Reduction of motion artefacts in on-board cone beam CT by warping of projection images.

Abstract

A local motion correction method for flat panel imager-based cone beam CT by warping of projection images has been developed and tested. Markers within or on the surface of the patient are tracked and their mean three-dimensional (3D) position is calculated. The two-dimensional (2D) cone beam projection images are then warped before reconstruction to place each marker at the projection from its mean 3D position. The motion correction method was tested using simulated cone beam projection images of a deforming virtual phantom, real CBCT images of a moving breast phantom and clinical CBCT images of a patient with breast cancer and another with pancreas cancer undergoing radiotherapy. In phantom studies, the method was shown to greatly reduce motion artefacts in the locality of the radiotherapy target and allowed the true surface shape to be accurately recovered. The breast phantom motion-compensated surface was within 1 mm of the true surface shape for 90% of surface points and greater than 2 mm from the true surface at only 2% of points. Clinical CBCT images showed improved image quality in the locality of the radiotherapy target after motion correction.