Characterization of electron contamination in megavoltage photon beams
Characterization of electron contamination in megavoltage photon beams
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DOI：
10.1118/1.1895793
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发表时间：
2005-05-01
期刊：
影响因子：
3.8
通讯作者：
Esperon, J
中科院分区：
文献类型：
--
作者：
Medina, AL;Teijeiro, A;Esperon, J
本研究的目的是表征在不同的临床情况下的光子束中的电子污染。研究了射野大小、射束修改器（托盘、成形块）和源-表面距离（SSD）的变化。在有和没有净化磁体以及用氦气代替空气的情况下进行了百分比深度剂量测量，以确定两种明显不同的电子源：空气和治疗头。利用已有的分析方法对实测数据进行拟合，探讨了模型的有效性。治疗头中产生的电子能量更大，对于更大的场尺寸、更短的SSD和更大的深度更重要。这种差异对于18 MV射束比对于6 MV射束更明显。如果.使用托盘作为射束调节器，电子污染增加，但这些电子的能量与来自治疗头的电子的能量相似。电子污染可以用修正的指数曲线拟合。对于治疗计划系统中的机器建模，将输入数据的SSD设置为90 cm可以减少大多数等中心治疗的错误，因为它们将在80至100 cm的SSD范围内进行输送。对于非常小的场尺寸，空气产生的电子必须被独立地考虑，因为它们不同的能量谱和剂量影响。(c)2005年美国医学物理学家协会。
The purpose of the present study is to characterize electron contamination in photon beams in different clinical situations. Variations with field size, beam modifier (tray, shaping block) and source-surface distance (SSD) were studied. Percentage depth dose measurements with and without a purging magnet and replacing the air by helium were performed to identify the two electron sources that are clearly differentiated: air and treatment head. Previous analytical methods were used to fit the measured data, exploring the validity of these models. Electrons generated in the treatment head are more energetic and more important for larger field sizes, shorter SSD, and greater depths. This difference is much more noticeable for the 18 MV beam than for the 6 MV beam. If. a tray is used as beam modifier, electron contamination increases, but the energy of these electrons is similar to that of electrons coming from the treatment head. Electron contamination could be fitted to a modified exponential curve. For machine modeling in a treatment planning system, setting SSD at 90 cm for input data could reduce errors for most isocentric treatments, because they will be delivered for SSD ranging from 80 to 100 cm. For very small field sizes, air-generated electrons must be considered independently, because of their different energetic spectrum and dosimetric influence. (c) 2005 American Association of Physicists in Medicine.