A method, comprising: generating a first image data set using a first imaging modality, the first image data set comprising a first plurality of images of a target volume within a human body, and of a plurality of markers (110, 200) internally implanted in proximity or relative to the target volume; generating a treatment plan based on a selected treatment plan center and the first image data set; determining a first internal three-dimensional coordinate system based on locations of the plurality of markers (110, 200) in the first image data set and the selected treatment plan center; determining a first set of three-dimensional coordinates of locations of the plurality of markers in the first image data set based on the first internal coordinate system; generating a second image data set using a second imaging modality, the second image data set comprising a second plurality of images of the target volume within the human body, and of the plurality of markers (110, 200) internally implanted in proximity of relative to the target volume; determining a second internal three-dimensional coordinate system based on locations of the plurality of markers (110, 200) in the second image data set and a treatment machine isocenter of the second imaging modality; determining a second set of three-dimensional coordinates of locations of the plurality of markers in the second image data set based on the second internal coordinate system; determining an offset between the first set of three-dimensional coordinates of the plurality of markers and the second set of three-dimensional coordinates of the plurality of markers; and adjusting the treatment plan based on the determined offset. generating a first image data set using a first imaging modality, the first image data set comprising a first plurality of images of a target volume within a human body, and of a plurality of markers (110, 200) internally implanted in proximity or relative to the target volume; generating a treatment plan based on a selected treatment plan center and the first image data set; determining a first internal three-dimensional coordinate system based on locations of the plurality of markers (110, 200) in the first image data set and the selected treatment plan center; determining a first set of three-dimensional coordinates of locations of the plurality of markers in the first image data set based on the first internal coordinate system; generating a second image data set using a second imaging modality, the second image data set comprising a second plurality of images of the target volume within the human body, and of the plurality of markers (110, 200) internally implanted in proximity of relative to the target volume; determining a second internal three-dimensional coordinate system based on locations of the plurality of markers (110, 200) in the second image data set and a treatment machine isocenter of the second imaging modality; determining a second set of three-dimensional coordinates of locations of the plurality of markers in the second image data set based on the second internal coordinate system; determining an offset between the first set of three-dimensional coordinates of the plurality of markers and the second set of three-dimensional coordinates of the plurality of markers; and adjusting the treatment plan based on the determined offset.