Detector dose response in megavoltage small photon beams. I. Theoretical concepts
Detector dose response in megavoltage small photon beams. I. Theoretical concepts
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DOI：
10.1118/1.4930053
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发表时间：
2015-10-01
期刊：
影响因子：
3.8
通讯作者：
Palmans, Hugo
中科院分区：
文献类型：
--
作者：
Bouchard, Hugo;Seuntjens, Jan;Palmans, Hugo
用途：为了解释在兆伏级小光子领域的质量校正因子的原因，并澄清相关的剂量学在这种conditions.Methods的基本概念：腔理论的有效性和带电粒子平衡（CPE）的要求从理论的角度来看，在非标准光束的背景下解决。微扰效应被描述为四个主要的子效应，解释它们的性质，并指出它们在小光子field.Results的相对重要性：它表明，未能满足经典腔理论的要求，如CPE，是不是显着的质量校正因子的原因。相反，它表明，CPE的缺乏不能单独解释这些修正，什么是最重要的，除了体积平均效应，是缺乏CPE在小字段本身和探测器腔的密度之间的关系。基于Fano定理解释了密度扰动效应，描述了两种主要贡献对腔体吸收剂量的补偿作用。使用相同的方法，微扰效应所产生的腔介质的原子性质的差异和extrameral组件的存在下进行解释。体积平均效应也进行了详细的讨论。结论：小兆伏光子场的质量校正因子主要是由于水和探测器介质之间的电子密度的差异和体积平均超过探测器腔。其他的影响，如存在的extramemeral组件和不同的原子性质的检测介质相对于水，也可以发挥突出的作用，在小光子领域相比，标准光束。(C)2015年美国医学物理学家协会。
Purpose: To explain the reasons for significant quality correction factors in megavoltage small photon fields and clarify the underlying concepts relevant to dosimetry under such conditions.Methods: The validity of cavity theory and the requirement of charged particle equilibrium (CPE) are addressed from a theoretical point of view in the context of nonstandard beams. Perturbation effects are described into four main subeffects, explaining their nature and pointing out their relative importance in small photon fields.Results: It is demonstrated that the failure to meet classical cavity theory requirements, such as CPE, is not the reason for significant quality correction factors. On the contrary, it is shown that the lack of CPE alone cannot explain these corrections and that what matters most, apart from volume averaging effects, is the relationship between the lack of CPE in the small field itself and the density of the detector cavity. The density perturbation effect is explained based on Fano's theorem, describing the compensating effect of two main contributions to cavity absorbed dose. Using the same approach, perturbation effects arising from the difference in atomic properties of the cavity medium and the presence of extracameral components are explained. Volume averaging effects are also discussed in detail.Conclusions: Quality correction factors of small megavoltage photon fields are mainly due to differences in electron density between water and the detector medium and to volume averaging over the detector cavity. Other effects, such as the presence of extracameral components and differences in atomic properties of the detection medium with respect to water, can also play an accentuated role in small photon fields compared to standard beams. (C) 2015 American Association of Physicists in Medicine.