Publications

Regoli, L.; Herrmann, C.; Ravandoor, K.; Schilling, K.;
New Testing Facility for Proximity Operations in Space
Proceedings of 19th IFAC Symposium on Automatic Control in Aerospace. Würzburg, Germany, September 2-6, 2013, pp. xx-xx
[BibTeX]

@inproceedings{Regoli2013a, author = {L. Regoli and C. Herrmann and K. Ravandoor and K. Schilling}, title = {New Testing Facility for Proximity Operations in Space}, booktitle = {Proceedings of 19th IFAC Symposium on Automatic Control in Aerospace}, year = {2013}, month = {September 2-6}, pages = {xx--xx}, address = {Würzburg, Germany} }

[Abstract]

On-Earth testing of space scenarios is one of the key steps during the development of new technologies, being the reproduction of space-like conditions one of the main challenges. In this paper, a testbed designed and developed for testing of proximity operations scenarios such as rendezvous and docking (RvD) or formation flying is presented. The testbed is based on two industrial manipulators and has been developed and used for the validation of pose estimation algorithms for RvD with non-cooperative targets at the University of Würzburg.

Leutert, F.; Herrmann, C.; &. Schilling, K.;
A Spatial Augmented Reality system for intuitive display of robotic data
8th ACM/IEEE International Conference on Human-Robot Interaction (HRI). 2013, ISBN: 978-1-4673-3099-2
[BibTeX]

@INPROCEEDINGS{Leutert2013a, author = {Leutert, F. and Herrmann, C. and Schilling, K.}, title = {A Spatial Augmented Reality system for intuitive display of robotic data}, booktitle = {Human-Robot Interaction (HRI), 2013 8th ACM/IEEE International Conference on}, year = {2013}, pages = {179-180}, isbn = {978-1-4673-3099-2} }

[Abstract]

In the emerging field of close human-robot-collaboration the human worker needs to be able to quickly and easily understand data of the robotic system. To achieve this even for untrained personnel, we propose the use of a Spatial Augmented Reality system to project the necessary information directly into the users' workspace. The projection system consists of a fixed as well as a mobile projector mounted directly on the manipulator, allowing for visualizing data anywhere in the surroundings of the robot. By enabling the user to simply see the necessary complex information he can better understand the data and behavior of the robotic assistant and has the opportunity to analyze and potentially optimize the working process. Together with an input device, arbitrary interfaces can be realized with the projection system.

Herrmann, C.; & Schilling, K.;
Improving Patient Comfort using Model Predictive Control in Robot-Assisted Radiotherapy
In Proceedings of the 2013 IEEE International Conference on Robotics and Automation (ICRA), Karlsruhe, Germany, May 6-10, 2013, pp. 5426-5432
[BibTeX]

@inproceedings{Her13, author = {Herrmann, C. and Schilling, K.}, title = {Improving Patient Comfort using Model Predictive Control in Robot-Assisted Radiotherapy}, booktitle = {Proceedings of the 2013 IEEE International Conference on Robotics and Automation (ICRA)}, year = {2013}, pages = {5426--5432}, address = {Karlsruhe, Germany}, month = {May 6-10}, }

[Abstract]

Moving tumors, especially in the vicinity of lungs, pose a challenging problem in radiotherapy as healthy tissue should not be irradiated. We developed a system to compensate tumor motion with the robotic treatment couch HexaPOD to improve treatment quality. The HexaPOD, carrying the patient, counteracts the tumor motion so that it is eliminated in the beams-eye-view of the linear accelerator. The focus of this work is on two control methods for the HexaPOD in order to realize reference tracking. The first method is a simple position control scheme to enable reference tracking. It is reformulated as second method to be adopted by a model predictive controller to better account for patient comfort and to maintain tracking accuracy. The performance of both methods is compared in experiments with real hardware using prerecorded patient trajectories and human volunteers whose breathing motion was compensated.

Wilbert, J.; Baier, K.; Herrmann, C.; Flentje, M. & Guckenberger, M.;
Accuracy of Real-time Couch Tracking during 3-dimensional Conformal Radiation Therapy, Intensity modulated Radiation Therapy, and Volumetric modulated Arc Therapy for Prostate Cancer
Int. J. Radiation Oncology Biol. Phys., Vol. 85(1), January 2013, pp. 237-242
[BibTeX]

@ARTICLE{Wil13, author = {Wilbert, J. and Baier, K. and Herrmann, C. and Flentje, M. and Guckenberger, M.}, title = {Accuracy of Real-time Couch Tracking During 3-dimensional Conformal Radiation Therapy, Intensity Modulated Radiation Therapy, and Volumetric Modulated Arc Therapy for Prostate Cancer}, journal = {International Journal of Radiation Oncology Biology Physics}, year = {2013}, volume = {85}, pages = {237--242}, number = {1}, month = {January}, doi = {10.1016/j.ijrobp.2012.01.095} }

[Abstract]

Purpose: To evaluate the accuracy of real-time couch tracking for prostate cancer. Methods and Materials: Intrafractional motion trajectories of 15 prostate cancer patients were the basis for this phantom study; prostate motion had been monitored with the Calypso System. An industrial robot moved a phantom along these trajectories, motion was detected via an infrared camera system, and the robotic HexaPOD couch was used for real-time counter-steering. Residual phantom motion during real-time tracking was measured with the infrared camera system. Film dosimetry was performed during delivery of 3-dimensional conformal radiation therapy (3D-CRT), step-and-shoot intensity modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT). Results: Motion of the prostate was largest in the anterioreposterior direction, with systematic (S) and random (R) errors of 2.3 mm and 2.9 mm, respectively; the prostate was outside a threshold of 5 mm (3D vector) for 25.0%+/-19.8% of treatment time. Real-time tracking reduced prostate motion to S=0.01 mm and R=0.55 mm in the anterioreposterior direction; the prostate remained within a 1-mm and 5-mm threshold for 93.9%+/-4.6% and 99.7%+/-0.4% of the time, respectively. Without real-time tracking, pass rates based on a g index of 2%/2 mm in film dosimetry ranged between 66% and 72% for 3D-CRT, IMRT, andVMAT, on average. Real-time tracking increased pass rates to minimum 98% on average for 3D-CRT, IMRT, and VMAT. Conclusions: Real-time couch tracking resulted in submillimeter accuracy for prostate cancer, which transferred into high dosimetric accuracy independently of whether 3D-CRT, IMRT, or VMAT was used.

Menten, M.J.; Guckenberger, M.; Herrmann, C.; Krauß, A.; Nill, S.; Oelfke, U. & Wilbert, J.;
Comparison of a multileaf collimator tracking system and a robotic treatment couch tracking system for organ motion compensation during radiotherapy
Medical Physics, Vol. 39(11), November 2012, pp. 7032-7041
[BibTeX]

@ARTICLE{Men12, author = {Menten, M.J. and Guckenberger, M. and Herrmann, C. and Krauß, A. and Nill, S. and Oelfke, U. and Wilbert, J.}, title = {Comparison of a multileaf collimator tracking system and a robotic treatment couch tracking system for organ motion compensation during radiotherapy}, journal = {Medical Physics}, year = {2012}, volume = {39}, pages = {7032--7041}, number = {11}, month = {November}, doi = {10.1118/1.4761868} }

[Abstract]

One limitation of accurate dose delivery in radiotherapy is intrafractional movement of the tumor or the entire patient which may lead to an underdosage of the target tissue or an overdosage of adjacent organs at risk. In order to compensate for this movement, different techniques have been developed. In this study the tracking performances of a multileaf collimator (MLC) tracking system and a robotic treatment couch tracking system were compared under equal conditions.
METHODS: MLC tracking was performed using a tracking system based on the Siemens 160 MLC. A HexaPOD robotic treatment couch tracking system was also installed at the same linac. A programmable 4D motion stage was used to reproduce motion trajectories with different target phantoms. Motion localization of the target was provided by the 4D tracking system of Calypso Medical Inc. The gained positional data served as input signal for the control systems of the MLC and HexaPOD tracking systems attempting to compensate for the target motion. The geometric and dosimetric accuracy for the tracking of eight different respiratory motion trajectories was investigated for both systems. The dosimetric accuracy of both systems was also evaluated for the tracking of five prostate motion trajectories.
RESULTS: For the respiratory motion the average root mean square error of all trajectories in y direction was reduced from 4.1 to 2.0 mm for MLC tracking and to 2.2 mm for HexaPOD tracking. In x direction it was reduced from 1.9 to 0.9 mm (MLC) and to 1.0 mm (HexaPOD). The average 2%/2 mm gamma pass rate for the respiratory motion trajectories was increased from 76.4% for no tracking to 89.8% and 95.3% for the MLC and the HexaPOD tracking systems, respectively. For the prostate motion trajectories the average 2%/2 mm gamma pass rate was 60.1% when no tracking was applied and was improved to 85.0% for MLC tracking and 95.3% for the HexaPOD tracking system.
CONCLUSIONS: Both systems clearly increased the geometric and dosimetric accuracy during tracking of respiratory motion trajectories. Thereby, the geometric accuracy was increased almost equally by both systems, whereas the dosimetric accuracy of the HexaPOD tracking system was slightly better for all considered respiratory motion trajectories. Substantial improvement of the dosimetric accuracy was also observed during tracking of prostate motion trajectories during an intensity-modulated radiotherapy plan. Thereby, the HexaPOD tracking system showed better results than the MLC tracking.

Herrmann, C.; Ma, L.; Wilbert, J.; Baier, K. & Schilling, K.;
Control of a HexaPOD Treatment Couch for Robot Assisted Radiotherapy
Biomedical Engineering/Biomedizinische Technik (BMT), Vol. 57(5), July 2012, pp.333-351
[BibTeX]

@ARTICLE{Her12, author = {Herrmann, C. and Ma, L. and Wilbert, J. and Baier, K. and Schilling, K.}, title = {Control of a HexaPOD Treatment Couch for Robot-Assisted Radiotherapy}, journal = {Biomedical Engineering / Biomedizinische Technik}, year = {2012}, volume = {57}, pages = {333--351}, number = {5}, month = {July}, doi = {10.1515/bmt-2011-0125} }

[Abstract]

Moving tumors, for example in the vicinity of the lungs, pose a challenging problem in radiotherapy, as healthy tissue should not be irradiated. Apart from gating approaches, one standard method is to irradiate the complete volume within which a tumor moves plus a safety margin containing a considerable volume of healthy tissue. This work deals with a system for tumor motion compensation using the HexaPOD robotic treatment couch (Medical Intelligence GmbH, Schwabmünchen, Germany). The HexaPOD, carrying the patient during treatment, is instructed to perform translational movements such that the tumor motion, from the beams-eye view of the linear accelerator, is eliminated. The dynamics of the HexaPOD are characterized by time delays, saturations, and other non-linearities that make the design of control a challenging task. The focus of this work lies on two control methods for the HexaPOD that can be used for reference tracking. The first method uses a model predictive controller based on a model gained through system identification methods, and the second method uses a position control scheme useful for reference tracking. We compared the tracking performance of both methods in various experiments with real hardware using ideal reference trajectories, prerecorded patient trajectories, and human volunteers whose breathing motion was compensated by the system.

Herrmann, C.; Ma, L. & Schilling, K.;
Model Predictive Control for Tumor Motion Compensation in Robot Assisted Radiotherapy
In Proceedings of the 18th IFAC World Congress 2011, Milano, Italy, September 2011, pp. 5968-5973
[Free download from IFAC-PapersOnLine]
[BibTeX]

@inproceedings{Herrmann2011, author = {Christian Herrmann and Lei Ma and Klaus Schilling}, title = {Model Predictive Control for Tumor Motion Compensation in Robot Assisted Radiotherapy}, booktitle = {Proceedings of the 18th IFAC World Congress 2011}, year = {2011}, pages = {5968--5973}, address = {Milano, Italy}, month = {September} }

[Abstract]

This paper presents model predictive control (MPC) of a HexaPOD treatment couch used in robot assisted radiotherapy for motion compensation of lung tumors. The HexaPOD, carrying the patient during treatment, performs translational movements such that the tumor motion in the beams-eye-view of the linear accelerator is eliminated. We first briefly discuss appropriate dynamic models of the treatment couch usable for MPC. It is shown how MPC can be applied to the problem of motion compensation. The influence of horizon parameters and control increment weighting in MPC as well as the performance w.r.t. the tracking error for several test and patient data sets is evaluated with experiments on the hardware.

Ma, L.; Herrmann, C. & Schilling, K.;
On Challenges of Robot Assisted Radiotherapy for Lung Tumors
In Proceedings of the IEEE International Conference on Robotics and Biomimetics (ROBIO 2010), Tianjin, China, December 10-14, 2010, pp. 773-778
[BibTeX]

@inproceedings{Ma2010, author = {L. Ma and C. Herrmann and K. Schilling}, title = {On Challenges of Robot Assisted Radiotherapy for Lung Tumors}, booktitle = {Proceedings of the IEEE International Conference on Robotics and Biomimetics (ROBIO 2010)}, year = {2010}, pages = {773-778}, address = {Tianjin, China}, month = {December 10-14} }

[Abstract]

This paper is concerned with recent development in robot assisted radiotherapy for lung tumors. The paper first analyzes technical challenges regarding tumor position determination and prediction, by invasive and non-invasive methods, correlation models of the tumor motion and the respiratory signals, as well as modeling and control of the robot manipulator. Several currently available solutions and concepts are then briefly introduced. Emphasis is placed on the ATTS (adaptive tumor tracking system) system developed at the University of Würzburg. Within the ATTS, information of the tumor motion is used to control a robotic treatment couch HexaPOD, which moves in six degrees of freedom and maintains the tumor in a certain fixed spatial position. With this new technology it is possible to avoid gating during the radiotherapy as well as active breathing control, such that duration and cost of the therapy as well as trauma of the patient can be reduced. The tumor position is obtained by data fusion from two sensing system. Correlation methods for data fusion were extensively investigated and a prediction model for tumor motion is found that can forecast the tumor position for up to one respiratory period. Modeling of the HexaPOD treatment couch is addressed. The most suitable model is found to be a low-order linear dynamic equation together with a saturation component. Three different control methods and comparative test results are then presented to show feasibility of the proposed model and control schemes.

Wilbert, J.; Baier, K.; Richter, A.; Herrmann, C.; Ma, L.; Flentje, M. & Guckenberger, M.;
Influence of Continuous Table Motion On Patient Breathing Patterns
Int. J. Radiation Oncology Biol. Phys., Vol. 77(2), June 2010. pp. 622-629
[BibTeX]

@ARTICLE{Wil10, author = {J. Wilbert and K. Baier and A. Richter and C. Herrmann and L. Ma and M. Flentje and M. Guckenberger}, title = {Influence of Continuous Table Motion on Patient Breathing Patterns}, journal = {International Journal of Radiation Oncology Biology Physics}, year = {2010}, volume = {77}, pages = {622--629}, number = {2}, month = {June}, doi = {10.1016/j.ijrobp.2009.08.033}, issn = {0360-3016} }

[Abstract]

Purpose: To investigate the influence of continuous table motion on patient breathing patterns for compensation of moving targets by a robotic treatment couch.
Methods and Materials: Fifteen volunteers were placed on a robotic treatment couch, and the couch was moved on different breathing-correlated and - uncorrelated trajectories. External abdominal breathing motion of the patients was measured using an infrared camera system. The influence of table motion on breathing range and pattern was analyzed.
Results: Continuous table motion was tolerated well by all test persons. Volunteers reacted differently to table motion. Four test persons showed no change of breathing range and pattern. Increased irregular breathing was observed in 4 patients; however, irregularity was not correlated with table motion. Only 4 test persons showed an increase in mean breathing amplitude of more than 2mm during motion of the couch. The mean cycle period decreased by more than 1 s for 2 test persons only. No abrupt changes in amplitude or cycle period could be observed.
Conclusions: The observed small changes in breathing patterns support the application of motion compensation by a robotic treatment couch.

Herrmann, C.; Ma, L. & Schilling, K.;
Modeling a HexaPOD for Tumor Motion Compensation in Robot Assisted Radiotherapy
In Proceedings of the Joint Conference of 41st International Symposium on Robotics and 6th German Conference on Robotics (ISR 2010), Munich, Germany, June 2010, pp. 1019-1025
[BibTeX]

@inproceedings{Herrmann2010, author = {C. Herrmann and L. Ma and K. Schilling}, title = {Modeling a HexaPOD for Tumor Motion Compensation in Robot AssistedRadiotherapy}, booktitle = {Proceedings of the Joint Conference of 41st International Symposium on Robotics and 6th German Conference on Robotics (ISR 2010)}, year = {2010}, pages = {1019-1025}, address = {Munich, Germany}, month = {June} }

[Abstract]

This paper addresses modeling a HexaPOD treatment couch used in robot assisted radiotherapy for motion compensation of lung tumors. The HexaPOD, on which the patient is lying, is supposed to move the patient to counteract the tumor motion. For the purpose of modeling the dynamic behavior of the HexaPOD, linear ARX models are used. It was found that these models work when no velocity saturation occurs. However, from real patient data acquired by our clinical system it is shown in this work that, during some phases, the HexaPOD needs to operate at its maximum velocity. This imposes nonlinearities on the ARX model which cause their performance to degrade. To overcome this drawback, the models are enhanced with a nonlinear extension which can be applied in a generic way to a wide variety of models. It is proved by experimental data that the extended model is capable of exhibiting linear behavior from the underlying ARX model where it is necessary while it can simultaneously deal with velocity saturation. Emphasis is laid on system identification as this is a crucial topic to achieve good model performance.

Wilbert, J.; Meyer, J.; Baier, K.; Guckenberger, M.; Herrmann, C.; Hess, R.; Janka, C.; Ma, L.; Mersebach, T.; Richter, A.; Roth, M.; Schilling, K. & Flentje, M.;
Tumor tracking and motion compensation with an adaptive tumor tracking system (ATTS): System description and prototype testing.
Medical Physics, Vol. 35(9), September 2008, pp. 3911-3921
[BibTeX]

@article{Wilbert2008, author = {J. Wilbert and J. Meyer and K. Baier and M. Guckenberger and C. Herrmann and R. Hess and C. Janka and L. Ma and T. Mersebach and A. Richter and M. Roth and K. Schilling and M. Flentje}, journal = {Medical Physics}, pages = {3911--3921}, title = {Tumor tracking and motion compensation with an adaptive tumor tracking system ({ATTS}): System description and prototype testing}, volume = {35}, number = {9}, year = {2008}, month = {September}, doi = {10.1118/1.2964090} }

Ma, L.; Herrmann, C. & Schilling, K.;
Modeling and Prediction of Lung Tumor Motion for Robotic Assisted Radiotherapy.
Proceedings of the 2007 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2007), San Diego, CA, USA, October 29 - November 2, 2007, pp. 189-194
[BibTeX]

@inproceedings{Ma2007, author = {L. Ma and C. Herrmann and K. Schilling}, title = {Modeling and Prediction of Lung Tumor Motion for Robotic Assisted Radiotherapy}, booktitle = {Proceedings of the 2007 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2007)}, year = {2007}, pages = {189--194}, address = {San Diego, CA, USA}, month = {October 29 - November 2,} }

Herrmann, C.; Zeiger, F.; Ma, L.; Selbach, C. & Schilling, K.;
Design and Test of an Autonomous Helicopter for Multi-Vehicle Cooperation.
In Proceedings of the 6th IFAC Symposium on Intelligent Autonomous Vehicles (IAV2007), Toulouse, France, September 3-5, 2007
[Free download from IFAC-PapersOnLine]
[BibTeX]

@inproceedings{HerrmannSeptember2007, author = {C. Herrmann and F. Zeiger and L. Ma and C. Selbach and K. Schilling}, title = {Design and Test of an Autonomous Helicopter for Multi-Vehicle Cooperation}, booktitle = {Proceedings of the 6th IFAC Symposium on Intelligent Autonomous Vehicles (IAV2007)}, year = {2007}, pages = {276-281}, address = {Toulouse, France}, month = {September 3-5,} }

Ma, L.; Herrmann, C.; Schilling, K.; Wilbert, J. & Baier, K.;
Real-Time Tumor Tracking with a Robotic Treatment Couch.
In Proceedings of the 2nd International Conference on Computer Aided Medical Interventions: Tools and Applications (SURGETICA), Chambery, France, 2007, pp. 215-221
[BibTeX]

@inproceedings{Ma2007a, author = {L. Ma and C. Herrmann and K. Schilling and J. Wilbert and K. Baier}, title = {Real-Time Tumor Tracking with a Robotic Treatment Couch}, booktitle = {Proceedings of the 2nd International Conference on Computer Aided Medical Interventions: Tools and Applications (SURGETICA)}, year = {2007}, pages = {215-221}, address = {Chambery, France} }

Herrmann, C.; Ma, L.; Schilling, K.; Wilbert, J. & Baier, K.;
Tumorverfolgung und Nachführung mittels eines automatisierten Bestrahlungstisches.
In Proceedings of the 8th Würzburger Medizintechnik-Kongress, Würzburg, Germany, May 21-23, 2007, pp. 77-80, ISBN 978-3-937988-06-01
[BibTeX]

@inproceedings{C.Herrmann2007, author = {C. Herrmann and L. Ma and K. Schilling and J. Wilbert and K. Baier}, title = {Tumorverfolgung und Nachführung mittels eines automatisierten Bestrahlungstisches}, booktitle = {Proceedings of the 8th Würzburger Medizintechnik-Kongress, Würzburg, Germany}, year = {2007}, pages = {77--80}, isbn = {978-3-937988-06-01}, address = {Würzburg, Germany}, month = {May 21-23,} }