Instituto de Pesquisas Energéticas e Nucleares, IPEN-CNEN/SP, São Paulo 05508-000, Brazil.
Med Phys. 2009 Nov;36(11):5198-213. doi: 10.1118/1.3242304.
Radiopharmaceutical applications in nuclear medicine require a detailed dosimetry estimate of the radiation energy delivered to the human tissues. Over the past years, several publications addressed the problem of internal dose estimate in volumes of several sizes considering photon and electron sources. Most of them used Monte Carlo radiation transport codes. Despite the widespread use of these codes due to the variety of resources and potentials they offered to carry out dose calculations, several aspects like physical models, cross sections, and numerical approximations used in the simulations still remain an object of study. Accurate dose estimate depends on the correct selection of a set of simulation options that should be carefully chosen. This article presents an analysis of several simulation options provided by two of the most used codes worldwide: MCNP and GEANT4.
For this purpose, comparisons of absorbed fraction estimates obtained with different physical models, cross sections, and numerical approximations are presented for spheres of several sizes and composed as five different biological tissues.
Considerable discrepancies have been found in some cases not only between the different codes but also between different cross sections and algorithms in the same code. Maximum differences found between the two codes are 5.0% and 10%, respectively, for photons and electrons.
Even for simple problems as spheres and uniform radiation sources, the set of parameters chosen by any Monte Carlo code significantly affects the final results of a simulation, demonstrating the importance of the correct choice of parameters in the simulation.
核医学中的放射性药物应用需要对人体组织所接受的辐射能量进行详细的剂量估算。在过去的几年中，已经有几篇出版物针对不同体积的光子和电子源的内部剂量估算问题进行了探讨。其中大多数使用了蒙特卡罗辐射传输代码。尽管由于这些代码提供了各种资源和潜力，因此被广泛用于进行剂量计算，但模拟中使用的物理模型、截面和数值逼近等几个方面仍然是研究的对象。准确的剂量估算取决于对一组模拟选项的正确选择，这些选项应该仔细选择。本文分析了全球使用最广泛的两个代码（MCNP 和 GEANT4）提供的几种模拟选项。
为此，针对不同大小的球体以及由五种不同生物组织组成的球体，比较了不同物理模型、截面和数值逼近方法获得的吸收分数估算值。
在某些情况下，不仅不同代码之间，而且同一代码中的不同截面和算法之间也存在明显差异。两个代码之间发现的最大差异分别为光子和电子的 5.0%和 10%。
即使对于球体和均匀辐射源等简单问题，任何蒙特卡罗代码选择的参数集都会显著影响模拟的最终结果，这表明在模拟中正确选择参数的重要性。
