Katsuda Toshizo, Gotanda Rumi, Gotanda Tatsuhiro, Akagawa Takuya, Tanki Nobuyoshi, Kuwano Tadao, Yabunaka Kouichi
Tokai Gakuin University.
J Appl Clin Med Phys. 2015 Sep 8;16(5):427–434. doi: 10.1120/jacmp.v16i5.5664.
Gafchromic film has been used for X-ray dose measurement in diagnostic examinations. Their use has been initiated for three-dimensional X-ray dose measurement by using the high-resolution characteristics of Gafchromic films in computed tomography. However, it is necessary to solve the problem of nonuniform thickness in the active layers of Gafchromic films. A double exposure technique using X-rays is performed in therapeutic radiology; it is difficult to use in a diagnostic examination because of the heel effect. Therefore, it is suggested that ultraviolet (UV) rays be substituted for X-rays. However, the appropriate UV wavelength is unknown. In this study, we aimed to determine which UV wavelengths are effective to expose Gafchromic XR-RV3 and XR-SP2. UV lamps with peak wavelengths of 245 nm, 310 nm, and 365 nm were used. The three UV wavelengths were used to irradiate Gafchromic XR-RV3 and XR-SP2 films for 60 min, and irradiation was repeated every 60 min for 600 min thereafter. Films were scanned after each irradiation period on a flatbed scanner. The images were split into their red-green-blue components, and red images were stored using ImageJ version 1.44o image analysis software. Regions of interest (ROI), 0.5 inches in diameter, were placed at the centers of the subtracted Gafchromic film images, and graphs of UV irradiation duration and mean pixel values were plotted. There were reactions to UV-A on both Gafchromic XR-RV3 and XR-SP2; those to UV-B were moderate. However, UV-C demonstrated few reactions with Gafchromic XR-RV3 and XR-SP2. From these results, irradiation with UV-A may be able to correct nonuniformity errors. Uniform UV-A irradiation of Gafchromic films with large areas is possible, and UV rays can be used as a substitute for X-rays in the double exposure technique.
放射变色薄膜已用于诊断检查中的X射线剂量测量。利用放射变色薄膜在计算机断层扫描中的高分辨率特性，已开始将其用于三维X射线剂量测量。然而，有必要解决放射变色薄膜活性层厚度不均匀的问题。在放射治疗中采用了使用X射线的双重曝光技术；由于足跟效应，该技术难以用于诊断检查。因此，有人建议用紫外线（UV）代替X射线。然而，合适的紫外线波长尚不清楚。在本研究中，我们旨在确定哪些紫外线波长对放射变色XR-RV3和XR-SP2薄膜曝光有效。使用了峰值波长为245 nm、310 nm和365 nm的紫外线灯。用这三种紫外线波长对放射变色XR-RV3和XR-SP2薄膜照射60分钟，此后每隔60分钟重复照射一次，共照射600分钟。每次照射后，在平板扫描仪上扫描薄膜。将图像分解为红-绿-蓝分量，并使用ImageJ 1.44o图像分析软件存储红色图像。在减去背景后的放射变色薄膜图像中心放置直径为0.5英寸的感兴趣区域（ROI），并绘制紫外线照射持续时间与平均像素值的图表。放射变色XR-RV3和XR-SP2对UV-A均有反应；对UV-B的反应中等。然而，UV-C对放射变色XR-RV3和XR-SP2几乎没有反应。根据这些结果，UV-A照射可能能够校正不均匀误差。对大面积放射变色薄膜进行均匀的UV-A照射是可行的，并且紫外线可以在双重曝光技术中用作X射线的替代品。
