Magnetic confinement of electron and photon radiotherapy dose: A Monte Carlo simulation with a nonuniform longitudinal magnetic field
Magnetic confinement of electron and photon radiotherapy dose: A Monte Carlo simulation with a nonuniform longitudinal magnetic field
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DOI：
10.1118/1.2011091
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发表时间：
2005-12-01
期刊：
影响因子：
3.8
通讯作者：
Becchetti, FD
中科院分区：
文献类型：
--
作者：
Chen, Y;Bielajew, AF;Becchetti, FD
最近的实验表明，纵向非均匀高磁场的聚焦可以显著改善电子束的剂量谱。这可以精确定位关键区域附近的肿瘤，并最大限度地减少对周围健康组织的辐射剂量。实验结果和蒙特卡罗模拟表明，在某些情况下，电子放射治疗束的磁约束可以提供质子或重离子放射治疗的所有替代方案。在本工作中，利用蒙特卡罗代码PENELOPE的外部磁场能力，提供了一个子程序来模拟实验研究中使用的螺线管磁铁产生的实际磁场，我们模拟的磁场覆盖了从真空出口窗口到幻影的区域，包括周围的空气。在纵向非均匀磁场中，观察到电子剂量在横向和纵向上都有聚焦。在蒙特卡罗模拟中，只要精确地知道入射电子束的几何形状和能量，所测得的电子束的剂量分布一般能在感兴趣的区域内再现几个百分点。并对有磁场和无磁场时的光子束剂量谱进行了比较。实验结果在模拟中得到了定性再现。我们的模拟表明，光束入口的过量剂量是由于磁场捕获和聚焦了入射光子光束在空气中产生的散射二次电子。模拟还表明，通过适当控制束流能量、纵向磁场强度和位移，可以控制电子剂量分布。(c) 2005年美国医学物理学家协会。
It recently has been shown experimentally that the focusing provided by a longitudinal nonuniform high magnetic field can significantly improve electron beam dose profiles. This could permit precise targeting of tumors near critical areas and minimize the radiation dose to surrounding healthy tissue. The experimental results together with Monte Carlo simulations suggest that the magnetic confinement of electron radiotherapy beams may provide all alternative to proton or heavy ion radiation therapy in some cases. In the present work, the external magnetic field capability of the Monte Carlo code PENELOPE was utilized by providing a subroutine that modeled the actual field produced by the solenoid magnet used in the experimental studies, The magnetic field in our simulation covered the region from the vacuum exit window to the phantom including surrounding air. In a longitudinal nonuniform magnetic field, it is observed that the electron dose can be focused in both the transverse and longitudinal directions. The measured dose profiles of the electron beam are generally reproduced in the Monte Carlo simulations to within a few percent in the region of interest provided that the geometry and the energy of the incident electron beam are accurately known. Comparisons for the photon beam dose profiles with and without the magnetic field are also made. The experimental results are qualitatively reproduced in the simulation. Our simulation shows that the excessive dose at the beam entrance is due to the magnetic field trapping and focusing scattered secondary electrons that were produced in the air by the incident photon beam. The simulations also show that the electron dose profile can he manipulated by the appropriate control of the beam energy together with the strength and displacement of the longitudinal magnetic field. (c) 2005 American Association of Physicists in Medicine.