Purpose: A model for the kerma correction factor (KCF), used for improving peak skin dose (PSD) calculation of fluoroscopy guided procedures, was presented by DeLorenzo and Goode (DG-KCF). We propose to validate the author’s KCF model, and extend its application to other fluoroscopy systems.
Methods: Under fluoroscopic service mode, table attenuated/scatter included air-kerma rates and free-in-air kerma rates were measured, using a 0.6cc thimble ionization chamber (IC) (10X6-0.6, Radcal®). The measurements were acquired with a Siemens Artis Zee under different tube voltages [60–120kVp], pre-patient copper filtration [0–0.9mm] and X-ray field sizes [9×9, 12×12, 14.5×14.5cm²], defined at an clinical patient skin location. The KCF is computed from the ratio of the two types of kerma rates. Other analytical nonlinear fits of the KCF are then generated and compared against DG-KCF.
Results: Preliminary KCF values range between 0.79 and 1.26 for all parameters. For different kVp, the KCF directly correlates with the maximum energy output of the X-ray tube for most circumstances, except for high filtration. The change in the KCF with tube voltage was the highest in the absence of copper filtration and 14.5×14.5cm² field size and lowest in the presence of 0.9mm copper filtration and 9×9cm² field size. The increase in copper filtration increased the KCF by 1.13, 1.25 and 1.36 for the respective field sizes of 9×9cm², 12×12cm², 14.5×14.5cm². The fitted nonlinear model demonstrates a strong correlation to the recorded KCF with a square residual norm of 0.051 and maximum percent difference of 7%.
Conclusion: Validation of the DG-KCF model was performed. Preliminary results suggest good agreement to measured data. Further validation of the model will be extended to other fluoroscopy systems and parameters. Use of the KCF model with the radiation dose structured report data will improve the accuracy of PSD calculation.