Parach Ali Asghar, Rajabi Hossein, Askari Mohammad Ali
Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares University, P.O. Box 14115-331, Tehran, Iran.
Radiat Environ Biophys. 2011 Aug;50(3):441-50. doi: 10.1007/s00411-011-0370-0. Epub 2011 May 15.
GATE/GEANT is a Monte Carlo code dedicated to nuclear medicine that allows calculation of the dose to organs of voxel phantoms. On the other hand, MIRD is a well-developed system for estimation of the dose to human organs. In this study, results obtained from GATE/GEANT using Snyder phantom are compared to published MIRD data. For this, the mathematical Snyder phantom was discretized and converted to a digital phantom of 100 × 200 × 360 voxels. The activity was considered uniformly distributed within kidneys, liver, lungs, pancreas, spleen, and adrenals. The GATE/GEANT Monte Carlo code was used to calculate the dose to the organs of the phantom from mono-energetic photons of 10, 15, 20, 30, 50, 100, 200, 500, and 1000 keV. The dose was converted into specific absorbed fraction (SAF) and the results were compared to the corresponding published MIRD data. On average, there was a good correlation (r (2)>0.99) between the two series of data. However, the GATE/GEANT data were on average -0.16 ± 6.22% lower than the corresponding MIRD data for self-absorption. Self-absorption in the lungs was considerably higher in the MIRD compared to the GATE/GEANT data, for photon energies of 10-20 keV. As for cross-irradiation to other organs, the GATE/GEANT data were on average +1.5 ± 8.1% higher than the MIRD data, for photon energies of 50-1000 keV. For photon energies of 10-30 keV, the relative difference was +7.5 ± 67%. It turned out that the agreement between the GATE/GEANT and the MIRD data depended upon absolute SAF values and photon energy. For 10-30 keV photons, where the absolute SAF values were small, the uncertainty was high and the effect of cross-section prominent, and there was no agreement between the GATE/GEANT results and the MIRD data. However, for photons of 50-1,000 keV, the bias was negligible and the agreement was acceptable.
GATE/GEANT是一款专门用于核医学的蒙特卡罗代码，可用于计算体素模型中各器官的剂量。另一方面，MIRD是一个成熟的用于估算人体器官剂量的系统。在本研究中，将使用斯奈德模型从GATE/GEANT获得的结果与已发表的MIRD数据进行比较。为此，将数学斯奈德模型离散化并转换为一个100×2×360体素的数字模型。假设放射性活度在肾脏、肝脏、肺、胰腺、脾脏和肾上腺内均匀分布。使用GATE/GEANT蒙特卡罗代码计算来自能量为10、15、20、30、50、100、200、500和1000 keV的单能光子对模型各器官的剂量。将剂量转换为比吸收分数（SAF），并将结果与相应的已发表MIRD数据进行比较。平均而言，这两组数据之间存在良好的相关性（r²>0.99）。然而，就自吸收而言，GATE/GEANT数据平均比相应的MIRD数据低0.16±6.22%。对于10 - 20 keV的光子能量而言，与GATE/GEANT数据相比，MIRD中肺的自吸收要高得多。至于对其他器官的交叉照射，对于50 - 1000 keV的光子能量，GATE/GEANT数据平均比MIRD数据高1.5±8.1%。对于10 - 30 keV的光子能量，相对差异为+7.5±67%。结果表明，GATE/GEANT和MIRD数据之间的一致性取决于绝对SAF值和光子能量。对于10 - 30 keV的光子，由于绝对SAF值较小，不确定性较高且截面效应显著，GATE/GEANT结果与MIRD数据之间不一致。然而，对于50 - 1000 keV的光子，偏差可忽略不计且一致性是可接受的。
