X射线摄影所致受检者器官剂量-入射体表剂量转换系数的研究

目的 比较简单程式化数学模型(MIRD)与体素模型在常见X射线摄影下得到的器官剂量-入射体表剂量的转换系数差异。方法 利用蒙特卡罗模拟技术,分别模拟计算体素模型的5种常见摄影下受检者的器官剂量与入射体表剂量,并计算两者的转换系数,与MIRD模型所得结果进行比较。结果 体素模型得到射野内器官的转换系数分别是,胸部后前位0.149~0.650,胸部左侧位0.067~0.382,胸部右侧位0.023~0.374,腹部前后位0.035~0.431,腰椎前后位0.083~0.432。在胸部后前位下,两种模型模拟肺的剂量转换系数结果相差最大约54.3%;胸部左侧位照射的肝脏剂量转换系数差异最大为54.5%;胸部右侧位照射胃剂量转换系数差异最大为63.8%;而腹部前后位,两种模型模拟脾脏的剂量转换系数差异最大为65.0%;腰椎前后位发现胃的剂量转换系数相差最大约43.7%。结论 利用两种模型模拟得到的器官剂量转换系数偏差可达50%以上,由于MIRD模型的解剖结构过于简化,计算误差较大。利用体素模型得到的转换系数数据更加科学合理。

Estimation of patient radiation doses form conventional X-ray radiography

Objective To compare patient organ doses and entrance surface dose conversion coefficients in conventional radiography using medical internal radiation dose(MIRD) phantom and voxel human phantom.Methods The voxel phantom was adapted to the Monte Carlo transport code to simulate the organ doses and entrance surface dose in five common projections, and thus the dose conversion coefficients between the entrance skin dose and organ dose were calculated. The results were compared with the reported mean values which were simulated using MIRD phantom. Results The dose conversion coefficients values of organs covered or partially covered by the X-ray field ranged from 0.149-0.650 in chest postero-anterior projection, 0.067-0.382 in chest left lateral projection, 0.023-0.374 in chest right lateral projection, 0.035-0.431 in abdominal antero-posterior projection, 0.083-0.432 in lumbar spine antero-posterior projection. In chest postero-anterior projection, significant differences were most obviously observed in lung, the dose conversion coefficients difference was 54.3%. In chest left lateral projection, the dose conversion coefficients difference of liver was greatest, which was 54.5%. In chest right lateral projection, the dose conversion coefficients differences of stomach wall was most obviously 63.8%. In abdominal antero-posterior projection, dose conversion coefficients discrepancy was most obviously observed in spleen, with the value of 65.0%;while in lumbar spine antero-posterior projection, the dose conversion coefficients differences of stomach wall was most obviously 43.7%. Conclusions Compared with the stylized MIRD phantoms, the anatomical realism in voxel phantom is evident. Therefore, the dose conversion coefficients calculated by voxel phantoms are more accurate and scientific in conventional radiology.