Experimental study on relative deviation between display value and measured value of entrance surface dose (ESD) in digital radiography and influencing factors / 中华放射医学与防护杂志

ABSTRACT

Objective:To compare the relative deviation between display value and measured value of entrance surface dose (ESD) at different tube voltages, source-to-image distances and phantom thicknesses, so as to provide the basis for the feasibility of using real-time ESD display value to evaluate the radiation dose and the suitability of exposure parameters.Methods:At two different tube voltages and source-to-image distances, the exposure experiments were carried out using three polyethylene models with surface area of 30 cm×30 cm and thickness of 5 cm, 10 cm and 20 cm, respectively. After each exposure, the ESD display values on DR equipment and the measured values on radiation dose detector were recorded. The Wilcoxon rank sum test was used to compare the difference between them, with the relative deviation of ESD display value calculated using formula.Results:At the same tube voltage and source-to-image distance, the ESD display values were not affected by the thickness of phantom, but the measured value changed with the thickness of the phantom. When the thickness of the phantom was 10 cm and 20 cm respectively, the ESD display value was smaller than the measured value and the difference was statistically significant ( Z=-2.201, -2.203, P<0.05). The thicker mold would lead to the larger relative deviation between display value and measured value. Only when the thickness of mold was 20 cm and source-to-image distance 100 cm, the relative deviation was greater than ±20%. Conclusions:The ESD display value on DR equipment can be used to evaluate the skin incident dose to the examinee, with necessary account taken of the influence of their body thickness.