Patient positioning and tracking
Successful radiotherapy essentially relies on accurate and reproducible positioning of the patient during the treatment course. Especially, the setup of the patient should be the same at imaging for treatment planning and at the treatment itself. While fixation techniques for the head-and-neck region are well-developed, accurate and reproducible fixation for the whole-body region remains a challenge. Whole-body stereotaxy yields a high degree of accuracy, however, is related to a rather high logistic effort, which may not be feasible in every radiotherapy department.
Setup variations may occur between two subsequent fractions (inter-fractional setup errors), as well as within fractions (intra-fractional setup errors). The uncertainty of such setup errors has to be addressed by selection of an adequate safety margin between the clinical target volume (CTV) which delineated the tumor to be treated and the planning target volume (PTV) to which dose is planned to be delivered. The probability of side-effect may be reduced, if the safety margin is minimized. This is, however, only possible, if the setup error is also reduced. Otherwise the tumor control probability will decrease.
Stereo-camera-systems for patient positioning
Fig. 1. a) Setup for the in-house developed video-based stereo-camera system FIVE (Fast Intergrated Video-based Environment). The markers are attached to a dento-maxilary-fixation plate (b). For extracranial applications, the markers are directly attached to the skin of the patient.
© dkfz.de
Application of video-based stereo-camera-systems allows a non-invasive and quantitative comparison of the actual patient position with that of a reference setup at the first fraction or with the position at imaging for treatment planning. These video-based systems may use external markers or may register the body surface of the patient without the use of markers. Furthermore, these systems may be operated in real-time, which allow tracking if inter-fractional movements of the patient e.g. caused by respirations. If in addition, the correlation of the movements between external and internal structures is known, the real-time tracking may in principle be used perform either a gated or adapted treatment.
It is the aim to investigate the applicability of self-developed (fig. 1) as well as commercial video-based systems to increase setup accuracy and reproducibility for different tumor sites. The inter- and intra-fractional setup-errors shall be quantified. In combination with time-dependent imaging protocols (e.g., 4D-CT, 4D MRI), the correlation between the movement of internal and external Markers shall be investigad and the applicability of video-based systems for gated or adapted radiotherapy treatment shall be assessed.
Cooperations
- Prof. Dr. Dr. J. Debus, Dept. of Radiation Oncology and Radiotherapy, University Clinic Heidelberg, Germany
Selected References (in chronological order)
- Hub M., Liebler T., Sanner C., Barthold-Bess S., Thilmann C., Schlegel W., Lübbert U.: Evaluierung und optimierung eines Differenzbildverfahrens zur Positionierung von Patientinnen mit Mammakarzinom. Z. Med. Phys. 2005 (in press)
- Karger C.P., Schulz-Ertner D., Didinger B.H., Debus J., Jäkel O.: Influence of setup errors on spinal cord dose and treatment plan quality for cervical spine tumors: A phantom study for photon IMRT and heavy charged particle radiotherapy. Physics in Medicine and Biology 48, 3171-3189, 2003
- Liebler T., Hub M., Sanner C., Schlegel W.: An application framework for computer-aided patient positioning in radiation therapy. Med Inform Internet Med. 28, 161-82, 2003
- Karger C.P., Jäkel O., Debus J., Kuhn S., Hartmann G.H.: Three-dimensional accuracy and interfractional reproducibility of patient fixation and positioning using a stereotactic head mask system. International Journal of Radiation Oncology, Biology, Physics 49, 1493-1504, 2001
- Schneberger M.: Implementierung und Test eines videobasierten 3D-Messsystems zur Patientenpositionierung in der Präzisionsstrahlentherapie. Diplomarbeit, Fakultät für Physik und Astronomie, Universität Heidelberg, 2000.
- Kuhr G.: Ein optisches Messsystem zur Patientenpositionierung in der Präzisionsstrahlentherapie von Tumoren. Inauguraldissertation, Naturwissenschaftl.-Mathematische Gesamtfakultät, Universität Heidelberg, 2000.
- Lappe C.: Spezifikation und Implementierung eines videobasierten Systems zur Patientenpositionierung in der Präzisionsstrahlentherapie. Inauguraldissertation, Medizinische Fakultät, Universität Heidelberg, 1999.