Enhanced spectral discrimination through the exploitation of interface effects in photon dose data.
Enhanced spectral discrimination through the exploitation of interface effects in photon dose data.
复制标题
通过利用光子剂量数据中的界面效应增强光谱辨别力。
DOI：
10.1118/1.1637731
复制
发表时间：
2004
期刊：
影响因子：
3.8
通讯作者：
Fraass,BenedickA
中科院分区：
文献类型：
--
作者：
Charland,PauleM;Chetty,IndrinJ;Paniak,LoriD;Bednarz,BryanP;Fraass,BenedickA
用于在放射治疗计划中计算来自光子束的剂量的卷积/叠加算法需要能量谱的知识。该算法可以将多能射束的剂量计算为来自单能射束的个体剂量贡献的加权和。在这项研究中，我们利用明显的剂量分布的界面效应来区分高能光子束的光谱。我们已经研究了深度剂量分布的敏感性的能量成分，使用一个假设的光束为各种领域的大小和深度在水和水肺水介质。模拟了六个理论光谱。我们比较了深度剂量数据从这些光谱使用三个定量措施，这是固有的免费的归一化模糊性：均匀的水，在集结区的比率和对数导数和非均匀的肺/水，肺校正因子（CF）。结果发现，CF和测试区分各种理论光谱的能力上级测试。由于恢复了电子平衡，CF测试的这种鉴别能力随着场大小的增加而降低。然而，CF测试比测试有一些优势，因为它不太容易出现电子污染问题和数值误差。一个15 MV光子束的实际例子说明了这一过程。因此，我们建议，作为束流调试方法的一部分，在明确确定要使用的正确能谱时，应实施指定的电子不平衡测试用例。
The convolution/superposition algorithm for computing dose from photon beams in radiation therapy planning requires knowledge of the energy spectrum. The algorithm can compute the dose for a polyenergetic beam as the weighted sum of the individual dose contributions from monoenergetic beams. In this study we exploit interface effects apparent in the dose distributions to discriminate among spectra of high energy photon beams. We have studied the sensitivity of the depth dose distribution to the energy components using a hypothetical beam for various field sizes and depths in water and water–lung–water media. Six theoretical spectra were simulated. We compared depth dose data from these spectra using three quantitative measures which are inherently free of normalization ambiguities: for homogeneous water, the ratio and a logarithmic derivative in the buildup region and for inhomogeneous lung/water, the lung correction factor (CF). It was found that the ability of both the CF and the tests to discriminate between the various theoretical spectra were superior to that of the test. This discriminating power of the CF test decreases with increasing field size due to restored electronic equilibrium. The CF test, though, has some advantages over the test since it is less prone to electron contamination issues and numerical errors. A practical example with a 15 MV photon beam illustrates the process. Consequently, we suggest that as part of a beam‐commissioning methodology, designated electronic disequilibrium test cases be implemented in unambiguously determining the correct energy spectrum to be used.