Background and purpose: Radiation-therapy methods such as dose painting and image-guided radiation-therapy (IGRT) aim to spare organs at risk by applying improved dose distributions on the tumor. For effective application of these methods, exact positioning of the patient and localization of the planning target volume are vital. We have built a new positioning system which uses tracked three dimensional ultrasound both in the computed tomography (CT) room and the intervention room. A patient study was done and the results were compared to a gold standard. Additionally we present a detailed error analysis for all system components.
Methods: At the time of the planning CT scan we acquire three 3D ultrasound images while the US scanhead is tracked by an optical tracking system.
Based on these images a suitable image metric is selected for each patient individually. Before each fraction another US image is taken. This image is filtered and registered to the images from the CT room. From registration results, tracking data and a calibration matrix, we calculate a translation vector for final patient repositioning. We compare the translation vectors with results from the commercial ExacTrac system.
Results: The procedure succeeded for ten out of eleven patients. The overall positioning error for ten patients averaged to 4.15 1.20 mm.
Conclusion: We developed a fully automatic system for patient repositioning.
The accuracy is suitable for clinical application and can be improved further by optimizing system components. We performed a detailed error analysis of the overall system and its components.