Effects of tertiary MLC configuration on secondary neutron spectra from 18 MV x-ray beams for the Varian 21EX linear accelerator.
Effects of tertiary MLC configuration on secondary neutron spectra from 18 MV x-ray beams for the Varian 21EX linear accelerator.
复制标题
三级 MLC 配置对瓦里安 21EX 直线加速器 18 MV X 射线束的二次中子能谱的影响。
DOI：
10.1118/1.3159301
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发表时间：
2009
期刊：
影响因子：
3.8
通讯作者：
Hertel,NolanE
中科院分区：
文献类型：
--
作者：
Howell,RebeccaM;Kry,StephenF;Burgett,Eric;Followill,David;Hertel,NolanE
详细研究了18 MV瓦里安21EX直线加速器的颚形和三级多叶准直器（MLC）的存在及配置对二次中子能谱的影响。作者报告了四种准直器（颚型和MLC型）配置的测量光谱。这些配置代表了钳口和MLC的极端设置，因此应该描述在使用该直线器期间可能遇到的影响范围和光谱。除了测量外，还使用蒙特卡罗模型模拟了四种准直器配置，并计算了测量时同一位置的能谱和影响。蒙特卡罗模型还用于计算每个准直器配置的直线头中子产生源。他们发现直线处理头的光子中子产生是由主光子束拦截高物质的顺序决定的。主准直器在直线机头的最高位置（在一个固定的位置），是次级中子的最大来源。此后，准直器的结构在中子的起源中起作用。例如，如果钳口是闭合的，它们就会拦截光束，并对二次中子的产生作出重大贡献。相反，如果钳口打开，则MLC在中子产生中发挥更大的作用（当然，假设它拦截了光束）。他们发现，不同的准直器配置会造成环境剂量当量的2倍差异。
The effect of the jaw configuration and the presence and configuration of the tertiary multileaf collimator (MLC) on the secondary neutron spectra for an 18 MV Varian 21EX linear accelerator (linac) is investigated in detail. The authors report the measured spectra for four collimator (jaw‐and‐MLC) configurations. These configurations represent the extreme settings of the jaws and MLC and should therefore describe the range of possible fluence and spectra that may be encountered during use of this linac. In addition to measurements, a Monte Carlo model was used to simulate the four collimator configurations and calculate the energy spectra and fluence at the same location as it was measured. The Monte Carlo model was also used to calculate the sources of neutron production in the linac head for each collimator configuration. They found that photoneutron production in the linac treatment head is dominated by the order in which the primary photon beam intercepts the high‐ material. The primary collimator, which has the highest position in the linac head (in a fixed location), is the largest source of secondary neutrons. Thereafter, the collimator configuration plays a role in where the neutrons originate. For instance, if the jaws are closed, they intercept the beam and contribute substantially to the secondary neutron production. Conversely, if the jaws are open, the MLC plays a larger role in neutron production (assuming, of course, that it intercepts the beam). They found that different collimator configurations make up to a factor of 2 difference in the ambient dose equivalent.