A simple and accurate coordinate transformation for a stereotactic radiotherapy system

A global registration algorithm using only two CT slices was developed to transform target points known in the Brown-Roberts-Wells frame back to a CT-simulator coordinate system. The algorithm uses exact solutions to determine all of the points of interest based on BRW pins in the two CT- slices. In comparison with the algorithms based on individual slices, there is no requirement of digitization of BRW pins in every CT slice. There is no approximation (or linear interpolation) for determination of the target points that fell in between two CT slices. Results in 60 clinical cases demonstrate that the accuracy and precision of the isocentric positions are within the digitization uncertainty. Application of this global image registration can simplify the coordinate transformation in stereotactic radiation therapy.