22 March 2007 Motion correction for radiation therapy of prostate using B-mode ultrasound
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The use of intensity modulated radiation therapy promises to spare organs at risk by applying better dose distribution on the tumor. The specific challenge of this methods is the exact positioning of the patient and the localization of the exposured organ. With respect to the filling of rectum and bladder the prostate can move several millimeters up to centimeters. Therefore, the position of the prostate should be determinated and corrected daily before irradiation. We used a B-mode US machine (Ultramark 9, advanced Technology Laboratories, USA) which was calibrated using an optical tracking system (Polaris, NDI, Can). After correct positioning of the patient in the simulation room three anatomical markers (apex prostate, prostate lateral sinister/dexter) were identified and their positions calculated with respect to the coordinate system of the simulator. The same situation is given in the treatment room. Both, simulator and accelerator are registered by a simple point-to-point registration using a block with five drilled holes with known coordinates in the block coordinate system. The block is aligned by means of laser markers. When the patient is placed on the treatment table, the three anatomical landmarks are located on the US images and their positions are calculated with respect to the coordinate system of the treatment room. Applying a point-to-point registration results in a rotation matrix and a translation vector in the desired coordinate system which can be used for repositioning by translating and rotating the patient table. Additionally, a fiducial registration error (FRE) is calculated which gives a dimension of the accuracy the three points were identified. We found an fiducial registration error (FRE) of 2.4 mm +/- 1.2 mm for the point-to-point registration of the anatomical landmarks. The FRE for the point-to-point registration between the block and the optical tracking system was 0.5 mm +/- 0.2 mm. According to the US calibration we found an error of 0.8 mm +/- 0.2 mm.
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Johann Hummel, Johann Hummel, Michael Figl, Michael Figl, Jörg Schmidbauer, Jörg Schmidbauer, Martina Tinzl, Martina Tinzl, Helmar Bergmann, Helmar Bergmann, Wolfgang Birkfellner, Wolfgang Birkfellner, } "Motion correction for radiation therapy of prostate using B-mode ultrasound", Proc. SPIE 6509, Medical Imaging 2007: Visualization and Image-Guided Procedures, 65092F (22 March 2007); doi: 10.1117/12.708190; https://doi.org/10.1117/12.708190

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