Quality assurance of a system for improved target localization and patient set-up that combines real-time infrared tracking and stereoscopic X-ray imaging

Background and purpose: The aim of this study is to investigate the positional accuracy of a prototype X-ray imaging tool in combination with a real-time infrared tracking device allowing automated patient set-up in three dimensions. Material and methods: A prototype X-ray imaging tool has been integrated with a commercially released real-time infrared tracking device. The system, consisting of two X-ray tubes mounted to the ceiling and a centrally located amorphous silicon detector has been developed for automated patient positioning from outside the treatment room prior to treatment. Two major functions are supported: (a) automated fusion of the actual treatment images with digitally reconstructed radiographs (DRRs) representing the desired position; (b) matching of implanted radio opaque markers. Measurements of known translational (up to 30.0 mm) and rotational (up to 4.0°) set-up errors in three dimensions as well as hidden target tests have been performed on anthropomorphic phantoms. Results: The system's accuracy can be represented with the mean three-dimensional displacement vector, which yielded 0.6 mm (with an overall SD of 0.9 mm) for the fusion of DRRs and X-ray images. Average deviations between known translational errors and calculations varied from −0.3 to 0.6 mm with a standard deviation in the range of 0.6–1.2 mm. The marker matching algorithm yielded a three-dimensional uncertainty of 0.3 mm (overall SD: 0.4 mm), with averages ranging from 0.0 to 0.3 mm and a standard deviation in the range between 0.3 and 0.4 mm. Conclusions: The stereoscopic X-ray imaging device integrated with the real-time infrared tracking device represents a positioning tool allowing for the geometrical accuracy that is required for conformal radiation therapy of abdominal and pelvic lesions, within an acceptable time-frame.