Accurate dosimetry with GafChromic™ EBT film of a 6 MV photon beam in water:: What level is achievable?
Accurate dosimetry with GafChromic™ EBT film of a 6 MV photon beam in water:: What level is achievable?
复制标题
DOI：
10.1118/1.2828196
复制
发表时间：
2008-02-01
期刊：
影响因子：
3.8
通讯作者：
Heukelom, S.
中科院分区：
文献类型：
--
作者：
van Batturn, L. J.;Hoffmans, D.;Heukelom, S.
本文重点研究了GafChromic (TM) EBT薄膜在6 MV、2.3 Gy剂量的光子束下在水中的绝对剂量测量精度。动机是得到一个绝对剂量检测系统来测量（水）幻体中的剂量分布，以检查剂量计算。使用爱普生1680彩色（红绿蓝）透射平板扫描仪作为薄膜扫描系统，提取红色通道中的响应并用于分析。研究了平板膜扫描仪对基于膜的剂量检测过程的影响。扫描程序已优化；例如，导出一个横向校正曲线，以校正扫描值，高达10%，作为光密度和横向位置的函数。在纵向和横向扫描模式下，对不同批次的胶片进行了灵敏度曲线评价。在不同批次之间，观察到灵敏度曲线的重要变化。薄膜的能量依赖性可以忽略不计，而对于薄膜表面和入射光子束之间的非常大的角度，可以观察到剂量响应的轻微变化。通过重复膜测量来处理至少固有存在的膜不均匀结构，可以获得绝对剂量检测的改进精度。我们指出，在绝对EBT膜剂量检测中，总体不确定度是随机的，在扫描仪上有限的中心区域扫描膜，并且至少使用了两层膜的情况下，不确定度约为1.3% （1 SD）。最后，我们建议在使用新批膜进行绝对剂量测量之前，将其特性与现有信息进行比较。(C) 2008年美国医学物理学家协会。
This paper focuses on the accuracy, in absolute dose measurements, with GafChromic (TM) EBT film achievable in water for a 6 MV photon beam up to a dose of 2.3 Gy. Motivation is to get an absolute dose detection system to measure up dose distributions in a (water) phantom, to check dose calculations. An Epson 1680 color (red green blue) transmission flatbed scanner has been used as film scanning system, where the response in the red color channel has been extracted and used for the analyses. The influence of the flatbed film scanner on the film based dose detection process was investigated. The scan procedure has been optimized; i.e. for instance a lateral correction curve was derived to correct the scan value, up to 10%, as a function of optical density and lateral position. Sensitometric curves of different film batches were evaluated in portrait and landscape scan mode. Between various batches important variations in sensitometric curve were observed. Energy dependence of the film is negligible, while a slight variation in dose response is observed for very large angles between film surface and incident photon beam. Improved accuracy in absolute dose detection can be obtained by repetition of a film measurement to tackle at least the inherent presence of film inhomogeneous construction. We state that the overall uncertainty is random in absolute EBT film dose detection and of the order of 1.3% (1 SD) under the condition that the film is scanned in a limited centered area on the scanner and at least two films have been applied. At last we advise to check a new film batch on its characteristics compared to available information, before using that batch for absolute dose measurements. (C) 2008 American Association of Physicists in Medicine.