A novel verification method using a plastic scintillator imagining system for assessment of gantry sag in radiotherapy
A novel verification method using a plastic scintillator imagining system for assessment of gantry sag in radiotherapy
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DOI：
10.1002/mp.12922
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发表时间：
2018-06-01
期刊：
影响因子：
3.8
通讯作者：
Nagata, Yasushi
中科院分区：
文献类型：
--
作者：
Tsuneda, Masato;Nishio, Teiji;Nagata, Yasushi
目的：对于诸如立体定向体放射治疗（SBRT）、体积调制弧治疗（VMAT）和强度调制放射治疗（IMRT）的高精度放射治疗，需要束照射位置的高精度。用户通常使用星星发射测试和Winston Lutz测试（允许评价等中心点处的位移）来验证机械和辐射等中心点。然而，这些方法无法直接且定量地评估由机架本身的重量沿机架旋转轴沿着引起的下垂角。此外，对于非等中心照射技术的机械质量保证，需要验证不依赖于等中心的照射束的中心轴。在这项研究中，我们已经开发了一个原型系统的验证三维（3D）光束对准，我们已经验证了系统的概念，三维等中心。我们的系统允许在3D坐标中检测中心轴并评估与机架旋转轴的照射倾斜角，即，材料与方法：为了测量三维坐标系中照射光束的中心轴，我们构建了由柱形塑料闪烁体（CoPS）、截锥形反射镜（TCsM）和冷却电荷耦合器件（CCD）相机组成的原型验证系统。用6 MV光子束照射该验证系统，并使用CCD相机测量闪烁光。轴平面上的中心轴（二维（2D）中心轴）是从闪烁光沿CoPS的长轴沿着的积分获得的，并且3D坐标中的中心轴（3D中心轴）是从由TCsM反射的两个曲线形状的轮廓获得的。我们验证了机架旋转轴O的计算精度。结果：获得了由二维中心轴和两个曲线轮廓组成的测量图像。相对于机架旋转轴的照射角度和测量角度之间的关系具有良好的线性。照射角度和测量角度之间的差异的平均值和标准差分别为0.012度和0.078度。2D和3D辐射等中心的尺寸在轴向平面和3D坐标上分别为0.470和0.652 mm。下垂角分别为0.31，0.39和0.38度，在机架角度为0，180，和180E degrees.Conclusion：我们开发了一种新的验证系统，指定为“kompeito射击测试系统”，以验证三维光束对准。该系统概念适用于3D等中心度的验证和下垂角的直接评估。接下来，我们想要改进该系统的各个方面，例如闪烁体的形状和类型，以提高系统精度和非等中心光束对准性能。(C)2018年美国医学物理学家协会
Purpose: High accuracy of the beam-irradiated position is required for high-precision radiation therapy such as stereotactic body radiation therapy (SBRT), volumetric modulated arc therapy (VMAT), and intensity modulated radiation therapy (IMRT). Users generally perform the verification of the mechanical and radiation isocenters using the star shot test and the Winston Lutz test that allow evaluation of the displacement at the isocenter. However, these methods are unable to evaluate directly and quantitatively the sagging angle that is caused by the weight of the gantry itself along the gantry rotation axis. In addition, the verification of the central axis of the irradiated beam that is not dependent at the isocenter is needed for the mechanical quality assurance of a nonisocentric irradiation technique. In this study, we have developed a prototype system for the verification of three-dimensional (3D) beam alignment and we have verified the system concept for 3D isocentricity. Our system allows detection of the central axis in 3D coordinates and evaluation of the irradiated oblique angle to the gantry rotation axis, i.e., the sagging angle.Materials & Methods: In order to measure the central axis of the irradiated beam in 3D coordinates, we constructed the prototype verification system consisting of a column-shaped plastic scintillator (CoPS), a truncated cone-shaped mirror (TCsM), and a cooled charged-coupled device (CCD) camera. This verification system was irradiated with 6-MV photon beams and the scintillation light was measured using the CCD camera. The central axis on the axial plane (two-dimensional (2D) central axis) was acquired from the integration of the scintillation light along the major axis of the CoPS, and the central axis in 3D coordinates (3D central axis) was acquired from two curve-shaped profiles which were reflected by the TCsM. We verified the calculation accuracy of the gantry rotation axis, O,. Additionally, we calculated the 3D central axis and the sagging angle at each gantry angle.Results: We acquired the measurement images composed of the 2D central axis and the two curve shaped profiles. The relationship between the irradiated and measured angles with respect to the gantry rotation axis had good linearity. The mean and standard deviation of the difference between the irradiated and measured angles were 0.012 and 0.078 degrees, respectively. The size of the 2D and 3D radiation isocenters were 0.470 and 0.652 mm on the axial plane and in 3D coordinates, respectively. The sagging angles were 0.31, 0.39, and 0.38 degrees at the gantry angles of 0, 180, and 180E degrees, respectively.Conclusion: We developed a novel verification system, designated as the "kompeito shot test system," to verify the 3D beam alignment. This system concept works for both verification of the 3D isocentricity and the direct evaluation of the sagging angle. Next, we want to improve the aspects of this system, such as the shape and the type of scintillator, to increase the system accuracy and nonisocentric beam alignment performance. (C) 2018 American Association of Physicists in Medicine