Matsumoto Masao
School of allied Health Science, Faculty of Medicine, Osaka University, Japan.
Igaku Butsuri. 2002;22(2):110-7.
Several recent studies have a questionnaire survey of many hospitals regarding the radiation exposure conditions of X-ray examinations. From the survey result the entrance surface doses (first quartile, median, third quartile and mean values) have calculated by using the Numerical Dose Determination (NDD) method. The calculated result for all types of examinations showed that the median values were lower than the mean values, whereas the median values of the results were lower than those in the NRPB 21 in England. The mean values of the results were lower than those in the NRPB 21 in England. The mean values were lower than IAEA guidance levels. The results have indicated that the medical exposure dose (entrance surface dose) is lower with Computed Radiography (CR) than with the Screen/Film (S/F) system except the case of chest radiography. In the case of chest radiography (adult patients) by CR exposure set-up using a lower voltage and high mAs than the S?F method, the entrance surface doses were 150 % of the median value for the overall examination and 160 % of the median value for orthochromatic S/F systems. A difference in patient dose among hospitals using CR system was also found. Mean entrance surface dose in CR system was 0.12 mGy in a quartile, 0.19 mGy in the middle and 0.27 mGy in the third quartile. Among the hospitals that showed higher doses of third quartile than above mentioned, dose differences of a quartile were distributed 2 to 10 times higher than mean exposure doses. Mori et al. propose guidance levels are lower than IAEA guidance levels of entrance surface doses for examinations carried out in Japanese institutions as the 3rd quartile of the dose distributions. Therefore the quality control of tube voltage, tube current and mAs and a regular measurement of exposure for X-ray units are required.
最近的几项研究对多家医院进行了关于X射线检查辐射暴露情况的问卷调查。根据调查结果，使用数值剂量测定（NDD）方法计算了入射表面剂量（第一四分位数、中位数、第三四分位数和平均值）。所有类型检查的计算结果表明，中位数低于平均值，而结果的中位数低于英国NRPB 21中的数值。结果的平均值低于英国NRPB 21中的数值。平均值低于国际原子能机构的指导水平。结果表明，除胸部X线摄影外，计算机X线摄影（CR）的医疗照射剂量（入射表面剂量）低于屏/片（S/F）系统。在成人胸部X线摄影中，采用CR曝光设置，电压低于S/F方法且毫安秒（mAs）较高，其入射表面剂量为总体检查中位数的150%，正色S/F系统中位数的160%。还发现使用CR系统的医院之间患者剂量存在差异。CR系统的平均入射表面剂量在第一四分位数为0.12毫戈瑞，中位数为0.19毫戈瑞，第三四分位数为0.27毫戈瑞。在第三四分位数剂量高于上述水平的医院中，四分位数剂量差异比平均暴露剂量高2至10倍。森等人提出的指导水平低于国际原子能机构针对日本机构进行的检查的入射表面剂量指导水平，作为剂量分布的第三四分位数。因此，需要对管电压、管电流和mAs进行质量控制，并定期测量X射线设备的曝光量。
