Phys Med Biol. 2010 Aug 7;55(15):L37-42. doi: 10.1088/0031-9155/55/15/L02. Epub 2010 Jul 8.
To enhance the utility of radiochromic films for high-resolution dosimetry of small and modulated radiotherapy fields, we propose a means to negate the effects of heterogeneities in EBT2 (and other) films. The results of using our simple procedure for evaluating radiation dose in EBT2 film are compared with the results of using the manufacturer's recommended procedure as well as a procedure previously established for evaluating dose in older EBT film. It is shown that Newton's ring-like scanning artefacts can be avoided through the use of a plastic frame, to elevate the film above the scanner's surface. The effects of film heterogeneity can be minimized by evaluating net optical density, pixelwise, as the logarithm of the ratio of the red-channel pixel value in each pixel of each irradiated film to the red-channel pixel value in the same pixel in the same film prior to irradiation. The application of a blue-channel correction was found to result in increased noise. It is recommended that, when using EBT2 film for radiotherapy quality assurance, the films should be scanned before and after irradiation and analysed using the method proposed herein, without the use of the blue-channel correction, in order to produce dose images with minimal film heterogeneity effects.
为了提高光致变色胶片在小剂量和调制放疗场的高分辨率剂量测定中的实用性，我们提出了一种消除 EBT2（和其他）胶片不均匀性影响的方法。我们使用简单的程序评估 EBT2 胶片中的辐射剂量的结果与制造商推荐的程序以及先前用于评估旧 EBT 胶片中剂量的程序的结果进行了比较。结果表明，通过使用塑料框架将胶片抬高到扫描仪表面上方，可以避免牛顿环状扫描伪影。通过评估每个照射胶片中每个像素的红色通道像素值与照射前同一胶片中同一像素的红色通道像素值的比值的对数来评估净光学密度，可以最小化胶片不均匀性的影响。应用蓝色通道校正会导致噪声增加。建议在使用 EBT2 胶片进行放射治疗质量保证时，在照射前后扫描胶片，并使用本文提出的方法进行分析，而不使用蓝色通道校正，以产生具有最小胶片不均匀性影响的剂量图像。
