Cheung Tsang, Butson Martin J, Yu Peter K N
Deptment of Physics and Materials Science, City University of Hong Kong, Kowloon Tong, Hong Kong.
Phys Med Biol. 2005 Oct 21;50(20):N281-5. doi: 10.1088/0031-9155/50/20/N04. Epub 2005 Oct 4.
Gafchromic EBT (International Specialty Products, NJ, USA), radiochromic film is one of the newest radiation-induced auto-developing x-ray analysis films available for therapeutic radiation dosimetry in radiotherapy applications. Part of any radiochromic film product which undergoes a polymerization reaction for automatic darkening is an associated post-irradiation colouration whereby the film continues to darken after irradiation has ceased. The Gafchromic EBT film has been shown to produce an approximate 6% to 9% increase in post-irradiation optical density within the first 12 h of irradiation within the 1 Gy to 5 Gy dose range. This is compared to approximately 13%, 15% and 19% for MD-55-2, XR type T and HS radiochromic film, respectively. It is also shown that the EBT film's post-irradiation growth stabilizes to within 1% within the first 6 h. Thus EBT provides a reduced post-irradiation growth effect. However, to increase the accuracy of the film analysis, it is recommended that films be left for a significant period (at least 6 h) before the analysis is performed to provide a high level of accuracy. Also, calibration films must be read out with the same post-irradiation time to further enhance the accuracy of dosimetry.
Gafchromic EBT（国际特殊产品公司，美国新泽西州）放射变色胶片是最新的辐射诱导自动显影X射线分析胶片之一，可用于放射治疗应用中的治疗辐射剂量测定。任何经历聚合反应以自动变黑的放射变色胶片产品的一部分是相关的辐照后着色，即胶片在辐照停止后继续变黑。已证明Gafchromic EBT胶片在1 Gy至5 Gy剂量范围内辐照的前12小时内，辐照后光密度会增加约6%至9%。相比之下，MD - 55 - 2、XR型T和HS放射变色胶片的这一数值分别约为13%、15%和19%。还表明EBT胶片的辐照后增长在最初6小时内稳定在1%以内。因此，EBT提供了降低的辐照后增长效应。然而，为了提高胶片分析的准确性，建议在进行分析之前将胶片放置相当长的一段时间（至少6小时），以提供高水平的准确性。此外，校准胶片必须在相同的辐照后时间读出，以进一步提高剂量测定的准确性。
