To evaluate the spatial accuracy of radiation centers (RCs) of Elekta stereotactic cones while changing the cone sizes during intra-fraction treatment of multiple brain metastases (MBM). In this study, nine cones of varying sizes (5, 10, 12.5, 15, 17.5, 20, 25, 30, and 35 mm) were used. The ball bearing (BB) was used as the target. The positions of BBs and RCs obtained using electronic portal imaging device (EPID) were transformed to a coordinate system X/Y/Z that was fixed with respect to the treatment room. The positions of BBs when using cones sized between 12.5 and 35 mm were relatively stable. The maximum deviations between BBs and RCs were as follows: 1.11 mm in negative X and 1.30 mm in positive X, 0.87 mm in negative Y and 0.69 mm in positive Y, and 0.06 mm in negative Z and 0.58 mm in positive Z. The maximum offset between BBs and RCs gradually increased as the cone size decreased in the X and Y directions. The maximum offsets were 2.30, 1.56, and 0.64 mm in the X, Y, and Z directions, respectively, for the 12.5-mm cone. The maximum distance between the RCs was 0.43 mm when using the G135T270 beam between the 17.5-mm and 12.5-mm cones. The treatment of MBM with Elekta stereotactic cones demonstrated good spatial uncertainty. However, we need to pay particular attention to treatment using two or more cones in clinical practice. More external expansion margins are required in such cases.

中文翻译：

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Elekta 立体定向锥体在使用多个锥体治疗多发性脑转移瘤时的空间不确定性

评估 Elekta 立体定向锥体放射中心 (RC) 的空间精度，同时在多发性脑转移瘤 (MBM) 的分次治疗期间改变锥体尺寸。在这项研究中，使用了九个不同尺寸的锥体（5、10、12.5、15、17.5、20、25、30 和 35 毫米）。滚珠轴承 (BB) 用作目标。使用电子射野成像设备（EPID）获得的 BB 和 RC 的位置被转换到相对于治疗室固定的坐标系 X/Y/Z。使用尺寸在 12.5 至 35 mm 之间的锥体时，BB 的位置相对稳定。 BB和RC之间的最大偏差为：负X轴1.11 mm，正X轴1.30 mm，负Y轴0.87 mm，正Y轴0.69 mm，负Z轴0.06 mm，正Z轴0.58 mm。随着 X 和 Y 方向上锥体尺寸的减小，BB 和 RC 之间的偏移逐渐增加。对于 12.5 毫米锥体，X、Y 和 Z 方向的最大偏移分别为 2.30、1.56 和 0.64 毫米。当在 17.5 毫米和 12.5 毫米锥体之间使用 G135T270 梁时，RC 之间的最大距离为 0.43 毫米。用 Elekta 立体定向锥治疗 MBM 表现出良好的空间不确定性。然而，在临床实践中，我们需要特别注意使用两个或多个锥体的治疗。在这种情况下需要更多的外部扩张余量。