Motion compensated digital tomosynthesis

Digital tomosynthesis (DTS) is a limited angle image reconstruction method for cone beam projections that offers patient surveillance capabilities during VMAT based SBRT delivery. Motion compensation (MC) has the potential to mitigate motion artifacts caused by respiratory motion, such as blur. The purpose of this feasibility study was therefore to develop and evaluate motion-compensated DTS (MC-DTS). MC-DTS images were reconstructed by back projection of X-ray projection images acquired over 30° arcs. Back projection lines were deformed according to an a priori motion model derived from the 4D planning CT. MC-DTS was evaluated on a respiratory motion phantom and 3 lung cancer patients. Respiratory artifact reduction was assessed visually and quantified by fitting a cumulative Gaussian function to profiles along the background-GTV transition in the CC direction. MC reconstruction was fast enough to keep up with image acquisition and considerably reduced motion blur visually. Quantitatively, MC reduced the background-GTV transition distance by 49%. Motion compensation considerably improved the image quality of DTS images of lung cancer patients, giving an opportunity for more accurate DTS guidance and intra-fraction monitoring concurrent with VMAT delivery