gms | German Medical Science

Background: Image guidance using planar orthogonal X-Ray Digital Radiography is the standard technique for patient positioning in particle therapy (PT). Intensity or point-based image registration using bony anatomy or implanted markers is used to evaluate position error and apply a 6 degree of freedom correction with patient positioner. Outside the treatment room positioning has been recently validated using CT imaging of the patient onto the treatment table-top and accurate transfer to treatment room using a guided transport system. In radiotherapy, new techniques are now available, CBCT with improved image quality, 3D surface optical imaging and RF localizers with improved efficiency, accuracy and online tracking of motion. We present an advanced positioning product extending outside of treatment room concepts towards 3D CT and MRI modalities for improved imaging specificity and integration with optical and RF technologies for streamlined and safe workflow of positioning.

Material and methods: We have developed a solution for transfer of patient and treatment table-top between preparation, imaging and treatment rooms and positioning devices including: a loading station for comfortable installation with motorized tilting of patient from vertical posture, an automatically guided trolley for smooth transportation between rooms, a treatment table-top and docking mechanism for smooth and reproducible transfer of patient to positioning devices. Smoothness is controlled at all stages through optical and ultrasound guidance. MRI safety and compatibility and one working day autonomy is provided. A new positioning workflow is defined with associated 3D image registration tools where reference imaging is the first fraction CT series, subsequent fractions imaging space are matched using fiducials or calibration, potential patient motion is detected using 3D surface optical imaging or RF localizers. All components were designed to reach a submillimetric positioning accuracy for a phantom-based setup.

Results: Individual components have been designed, produced and tested. A first unit has been installed and tested in a PT center. Docking tests to MRI and treatment positioner equipments were successful. Reproducibility of docking process is below 0.3mm. Smoothness of transport and docking is controlled down to 1 m/s² and 0.3 m/s³. MRI safety and compatibility was assessed using standard MRI QA phantom.

Conclusion: A new positioning paradigm based on 3D CT and MRI system with integrated workflow has been developed for improved performance and increased efficiency aiming at broader acceptance of PT. Future work shall include clinical studies for patient-based accuracy assessment.