A system for controlling real-time image-guided adaptive radiation treatment of at least a portion of a region of a patient, the system comprising a treatment adaptation system and a therapy controller circuit , wherein the treatment adaptation system is configured to: obtain a plurality of real-time image data corresponding to 2-dimensional, "2D", magnetic resonance imaging images including at least a portion of the region; perform 2D motion field estimation on the plurality of image data; approximate a 3-dimensional, "3D", motion field estimation, including application of a conversion model to the 2D motion field estimation, wherein the conversion model is specified by performing 3D motion field estimation on at least two 3D image data volumes that include at least a portion of the region obtained during a first time frame, performing 2D motion field estimation on 2D image data corresponding to at least two 2D images that include at least a portion of the region obtained during the first time frame, and determining the conversion model using a reduced 3D motion field and the 2D motion field; wherein the treatment adaptation system is furthermore configured to determine at least one real-time change of the at least a portion of the region based on the approximated 3D motion field estimation; and wherein the therapy controller circuit is configured to: control the treatment of the at least a portion of the region using the determined at least one change. obtain a plurality of real-time image data corresponding to 2-dimensional, "2D", magnetic resonance imaging images including at least a portion of the region; perform 2D motion field estimation on the plurality of image data; approximate a 3-dimensional, "3D", motion field estimation, including application of a conversion model to the 2D motion field estimation, wherein the conversion model is specified by performing 3D motion field estimation on at least two 3D image data volumes that include at least a portion of the region obtained during a first time frame, performing 2D motion field estimation on 2D image data corresponding to at least two 2D images that include at least a portion of the region obtained during the first time frame, and determining the conversion model using a reduced 3D motion field and the 2D motion field; wherein the treatment adaptation system is furthermore configured to determine at least one real-time change of the at least a portion of the region based on the approximated 3D motion field estimation; and wherein the therapy controller circuit is configured to: control the treatment of the at least a portion of the region using the determined at least one change. performing 3D motion field estimation on at least two 3D image data volumes that include at least a portion of the region obtained during a first time frame, performing 2D motion field estimation on 2D image data corresponding to at least two 2D images that include at least a portion of the region obtained during the first time frame, and determining the conversion model using a reduced 3D motion field and the 2D motion field; wherein the treatment adaptation system is furthermore configured to determine at least one real-time change of the at least a portion of the region based on the approximated 3D motion field estimation; and wherein the therapy controller circuit is configured to: control the treatment of the at least a portion of the region using the determined at least one change. <EOS>