Thayer School of Engineering, Dartmouth College, Hanover, NH, 03755, USA.
DoseOptics LLC, Lebanon, NH, 03766, USA.
Med Phys. 2019 Feb;46(2):811-821. doi: 10.1002/mp.13303. Epub 2018 Dec 14.
A remote imaging system tracking Cherenkov emission was analyzed to verify that the linear accelerator (linac) beam shape could be quantitatively measured at the irradiation surface for Quality Audit (QA).
The Cherenkov camera recorded 2D dose images delivered on a solid acrylonitrile butadiene styrene (ABS) plastic phantom surface for a range of square beam sizes, and 6 MV photons. Imaging was done at source to surface distance (SSD) of 100 cm and compared to GaF film images and linac light fields of the same beam sizes, ranging over 5 × 5 cm up to 20 × 20 cm . Line profiles of each field were compared in both X and Y jaw directions. Each measurement was repeated on two different Clinac2100 machines. An interreader comparison of the beam width interpretation was completed using procedures commonly employed for beam to light field coincidence verification. Cherenkov measurements are also done for beams of complex treatment plan and isocenter QA.
The Cherenkov image widths matched with the measured GaF images and light field images, with accuracy in the range of ±1 mm standard deviation. The differences between the measurements were minor and within tolerance of geometrical requirement of standard linac QA procedures conducted by human setup verification, which had a similar error range. The measurement made by the remote imaging system allowed for beam shape extraction of radiation fields at the SSD location of the beam.
The proposed Cherenkov image acquisition system provides a valid way to remotely confirm radiation field sizes and provides similar information to that obtained from the linac light field or GaF film estimates of the beam size. The major benefit of this approach is that with a fixed installation of the camera, testing could be done completely under software control with automated image analysis, potentially simplifying conventional QA procedures with appropriate calibration of boundary definitions, and the natural extension to capturing dynamic treatment beamlets at SSD could have future value, such as verification of beam plans with complex beam shapes, like IMRT or "star-shot" QA for the isocenter.
分析一种远程成像系统，以跟踪切伦科夫发射，以验证线性加速器（linac）束形状可以在照射表面进行定量测量，以进行质量保证（QA）。
切伦科夫相机记录了在一系列方形束尺寸和 6MV 光子的固态丙烯腈丁二烯苯乙烯（ABS）塑料体模表面上传递的 2D 剂量图像。在源到表面距离（SSD）为 100cm 处进行成像，并与相同束尺寸的 GaF 胶片图像和 linac 光场进行比较，范围从 5×5cm 到 20×20cm。在 X 和 Y 颌方向上比较每个场的线轮廓。在两台不同的 Clinac2100 机器上重复进行了每个测量。使用常用于光束与光场重合验证的程序，完成了对束宽解释的读者间比较。切伦科夫测量还用于复杂治疗计划和等中心 QA 的光束。
切伦科夫图像宽度与测量的 GaF 图像和光场图像匹配，精度在±1mm 标准差范围内。测量之间的差异很小，并且在由人工设置验证进行的标准 linac QA 程序的几何要求容差内，该容差具有相似的误差范围。远程成像系统的测量允许在光束的 SSD 位置提取辐射场的束形状。
所提出的切伦科夫图像采集系统提供了一种有效的远程确认辐射场尺寸的方法，并提供了类似于从 linac 光场或 GaF 胶片估计束尺寸获得的信息。这种方法的主要优点是，通过相机的固定安装，可以在软件控制下进行完全测试，并通过自动图像分析进行测试，这可能会简化传统 QA 程序，同时适当校准边界定义，并将其自然扩展到 SSD 处捕获动态治疗射束，将来可能具有价值，例如验证具有复杂束形状的束计划，例如 IMRT 或等中心的“星射”QA。
