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Development of an optical‐based image guidance system: Technique detecting external markers behind a full facemask
Author(s) -
Kim Hwiyoung,
Park YangKyun,
Kim Il Han,
Lee Kunwoo,
Ye SungJoon
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3589137
Subject(s) - computer vision , medical imaging , computer science , medical physics , image processing , artificial intelligence , image registration , optical imaging , optics , computer graphics (images) , image (mathematics) , physics
Purpose : Optical image‐guided systems (e.g., AlignRT®, frameless SonArray, ExacTrac®) have been used with advantages of avoiding excessive radiation exposure and real‐time patient monitoring. Although these systems showed proven accuracy, they need to modify a full facemask for patients with H&N cancer and brain tumor. We developed an optical‐based guidance system to manage interfractional and intrafractional setup errors by tracking external markers behind a full facemask. Methods : Infra‐red (IR) reflecting markers were attached on the face of a head phantom and then the phantom was immobilized by a full face thermoplastic mask. A stereo camera system consisting of two CCD cameras was mounted on the inferior wall of treatment room. The stereo camera system was calibrated to reconstruct 3D coordinates of multiple markers with respect to the isocenter using the direct linear transform (DLT) algorithm. The real‐time position of the phantom was acquired, through the stereo camera system, by detecting the IR markers behind the full facemask. The detection errors with respect to the reference positions of planning CT images were calculated in six degrees of freedom (6‐DOF) by a rigid‐body registration technique. Results : The calibration accuracy of the system was in submillimeter (0.33 mm ± 0.27 mm), which was comparable to others. The mean distance between each of marker positions of optical images and planning CT images was 0.50 mm ± 0.67 mm. The maximum deviations of 6‐DOF registration were less than 1 mm and 1° for the couch translation and rotation, respectively. Conclusions : The developed system showed the accuracy and consistency comparable to the commercial optical guided systems, while allowing us to simultaneously immobilize patients with a full face thermoplastic mask.