A simple measurement method for verifying the accuracy of the displayed dose on an over-couch-type X-ray fluoroscopic system

The purpose of this study was to establish a simple measurement method to verify the accuracy of incident air kerma (K_{a, r}) and air kerma area product (P_KA) displayed on an over-couch-type X-ray fluoroscopy system. A dosimeter was located at the patient entrance reference point, and the irradiation field size was set to 10×10 cm. A lead plate was placed on the couchtop to protect the image receptor, and the duration of fluoroscopy was set to 1 min. The K_{a, r} was measured with the proposed method and the Japanese Industrial Standards (JIS) method on three X-ray fluoroscopy units of different manufactures. The effect of backscattered X-rays from the lead plate was calculated using Monte Carlo methods. The errors of the displayed K_{a, r} and P_KA to the measured K_{a, r} and P_KA with our proposed method were calculated. There was no significant difference in the measured K_{a, r} between the proposed method and the JIS method in all units. The effect of backscattered X-ray was ≤0.5%. The errors of displayed K_{a, r} and P_KA to those measured were in the range of 3.4 to 15.7% and −4.1 to 20.3%, respectively, which met the tolerance for accuracy of ±35% in accordance with the JIS method. We found that our proposed method was simple and that the accuracy of measured values was comparable to that of the JIS method. (author)