【作者】 张晓敏；

【导师】 杨国山；

【作者基本信息】 中国人民解放军军事医学科学院 ， 放射医学， 2010， 博士

【摘要】 动物照射实验是电离辐射生物效应研究的重要手段,相比较平均剂量而言,实验动物的器官剂量可为生物效应评价、剂量-效应关系研究提供更丰富的信息和依据。动物器官剂量难以采用物理方法直接测量。近年来,随着断层成像技术的发展,基于体素模型与蒙特卡罗技术的器官剂量模拟计算方法已日趋成熟,并已在辐射防护人体剂量学中得到了应用,而目前以生物效应评价为目的的动物器官剂量计算还处于起步阶段,缺乏体素模型及器官剂量评价数据。本文针对小鼠建立体素模型,采用蒙特卡罗技术获得了光子、中子外照射情况下小鼠的器官剂量转换系数,分析并总结了小鼠的器官剂量分布规律。主要研究结果及结论包括:1、采用Matlab7.0和Photoshop8.0图像处理软件软件对质量为28 g的雄性小鼠断层序列彩色解剖图片(418张)进行了图像配准、识别与分割,然后利用Visual C++与可视化工具包(VTK)编程对小鼠进行三维重建,建立了一个体素精度为0.2 mm×0.2 mm×0.2 mm、体素数量为9,424,000的小鼠体素模型,模型中含有14个关键器官或组织,分别为:皮肤、骨骼、眼睛、心脏、肺、肝、肾、肾上腺、胃、脾、胰腺、睾丸、膀胱、肌肉等。2、采用Matlab 7.0软件和蒙特卡罗程序MCNP混合编程,确定了小鼠体素模型中每个体素的空间几何位置和物理属性,并编写了小鼠体素模型的MCNP输入文件,使得小鼠体素模型可以与蒙特卡罗方法结合进行粒子输运模拟。3、针对蒙特卡罗程序MCNP,论文深入研究了基于体素模型的光子、中子外照射器官剂量计算方法,总结了不同光子、中子能量情况下物理模型及计数类型选择的规律,为获得准确的小鼠器官剂量提供了方法学基础。4、利用MCNP程序,分别模拟计算了五种照射几何条件(左侧向、右侧向、腹背向、背腹向、各向同性)下,光子能量为0.01MeV～10MeV共22个能量点、中子能量为10-9MeV～20MeV共37个能量点的小鼠器官剂量转换系数,并以表格的形式给出了计算结果及其不确定度。此套转换系数是小鼠剂量学的基础数据,在照射条件已知时,可以用来获得小鼠的器官剂量。5、深入分析讨论了照射几何条件、粒子能量、器官的位置、形状、大小及小鼠个体差异对小鼠器官剂量的影响,结果表明小鼠器官剂量在这些因素的影响下,光子外照射时同一个器官的器官剂量差异最高可达50%～60%,而中子外照射时差异最高可达100%～120%。6、构建了一个小鼠剂量学理论研究平台,利用该平台可以模拟计算光子、中子及其他粒子(如电子、质子)内外照射情况下的小鼠剂量学数据。更多还原

【Abstract】 Animal irradiation experiment is vital to study biological effects of radiation. Compared with the average dose, the organ dose of animal can provide more plentiful information and basis for evaluating biological effects and dose-effect relation research. The animal organ dose is difficult to be measured directly by physical methods. In recent years, with the development of tomograph imaging technologies, the organ dose calculation methods based on the voxel model and Monte Carlo technique have been increasingly maturing and have been used for human dosimetry in radiation protection. However, the organ dose calculations aiming at evaluation of biologicial effects are being on the beginning stage, which lacks voxel models and organ dose data.In this paper, a voxel model of mouse was constructed, a set of mouse organ dose conversion coefficients for external photon and neutron irradiation were obtainded by using Monte Carlo method, and the mouse organ dose distribution also was analyzed and concluded. The main results and conclusions are as follows:1. At first, a series of image processes including registration, identification and segmentation were carried out for a total of 418 color images of successive cryosections of a normal male mouse, 28g in weight by using Matlab 7.0 and Photoshop 8.0 software.Then 3D reconstruction of the mouse model was achieved through programming with Visual C++ and Visualization Toolkit (VTK). After these, a mouse voxel model comprised by total number of 9,424,000 voxels, each of which is size of 0.2mm×0.2mm×0.2mm, was constructed. The model contained 14 key organs or tissues including skin, bone, eye, brain, heart, lungs, liver, kidneys, adrenal glands, stomach, spleen, pancreas, bladder, testis and muscle.2. The location and physical property of each voxel in the mouse model were confirmed through coupled programming with Matlab 7.0 and Monte Carlo code MCNP. The input file of the mouse voxel model used in MCNP was achieved to perform particle transport simulation by combining the mouse voxel model and Monte Carlo method.3. As for the Monte Carlo code MCNP, the organ dose calculation methods of voxel model used for external photon and neutron irradiation were thoroughly investigated and the selection rules of physical models and tally types for different energy of photon and neutron were also concluded,which provide basis of methodology for acquiring correct mouse organ dose . 4. Monte Carlo simulation with MCNP was carried out to obtain mouse organ dose conversion coefficients for 22 external monoenergetic photon beams (0.01MeV ~10 MeV) and 37 external monoenergetic neutron beams(10-9MeV~20MeV) under five different irradiation geometry conditions (left lateral, right lateral, dorsal-ventral, ventral-dorsal, and isotropic). The results and uncertainty were given in form of table. The set of organ dose conversion coefficients are basic data of mouse dosimetry and can be used to acquire organ dose when irradiation conditions have been known.5. The paper have discussed the organ dose difference affected by a series of factors including irradiation geometry conditions, particle energy, location, shape and size of organ, the individual difference. The results show that the organ dose difference can reach almostly 50%～60% for photon irradiation and 100%～120% for neutron irradiation.6. A platform for theoretical study of mouse dosimetry was constructed, which can be used to simulate and calculate the mouse dosimetry data for photon, neutron and other particles (such as electron and proton) irradiation under internal and external irradiation conditions.更多还原