Shameem Tarafder, Bennie Nick, Butson Martin, Thwaites David
North Coast Cancer Institute, Lismore, NSW, Australia.
Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW, Australia.
Phys Eng Sci Med. 2024 Dec;47(4):1651-1663. doi: 10.1007/s13246-024-01478-x. Epub 2024 Sep 12.
Radiochromic film, evaluated with flatbed scanners, is used for practical radiotherapy QA dosimetry. Film and scanner component effects contribute to the Lateral Response Artefact (LRA), which is further enhanced by light polarisation from both. This study investigates the scanner bed's contribution to LRA and also polarisation from the mirrors for widely used EPSON scanners, as part of broader investigations of this dosimetry method aiming to improve processes and uncertainties. Alternative scanner bed materials were compared on a modified EPSON V700 scanner. Polarisation effects were investigated for complete scanners (V700, V800, on- and off-axis, and V850 on-axis), for a removed V700 mirror system, and independently using retail-quality single mirror combinations simulating practical scanner arrangements, but with varying numbers (0-5) and angles. Some tests had no film present, whilst others included films (EBT3) irradiated to 6 MV doses of 0-11.3 Gy. For polarisation analysis, images were captured by a Canon 7D camera with 50 mm focal length lens. Different scanner bed materials showed only small effects, within a few percent, indicating that the normal glass bed is a good choice. Polarisation varied with scanner type (7-11%), increasing at 10 cm lateral off-axis distance by around a further 6%, and also with film dose. The V700 mirror system showed around 2% difference to the complete scanner. Polarization increased with number of mirrors in the single mirror combinations, to 14% for 4 and 5 mirrors, but specific values depend on angles and mirror quality. Novel film measurement methods could reduce LRA effect corrections and associated uncertainties.
用平板扫描仪评估的放射变色胶片用于实际放射治疗质量保证剂量测定。胶片和扫描仪组件的影响会导致横向响应伪影（LRA），而两者的光偏振会进一步增强这种伪影。本研究调查了扫描仪床对LRA的贡献以及广泛使用的爱普生扫描仪中镜子的偏振情况，这是旨在改进该剂量测定方法的过程和不确定性的更广泛研究的一部分。在改良的爱普生V700扫描仪上比较了替代扫描仪床材料。研究了完整扫描仪（V700、V800、轴上和轴外以及V850轴上）、拆除的V700镜子系统的偏振效应，并独立使用模拟实际扫描仪配置但数量（0 - 5）和角度不同的零售质量单镜组合进行研究。一些测试没有放置胶片，而其他测试包括照射到0 - 11.3 Gy的6 MV剂量的胶片（EBT3）。对于偏振分析，使用佳能7D相机搭配50毫米焦距镜头拍摄图像。不同的扫描仪床材料仅显示出百分之几的小影响，表明普通玻璃床是一个不错的选择。偏振随扫描仪类型而变化（7 - 11%），在横向离轴10厘米处增加约6%，并且还随胶片剂量而变化。V700镜子系统与完整扫描仪相比显示出约2%的差异。单镜组合中偏振随镜子数量增加，4面镜和5面镜时达到14%，但具体值取决于角度和镜子质量。新颖的胶片测量方法可以减少LRA效应校正和相关的不确定性。
