy, and single abdominal drainage, the median dose-length product was 2351, 657, 1175, and 1125 mGy ∙ cm, respectively. Procedure-specific CT utilization factors ranged between 0.6 and 3.6. Conclusion This study provides procedure-specific CT dose metric distributions and quantitative CT utilization factors on the basis of a large number of procedures and categorization of CT-guided interventional procedures. © RSNA, 2018.
PurposeThe purpose of this study was to measure fluoroscopic dose calculation factors for modern fluoroscopy‐guided interventional (FGI) systems, and to fit to analytical functions for peak skin dose (PSD) calculation.MethodsTable transmission factor (TTF), backscatter factor (BSF), and a newly termed kerma correction factor (KCF) were measured for two interventional fluoroscopy systems. For each setup, air kerma rates were measured using a small ionization chamber in fluoroscopic service mode while selecting kVp, copper (Cu) filter thickness, incident angle, and x‐ray field size at the assumed patient skin locations. Angle dependency on KCF was measured on the GE system at isocenter for angles of 0, 15, 30, and 40 degrees, using a range of kVp, Cu filters, and one field size. An analytical equation was created to fit the data to facilitate PSD calculation.ResultsFor the GE system, oblique incidence measurements show KCF decreased by about 2%, 8%, and 13% for incident angles of 15, 30, and 40°, respectively, relative to KCF at 0 degree. The GE and Siemens systems' KCFs ranged from 0.89 to 1.45, and 0.64 to 1.44, respectively. The KCFs increased with a power of field size, and generally increased with kVp and Cu filter. The average percentage difference between TTF × BSF × f and KCF was 16% at normal incidence. The KCF data were successfully fitted to function of angle, field size, kVp, and Cu filter thickness using seven parameters, with an average R‐squared value of 0.98 and maximum percentage difference of 6.0%.ConclusionsThis study evaluated scatter factors for two fluoroscopy systems, and dependencies on angle, kVp, Cu filter, and field size, with emphasis on under table beam orientations. Analytical fitting of the data with exposure parameters may facilitate PSD calculations, and more accurately determine the potential for radiation‐induced skin injury.
Modern fluoroscopes pose a challenge for the clinical physicist for annual testing and continued upkeep. These fluoroscopes are critical to providing care to patients for complex interventions, and continue to evolve in automated image quality adjustments. Few tools in software or hardware currently exist to assist the physicist or technologist in gauging fluoroscope constancy or readiness for procedures. Many modalities such as mammography, computed tomography or even magnetic resonance imaging are much more evolved with respect to testing or quality control. In this work we sought to provide simple reproducible tools and methods for spot evaluating or continued quality testing of interventional fluoroscopes.
This study evaluated the broad-beam transmission for three representative fluoroscopy systems and their dependency on angle, kVp, added Cu filter, and field size. The comprehensive data provided for patient support transmission will facilitate accurate calculation of peak skin dose (PSD) and may potentially be integrated into real-time and retrospective dose monitoring with access to Radiation Dose Structured Reports (RDSR) and radiation event data.
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