表征 Gafchromic(®) EBT2 胶片的标记染料校正：三种分析方法的比较。

Characterizing the marker-dye correction for Gafchromic(®) EBT2 film: a comparison of three analysis methods.

机构信息

Department of Medical Physics, University of Wisconsin, Madison, WI 53705, USA.

出版信息

Med Phys. 2011 Oct;38(10):5771-7. doi: 10.1118/1.3639997.

DOI:10.1118/1.3639997

PMID:21992391

Abstract

PURPOSE

Gafchromic(®) 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 (60)Co field to provide a high-spatial resolution evaluation of the film uniformity. As a reference, the flatness of the (60)Co 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.

摘要

目的

Gafchromic（®）EBT2 胶片的活性层中掺入了黄色标记染料，可用于校正胶片厚度小变化引起的响应。本工作对 EBT2 胶片剂量测量的均匀性和不准确性的标记染料校正效果进行了描述。还研究了曝光后时间变化对 EBT2 均匀性的影响。

方法

使用 EBT2 胶片测量（60）Co 场的平坦度，为胶片均匀性提供高空间分辨率评价。作为参考，（60）Co 场的平坦度也使用柯达 EDR2 胶片进行了测量。EBT2 胶片在曝光后 24、48 和 72 小时用平板文档扫描仪数字化，并使用三种方法对图像进行分析：（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。使用每种分析方法通过场中心的正交轮廓计算场平坦度，并将结果与 EDR2 测量值进行比较。通过剂量计算传播了每个分析方法的不确定性。还确定了随着曝光后时间的增加，测量的场平坦度的变化。

结果

两种标记染料校正方法都改善了 EBT2 胶片测量的场平坦度，与净 OD 方法相比，最大改善为 1%，使用制造商推荐的校正方法。然而，制造商推荐的校正方法也导致剂量不确定性比其他两种方法高一个数量级。内部标记染料校正降低了与净 OD 方法相比的剂量不确定性。测量的场平坦度没有表现出随着曝光后时间的增加而出现单向变化，最大变化为 0.3%。