A Preliminary Study on Development of QA System for Stereotactic Head Frame and Its Reliability and Accuracy

Abstract

Stereotactic radiosurgery is considered one of the precisest treatments because of its mechanical fixation of cranium using a stereotactic head frame (SHF). Several studies, however, presented the SHF could be bent and/or displaced due to jostling and/or changing of force/weight to SHF, which might cause significant inaccuracy up to 6 mm in certain circumstances. Nevertheless, to our best knowledge, no clear mechanism of SHF QA has been established. We are under development of a stereo-camera-based QA system for SHF to check its integrity of shape and placement. In this preliminary study, a prototype of camera system was developed and its reliability and accuracy were evaluated. The initial prototype of stereo camera system was developed using two CMOS cameras (with maximum resolution of 2048×1536) and a control computer. The system was designed to measure the 3D coordinates of points from left-right image pair through camera calibration and triangulation. A software program for image reconstruction and control was written using C-language. For reliability test, six image pairs of a fixed circle-pattern were obtained every 5 minutes for 25 minutes. Then, the vector of each circle’s center was calculated between the first- and n-th image pair. To evaluate accuracy, sets of image pair for translation and rotation were obtained. Then, differences in translation and rotation from the reference were calculated using singular value decomposition. The camera system showed reliability of within 0.5 mm during 25 minutes. The accuracy was within 1 mm in translation and 1° in rotation. The prototype of stereo camera system developed in this study demonstrated its potential of being applied for SHF QA. The study will be continued for further evaluation and improvement.