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

ABSTRACT

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 30.0mm) and rotational (up to 4.0 degrees ) 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 0.6mm (with an overall SD of 0.9mm) for the fusion of DRRs and X-ray images. Average deviations between known translational errors and calculations varied from -0.3 to 0.6mm with a standard deviation in the range of 0.6-1.2mm. The marker matching algorithm yielded a three-dimensional uncertainty of 0.3mm (overall SD 0.4mm), with averages ranging from 0.0 to 0.3mm and a standard deviation in the range between 0.3 and 0.4mm. 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.