A system includes obtaining of a reference projection image of a target volume at an isocenter of a computed tomography scanner； obtaining of a plurality of two-dimensional fluoroscopic images by the computed tomography scanner of at least a portion of the target volume at the isocenter of the computed tomography scanner； displaying the reference projection image and the plurality of two-dimensional fluoroscopic images in a combined view； measuring a two-dimensional contour of a projection of a movement of the target volume in the combined view； and determining a true contour of the movement in a plane containing a point-of-interest within the target volume based on the two-dimensional contour of the projection of the movement.
