Centre for Medical Radiation Physics (CMRP), University of Wollongong, NSW, Australia. Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany.
Phys Med Biol. 2012 Mar 7;57(5):1231-50. doi: 10.1088/0031-9155/57/5/1231. Epub 2012 Feb 14.
The concept of nanodosimetry is based on the assumption that initial damage to cells is related to the number of ionizations (the ionization cluster size) directly produced by single particles within, or in the close vicinity of, short segments of DNA. The ionization cluster-size distribution and other nanodosimetric quantities, however, are not directly measurable in biological targets and our current knowledge is mostly based on numerical simulations of particle tracks in water, calculating track structure parameters for nanometric target volumes. The assessment of nanodosimetric quantities derived from particle-track calculations using different Monte Carlo codes plays, therefore, an important role for a more accurate evaluation of the initial damage to cells and, as a consequence, of the biological effectiveness of ionizing radiation. The aim of this work is to assess the differences in the calculated nanodosimetric quantities obtained with Geant4-DNA as compared to those of the ad hoc particle-track Monte Carlo code 'PTra' developed at Physikalisch-Technische Bundesanstalt (PTB), Germany. The comparison of the two codes was made for incident electrons of energy in the range between 50 eV and 10 keV, for protons of energy between 300 keV and 10 MeV, and for alpha particles of energy between 1 and 10 MeV as these were the energy ranges available in both codes at the time this investigation was carried out. Good agreement was found for nanodosimetric characteristics of track structure calculated in the high-energy range of each particle type. For lower energies, significant differences were observed, most notably in the estimates of the biological effectiveness. The largest relative differences obtained were over 50%; however, generally the order of magnitude was between 10% and 20%.
纳米剂量学的概念基于这样一种假设，即细胞的初始损伤与单个粒子在 DNA 的短片段内或其附近直接产生的离子数（离子簇大小）有关。然而，离子簇大小分布和其他纳米剂量学参数不能直接在生物靶标中测量，我们目前的知识主要基于在水中的粒子轨迹的数值模拟，计算纳米级靶标体积的轨迹结构参数。因此，使用不同的蒙特卡罗代码对源自粒子轨迹计算的纳米剂量学参数进行评估，对于更准确地评估细胞的初始损伤以及因此对于电离辐射的生物学效应起着重要作用。本工作的目的是评估使用 Geant4-DNA 计算得出的纳米剂量学参数与德国联邦物理技术研究院（PTB）专门开发的粒子轨迹蒙特卡罗代码“PTra”之间的差异。对这两种代码进行了比较，比较范围包括 50 eV 到 10 keV 之间的入射电子、300 keV 到 10 MeV 之间的质子以及 1 到 10 MeV 之间的α粒子，因为在进行这项研究时，这两种代码都能提供这些能量范围内的计算。在每种粒子类型的高能范围内，计算出的轨迹结构纳米剂量学特征具有良好的一致性。对于较低的能量，观察到显著的差异，特别是在生物学效应的估计方面。获得的最大相对差异超过 50%；然而，一般来说，数量级在 10%到 20%之间。
