Iriuchijima Akiko, Fukushima Yasuhiro, Ogura Akio
Department of Radiology, Gunma University Hospital.
Graduate School of Radiological Technology, Gunma Prefectural College of Health Sciences.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2018;74(2):166-171. doi: 10.6009/jjrt.2018_JSRT_74.2.166.
Direct measurement of each patient organ dose from computed tomography (CT) is not possible. Most methods to estimate patient organ dose is using Monte Carlo simulation with dedicated software. However, the method and the relative differences between organ dose simulation and measurement is unclear. The purpose of this study was to compare organ doses evaluated by Monte Carlo simulation with doses evaluated by in-phantom dosimetry. The simulation software Radimetrics (Bayer) was used for the calculation of organ dose. Measurement was performed with radio-photoluminescence glass dosimeter (RPLD) set at various organ positions within RANDO phantom. To evaluate difference of CT scanner, two different CT scanners were used in this study. Angular dependence of RPLD and measurement of effective energy were performed for each scanner. The comparison of simulation and measurement was evaluated by relative differences. In the results, angular dependence of RPLD at two scanners was 31.6±0.45 mGy for SOMATOM Definition Flash and 29.2±0.18 mGy for LightSpeed VCT. The organ dose was 42.2 mGy (range, 29.9-52.7 mGy) by measurements and 37.7 mGy (range, 27.9-48.1 mGy) by simulations. The relative differences of organ dose between measurement and simulation were 13%, excluding of breast's 42%. We found that organ dose by simulation was lower than by measurement. In conclusion, the results of relative differences will be useful for evaluating organ doses for individual patients by simulation software Radimetrics.
直接测量计算机断层扫描（CT）中每位患者的器官剂量是不可能的。大多数估计患者器官剂量的方法是使用专用软件进行蒙特卡罗模拟。然而，该方法以及器官剂量模拟与测量之间的相对差异尚不清楚。本研究的目的是比较通过蒙特卡罗模拟评估的器官剂量与通过体模内剂量测定法评估的剂量。使用模拟软件Radimetrics（拜耳公司）计算器官剂量。使用放射性光致发光玻璃剂量计（RPLD）在RANDO体模内的不同器官位置进行测量。为了评估CT扫描仪的差异，本研究使用了两台不同的CT扫描仪。对每台扫描仪进行了RPLD的角度依赖性和有效能量的测量。通过相对差异评估模拟与测量的比较。结果显示，两台扫描仪处RPLD的角度依赖性，对于SOMATOM Definition Flash扫描仪为31.6±0.45 mGy，对于LightSpeed VCT扫描仪为29.2±0.18 mGy。测量得到的器官剂量为42.2 mGy（范围为29.9 - 52.7 mGy），模拟得到的器官剂量为37.7 mGy（范围为27.9 - 48.1 mGy）。测量与模拟之间器官剂量的相对差异为13%，不包括乳房的42%差异。我们发现模拟得到的器官剂量低于测量得到的剂量。总之，相对差异的结果将有助于通过模拟软件Radimetrics评估个体患者的器官剂量。
