The assessment of the coincidence of imaging and radiation isocenters is an important task of regular quality assurance of medical linear accelerators (linacs) as recommended in national and international quality assurance guidelines. A previously reported investigation of the accuracy of the Elekta XVI software to localize the linac radiation isocenter, by comparing statistically with other independent software, has shown some discrepancies at the sub‐mm level. A further investigation is carried out here using a set of reference images and mathematical operations to observe how the Elekta XVI software analyses them. Symmetric mathematical operations on reference images should result in symmetrical outcomes. Three different rotation functions are used in increasing degree of complexity to characterize the Elekta XVI software error in the linac radiation isocenter position. No independent algorithms or phantoms are used in this methodology. The magnitude and direction of the radiation isocenter localization error has been determined to be consistently 0.13 mm or 0.14 mm in the longitudinal direction towards the target depending on the case. The radiation isocenter localization error comprises two separated errors of the Ball Bearing Center by 0.13 mm and MV Field Center by either 0.00 mm or −0.01 mm in the longitudinal direction towards the target. The calculation of the MV Field Center is influenced by the polymethyl methacrylate rod supporting the ball‐bearing. The precise value and the root cause of the error cannot be assessed due to the rounding effect of the results reported by the Elekta XVI software and lack of access to the source code.

中文翻译：

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使用Elekta XVI软件计算出的MV辐射等中心点位置的误差评估。

根据国家和国际质量保证准则的建议，对成像和辐射等中心点的重合性进行评估是定期对医用线性加速器（直线加速器）进行质量保证的重要任务。通过与其他独立软件进行统计比较，以前报道的Elekta XVI软件对直线加速器辐射等中心线定位精度的调查显示，亚毫米级存在一些差异。这里使用一组参考图像和数学运算来进行进一步的研究，以观察Elekta XVI软件如何分析它们。参考图像上的对称数学运算应导致对称结果。使用三种不同的旋转函数来增加复杂度，以表征直线加速器辐射等角点位置中的Elekta XVI软件错误。此方法中没有使用独立的算法或模型。视情况而定，辐射等中心点定位误差的大小和方向在朝向目标的纵向上始终为0.13 mm或0.14 mm。辐射等中心点定位误差包括两个分开的误差，分别是：在朝向目标的纵向方向上，滚珠轴承中心为0.13 mm，MV场中心为0.00 mm或-0.01 mm。MV场中心的计算受支撑滚珠轴承的聚甲基丙烯酸甲酯棒的影响。