Real-time estimation of surface dose based on incident air kerma in diagnostic radiology.

Abstract

To estimate the surface dose in diagnostic radiology in real time based on the relationship between the incident air kerma and the surface dose. The air kerma for 20 X-ray beams with tube voltages of 50-140kV and a half-value layer (HVL) of 2.27-9.65mm Al was measured using an ionization chamber. The beam quality was classified based on the quality indexes (QIs) of 0.4, 0.5, and 0.6, which are defined as the ratio of the effective energy to the maximum energy corresponding to the tube potential. The surface dose for 20 X-ray beams was evaluated based on the measured air kerma, backscatter factor, and ratio of the mass-energy absorption coefficients of water to air, which were calculated using the Monte Carlo method. Finally, the relationship between the air kerma and the surface dose was investigated for X-ray beams with the specific QI values. The surface dose at a water phantom was represented by a linear approximation of R2>0.98, with the air kerma, regardless of the X-ray beam quality. The surface dose estimated based on a linear approximation with the air kerma indicated an agreement within 8% with that evaluated by the chamber measurements at HVL>3.4mm Al. It is possible to estimate the surface dose in real time using the linear relationship between the incident air kerma and the surface dose regardless of the X-ray beam quality by accepting ±10% uncertainty in the surface dose estimation.