Bousis C, Emfietzoglou D, Hadjidoukas P, Nikjoo H
Department of Medical Physics, University of Ioannina, Ioannina 451 10, Greece.
Phys Med Biol. 2009 Aug 21;54(16):5023-38. doi: 10.1088/0031-9155/54/16/012. Epub 2009 Aug 4.
A systematic study of cellular S-factors and absorbed fractions for monoenergetic electrons of initial energy from 1 keV to 1 MeV is presented. The calculations are based on our in-house Monte Carlo codes which have been developed to simulate electron transport up to a few MeV using both event-by-event and condensed-history techniques. An extensive comparison with the MIRD tabulations is presented for spherical volumes of 1-10 microm radius and various source-to-target combinations relevant to the intracellular localization of the emitted electrons. When the primary electron range is comparable to the sphere radius, we find significantly higher values from the MIRD, while with increasing electron energy the escape of delta-rays leads gradually to the opposite effect. The largest differences with the MIRD are found for geometries where the target region is at some distance from the source region (e.g. surface-to-nucleus or cytoplasm-to-nucleus). The sensitivity of the results to different transport approximations is examined. The grouping of inelastic collisions is found adequate as long as delta-rays are explicitly simulated, while the inclusion of straggling for soft collisions has a negligible effect.
本文对初始能量从1 keV到1 MeV的单能电子的细胞S因子和吸收分数进行了系统研究。计算基于我们内部开发的蒙特卡罗代码，这些代码已被开发用于使用逐事件和凝聚历史技术模拟高达几MeV的电子输运。对于半径为1 - 10微米的球形体积以及与发射电子的细胞内定位相关的各种源到靶组合，本文与MIRD表格进行了广泛比较。当初级电子射程与球体半径相当时，我们发现MIRD的值明显更高，而随着电子能量的增加，δ射线的逸出逐渐导致相反的效果。在靶区域与源区域有一定距离的几何结构中（例如表面到细胞核或细胞质到细胞核），发现与MIRD的差异最大。研究了结果对不同输运近似的敏感性。只要明确模拟了δ射线，非弹性碰撞的分组就被认为是足够的，而包含软碰撞的离散对结果的影响可以忽略不计。
