A radiotherapy system, comprising: an image acquisition device configured to acquire images of an anatomical region of interest of a patient; a radiotherapy device configured to deliver a dose of radiation to the anatomical region of interest based on the images of the anatomical region of interest; and a processor device configured to: control the image acquisition device to acquire a plurality of two-dimensional images, the plurality of 2D images comprising a first 2D image acquired at a first time point and a second 2D image acquired at a second time point, the second time point being more recent than the first time point, each of the first and second 2D images including a cross-sectional image of the anatomical region of interest; generate a predicted image by advancing the first 2D image forward in time to the second time point; perform automatic contouring to extract a first set of contour elements segmenting the cross-sectional image of the anatomical region of interest in the predicted image and a second set of contour elements segmenting the cross-sectional image of the anatomical region of interest in the second 2D image; match the first and second sets of contour elements to a three-dimensional surface image of the anatomical region of interest to determine a motion of the anatomical region of interest; and control radiation delivery based on the determined motion. an image acquisition device configured to acquire images of an anatomical region of interest of a patient; a radiotherapy device configured to deliver a dose of radiation to the anatomical region of interest based on the images of the anatomical region of interest; and a processor device configured to: control the image acquisition device to acquire a plurality of two-dimensional images, the plurality of 2D images comprising a first 2D image acquired at a first time point and a second 2D image acquired at a second time point, the second time point being more recent than the first time point, each of the first and second 2D images including a cross-sectional image of the anatomical region of interest; generate a predicted image by advancing the first 2D image forward in time to the second time point; perform automatic contouring to extract a first set of contour elements segmenting the cross-sectional image of the anatomical region of interest in the predicted image and a second set of contour elements segmenting the cross-sectional image of the anatomical region of interest in the second 2D image; match the first and second sets of contour elements to a three-dimensional surface image of the anatomical region of interest to determine a motion of the anatomical region of interest; and control radiation delivery based on the determined motion. control the image acquisition device to acquire a plurality of two-dimensional images, the plurality of 2D images comprising a first 2D image acquired at a first time point and a second 2D image acquired at a second time point, the second time point being more recent than the first time point, each of the first and second 2D images including a cross-sectional image of the anatomical region of interest; generate a predicted image by advancing the first 2D image forward in time to the second time point; perform automatic contouring to extract a first set of contour elements segmenting the cross-sectional image of the anatomical region of interest in the predicted image and a second set of contour elements segmenting the cross-sectional image of the anatomical region of interest in the second 2D image; match the first and second sets of contour elements to a three-dimensional surface image of the anatomical region of interest to determine a motion of the anatomical region of interest; and control radiation delivery based on the determined motion. <EOS>