Taleei Reza, Guan Fada, Peeler Chris, Bronk Lawrence, Patel Darshana, Mirkovic Dragan, Grosshans David R, Mohan Radhe, Titt Uwe
Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, 1400 Pressler Street, Houston, Texas 77030.
Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030.
Med Phys. 2016 Feb;43(2):761-76. doi: 10.1118/1.4939440.
(3)He ions may hold great potential for clinical therapy because of both their physical and biological properties. In this study, the authors investigated the physical properties, i.e., the depth-dose curves from primary and secondary particles, and the energy distributions of helium ((3)He) ions. A relative biological effectiveness (RBE) model was applied to assess the biological effectiveness on survival of multiple cell lines.
In light of the lack of experimental measurements and cross sections, the authors used Monte Carlo methods to study the energy deposition of (3)He ions. The transport of (3)He ions in water was simulated by using three Monte Carlo codes-FLUKA, GEANT4, and MCNPX-for incident beams with Gaussian energy distributions with average energies of 527 and 699 MeV and a full width at half maximum of 3.3 MeV in both cases. The RBE of each was evaluated by using the repair-misrepair-fixation model. In all of the simulations with each of the three Monte Carlo codes, the same geometry and primary beam parameters were used.
Energy deposition as a function of depth and energy spectra with high resolution was calculated on the central axis of the beam. Secondary proton dose from the primary (3)He beams was predicted quite differently by the three Monte Carlo systems. The predictions differed by as much as a factor of 2. Microdosimetric parameters such as dose mean lineal energy (y(D)), frequency mean lineal energy (y(F)), and frequency mean specific energy (z(F)) were used to characterize the radiation beam quality at four depths of the Bragg curve. Calculated RBE values were close to 1 at the entrance, reached on average 1.8 and 1.6 for prostate and head and neck cancer cell lines at the Bragg peak for both energies, but showed some variations between the different Monte Carlo codes.
Although the Monte Carlo codes provided different results in energy deposition and especially in secondary particle production (most of the differences between the three codes were observed close to the Bragg peak, where the energy spectrum broadens), the results in terms of RBE were generally similar.
由于³He离子的物理和生物学特性，其在临床治疗中可能具有巨大潜力。在本研究中，作者研究了³He离子的物理特性，即初级和次级粒子的深度剂量曲线以及氦（³He）离子的能量分布。应用相对生物效应（RBE）模型评估对多种细胞系存活的生物学效应。
鉴于缺乏实验测量值和截面数据，作者使用蒙特卡罗方法研究³He离子的能量沉积。使用三种蒙特卡罗代码——FLUKA、GEANT4和MCNPX——对³He离子在水中的传输进行模拟，入射束具有高斯能量分布，两种情况下平均能量分别为527 MeV和699 MeV，半高宽均为3.3 MeV。使用修复-错配-固定模型评估每种代码的RBE。在使用这三种蒙特卡罗代码进行的所有模拟中，均使用相同的几何结构和初级束参数。
在束的中心轴上计算了作为深度函数的能量沉积和高分辨率能谱。三种蒙特卡罗系统对初级³He束产生的次级质子剂量的预测差异很大。预测差异高达两倍。使用微剂量学参数，如剂量平均线能量（y(D)）、频率平均线能量（y(F)）和频率平均比能（z(F)）来表征布拉格曲线四个深度处的辐射束质量。计算得到的RBE值在入口处接近1，在两种能量的布拉格峰处，前列腺癌细胞系和头颈癌细胞系的RBE值平均分别达到1.8和1.6，但不同蒙特卡罗代码之间存在一些差异。
尽管蒙特卡罗代码在能量沉积方面，尤其是在次级粒子产生方面提供了不同的结果（三种代码之间的大多数差异在布拉格峰附近观察到，此处能谱变宽），但在RBE方面的结果总体上相似。
