Six parameter patient registration directly from projection data

Patient registration, a technique to ensure dose conformity, is an essential part of tomographic radiotherapy. A new six parameter (three translational and three angular) algorithm to implement this technique has been developed. The method is stable, accurate, and most importantly uses sinogram data as input, obviating image reconstruction. A sinogram, an array of Radon transforms, is derived directly from the raw data, which are photon transmission fluences from either a diagnostic or a megavoltage X-ray source. The algorithm uses properties of the Radon and Fourier transforms, such as the central slice theorem and Fourier shift theorem, to decouple translational and angular offsets. The theoretical underpinnings of this algorithm are presented here, whereas numerical verification using synthetic and experimental data is presented elsewhere.