Detector dose response in megavoltage small photon beams. II. Pencil beam perturbation effects
Detector dose response in megavoltage small photon beams. II. Pencil beam perturbation effects
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DOI：
10.1118/1.4930798
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发表时间：
2015-10-01
期刊：
影响因子：
3.8
通讯作者：
Duane, Simon
中科院分区：
文献类型：
--
作者：
Bouchard, Hugo;Kamio, Yuji;Duane, Simon
目的：为了量化探测器的微扰效应在兆伏级小光子领域，并支持在这些conditions.Methods质量校正因子的性质的理论解释：在这第二篇论文中，辐射剂量学的现代方法定义为任何探测器和应用到小光子领域。法诺定理适用于腔理论的形式，并应用于非标准光束，以扰动因子的形式表示四个主要效应。文中详细介绍了微扰因子和质量修正因子的计算方法-光束分解法。该方法定义了一个扰动函数，对于一个给定的字段大小或光束调制，完全确定这些剂量因子。Monte Carlo计算在不同的腔体尺寸为不同的检测材料，电子密度，和extraameral component.Results：微扰效应详细计算的扰动函数，显示的相对大小的影响，以及几何程度准直或调制的光束影响的剂量因素。周围的探测器腔的扰动区的存在被证明和方法进行了讨论，并链接到以前的方法在文献中，以确定临界字段sizes.Conclusions：蒙特卡罗模拟是有价值的笔形束扰动效应和详细的性质，在兆伏级小光子场的剂量因素。在实践中，它表明，剂量测定因素可以避免，如果字段的大小仍然大于探测器扰动区。然而，给定探测器和光束质量，必须充分考虑探测器的几何形状以确定临界场尺寸。(C)2015年美国医学物理学家协会。
Purpose: To quantify detector perturbation effects in megavoltage small photon fields and support the theoretical explanation on the nature of quality correction factors in these conditions.Methods: In this second paper, a modern approach to radiation dosimetry is defined for any detector and applied to small photon fields. Fano's theorem is adapted in the form of a cavity theory and applied in the context of nonstandard beams to express four main effects in the form of perturbation factors. The pencil-beam decomposition method is detailed and adapted to the calculation of perturbation factors and quality correction factors. The approach defines a perturbation function which, for a given field size or beam modulation, entirely determines these dosimetric factors. Monte Carlo calculations are performed in different cavity sizes for different detection materials, electron densities, and extracameral components.Results: Perturbation effects are detailed with calculated perturbation functions, showing the relative magnitude of the effects as well as the geometrical extent to which collimating or modulating the beam impacts the dosimetric factors. The existence of a perturbation zone around the detector cavity is demonstrated and the approach is discussed and linked to previous approaches in the literature to determine critical field sizes.Conclusions: Monte Carlo simulations are valuable to describe pencil beam perturbation effects and detail the nature of dosimetric factors in megavoltage small photon fields. In practice, it is shown that dosimetric factors could be avoided if the field size remains larger than the detector perturbation zone. However, given a detector and beam quality, a full account for the detector geometry is necessary to determine critical field sizes. (C) 2015 American Association of Physicists in Medicine.