Hiroshima High-Precision Radiotherapy Cancer Center, Hiroshima, Japan.
Department of Radiation Oncology, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan.
J Appl Clin Med Phys. 2024 Aug;25(8):e14373. doi: 10.1002/acm2.14373. Epub 2024 May 2.
Lateral response artifact (LRA) is caused by the interaction between film and flatbed scanner in the direction perpendicular to the scanning direction. This can significantly affect the accuracy of patient-specific quality assurance (QA) in cases involving large irradiation fields. We hypothesized that by utilizing the central area of the flatbed scanner, where the magnitude of LRA is relatively small, the LRA could be mitigated effectively. This study proposes a practical solution using the image-stitching technique to correct LRA for patient-specific QA involving large irradiation fields.
Gafchromic™ EBT4 film and Epson Expression ES-G11000 flatbed scanner were used in this study. The image-stitching algorithm requires a spot between adjacent images to combine them. The film was scanned at three locations on a flatbed scanner, and these images were combined using the image-stitching technique. The combined film dose was then calculated and compared with the treatment planning system (TPS)-calculated dose using gamma analysis (3%/2 mm). Our proposed LRA correction was applied to several films exposed to 18 × 18 cm open fields at doses of 200, 400, and 600 cGy, as well as to four clinical Volumetric Modulated Arc Therapy (VMAT) treatment plans involving large fields.
For doses of 200, 400, and 600 cGy, the gamma analysis values with and without LRA corrections were 95.7% versus 67.8%, 95.5% versus 66.2%, and 91.8% versus 35.9%, respectively. For the clinical VMAT treatment plan, the average pass rate ± standard deviation in gamma analysis was 94.1% ± 0.4% with LRA corrections and 72.5% ± 1.5% without LRA corrections.
The effectiveness of our proposed LRA correction using the image-stitching technique was demonstrated to significantly improve the accuracy of patient-specific QA for VMAT treatment plans involving large irradiation fields.
侧向响应伪影（LRA）是由胶片与平板扫描仪在与扫描方向垂直的方向上相互作用引起的。这会显著影响大照射野情况下患者特定质量保证（QA）的准确性。我们假设，通过利用平板扫描仪的中心区域，其中 LRA 的幅度相对较小，可以有效地减轻 LRA。本研究提出了一种实用的解决方案，即使用图像拼接技术来校正大照射野情况下的患者特定 QA 的 LRA。
本研究使用 Gafchromic™ EBT4 胶片和 Epson Expression ES-G11000 平板扫描仪。图像拼接算法需要在相邻图像之间有一个点来组合它们。胶片在平板扫描仪上的三个位置进行扫描，并使用图像拼接技术将这些图像组合在一起。然后计算组合胶片剂量，并与使用伽马分析（3%/2 毫米）的治疗计划系统（TPS）计算剂量进行比较。我们提出的 LRA 校正应用于几张在 200、400 和 600 cGy 剂量下暴露于 18×18 cm 开放野的胶片，以及涉及大野的四个临床容积调制弧形治疗计划（VMAT）。
对于 200、400 和 600 cGy 的剂量，有和没有 LRA 校正的伽马分析值分别为 95.7% 对 67.8%、95.5% 对 66.2% 和 91.8% 对 35.9%。对于临床 VMAT 治疗计划，在有和没有 LRA 校正的情况下，伽马分析的平均通过率±标准偏差分别为 94.1%±0.4%和 72.5%±1.5%。
使用图像拼接技术的我们提出的 LRA 校正的有效性证明，可以显著提高涉及大照射野的 VMAT 治疗计划的患者特定 QA 的准确性。
