Figueroa R G, Rojas L, Valente M
Centro de Física e Ingeniería en Medicina, CFIM, Universidad de La Frontera, Temuco, Chile; Departamento de Ciencias Físicas, Universidad de La Frontera, Temuco, Chile.
Departamento de Ciencias Físicas, Universidad de La Frontera, Temuco, Chile.
Appl Radiat Isot. 2019 Sep;151:13-18. doi: 10.1016/j.apradiso.2019.05.032. Epub 2019 May 24.
Convergent beam radiotherapy, or CBRT, currently under development is based on the adaptation of a linear accelerator (linac) to a device which allows to dynamically curve the original trajectory of the electron beam so that it impacts upon a target. This produces a photon beam via Bremsstrahlung which converges on a predetermined focus point (isocenter). Adaptation of the RTHC device is only possible if it is sufficiently compact, as the device must be placed between the linac head exit and the gurney. This requires that new magnetic deflection devices be developed. This paper describes the theoretical and experimental development of controlled-deflection electron beam systems (at energies in MeV ranges) generated in a dual linear accelerator waveguide. A device which follows RTHC geometry is adapted for the system, using new magnetic deflector designs based on permanent neodymium magnets which reach magnetic field intensities in the order of Tesla. The methodology that was developed includes calculations of the radii of curvature with relativistic considerations for mono- and poly-energetic electrons. Deflection angles were calculated based on this theoretical foundation, using a program developed in MatLab® which shows the trajectory of electrons both under ideal conditions (uniform magnetic field) and real conditions (magnetic field defined through intensity distribution). Monte Carlo simulation subroutines were implemented in order to estimate the spectrum of electrons issuing from the linac as well as to directly determine the electron beam trajectory with magnetic deflectors present. Theoretical and simulated results were compared to experiments performed with a clinical linear accelerator, demonstrating correspondence between different methodologies and confirming the ability to achieve electron beam deflection levels necessary for implementation of convergent beam radiotherapy device.
正在研发的会聚束放射疗法（CBRT）是基于对直线加速器（linac）进行改造，使其成为一种能够动态弯曲电子束原始轨迹，从而使其撞击靶标的设备。这会通过轫致辐射产生一束光子束，该光子束会聚于一个预定的焦点（等中心）。只有当RTHC设备足够紧凑时，才有可能对其进行改造，因为该设备必须放置在直线加速器机头出口和治疗床之间。这就需要开发新的磁偏转装置。本文描述了在双直线加速器波导中产生的可控偏转电子束系统（能量处于兆电子伏特范围）的理论和实验进展。一种遵循RTHC几何结构的设备被应用于该系统，采用基于钕永磁体的新型磁偏转器设计，其磁场强度可达特斯拉量级。所开发的方法包括考虑相对论效应计算单能和多能电子的曲率半径。基于这一理论基础计算了偏转角，使用在MatLab®中开发的程序，该程序展示了电子在理想条件（均匀磁场）和实际条件（通过强度分布定义的磁场）下的轨迹。实施了蒙特卡罗模拟子程序，以估计直线加速器发出的电子能谱，并直接确定存在磁偏转器时的电子束轨迹。将理论和模拟结果与使用临床直线加速器进行的实验进行了比较，证明了不同方法之间的一致性，并证实了实现会聚束放射疗法设备所需电子束偏转水平的能力。
