Simulation of large x-ray fields using independently measured source and geometry details
Simulation of large x-ray fields using independently measured source and geometry details
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DOI：
10.1118/1.3259729
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发表时间：
2009-12-01
期刊：
影响因子：
3.8
通讯作者：
Faddegon, B. A.
中科院分区：
文献类型：
--
作者：
Sawkey, D.;Faddegon, B. A.
目的：通过模拟与测量的比较，获得来自西门子Oncor直线加速器的6 mV和18 mV X射线束的精确模拟剂量。通过独立确定治疗头和入射光束的参数，特别是能量和光斑大小来约束模拟。方法：用治疗头在三种不同的配置下进行测量：(1)临床配置；(2)去掉平坦滤光片；(3)去掉靶标和平坦滤光片。直接测量了入射光束和治疗头的参数。入射光束能量和光谱宽度由原始光束的百分比深度电离确定(如上所述)，光斑大小使用光斑相机确定，平坦滤光片的密度通过称重来确定。用EGSnrc/BEAMnrc程序进行了模拟。采用非对称模拟，包括光斑、主准直器和平坦滤光片相对于准直器旋转轴的偏移量。结果：在6 mV时，除积聚区外，无论是否安装平坦化滤光片，测量结果与模拟结果的一致性最小，仅为1%或1 mm。在18 mV时，除积聚区外，压平滤器到位时的吻合程度为1.5%/1.5 mm，去除后的吻合程度为1%/1 mm。在积聚区，去除或就位平坦过滤器后，18 mV和6 mV时的偏差分别为2%/2 mm和1.5%/1.5 mm。描述了用于治疗头模拟的源参数和几何参数的测量方法。除了确定压平过滤器的密度外，不需要对处理头进行物理修改来获得这些参数。特别是，不需要像本工作那样拆除平坦化滤光片。结论：即使在积聚区，测量的剂量分布与模拟的剂量分布也是一致的。模拟受到入射光束和治疗头参数的独立测量的严格限制。描述了获得输入参数的方法，并可在临床直线加速器上实现。(C)2009年美国医学物理学家协会。[DOI：10.1118/1.3259729]
Purpose: Obtain an accurate simulation of the dose from the 6 and 18 MV x-ray beams from a Siemens Oncor linear accelerator by comparing simulation to measurement. Constrain the simulation by independently determining parameters of the treatment head and incident beam, in particular, the energy and spot size.Methods: Measurements were done with the treatment head in three different configurations: (1) The clinical configuration, (2) the flattening filter removed, and (3) the target and flattening filter removed. Parameters of the incident beam and treatment head were measured directly. Incident beam energy and spectral width were determined from the percent-depth ionization of the raw beam (as described previously), spot size was determined using a spot camera, and the densities of the flattening filters were determined by weighing them. Simulations were done with EGSnrc/BEAMnrc code. An asymmetric simulation was used, including offsets of the spot, primary collimator, and flattening filter from the collimator rotation axis.Results: Agreement between measurement and simulation was obtained to the least restrictive of 1% or 1 mm at 6 MV, both with and without the flattening filter in place, except for the buildup region. At 18 MV, the agreement was 1.5%/1.5 mm with the flattening filter in place and 1%/1 mm with it removed, except for in the buildup region. In the buildup region, the discrepancy was 2%/2 mm at 18 MV and 1.5%/1.5 mm at 6 MV with the flattening filter either removed or in place. The methodology for measuring the source and geometry parameters for the treatment head simulation is described. Except to determine the density of the flattening filter, no physical modification of the treatment head is necessary to obtain those parameters. In particular, the flattening filter does not need to be removed as was done in this work.Conclusions: Good agreement between measured and simulated dose distributions was obtained, even in the buildup region. The simulation was tightly constrained by independent measurements of parameters of the incident beam and treatment head. The method of obtaining the input parameters is described, and can be carried out on a clinical linear accelerator. (C) 2009 American Association of Physicists in Medicine. [DOI: 10.1118/1.3259729]