Emfietzoglou D, Kostarelos K, Hadjidoukas P, Bousis C, Fotopoulos A, Pathak A, Nikjoo H
Medical Physics Laboratory, University of Ioannina Medical School, Ioannina, Greece.
Int J Radiat Biol. 2008 Dec;84(12):1034-44. doi: 10.1080/09553000802460180.
To study the energy deposition by low-energy electrons in submicron tissue-equivalent targets by comparing two widely used methodologies, namely, the continuous-slowing-down-approximation (CSDA) convolution integral and the Monte Carlo (MC) simulation.
An MC track-structure code that simulates collision-by-collision the complete slowing down process is used to calculate the energy deposition in spherical volumes of unit density water medium. Comparisons are made with calculations based on the CSDA convolution integral using both empirical and MC-based range-energy analytic formulae.
We present self-irradiation absorbed fractions and S-factors for monoenergetic electrons of initial energies from 0.1-10 keV distributed uniformly in spheres of 5, 10, 50, 100, 500, and 1000 nm radius. The MC and CSDA results were found, in some cases, to differ by a factor of 2 or more; differences generally increase with decreasing sphere size. Contrary to high energies, the uncertainties associated with the straight-ahead approximation implicit in the CSDA calculations are of the same order as those related to straggling and delta-ray effects.
The use of the CSDA methodology may be unsuitable for the sub-micron scale where a more realistic description of electron transport becomes important.
通过比较两种广泛使用的方法，即连续慢化近似（CSDA）卷积积分法和蒙特卡罗（MC）模拟法，研究低能电子在亚微米组织等效靶中的能量沉积情况。
使用一个能逐次碰撞模拟完整慢化过程的MC径迹结构代码，来计算单位密度水介质球形体积内的能量沉积。将其与基于CSDA卷积积分、使用经验性和基于MC的射程-能量解析公式的计算结果进行比较。
我们给出了初始能量为0.1 - 10 keV的单能电子在半径为5、10、50、100、500和1000 nm的球体中均匀分布时的自辐照吸收分数和S因子。在某些情况下，发现MC和CSDA结果相差2倍或更多；差异通常随着球体尺寸的减小而增大。与高能情况相反，CSDA计算中隐含的直线前进近似相关的不确定性与那些与散射和δ射线效应相关的不确定性处于同一量级。
在亚微米尺度下，电子输运的更真实描述变得很重要，此时使用CSDA方法可能不合适。
