Department of Oncology and Experimental Radiation Oncology, University of Leuven, Belgium.
Med Phys. 2007 Jul;34(7):2917-27. doi: 10.1118/1.2745239.
This article provides a quantitative evaluation of Varian Medical Systems' beam matching procedure. A one-dimensional y analysis is employed to investigate the level of agreement of matched beams. A customized concept of one-dimensional gamma evaluation was designed. Our algorithm first performs a "local" fit of the reference and the evaluated datasets. For a particular point on the fitted evaluated curve, the y is derived as the shortest distance between the point and the fitted reference curve. This approach removes variations of the obtained y value related to the discrete character and noise in the original datasets. Criteria of 1 mm distance-to-agreement and 1% dose difference were used to evaluate the level of agreement of according profiles. Relative point and profile measurements were performed for all photon and electron beams of two Varian Clinacs 2100C/D. Matched beams show a good level of agreement. 70% of profiles completely pass the chosen criteria. The analysis of remaining 30% of the profiles demonstrates that measurement error becomes a limiting factor in achieving a better score. The highest obtained y value was 1.70. The quality of beam matching allowed us to treat according beams of both treatment units as "identical" and to use the reference beam data for the new unit. Nevertheless, the vendor's acceptance criteria of beam matching are much more benevolent. It might happen that the acceptance criteria are met, however, resulting quality of beam matching does not allow full interchangeability of beams.
本文对瓦里安医疗系统的射束匹配程序进行了定量评估。采用一维γ分析来评估匹配射束的一致性程度。设计了一种定制的一维伽马评估概念。我们的算法首先对参考数据集和评估数据集进行“局部”拟合。对于拟合评估曲线上的特定点，y 定义为该点与拟合参考曲线之间的最短距离。这种方法消除了与原始数据集的离散特征和噪声相关的 y 值变化。采用 1mm 距离一致性和 1%剂量差异标准来评估相应射束轮廓的一致性水平。对两台瓦里安 Clinacs 2100C/D 的所有光子和电子射束进行了相对点和相对射束轮廓测量。匹配射束显示出良好的一致性水平。70%的轮廓完全符合所选标准。对其余 30%的轮廓进行分析表明，测量误差成为获得更好分数的限制因素。获得的最高 y 值为 1.70。射束匹配的质量使我们能够将两个治疗单元的相应射束视为“相同”，并使用参考射束数据对新单元进行治疗。然而，束匹配的供应商验收标准要宽松得多。虽然可能符合验收标准，但最终的束匹配质量不允许射束完全互换。
