GafChromic EBT film dosimetry with flatbed CCD scanner: A novel background correction method and full dose uncertainty analysis
GafChromic EBT film dosimetry with flatbed CCD scanner: A novel background correction method and full dose uncertainty analysis
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DOI：
10.1118/1.2938522
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发表时间：
2008-07-01
期刊：
影响因子：
3.8
通讯作者：
Frengen, Jomar
中科院分区：
文献类型：
--
作者：
Saur, Sigrun;Frengen, Jomar
使用辐射变色EBT胶片结合平板电荷耦合器件扫描仪的胶片剂量测定是一种有用的方法，既可用于强度调制辐射治疗计划的二维验证，也可用于治疗计划系统和直线加速器的一般质量保证。不幸的是，在扫描器区域上的响应是不均匀的，并且当不进行校正时，这导致所测量的剂量中的系统误差，该系统误差是剂量和位置相关的。提出了一种新的背景校正方法。该方法基于校正矩阵的减法，校正矩阵基于被照射到0.08-2.93戈伊范围内的九个剂量水平的胶片的扫描。由于胶片的响应取决于胶片相对于扫描仪的方向，因此制作了横向和纵向扫描的校正矩阵。除了本底校正方法外，还对胶片剂量测定程序进行了全剂量不确定性分析。该分析考虑了校准曲线的拟合不确定性、不同胶片响应的变化、背景校正后的不均匀性以及扫描胶片中的噪声。对尺寸为16 x 16 cm的薄膜片进行薄膜分析，所有薄膜片均具有相同的批号，并且所有辐照均垂直于薄膜进行。结果表明，在2戈伊的2-sigma剂量不确定性是约5%和3.5%的横向和纵向扫描，分别。随着剂量的降低，不确定性逐渐增加，但在1戈伊时，横向和纵向扫描的2-sigma剂量不确定性仍然分别为6%和4%。研究表明，使用GafChromic（R）EBT胶片、Epson Expression 1680 Professional扫描仪和专用背景校正技术进行的胶片剂量测定可提供精确和准确的结果。为了进行剂量测定验证，对于1 - 3戈伊之间的剂量，可以使用4%的剂量约束（相对于测量剂量）将计算的剂量分布与胶片测量的剂量分布进行比较。在较低剂量下，必须放松剂量限制。(C)2008年美国医学物理学家协会。
Film dosimetry using radiochromic EBT film in combination with a flatbed charge coupled device scanner is a useful method both for two-dimensional verification of intensity-modulated radiation treatment plans and for general quality assurance of treatment planning systems and linear accelerators. Unfortunately, the response over the scanner area is nonuniform, and when not corrected for, this results in a systematic error in the measured dose which is both dose and position dependent. In this study a novel method for background correction is presented. The method is based on the subtraction of a correction matrix, a matrix that is based on scans of films that are irradiated to nine dose levels in the range 0.08-2.93 Gy. Because the response of the film is dependent on the film's orientation with respect to the scanner, correction matrices for both landscape oriented and portrait oriented scans were made. In addition to the background correction method, a full dose uncertainty analysis of the film dosimetry procedure was performed. This analysis takes into account the fit uncertainty of the calibration curve, the variation in response for different film sheets, the nonuniformity after background correction, and the noise in the scanned films. The film analysis was performed for film pieces of size 16 x 16 cm, all with the same lot number, and all irradiations were done perpendicular onto the films. The results show that the 2-sigma dose uncertainty at 2 Gy is about 5% and 3.5% for landscape and portrait scans, respectively. The uncertainty gradually increases as the dose decreases, but at 1 Gy the 2-sigma dose uncertainty is still as good as 6% and 4% for landscape and portrait scans, respectively. The study shows that film dosimetry using GafChromic (R) EBT film, an Epson Expression 1680 Professional scanner and a dedicated background correction technique gives precise and accurate results. For the purpose of dosimetric verification, the calculated dose distribution can be compared with the film-measured dose distribution using a dose constraint of 4% (relative to the measured dose) for doses between 1 and 3 Gy. At lower doses, the dose constraint must be relaxed. (C) 2008 American Association of Physicists in Medicine.