Butson M J, Cheung T, Yu P K N, Alnawaf H
City University of Hong Kong, Dept. of Physics and Materials Science, Kowloon Tong, Hong Kong.
Australas Phys Eng Sci Med. 2009 Dec;32(4):196-202. doi: 10.1007/BF03179239.
With new advancements in radiochromic film designs and sensitivity to suit different niche applications, EBT2 is the latest offering for the megavoltage radiotherapy market. New construction specifications including different physical construction and the use of a yellow coloured dye has provided the next generation radiochromic film for therapy applications. The film utilises the same active chemical for radiation measurement as its predecessor, EBT Gafchromic. Measurements have been performed using photo spectrometers to analyse the absorption spectra properties of this new EBT2 Gafchromic, radiochromic film. Results have shown that whilst the physical coloration or absorption spectra of the film, which turns yellow to green as compared to EBT film, (clear to blue) is significantly different due to the added yellow dye, the net change in absorption spectra properties for EBT2 are similar to the original EBT film. Absorption peaks are still located at 636nm and 585nm positions. A net optical density change of 0.590 +/- 0.020 (2SD) for a 1 Gy radiation absorbed dose using 6 MV x-rays when measured at the 636nm absorption peak was found. This is compared to 0.602 +/- 0.025 (2SD) for the original EBT film (2005 Batch) and 0.557 +/- 0.027 (2009 Batch) at the same absorption peak. The yellow dye and the new coating material produce a significantly different visible absorption spectra results for the EBT2 film compared to EBT at wavelengths especially below approximately 550nm. At wavelengths above 550nm differences in absolute OD are seen however, when dose analysis is performed at wavelengths above 550nm using net optical density changes, no significant variations are seen. If comparing results of the late production EBT to new production EBT2 film, net optical density variations of approximately 10 % to 15 % are seen. As all new film batches should be calibrated for sensitivity upon arrival this should not be of concern.
随着放射变色薄膜设计和灵敏度方面的新进展，以适应不同的特定应用，EBT2是兆伏级放射治疗市场的最新产品。新的构造规格包括不同的物理结构以及使用黄色染料，为治疗应用提供了下一代放射变色薄膜。该薄膜与之前的产品EBT Gafchromic使用相同的活性化学物质进行辐射测量。已使用光谱仪对这种新型EBT2 Gafchromic放射变色薄膜的吸收光谱特性进行了测量。结果表明，虽然该薄膜的物理着色或吸收光谱（与EBT薄膜相比，从透明变为蓝色，这里是从黄色变为绿色）由于添加了黄色染料而有显著差异，但EBT2吸收光谱特性的净变化与原始EBT薄膜相似。吸收峰仍位于636nm和585nm位置。当在636nm吸收峰处测量时，使用6MV x射线，1Gy辐射吸收剂量的净光密度变化为0.590±0.020（2标准差）。相比之下，原始EBT薄膜（2005批次）在相同吸收峰处为0.602±0.025（2标准差），2009批次为0.557±0.027。与EBT相比，黄色染料和新的涂层材料使EBT2薄膜在波长特别是低于约550nm时产生明显不同的可见吸收光谱结果。在波长高于550nm时，可以看到绝对光密度的差异，然而，当使用净光密度变化在波长高于550nm处进行剂量分析时，没有观察到显著差异。如果将后期生产的EBT与新生产的EBT2薄膜的结果进行比较，可以看到净光密度变化约为10%至15%。由于所有新的薄膜批次在到货时都应进行灵敏度校准，因此这不应成为问题。
