Cho S H, Reece W D
Department of Nuclear Engineering, Texas A&M University, College Station 77843-3133, USA.
Phys Med Biol. 1999 Jan;44(1):13-26. doi: 10.1088/0031-9155/44/1/003.
Recently, there has been growing interest in beta emitters for therapeutic uses, especially in connection with so-called endovascular (or intravascular) brachytherapy. Since accurate dose estimation is necessary for the success of such applications, some problems in beta-ray dosimetry need further study. Among these problems, we have investigated the effect of electron backscattering on dose, which has significance not only for accurate dose estimation but also for new source design. In this study, an empirical measure of electron backscattering, known as the dose backscatter factor, was calculated using EGS4 Monte Carlo calculations for monoenergetic electrons and various scattering materials. Electron energies were 0.1, 0.5, 1.0, 2.0 and 3.0 MeV in combination with Al (Z = 13), Ti (Z = 22), Sr (Z = 38), Ag (Z = 47) and Pt (Z = 78) scatterers. The dose backscatter factor ranged from 10% to 60%, depending on electron energy and material, and was found to increase with the atomic number Z by a log(Z + 1) relationship. A method is presented for calculating the beta-ray dose backscatter factors using the results of this study. To demonstrate the efficacy of this method, a dose backscatter factor depth profile for 32P near a water/aluminium interface was calculated and these calculated results were found to generally reproduce the depth profile obtained from direct EGS4 calculations using the 32P spectrum. The data presented in this study can be used to calculate dose backscatter factors for any combination of beta emitter/scatterer whose atomic number ranges from 13 to 78.
最近，人们对用于治疗用途的β发射体的兴趣日益浓厚，特别是与所谓的血管内（或血管内）近距离放射治疗相关。由于此类应用的成功需要准确的剂量估计，β射线剂量测定中的一些问题需要进一步研究。在这些问题中，我们研究了电子背散射对剂量的影响，这不仅对准确的剂量估计有意义，而且对新源设计也有意义。在本研究中，使用EGS4蒙特卡罗计算方法，针对单能电子和各种散射材料，计算了一种称为剂量背散射因子的电子背散射的经验度量。电子能量为0.1、0.5、1.0、2.0和3.0 MeV，分别与铝（Z = 13）、钛（Z = 22）、锶（Z = 38）、银（Z = 47）和铂（Z = 78）散射体组合。剂量背散射因子范围为10%至60%，具体取决于电子能量和材料，并且发现其随原子序数Z呈log(Z + 1)关系增加。本文提出了一种利用本研究结果计算β射线剂量背散射因子的方法。为了证明该方法的有效性，计算了水/铝界面附近32P的剂量背散射因子深度分布，发现这些计算结果通常能重现使用32P能谱通过直接EGS4计算得到的深度分布。本研究中给出的数据可用于计算原子序数范围为13至78的任何β发射体/散射体组合的剂量背散射因子。
