数字X射线摄影中入射表面剂量显示值与测量值相对偏差及影响因素的实验研究

Experimental study on relative deviation between display value and measured value of entrance surface dose(ESD)in digital radiography and influencing factors

目的比较DR设备在不同管电压、源像距和模体厚度条件下入射表面剂量(entrance surface dose,ESD)显示值与测量值之间的相对偏差,为利用ESD显示值实时评估患者受辐射剂量大小和曝光参数适宜性提供依据。方法在2种管电压、2种源像距条件下,用3个厚度分别为5、10和20 cm的聚乙烯模体(表面积30 cm×30 cm)进行曝光实验。每次曝光后记录DR设备上的ESD显示值以及辐射剂量检测仪测量值,采用Wilcoxon秩和检验对二者差异进行比较,并用公式计算ESD显示值相对偏差。结果在相同管电压和源像距曝光条件下,ESD显示值不受模体厚度影响,但测量值随模体厚度变化;模体厚度10和20 cm时,ESD显示值均小于测量值,差异有统计学意义(Z=-2.201、-2.203,P<0.05)。模体厚度越厚,显示值与测量值的相对偏差越大,但只有模体厚度20 cm、源像距100 cm时的相对偏差>±20%。结论 DR设备中ESD显示值可以用于评估受检者皮肤入射剂量,但要考虑受检者的体厚影响。

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.