Continuous CT Image Reconstruction during treatment by Amplitude-Phase Scaling of Deformation Vector Fields

Abstract

The anatomy of patients changes between treatment planning and delivery as well as over the course of radiotherapy treatment. This potential difference in patient anatomy is a pervasive challenge in radiotherapy and is more prevalent in organs associated with respiratory motion. This research aims to develop a method to reconstruct three-dimensional cine computed tomographic (cCT) images representing the moment of treatment irradiation from planning 4DCT images by fitting the DVF of the p4DCT images to the anatomical condition caused by internal motion at each treatment moment. An anthropomorphic digital phantom will be used to generate the 4D image sets based on two maximally different breathing traces in their shapes with tumors at different locations. DVFs are obtained by deformable image registration between a presumable pivot phase (end of exhale) and other phases of the p4DCT images. The projection images of all the phases are calculated through the p4DCT and t4DCT. On each projection image set, the motion amplitude of the visible tumor is quantified as the displacement of its COM coordinate at each phase from the coordinate at the pivot phase. The ratio of amplitudes on the treatment projection to the planning projection will be obtained for each phase. The amplitude ratio will then be used to get the scaled DVFs which will then be used to resample the p4DCT images to generate images at the time of beam irradiation (on-beam 4DCT or b4DCT). The b4DCT images will be compared with the t4DCT images. The comparison is expected to be in good agreement, and we further want to test the method with real patient tumor data. The method described could reconstruct the cCT images from p4DCT accurately.