Correction of prostate misalignment in radiation therapy using US-CT registration

Rainer Hoffmann; Michael Figl; Marcus Kaar; Amon Bhatia; Amar Bhatia; Wolfgang Birkfellner; Johann Hummel

doi:10.1117/12.844269

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23 February 2010 Correction of prostate misalignment in radiation therapy using US-CT registration

Rainer Hoffmann, Michael Figl, Marcus Kaar, Amon Bhatia, Amar Bhatia, Wolfgang Birkfellner, Johann Hummel

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Proceedings Volume 7625, Medical Imaging 2010: Visualization, Image-Guided Procedures, and Modeling; 76252B (2010) https://doi.org/10.1117/12.844269
Event: SPIE Medical Imaging, 2010, San Diego, California, United States

Abstract

Latest developments in radiation therapy such as IGRT (image guided radiation therapy) and IMRT (intensity modulated radiation therapy) promise to spare organs at risk by applying better dose distribution on the tumor. For any effective application of these methods the exact positioning of the patient and the localization of the exposured organ is crucially. With respect to the filling of rectum and bladder the prostate can move several millimeters up to centimeters. That implies the need of daily determination and correction of the position of the prostate before irradiation. We calibrated a scan head of a B-mode US machine (Ultramark 9, advanced Technology Laboratories, USA) by means of an optical tracking system (Polaris, NDI, Can). 2D/3D registration was accomplished by minimizing an adapted mutual information function. Before the registration procedure was started CT respectively US images were preprocessed by applying various filters and masks. For registration between the tracking system and the coordinate system of the Linac (defined by the positioning laser system) a block with three drilled holes was used. Since the coordinates of the holes are known in both coordinate systems a simple point-to-point registration fulfills the task. The complete system setup was evaluated by means of a water-filled balloon embedded in a gelatinetank. For additional evaluation of the 2D/3D registration we used real patient data. For evaluation of the 2D/3D registration on patient data the prostate was drawn in by a physician on the US image and the reformatted CT slice. Then, the Hausdorff distance between the two structures was calculated. The target registration error (TRE) with respect to the balloon experiments amounted to be 2.1mm±1.2mm for 10 targets. The US calibration was accomplished with an error of 0.8mm± 0.2mm (five calibrations). With respect to the 2D/3D registration we found an Hausdorff distance of 2.6mm. The results imply that the method is sufficiently accurate and robust. It can be easily applied to older linear accelerators at low costs.

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Rainer Hoffmann, Michael Figl, Marcus Kaar, Amon Bhatia, Amar Bhatia, Wolfgang Birkfellner, and Johann Hummel "Correction of prostate misalignment in radiation therapy using US-CT registration", Proc. SPIE 7625, Medical Imaging 2010: Visualization, Image-Guided Procedures, and Modeling, 76252B (23 February 2010); https://doi.org/10.1117/12.844269

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