Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
British Columbia Cancer, Prince George, British Columbia, Canada.
Vet Comp Oncol. 2020 Dec;18(4):607-614. doi: 10.1111/vco.12584. Epub 2020 Mar 14.
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.
日常图像引导可减少颅内放射治疗中患者位置的分次间变化。然而，在一定水平以下，检测和纠正定位误差的能力是有限的。由于这些限制，在图像引导之前定位系统所达到的准确性可能会影响图像引导后的残余误差（残余摆位误差）。本研究的目的是比较两种颅内定位系统在使用兆伏（MV）和锥形束 CT（CBCT）引导前后的摆位精度。设备包括一个可进行 1 毫米平移运动的四自由度治疗床。6 只狗尸体在头定位器（HPS）中以 24 次的频率定位为临床治疗，在图像引导校正前后测量五个基准标记的坐标。将 HPS 的值与该设施使用的标准定位系统（SPS）以前报告的值进行比较。在不使用图像引导的情况下，HPS 的三维距离向量（3DDV）均值小于 SPS（P=0.019）。在使用 MV 引导后，HPS 的 3DDV 均值小于 SPS（P=0.027），但在使用 CBCT 引导后没有差异（P=0.231）。在 MV 和 CBCT 引导后，HPS 的 3DDV 的 95%百分位数分别为 2.1 和 2.9mm，而 SPS 的 3DDV 的 95%百分位数分别为 2.8 和 3.6mm。在 MV 引导后，摆位误差较低的定位系统在图像引导之前实现了更准确的患者位置。
