According to the geometry deformation characteristic of scanned sequence image used in three-dimensional computer radiotherapy treatment planning system

a sequence image normalizing method based on scanning image rulers has been developed.The method first models the image deformation caused by the tilted film as a projection model

and makes use of CT and MRI sequence image rulers

both vertical and horizontal

to rectify the deformation and calculate a few user-defined marker's relative coordinates; then employs these markers to normalize the whole sequence image.The clinical result shows that the method is feasible and can satisfy the clinical image normalizing demand in three-dimensional radiotherapy treatment planning system.