Evaluation of skin dose calculation factors in interventional fluoroscopy

PURPOSE: The 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. METHODS: Table 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. RESULTS: For 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%. CONCLUSIONS: This 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.