电离辐射粒子在人体组织中能量沉积的微剂量学研究

【作者】 张文仲；

【导师】 郭勇；

【作者基本信息】 中国人民解放军军事医学科学院 ， 基础医学， 2003， 博士

【摘要】 自从1946年D.E.Lea指出辐射粒子的能量沉积微观分布在生物效应研究中的重要性以来,世界上许多国家都相继开展了这方面的研究。美国、德国和日本等许多国家从20世纪60年代起,就开始了电离辐射粒子(γ射线、中子、质子和电子)在μm尺度上的能量沉积研究,一开始它就和生物学密切结合,同时采用理论与实验方法进行,应用各种数学模型将物理测量与生物学效应联系起来,并解释了一些细胞失活现象。70年代以后,随着计算机技术的发展以及实验测量手段的创新和完善,对电离辐射能量沉积的研究范围又逐渐从μm量级深入到nm量级。以后伴随着航天事业的发展和各种大型重离子加速器运行,研究的范围逐步又扩展到各种类型的重离子在人体组织中产生能量沉积的微观行为和方式。 在人体组织物质中,电离辐射产生的瞬时(或永久)变化与电离辐射作用事件在靶物质中发生的能量沉积、能量转移等过程的空间分布有着非常密切的关系。在这种情况下,一些宏观(或微观)剂量学量,如传能线密度(LET)、阻止本领和平均授与能等,将不能很好地描述辐射的物理、化学过程以及生物学效应,必须进一步对受照射物质中的电离辐射粒子能量沉积方式和能量沉积分布进行研究。所以,有关电离辐射粒子在物质中射程、截面以及沿其径迹周围径向剂量分布等相关物理量的研究,无论在理论上还是在实验中都受到广泛的关注。通过这些研究,深刻认识电离辐射在人体物质中的能量沉积微观物理基础,以解释各种电离辐射的生物学效应,并建立电离辐射作用模型与相应的物理作用机制。在电离辐射微剂量学研究领域内,到目前为止,无论在理论计算还是在实验测量手段上,国内在这方面开展的工作非常有限,基于国内目前研究状况和当前实验设备乏缺的情况,作为本课题的立足点,首先拟从理论计算入手,研究电离辐射在人体组织内能量沉积的微观分布,以填补国内在该研究领域的空白。 在本课题研究的前期,进行了广泛的资料调研工作,由于国内资料非常有限,比较深入的相关研究工作还没有见到文献报导,因此,主要通过网上的国外文献资源,比较系统地了解了本学科前沿领域的研究状况,在此基础上逐渐形成了本课题工作的研究思路。由于利用Monte Carlo方法不用对介质内发生的物理过程做这样或那样的假设,能够真实模拟带电粒子能量沉积的微观过程和电离辐射粒子的空间行为,并能够对能量损失歧离、δ射线的产生及其它各种分叉径迹(forked track)等物理现象进行详细描述,所以,在课题研究方法的选择上,撇开了传统的数值计算方法,而首选了Monte Carlo计算更多还原

【Abstract】 The world wide research on biological effects had been spread in many countries since L.E.Lea recognized the importance of the micro-distribution of radiation energy deposition in biological material in 1946. The researches about these kinds of energy deposition events including photon, neutron, proton and electron on the scale of micron were begun in the 60’s of the last century in some foreign countries such as U.S.A, German, Japan etc. These researches were related tightly to biology since beginning. Both of experiment and theory method were used, and the relationship between physical measurement and biological effects was related through various mathematical models, with which the phenomena of cell-death could be explained. The investigation of the micro-distribution of radiation energy deposition has been extended largely from micron level to nanometer level with the development of computer technology and the perfection of the measuring methods since 1970. The research region was enlarged to heavy ions accompanied by the development of space-flight and the running of many large heavy ion accelerator after then.The instantaneous or permanent changes in tissue were close depended on the spatial micro-distribution of energy deposition and energy transfer process of radiation. In this case, some dosimetry concepts such as LET, stopping power and mean energy imparted would not be capable to describe the progress of physics, chemistry and biological effects. New concepts must be established, so the energy deposition fashion and the energy deposition distribution of various particles in tissue must be studied. The ranges, cross sections of ionizing particles and radial dose distributions along particles’ trace in targets should be given much more attention both in theory and in experiment. The physics basement of energy deposition micro-distribution in tissue will be recognized deeply after these research, and the biological effects of all sort of ionizing particles will be explained correctly, then the ionizing radiation action model and according physics action mechanism will be established also. Little has been done in our country in the region, no matter in theory calculation or in experiment aspects now. In our research we will do some theory calculations first, and give some results of energy deposition micro-distribution in tissue. This study will be the first step in our national research.we have done a lot of investigation to do the work. There is little clue about this research, so we find no papers in Chinese. We have obtained lots of knowledge on this study main from worldwide web, and formed ourselves framework doing the research. If the Monte Carlo method was accepted, charged particles energy deposition micro-progress and ionizing radiation spatial action will be simulated, then many physics phenomena such as energy loss fluctuation, delta ray produced and all of other forked track will be scribed particularly. The important thing is that some supposes about physics progresshappened in target will not be done. We give up mathematical calculation method and choice Monte Carlo method as our research means in this work.In our research progress, these problems have been resolved in turn: first, the tissue component was analyzed, and the rationality that liquid water (or water vapor-density is 1g/cm3) is the substitute of tissue equivalent material was made sure. Second, various cross section data on proton, alpha particles, electron and photon in water vapor were obtained, and these data were optimized. Third, the ESLOW3.1 code has been improved, and the new cross section data were adopted. The electron energy spectra from different energy photon (10keV~1.6MeV) in tissue equivalent materials were acquainted, and the electron mean energy was obtainted by this code also. Fourth, we acquainted energy deposition event position distribution, energy distribution from different energy electron (20eV~1.0MeV) in tissue equivalent material by the usage of ESLOW3.1 electron sub-code, and all sort of event type were analyzed. At the same time, according to DNA molecule diameter, the energy deposition cluster events were defined; the frequency distribution and energy distribution of cluster events were calculated. Fifth, neutron reaction types in body tissue were analyzed, and productions in these reactions were estimated. Sixth, using the latest code M0CA15 written by Wilson and Paretzke, we calculated track section of proton and alpha particle in the tissue equivalent material, and the energy deposition distribution, position distribution, energy distribution and radial dose distribution for second electron were all acquainted. The code-MOCA15 can dispose any proton and alpha particle with the energy region between 0.3MeV/u~5MeV/u. the wide particle energy region covers all energy proton and alpha particle we care about.Some energy deposition micro-distribution styles for different ionizing particles in tissue equivalent materials have been known thorough these researches. We have acquainted these particles energy deposition event distribution and dose distribution at nano-level also, and can recognized origin physics mechanism when various biological effects happen. This research will help us evaluated ionizing radiation latent physics injures in tissue at low dose. Meanwhile we can forecast the serious degree and happen probability of biological effects, and recognize ionizing radiation injure at molecule level. All these research are the physics base of ionizing radiation molecule biology.更多还原