On the selection of gantry and collimator angles for isocenter localization using Winston-Lutz tests.
On the selection of gantry and collimator angles for isocenter localization using Winston-Lutz tests.
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DOI：
10.1120/jacmp.v17i1.5792
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发表时间：
2016-01-08
影响因子：
2.1
通讯作者：
Kudchadker RJ
中科院分区：
文献类型：
--
作者：
Du W;Johnson JL;Jiang W;Kudchadker RJ
在Winston‐Lutz（WL）测试中，直线加速器（直线加速器）的等中心点被确定为来自多个机架、准直器和治疗床角度的辐射中心轴（CAX）的交点。众所周知，由于直线加速器的机械缺陷，CAX会摆动。先前的研究表明，摆动随机架和准直器角度而变化。因此，WL测试中确定的等中心点严重依赖于CAX采样的机架和准直器角度。在这项研究中，我们评估了系统和随机误差的等角点确定不同的CAX采样方案。在六个直线加速器上进行了数字WL测试。对于每个WL测试，在9个机架角度和7个准直器角度下对63个CAX进行采样。这些数据的子集被用来模拟各种CAX抽样方案的影响。从CAX的每个子集计算等中心点，并与参考等中心点进行比较，参考等中心点是从48个相对的CAX计算的。计算的等中心点和参考等中心点之间的差异范围从0到0.8 mm。当24个或更多CAX采样时，差异减小到小于0.2 mm。0°准直仪测得的等中心线垂直方向低于90°和270°准直仪测得的等中心线。纵向（沿着机架旋转轴）的等中心定位误差显示出对所选准直器角度的强烈依赖性。当采用相对的准直器角度和相对的机架角度时，在所有方向上的误差显著减小。等中心定位误差小于0.2毫米与常见的CAX采样方案，其中使用四个基数机架角度和两个相对的准直器角度。在一台直线加速器上的再现性研究表明，在WL测试期间，CAX的平均和最大变化分别为0.053 mm和0.30 mm。如果使用48个CAX，则所得等中心点的最大变化为0.068 mm，或者如果使用4个CAX，则为0.13 mm。本研究的定量结果有助于理解WL测试中的等中心不确定性并将其最小化。PACS编号：87.56.Fc
In Winston‐Lutz (WL) tests, the isocenter of a linear accelerator (linac) is determined as the intersection of radiation central axes (CAX) from multiple gantry, collimator, and couch angles. It is well known that the CAX can wobble due to mechanical imperfections of the linac. Previous studies suggested that the wobble varies with gantry and collimator angles. Therefore, the isocenter determined in the WL tests has a profound dependence on the gantry and collimator angles at which CAX are sampled. In this study, we evaluated the systematic and random errors in the isocenters determined with different CAX sampling schemes. Digital WL tests were performed on six linacs. For each WL test, 63 CAX were sampled at nine gantry angles and seven collimator angles. Subsets of these data were used to simulate the effects of various CAX sampling schemes. An isocenter was calculated from each subset of CAX and compared against the reference isocenter, which was calculated from 48 opposing CAX. The differences between the calculated isocenters and the reference isocenters ranged from 0 to 0.8 mm. The differences diminished to less than 0.2 mm when 24 or more CAX were sampled. Isocenters determined with collimator 0° were vertically lower than those determined with collimator 90° and 270°. Isocenter localization errors in the longitudinal direction (along the axis of gantry rotation) showed a strong dependence on the collimator angle selected. The errors in all directions were significantly reduced when opposing collimator angles and opposing gantry angles were employed. The isocenter localization errors were less than 0.2 mm with the common CAX sampling scheme, which used four cardinal gantry angles and two opposing collimator angles. Reproducibility studies on one linac showed that the mean and maximum variations of CAX during the WL tests were 0.053 mm and 0.30 mm, respectively. The maximal variation in the resulting isocenters was 0.068 mm if 48 CAX were used, or 0.13 mm if four CAX were used. Quantitative results from this study are useful for understanding and minimizing the isocenter uncertainty in WL tests. PACS number: 87.56.Fc
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DOI：
10.1016/j.ijrobp.2008.04.029
发表时间：
2008-08-01
影响因子：
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