Kainz K K, Hogstrom K R, Antolak J A, Almond P R, Bloch C D
Department of Radiation Physics, The University of Texas M D Anderson Cancer Center, Houston, TX 77030, USA.
Phys Med Biol. 2005 Jan 7;50(1):N1-10. doi: 10.1088/0031-9155/50/1/n01.
Given that laser wakefield acceleration (LWFA) has been demonstrated experimentally to accelerate electron beams to energies beyond 25 MeV, it is reasonable to assess the ability of existing LWFA technology to compete with conventional radiofrequency linear accelerators in producing electron and x-ray beams for external-beam radiotherapy. We present calculations of the dose distributions (off-axis dose profiles and central-axis depth dose) and dose rates of x-ray beams that can be produced from electron beams that are generated using state-of-the-art LWFA. Subsets of an LWFA electron energy distribution were propagated through the treatment head elements (presuming an existing design for an x-ray production target and flattening filter) implemented within the EGSnrc Monte Carlo code. Three x-ray energy configurations (6 MV, 10 MV and 18 MV) were studied, and the energy width deltaE of the electron-beam subsets varied from 0.5 MeV to 12.5 MeV. As deltaE increased from 0.5 MeV to 4.5 MeV, we found that the off-axis and central-axis dose profiles for x-rays were minimally affected (to within about 3%), a result slightly different from prior calculations of electron beams broadened by scattering foils. For deltaE of the order of 12 MeV, the effect on the off-axis profile was of the order of 10%, but the central-axis depth dose was affected by less than 2% for depths in excess of about 5 cm beyond d(max). Although increasing deltaE beyond 6.5 MeV increased the dose rate at d(max) by more than 10 times, the absolute dose rates were about 3 orders of magnitude below those observed for LWFA-based electron beams at comparable energies. For a practical LWFA-based x-ray device, the beam current must be increased by about 4-5 orders of magnitude.
鉴于激光尾场加速（LWFA）已通过实验证明能够将电子束加速到超过25 MeV的能量，因此评估现有LWFA技术在产生用于外照射放疗的电子束和X射线束方面与传统射频线性加速器竞争的能力是合理的。我们给出了利用最先进的LWFA产生的电子束所能够产生的X射线束的剂量分布（离轴剂量剖面和中心轴深度剂量）以及剂量率的计算结果。LWFA电子能量分布的子集通过EGSnrc蒙特卡罗代码中实现的治疗头元件（假定有用于X射线产生靶和均整过滤器的现有设计）进行传输。研究了三种X射线能量配置（6 MV、10 MV和18 MV），电子束子集的能量宽度ΔE从0.5 MeV变化到12.5 MeV。当ΔE从0.5 MeV增加到4.5 MeV时，我们发现X射线的离轴和中心轴剂量剖面受到的影响最小（在约3%以内），这一结果与先前关于通过散射箔展宽的电子束的计算结果略有不同。对于约12 MeV量级的ΔE，对离轴剖面的影响约为10%，但对于超过d(max)约5 cm深度以上的深度，中心轴深度剂量受到的影响小于2%。尽管将ΔE增加到超过6.5 MeV会使d(max)处的剂量率增加10倍以上，但绝对剂量率比在可比能量下基于LWFA的电子束所观察到的剂量率低约3个数量级。对于基于LWFA的实用X射线设备，束流必须增加约4 - 5个数量级。
