低能电磁扫描IMRT光子注量分布M-C模拟

M-C simulation of photon fluence distribution in IMRT by electromagnetic scanning low-energy E-beams

电磁扫描调强是用电子笔束轰击离散分布的靶点,产生脉冲化X线光子束,是实现调强放疗的技术方案之一。本文主要是考察当电子加速能量为低中能时,从可产生的光子注量分布的角度,来探讨低能电磁扫描调强技术的可行性。通过Monte Carlo模拟,计算了不同能量的电子笔束轰击靶材料产生的光子笔束注量分布,以确定较优的靶材料及其几何结构。然后计算不同靶点密度下的光子注量分布,确定合适的入射靶点间隔。最后,以两种常规放射治疗最常用的注量分布为例,通过最优化电子笔束强度来获得所要的注量分布。模拟结果表明,通过选用合适的靶材料结构,结合对电子轰击靶点的强度的最优化,可以实现临床要求的常规光子注量分布。

In intensity modulated radiation therapy （IMRT）,an approach to generate uniform photon beams is to use electron pencil beams to bombard a set of points that are discretely arranged on the target. It was considered that the E-beam energy in this technique should be greatly higher than that those from accelerators commonly available for radiation therapy. In this study,Monte Carlo simulation was used to explore the possibility of generating the needed photon fluence distribution by using a common medical accelerator. The fluence distributions produced by electrons pencil beam in different energies were compared. Optimal target materials,and the geometry,were determined. The photon fluence distributions of wide fields at various target point intervals were simulated for suitable density of the target points. Two fluence distributions in common request by conventional IMRT were taken as examples to show that the desired fluence distributions could be achieved by optimizing the intensity of electron beam on target points.