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首页> 外文期刊>Physics in medicine and biology. >Decoupling initial electron beam parameters for Monte Carlo photon beam modelling by removing beam-modifying filters from the beam path.
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Decoupling initial electron beam parameters for Monte Carlo photon beam modelling by removing beam-modifying filters from the beam path.

机译：通过从电子束路径中删除电子束修改滤镜，可以将用于蒙特卡洛光子束建模的初始电子束参数解耦。

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摘要

A new method is presented to decouple the parameters of the incident e(-) beam hitting the target of the linear accelerator, which consists essentially in optimizing the agreement between measurements and calculations when the difference filter, which is an additional filter inserted in the linac head to obtain uniform lateral dose-profile curves for the high energy photon beam, and flattening filter are removed from the beam path. This leads to lateral dose-profile curves, which depend only on the mean energy of the incident electron beam, since the effect of the radial intensity distribution of the incident e- beam is negligible when both filters are absent. The location of the primary collimator and the thickness and density of the target are not considered as adjustable parameters, since a satisfactory working Monte Carlo model is obtained for the low energy photon beam (6 MV) of the linac using the same target and primary collimator. This method was applied to conclude that the mean energy of the incident e- beam for the high energy photon beam (18 MV) of our Elekta SLi Plus linac is equal to 14.9 MeV. After optimizing the mean energy, the modelling of the filters, in accordance with the information provided by the manufacturer, can be verified by positioning only one filter in the linac head while the other is removed. It is also demonstrated that the parameter setting for Bremsstrahlung angular sampling in BEAMnrc ('Simple' using the leading term of the Koch and Motz equation or 'KM' using the full equation) leads to different dose-profile curves for the same incident electron energy for the studied 18 MV beam. It is therefore important to perform the calculations in 'KM' mode. Note that both filters are not physically removed from the linac head. All filters remain present in the linac head and are only rotated out of the beam. This makes the described method applicable for practical usage since no recommissioning process is required.
机译：提出了一种新方法来分离入射到线性加速器目标上的e（-）光束的参数，该方法主要在于优化差动滤波器（是在直线加速器中插入的附加滤波器）时测量和计算之间的一致性。为获得高能光子束获得均匀的横向剂量分布曲线，并从束路径中移除了平坦滤光片。这导致侧向剂量分布曲线，其仅取决于入射电子束的平均能量，因为当两个滤波器都不存在时，入射电子束的径向强度分布的影响可以忽略。主准直仪的位置以及靶材的厚度和密度不被视为可调参数，因为使用相同的靶标和主准直仪可为直线加速器的低能光子束（6 MV）获得令人满意的工作蒙特卡洛模型。应用该方法得出的结论是，我们的Elekta SLi Plus直线加速器的高能光子束（18 MV）入射电子束的平均能量等于14.9 MeV。在优化平均能量之后，可以根据制造商提供的信息，通过仅将一个过滤器放置在直线加速器头部中，而将另一个过滤器卸下来验证过滤器的建模。还证明了在BEAMnrc中Bre致辐射角采样的参数设置（使用Koch和Motz方程的前导项为“简单”或使用完整方程式为“ KM”）导致相同入射电子能量的不同剂量分布曲线用于研究的18 MV光束。因此，以“ KM”模式执行计算非常重要。请注意，这两个过滤器都没有从直线加速器头上物理移除。所有过滤器都保留在直线加速器头部中，并且仅从光束中旋转出来。由于不需要重新调试过程，这使得所描述的方法适用于实际使用。

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