Katsuda Toshizo, Gotanda Rumi, Gotanda Tatsuhiro, Akagawa Takuya, Tanki Nobuyoshi, Kuwano Tadao, Yabunaka Kouichi
Tokai Gakuin University.
J Appl Clin Med Phys. 2016 May 8;17(3):41-51. doi: 10.1120/jacmp.v17i3.5862.
This study investigates an X-ray dose measurement method for computed tomography using Gafchromic films. Nonuniformity of the active layer is a major problem in Gafchromic films. In radiotherapy, nonuniformity error is reduced by applying the double-exposure technique, but this is impractical in diagnostic radiology because of the heel effect. Therefore, we propose replacing the X-rays in the double-exposure technique with ultraviolet (UV)-A irradiation of Gafchromic EBT2 and EBT3. To improve the reproducibility of the scan position, Gafchromic EBT2 and EBT3 films were attached to a 3-mm-thick acrylic plate. The samples were then irradiated with a 10 W UV-A fluorescent lamp placed at a distance of 72cm for 30, 60, and 90 minutes. The profile curves were evaluated along the long and short axes of the film center, and the standard deviations of the pixel values were calculated over large areas of the films. Paired t-test was performed. UV-A irradiation exerted a significant effect on Gafchromic EBT2 (paired t-test; p = 0.0275) but not on EBT3 (paired t-test; p = 0.2785). Similarly, the homogeneity was improved in Gafchromic EBT2 but not in EBT3. Therefore, the double-exposure technique under UV-A irradiation is suitable only for EBT2 films.
本研究探讨了一种使用加感变色胶片进行计算机断层扫描的X射线剂量测量方法。活性层的不均匀性是加感变色胶片的一个主要问题。在放射治疗中，通过应用双曝光技术可减少不均匀性误差，但由于足跟效应，这在诊断放射学中不切实际。因此，我们建议用对加感变色EBT2和EBT3进行紫外线（UV）-A照射来替代双曝光技术中的X射线。为提高扫描位置的可重复性，将加感变色EBT2和EBT3胶片附着在一块3毫米厚的丙烯酸板上。然后，将样品用一盏10瓦的UV-A荧光灯照射，该灯放置在距离72厘米处，照射30、60和90分钟。沿着胶片中心的长轴和短轴评估轮廓曲线，并计算胶片大面积上像素值的标准差。进行配对t检验。UV-A照射对加感变色EBT2有显著影响（配对t检验；p = 0.0275），但对EBT3没有影响（配对t检验；p = 0.2785）。同样，加感变色EBT2的均匀性得到改善，但EBT3没有。因此，UV-A照射下的双曝光技术仅适用于EBT2胶片。
