Shiinoki Takehiro, Fujii Fumitake, Yuasa Yuki, Nonomura Tatsuki, Fujimoto Koya, Sera Tatsuhiro, Tanaka Hidekazu
Department of Radiation Oncology, Graduate School of Medicine, Yamaguchi University, 1-1-1 Minamikogushi, Ube, Yamaguchi, 755-8505, Japan.
Department of Mechanical Engineering, Graduate School of Science and Technology for Innovation, Yamaguchi University, 2-16-1 Tokiwadai, Ube, Yamaguchi, 755-8611, Japan.
Med Phys. 2020 Sep;47(9):3870-3881. doi: 10.1002/mp.14369. Epub 2020 Jul 28.
This study aimed to develop a six degrees-of-freedom (6DoF) robotic moving phantom for evaluating the dosimetric impact of intrafraction rotation during respiratory-gated radiotherapy with real-time tumor monitoring in the lung.
Fifteen patients who had undergone respiratory-gated stereotactic body radiotherapy (SBRT) with the SyncTraX system for lung tumors were enrolled in this study. A water-equivalent phantom (WEP) was set at the tip of the robotic arm. A log file that recorded the three-dimensional positions of three fiducial markers implanted near the lung tumor was used as the input to the 6DoF robotic moving phantom. Respiratory-gated radiotherapy was performed for the WEP, which was driven using translational and rotational motions of the lung tumor. The accuracy of the 6DoF robotic moving phantom was calculated as the difference between the actual and the measured positions. To evaluate the dosimetric impact of intrafraction rotation, the absolute dose distributions under conditions involving gating and movement were compared with those under static conditions.
For the sinusoidal patterns, the mean ± standard deviation (SD) of the root mean square errors (RMSEs) of the translation and rotation positional errors was <0.40 mm and 0.30°, respectively, for all directions. For the respiratory motion patterns of 15 patients, the mean ± SD of the RMSEs of the translation and rotation positional errors was <0.55 mm and 0.85°, respectively, for all directions. The γ values under translation with/without gating were 97.6 ± 2.2%/80.9 ± 18.1% and 96.8 ± 2.3%/80.0 ± 17.0% in the coronal and sagittal planes, respectively. Further, the γ values under rotation with/without gating were 91.5 ± 6.5%/72.8 ± 18.6% and 90.3 ± 6.1%/72.9 ± 15.7% in the coronal and sagittal planes, respectively.
The developed 6DoF robotic phantom system could determine the translational and rotational motions of lung tumors with high accuracy. Further, respiratory-gating radiotherapy with real-time tumor monitoring using an internal surrogate marker was effective in compensating for the translational motion of lung tumors but not for correcting their rotational motion.
本研究旨在开发一种六自由度（6DoF）机器人运动体模，用于评估肺部呼吸门控放疗期间分次内旋转对剂量学的影响，并进行实时肿瘤监测。
本研究纳入了15例使用SyncTraX系统对肺部肿瘤进行呼吸门控立体定向体部放疗（SBRT）的患者。在机器人手臂末端设置一个水等效体模（WEP）。将记录植入肺部肿瘤附近的三个基准标记物三维位置的日志文件用作6DoF机器人运动体模的输入。对WEP进行呼吸门控放疗，WEP通过肺部肿瘤的平移和旋转运动驱动。6DoF机器人运动体模的精度通过实际位置与测量位置之间的差异来计算。为了评估分次内旋转对剂量学的影响，将门控和运动条件下的绝对剂量分布与静态条件下的进行比较。
对于正弦模式，所有方向上平移和旋转位置误差的均方根误差（RMSE）的平均值±标准差（SD）分别<0.40 mm和0.30°。对于15例患者的呼吸运动模式，所有方向上平移和旋转位置误差的RMSE的平均值±SD分别<0.55 mm和0.85°。在冠状面和矢状面，平移时门控和非门控情况下的γ值分别为97.6±2.2%/80.9±18.1%和96.8±2.3%/80.0±17.0%。此外，在冠状面和矢状面，旋转时门控和非门控情况下的γ值分别为91.5±6.5%/72.8±18.6%和90.3±6.1%/72.9±15.7%。
所开发的6DoF机器人体模系统能够高精度地确定肺部肿瘤的平移和旋转运动。此外，使用内部替代标记物进行实时肿瘤监测的呼吸门控放疗在补偿肺部肿瘤的平移运动方面有效，但在纠正其旋转运动方面无效。
