The microdosimetry of boron neutron capture therapy in a randomised ellipsoidal cell geometry.
The microdosimetry of boron neutron capture therapy in a randomised ellipsoidal cell geometry.
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随机椭圆体细胞几何形状中硼中子俘获疗法的微剂量测定。
DOI：
10.1093/rpd/nci248
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发表时间：
2005
影响因子：
1
通讯作者：
G. Kabalka
中科院分区：
文献类型：
--
作者：
T. L. Nichols;Laurence F. Miller;G. Kabalka
在硼中子俘获治疗中，两种反应提供了大部分的局部剂量。10B(n, α, γ)7Li和14N(n,p)14O这两个反应产生的电离粒子（质子，α粒子和锂核）的范围很短，小于-14微米（这是一个典型的人类细胞直径的数量级）。电离后的粒子很重，在硼的反应中处于2+电荷状态。这些重的2+离子会对轨道附近的分子造成严重损害。因此，氮的分布，特别是硼的分布决定了辐射场的空间特征。由于氮在脑内的分布几乎是均匀的，不容易因放射治疗的目的而改变，因此辐射剂量的空间变化主要是由于硼的空间分布。这意味着硼的空间分布决定了微观能量沉积，从而决定了微观剂量的空间特征。（n, α）和（n,p）反应的显微剂量已被详细地检查过，而且，据推测，质子剂量除了统计变异外，是相对均匀的。统计变异性实质上增加了一种错误的空间变异性，如果执行大量的历史记录，就不会看到这种空间变异性。由于硼的空间变异性主要发生在硼的分布上，因此可以抑制（n,p）反应，从而更好地理解空间分布对微观剂量的影响。程序已经用FORTRAN编写，使用蒙特卡罗技术来模拟椭球细胞，这些椭球细胞要么是随机大小的，位于感兴趣的区域，要么是排列在面心立方阵列中，除了核的位置可能是随机的之外，它们是相同的。结果表明，致密排列的长形椭球细胞在一维上具有较大的离心率，比致密排列较稀疏的细胞接受更大的核剂量。这表明，一个细胞及其细胞核的硼含量可以对邻近细胞的剂量产生重大影响。局部硼在感兴趣区域的分布可以显示影响大剂量剂量，可能对临床结果有影响。
Two reactions deliver the majority of local dose in boron neutron capture therapy. The ionised particles (protons, alpha particles and lithium nuclei) produced in the two reactions, 10B(n,alpha,gamma)7Li and 14N(n,p)14O, have short ranges that are less than -14 microm (which is on the order of the diameter of a typical human cell). The ionised particles are heavy and are in the 2+ charge state in the case of the boron reactions. These heavy 2+ ions will do significant damage to molecules near their tracks. Thus, the distribution of nitrogen and, in particular, of boron determines the spatial characteristics of the radiation field. Since the distribution of nitrogen is nearly homogeneous in the brain and is not easily altered for the purpose of radiotherapy, the spatial variation in the radiation dose is due mainly to the spatial distribution of boron. This implies that the spatial distribution of boron determines the microscopic energy deposition and therefore the spatial characteristics of the microscopic dose. The microscopic dose from the (n,alpha) and (n,p) reactions has been examined in detail and, as averred, the proton dose is relatively homogeneous except for statistical variability. The statistical variability in essence adds a false spatial variability that would not be seen if a large number of histories were performed. Since the majority of spatial variability occurs in the boron distribution, the (n,p) reaction can be suppressed to better understand the spatial distribution effects on the microscopic dose. Programs have been written in FORTRAN using Monte Carlo techniques to model ellipsoidal cells that are either randomly sized and located in the region of interest or are arranged in a face centred cubic array and are identical except for the location of the nuclei, which may be random. It is shown that closely packed prolate ellipsoidal cells with a large eccentricity in one dimension will receive a larger nuclear dose than cells that are more sparsely packed. This demonstrates that the boron content of a cell and its nucleus can have a significant impact upon the dose to neighbouring cells. The local boron distribution in a region of interest can be shown to affect the macrodosimetric dose, with possible implications for clinical outcomes.