Minesinger Grace M, Laeseke Paul F, Falk Katrina L, Hennen Claire E, Speidel Michael A, Wagner Martin G
Department of Radiology, University of Wisconsin-Madison, Madison, Wisconsin, USA.
Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin, USA.
J Appl Clin Med Phys. 2025 Jul;26(7):e70132. doi: 10.1002/acm2.70132. Epub 2025 May 31.
Histotripsy is a focal tumor therapy that utilizes focused ultrasound (US) to mechanically destroy tissue. To overcome visualization limitations of diagnostic US-guidance, C-arm cone beam CT (CBCT)-guided histotripsy is being developed, for which a mobile C-arm could increase accessibility. CBCT-guided histotripsy uses a phantom with a helical fiducial pattern to determine the CBCT-to-histotripsy robot coordinate transformation. This study presents an image-to-robot registration method requiring only one phantom CBCT, evaluated for accuracy and reproducibility using a mobile C-arm.
The phantom is attached to a robotic arm (replacing the histotripsy transducer) and positioned at isocenter. A CBCT is acquired and image-to-robot registration performed by registering a digital model of the phantom to observed fiducials in CBCT coordinates. Registration was performed by one user (n = 8/day, 2 days) and by 12 different users (n = 4/day, 3 days) with fiducial registration errors (FREs) calculated. After each registration, the transducer was reattached to the robot and a treatment delivered in a multi-layered, agar-based phantom. Directional and target registration errors (TREs) were calculated as directional and Euclidean distances between planned and observed treatments. Directional error inter-day differences for the single-user experiment were evaluated for significance using 2-tailed unpaired Student t-tests. The effect of user variability on variability of FRE and directional error was evaluated for significance using 2-tailed F-tests.
Registrations yielded FRE of 0.12 ± 0.03 mm and TRE of 1.51 ± 0.83 mm. Targeting error significantly increased along the transducer's short axis between days (0.88 ± 0.60 vs 1.43 ± 0.18 mm, p = 0.025) for the single user, with a similar trend for the multi-user experiment (1.45 ± 0.79, 2.70 ± 0.19, and 2.83 ± 0.40 mm). User variability, and thus robot pose variability, did not significantly affect variability of FRE or directional error.
Mobile C-arm CBCT-guided histotripsy showed high accuracy with minimal yet nonnegligible TREs, consistent within but not between days, demonstrating that errors can be measured and accounted for, ideally near treatment day to maximize accuracy.
组织超声粉碎术是一种利用聚焦超声（US）机械破坏组织的局部肿瘤治疗方法。为克服诊断性超声引导的可视化局限性，正在开发C形臂锥束CT（CBCT）引导的组织超声粉碎术，使用移动C形臂可提高其可及性。CBCT引导的组织超声粉碎术使用带有螺旋基准图案的体模来确定CBCT与组织超声粉碎术机器人的坐标变换。本研究提出一种仅需一个体模CBCT的图像到机器人配准方法，并使用移动C形臂评估其准确性和可重复性。
将体模附着于机械臂（代替组织超声粉碎术换能器）并置于等中心。采集CBCT图像，并通过将体模的数字模型与CBCT坐标中观察到的基准进行配准来执行图像到机器人的配准。由一名用户（每天n = 8次，共2天）和12名不同用户（每天n = 4次，共3天）进行配准，并计算基准配准误差（FRE）。每次配准后，将换能器重新连接到机器人上，并在基于琼脂的多层体模中进行治疗。计算方向配准误差和目标配准误差（TRE），即计划治疗与观察到的治疗之间的方向距离和欧几里得距离。使用双尾非配对学生t检验评估单用户实验中方向误差的日间差异是否具有显著性。使用双尾F检验评估用户变异性对FRE变异性和方向误差的影响是否具有显著性。
配准产生的FRE为0.12±0.03 mm，TRE为1.51±0.83 mm。单用户实验中，靶向误差在不同日期沿换能器短轴显著增加（0.88±0.60 vs 1.43±0.18 mm，p = 0.025），多用户实验也有类似趋势（1.45±0.79、2.70±0.19和2.83±0.40 mm）。用户变异性以及因此产生的机器人姿态变异性，并未显著影响FRE或方向误差的变异性。
移动C形臂CBCT引导的组织超声粉碎术显示出高精度，TRE虽小但不可忽略，在同一天内具有一致性，但不同天之间不一致，这表明误差可以测量并加以考虑，理想情况下在治疗日附近进行以最大化准确性。
