A novel system for real-time tumor tracking and motion compensation with a robotic HexaPOD treatment couch is described. The approach is based on continuous tracking of the tumormotion in portal images without implanted fiducial markers, using the therapeutic megavoltage beam, and tracking of abdominal breathing motion with optical markers. Based on the two independently acquired data sets the table movements for motion compensation are calculated. The principle of operation of the entire prototype system is detailed first. In the second part the performance of the HexaPOD couch was investigated with a robotic four-dimensional-phantom capable of simulating real patient tumor trajectories in three-dimensional space. The performance and limitations of the HexaPOD table and the control system were characterized in terms of its dynamic behavior. The maximum speed and acceleration of the HexaPOD were and in the lateral direction, and and in longitudinal and anterior-posterior direction, respectively. Base line drifts of the mean tumor position of realistic lungtumor trajectories could be fully compensated. For continuous tumor tracking and motion compensation a reduction of tumormotion up to 68% of the original amplitude was achieved. In conclusion, this study demonstrated that it is technically feasible to compensate breathing induced tumormotion in the lung with the adaptive tumor tracking system.
This work was partially supported by a grant from the “Bayerische Forschungsstiftung,” Germany and Elekta Oncology Systems, Crawley, UK. The authors would like to thank Ulrich Achleitner and Barry Bishop from Medical Intelligence Innsbruck, Austria, for providing support for the MELFA Industrial Robot (UA) and the player program (BB) used to convert the tumor trajectories into robot movements. The authors would also like to thank Dr. Klaus Bratengeier for initiating this research project.
II. METHODS AND MATERIALS
II.A. Description of system concept
II.B. Status of current prototype system
II.C. Experimental verification of prototype system
II.C.2. Experiment 1: Performance of the HexaPOD table
II.C.3. Setup for experiments 2, 3, and 4
II.C.4. Experiment 2: Performance of the 4D phantom
II.C.5. Experiment 3: Automatic tumor tracking
II.C.6. Experiment 4: Counter-steering with the HexaPOD table
II.C.7. Data analysis
III.A. Dynamic behavior of the HexaPOD-table
III.B. Performance of the 4D phantom
III.C. Evaluation of automatic tumor tracking
III.D. Counter-steering with the HexaPOD table
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