Room: Room 207
Purpose: To measure and model backscatter factor (BSF), angle factor (FÎ¸), and to introduce kerma correction factor (KCF), for fluoroscopy guided interventional (FGI) procedures.
Methods: A General Electric (GE) Innova 2100 fluoroscope was used with manual selection of kVp, mA, pulse width, x-ray field size, and copper (Cu) filtration. A Radcal 10x6-60 ion chamber was suspended from the image receptor, and centered in the x-ray beam. Air kerma rate was measured for every Cu filter, for 60-120 kVp, in 10 kVp increments, under five conditions: (1) with the table and pad beneath the chamber, (2) free in air, (3) with the chamber between 5-20 cm acrylic and the patient support, (4) 20 cm acrylic between the chamber and patient support with the x-ray beam angled 15-40Â°, and (5) 90Â° lateral x-ray orientation, with the chamber suspended from a face shield, for 5-20 cm acrylic. Table transmission factor (TTF), KCF, FÎ¸, and BSF were found by dividing air kerma rates measured in setup (1) by (2), (3) by (2), (4) by (2), and (5) by (2), respectively. The experiment was repeated for fewer kVp-filter combinations, and four x-ray field sizes (25, 100, 225, 469 cm2), using a Siemens Artis Zee fluoroscope.
Results: KCF ranged from 0.63 to 1.39, and BSF ranged from 1.07 to 1.42. KCF and BSF were successfully fitted to a function of five variables (incident angle, x-ray field size, kVp, Cu filter, and acrylic phantom thickness), with four fluoroscope-specific fitting parameters. The average RÂ² for the fitting equation was 0.96 and average percent difference between fitted and measured values was 1.79%.
Conclusion: A data set for fluoroscopic scatter factors were measured and fitted analytically to exposure parameters and beam orientation, which can be directly used for automated fluoroscopic skin dose estimation using radiation dose structured reports.
Fluoroscopy, Backscatter, Modeling