直接摄影检查患者的照射剂量分析

Radiation exposure to patients during examinations of direct radiography system

目的通过对不同部位直接摄影（DR）检查的医学数字成像和传输（DICOM）文件信息中的患者剂量信息的统计，调查不同投照部位DR摄片的照射剂量分布范围，分析影响DR检查照射剂量的因素。方法随机选取浙江省某三甲医院2009年1月至4月5160次DR摄片，包括胸部、胸椎及腰椎正、侧位、腹部前后位及骨盆正位。应用软件自动提取每例患者检查中DICOM信息文件中的剂量面积乘积（DAP），并结合照射野的范围，计算各部位DR检查的入射表面剂量（ESD）。结果腹部前后位、腰椎侧位、胸椎正侧位的变异系数在60％以下；胸部正侧位、腰椎正位、骨盆正位的变异系数为60％～80％。各个部位的DAP最大值与最小值比值，除腹部前后位较小为3倍，其余部位差异较大。其中，腰椎正位最大差别为46倍、腰椎侧位30倍，胸椎侧位、胸部正位、侧位、骨盆正位、胸椎正位分别为23、23、18、16、11倍。通过计算得到ESD值选择75％分位点与现行普通摄片诊断参考水平（DRL）比较后发现，胸部正、侧位分别下降75％和73％；腰椎正侧位下降66％和77％；胸椎正侧位下降85％和84％；骨盆正位下降88％；腹部前后位下降88％。结论DR检查中各个部位的DAP与ESD值存在较大变动，ESD值与现行的常规摄片的DRL相比有较大下降；有必要回顾分析DR摄片的患者照射剂量，对患者照射剂量与图像质量进行质量管理。

Objective To evaluate and analyze the statistical distribution of patient dose during different examinations by using the data stored in a DICOM image archive of a direct digital radiography system. Methods An automatic procedure to extract dose data and exposure parameters from the image archives was implemented. 5160 images were collected from a Zhejiang province hospital including chest PA and LAT, thoracic spine AP and LAT,lumbar AP and LAT, abdomen and pelvis. Exposure parameters and the dose area product （DAP） stored in the image DICOM head were examined for each image. The entrance surface dose （ESD） was estimated considering the DAP and the geometric parameters during each examination. Results Thoracic spine AP and LAT, lumbar LAT and abdomen AP DAP had a variable coefficient below 60% , while the others ranged from 60 % to 80 % . Compared with DAP at different locations, the ratios between the maximum and the minimum value of DAP were high except for abdomen AP that the maximum value was 3 times than the minimum value. The ratios between the maximum and minmun value for PAP lumbar AP, lumbar LAT, thoracic spine LAT, chest PA and LAT, pelvis PA and thoracic spine PA were 46, 30, 23, 23, 18, 16 and 11, respectively. The ESD values obtained were substantially lower than DRL. DRL were over three times more than the 3rd quartile value of ESD distribution for the chest PA and LAT,lumbar AP and LAT. DRL were over five times more than the 3rd quartile value of ESD distribution for the abdomen and pelvis AP, thoracic spine AP and LAT projections. Conclusions There are great variation between DAP and ESD distributions. The radiographic device allows substantial dose savings compared with estimations made for nondigital or for phosphor-plate based systems. Frequent patient dose audits should occur when digital techniques are introduced. The quality management in image quality and patient dose in digital radiology should be necessary.