Schoenfeld Andreas A, Wieker Soeren, Harder Dietrich, Poppe Bjoern
Clinic of Radiotherapy and Radiation Oncology, Medical Radiation Physics, Pius-Hospital, Carl-von-Ossietzky University, Oldenburg, Germany.
Phys Med Biol. 2016 Nov 7;61(21):7704-7724. doi: 10.1088/0031-9155/61/21/7704. Epub 2016 Oct 14.
The optical origin of the lateral response and orientation artifacts, which occur when using EBT3 and EBT-XD radiochromic films together with flatbed scanners, has been reinvestigated by experimental and theoretical means. The common feature of these artifacts is the well-known parabolic increase in the optical density OD(x) = -log I(x)/I (x) versus offset x from the scanner midline (Poppinga et al 2014 Med. Phys. 41 021707). This holds for landscape and portrait orientations as well as for the three color channels. Dose-independent optical subjects, such as neutral density filters, linear polarizers, the EBT polyester foil and diffusive glass, also present the parabolic lateral artifact when scanned with a flatbed scanner. The curvature parameter c of the parabola function OD(x) = c + cx is found to be a linear function of the dose, the parameters of which are influenced by the film orientation and film type, EBT3 or EBT-XD. The ubiquitous parabolic shape of function OD(x) is attributed (a) to the optical path-length effect (van Battum et al 2016 Phys. Med. Biol. 61 625-49), due to the increasing obliquity of the optical scanner light associated with increasing offset x from the scanner midline, and (b) and (c) to the partial polarization and scattering of the light leaving the film, which affect the ratio [Formula: see text], thus making OD(x) increase with x . The orientation effect results from the changes of effects (b) and (c) associated with turning the film position, and thereby the orientation of the polymer structure of the sensitive film layer. In a comparison of experimental results obtained with selected optical subjects, the relative weights of the contributions of the optical path-length effect and the polarization and scattering of light leaving the films to the lateral response artifact have been estimated to be of the same order of magnitude. Mathematical models of these causes for the parabolic shape of function OD(x) are given as appendices.
使用EBT3和EBT-XD放射变色薄膜与平板扫描仪一起时出现的横向响应和取向伪影的光学起源，已通过实验和理论方法重新进行了研究。这些伪影的共同特征是光密度OD(x)= -log I(x)/I₀(x)相对于从扫描仪中线的偏移x呈现出众所周知的抛物线形增加（Poppinga等人，2014年，《医学物理》，41卷，021707）。这适用于横向和纵向取向以及三个颜色通道。与剂量无关的光学对象，如中性密度滤光片、线性偏振器、EBT聚酯薄膜和漫射玻璃，在用平板扫描仪扫描时也会出现抛物线形横向伪影。抛物线函数OD(x)= c₀ + c₁x²的曲率参数c被发现是剂量的线性函数，其参数受薄膜取向和薄膜类型（EBT3或EBT-XD）的影响。函数OD(x)普遍存在的抛物线形状归因于：(a) 光程长度效应（van Battum等人，2016年，《物理医学与生物学》，61卷，625 - 49），这是由于与从扫描仪中线增加的偏移x相关的光学扫描仪光的倾斜度增加；以及(b) 和(c) 离开薄膜的光的部分偏振和散射，这会影响比率[公式：见正文]，从而使OD(x)随x增加。取向效应源于与转动薄膜位置相关的(b) 和(c) 效应的变化，进而源于敏感薄膜层聚合物结构的取向变化。在对选定光学对象获得的实验结果进行比较时，光程长度效应以及离开薄膜的光的偏振和散射对横向响应伪影的贡献的相对权重估计处于相同数量级。这些导致函数OD(x)呈抛物线形状的原因的数学模型在附录中给出。
