Daily image guidance reduces inter‐fractional variation in patient position for intracranial radiation therapy. However, the ability to detect and correct positioning errors is limited below a certain level. Because of these limitations, the accuracy achieved with a positioning system prior to image guidance may affect the error remaining after image guidance (the residual setup error). The objective of this study was to compare the setup accuracy achieved before and after megavoltage (MV) and cone‐beam computed tomography (CBCT) guidance between two intracranial positioning systems. Equipment included a four degrees‐of‐freedom couch capable of 1 mm translational moves. Six dog cadavers were positioned 24 times as for clinical treatment in a head re‐positioner (HPS), and the coordinates of five fiducial markers were measured before and after image‐guided correction. The values obtained for the HPS were compared with those previously reported for the standard positioning system (SPS) used at this facility. The mean three‐dimensional distance vector (3DDV) was lower for the HPS than for the SPS when no image guidance was used (P = .019). The mean 3DDV after MV guidance was lower for the HPS than for the SPS (P = .027), but not different after CBCT guidance (P = .231). The 95th percentiles of the 3DDV after MV and CBCT guidance were 2.1 and 2.9 mm, respectively, for the HPS, and 2.8 and 3.6 mm for the SPS. The setup error after MV guidance was lower for the positioning system that achieved a more accurate patient position before image guidance.

中文翻译：

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使用两个用于放射治疗的犬颅内定位系统在有和没有图像引导的情况下设置错误

每日图像指导减少了颅内放射治疗患者位置的分数间变化。然而，检测和纠正定位错误的能力被限制在一定水平以下。由于这些限制，在图像引导之前使用定位系统实现的精度可能会影响图像引导后剩余的误差（残余设置误差）。本研究的目的是比较两个颅内定位系统在兆电压 (MV) 和锥形束计算机断层扫描 (CBCT) 引导之前和之后实现的设置精度。设备包括一个能够进行 1 毫米平移运动的四自由度沙发。六具狗尸体在头部重新定位器 (HPS) 中进行了 24 次临床治疗，并且在图像引导校正之前和之后测量了五个基准标记的坐标。将 HPS 获得的值与之前为该设施使用的标准定位系统 (SPS) 报告的值进行了比较。当不使用图像引导时，HPS 的平均三维距离向量（3DDV）低于 SPS（P = .019）。MV 指导后，HPS 的平均 3DDV 低于 SPS ( P = .027)，但在 CBCT 指导后没有差异 ( P = .231)。MV 和 CBCT 引导后 3DDV 的第 95 个百分位数分别为 HPS 的 2.1 和 2.9 mm，SPS 的 2.8 和 3.6 mm。对于在图像引导前实现更准确患者位置的定位系统，MV 引导后的设置误差较低。