Ye Sung-Joon, Ove Roger, Naqvi Shahid A
Department of Radiation Oncology, University of Alabama School of Medicine, Birmingham, AL 35209, USA.
Health Phys. 2006 Oct;91(4):361-6. doi: 10.1097/01.HP.0000223448.23229.6e.
Recent releases of the MCNP5 and PENELOPE Monte Carlo codes include the transport algorithm and momentum profiles that are necessary for accounting for Doppler broadening in Compton scattering processes. Such improvements might be particularly important in low-energy photon dose calculations. MCPLIB04 and PENDBASE (PENELOPE photon dataset) are based on the EPDL97 library with Compton momentum profiles, while MCPLIB03 and MCPLIB02 are based on the 1970's old library, with MCPLIB03 including the Compton momentum profiles. To isolate the dosimetric effects of Doppler broadening by the transport algorithm and Compton momentum profiles, we varied the choice of the above photon databases, in the same simulation geometry, using either version of MCNP5 or MCNP4 (no Doppler algorithm). We computed dose rate constants and dose distributions for r = 0.2-10 cm from a point source in a 50-cm-diameter sphere of water. Nine discrete energies for primary photon sources were chosen in the range of 10-150 keV. The results from both versions of MCNP with MCPLIB04 agreed with those of PENELOPE within statistical uncertainties (+/-1%) over the entire ranges of energies and radial distances investigated. MCNP5 with either MCPLIB03 or MCPLIB02 yielded almost identical data within statistical uncertainties (+/-1%) over the entire ranges of energies and radial distances investigated. This implies that in spite of the spectral broadening of scattered photons due to the orbital electron motion, the dosimetric effect of Doppler broadening for Compton interactions in water appears to be insignificant in the energy range investigated. The spectral dose analysis with and without the Doppler broadening supported this conclusion.
MCNP5和PENELOPE蒙特卡罗代码的最新版本包含了在康普顿散射过程中考虑多普勒展宽所需的输运算法和动量分布。这种改进在低能光子剂量计算中可能尤为重要。MCPLIB04和PENDBASE（PENELOPE光子数据集）基于带有康普顿动量分布的EPDL97库，而MCPLIB03和MCPLIB02基于20世纪70年代的旧库，其中MCPLIB03包含康普顿动量分布。为了通过输运算法和康普顿动量分布来分离多普勒展宽的剂量学效应，我们在相同的模拟几何结构中，使用MCNP5或MCNP4的任一版本（无多普勒算法），改变上述光子数据库的选择。我们计算了在直径为50 cm的水球中，距点源r = 0.2 - 10 cm处的剂量率常数和剂量分布。在10 - 150 keV范围内选择了九个离散能量作为初级光子源。在整个研究的能量和径向距离范围内，使用MCPLIB04的两个MCNP版本的结果在统计不确定度（±1%）内与PENELOPE的结果一致。在整个研究的能量和径向距离范围内，使用MCPLIB03或MCPLIB02的MCNP5在统计不确定度（±1%）内产生了几乎相同的数据。这意味着，尽管由于轨道电子运动导致散射光子的光谱展宽，但在所研究的能量范围内，水中康普顿相互作用的多普勒展宽的剂量学效应似乎并不显著。有无多普勒展宽的光谱剂量分析支持了这一结论。
