Characterizing the marker-dye correction for Gafchromic® EBT2 film: A comparison of three analysis methods
Characterizing the marker-dye correction for Gafchromic® EBT2 film: A comparison of three analysis methods
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DOI：
10.1118/1.3639997
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发表时间：
2011-10-01
期刊：
影响因子：
3.8
通讯作者：
DeWerd, Larry A.
中科院分区：
文献类型：
--
作者：
McCaw, Travis J.;Micka, John A.;DeWerd, Larry A.
用途：Gafchromic (R) EBT2 薄膜在薄膜的活性层中加入了黄色标记染料，可用于校正薄膜对厚度微小变化的响应。这项工作描述了标记染料校正对 EBT2 胶片剂量测量的均匀性和不确定性的影响。还研究了曝光后时间变化对 EBT2 均匀性的影响。方法：使用 EBT2 薄膜测量 Co-60 场的平坦度，以提供薄膜均匀性的高空间分辨率评估。作为参考，还使用柯达 EDR2 胶片测量了 Co-60 场的平坦度。曝光后 24、48 和 72 小时，使用平板文档扫描仪对 EBT2 胶片进行数字化，并使用三种方法分析图像：(1) 制造商推荐的标记染料校正，(2) 内部标记染料校正，以及 (3) 红色通道中的净光密度 (OD) 测量。使用每种分析方法根据通过场中心的正交剖面计算场平坦度，并将结果与 EDR2 测量结果进行比较。通过每种分析方法的剂量计算来传播不确定性。还确定了随着曝光次数的增加而测量的视场平坦度的变化。结果：相对于净 OD 方法，两种标记染料校正方法都改善了使用 EBT2 胶片测量的视场平坦度，使用制造商推荐的校正时最大改善为 1%。然而，制造商建议的校正也导致剂量不确定性比其他两种方法大一个数量级。相对于净 OD 方法，内部标记染料校正降低了剂量不确定性。随着曝光时间的增加，测量的场平坦度没有表现出任何单向变化，最大变化为0.3%。结论：EBT2中的标记染料可用于改善薄膜的响应均匀性。然而，根据所使用的胶片分析方法，标记染料校正的应用可以改善或降低相对于净 OD 方法的剂量不确定性。发现 EBT2 的均匀性与曝光后的时间无关。 (C) 2011 年美国医学物理学家协会。 [DOI：10.1118/1.3639997]
Purpose: Gafchromic (R) EBT2 film has a yellow marker dye incorporated into the active layer of the film that can be used to correct the film response for small variations in thickness. This work characterizes the effect of the marker-dye correction on the uniformity and uncertainty of dose measurements with EBT2 film. The effect of variations in time postexposure on the uniformity of EBT2 is also investigated.Methods: EBT2 films were used to measure the flatness of a Co-60 field to provide a high-spatial resolution evaluation of the film uniformity. As a reference, the flatness of the Co-60 field was also measured with Kodak EDR2 films. The EBT2 films were digitized with a flatbed document scanner 24, 48, and 72 h postexposure, and the images were analyzed using three methods: (1) the manufacturer-recommended marker-dye correction, (2) an in-house marker-dye correction, and (3) a net optical density (OD) measurement in the red color channel. The field flatness was calculated from orthogonal profiles through the center of the field using each analysis method, and the results were compared with the EDR2 measurements. Uncertainty was propagated through a dose calculation for each analysis method. The change in the measured field flatness for increasing times postexposure was also determined.Results: Both marker-dye correction methods improved the field flatness measured with EBT2 film relative to the net OD method, with a maximum improvement of 1% using the manufacturer-recommended correction. However, the manufacturer-recommended correction also resulted in a dose uncertainty an order of magnitude greater than the other two methods. The in-house marker-dye correction lowered the dose uncertainty relative to the net OD method. The measured field flatness did not exhibit any unidirectional change with increasing time postexposure and showed a maximum change of 0.3%.Conclusions: The marker dye in EBT2 can be used to improve the response uniformity of the film. Depending on the film analysis method used, however, application of a marker-dye correction can improve or degrade the dose uncertainty relative to the net OD method. The uniformity of EBT2 was found to be independent of the time postexposure. (C) 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3639997]