A computer implemented method, comprising: obtaining first volumetric image data, which is acquired at a first time, including a region of interest of a subject, wherein at least one structural feature in the region of interest is located at a first position in the first volumetric image data; obtaining second volumetric image data, which is acquired at a second time, including the region of interest of the subject, wherein the at least one structural feature in the region of interest is located at a second position in the second volumetric image data, wherein the second time is subsequent to the first time, and the first and second positions are different positions; determining a registration transformation that registers the first and second volumetric image data such that the at least one structural feature in the first volumetric image data aligns with the at least one structural feature in the second volumetric image data, wherein the registration transformation is based at least on a contour guided deformation registration, wherein the contour guided deformation registration is a deformation registration which propagates a contour in the first volumetric image data to a contour in the second volumetric image data, the contours identifying a volume and/or an anatomical structure of interest, and wherein determining the registration transformation is based on i) a direction guideline, which direction guideline is a user drawn line superimposed over the first volumetric image data and ii) an intensity gradient in the second volumetric image; and generating a signal indicative of the registration transformation. obtaining first volumetric image data, which is acquired at a first time, including a region of interest of a subject, wherein at least one structural feature in the region of interest is located at a first position in the first volumetric image data; obtaining second volumetric image data, which is acquired at a second time, including the region of interest of the subject, wherein the at least one structural feature in the region of interest is located at a second position in the second volumetric image data, wherein the second time is subsequent to the first time, and the first and second positions are different positions; determining a registration transformation that registers the first and second volumetric image data such that the at least one structural feature in the first volumetric image data aligns with the at least one structural feature in the second volumetric image data, wherein the registration transformation is based at least on a contour guided deformation registration, wherein the contour guided deformation registration is a deformation registration which propagates a contour in the first volumetric image data to a contour in the second volumetric image data, the contours identifying a volume and/or an anatomical structure of interest, and wherein determining the registration transformation is based on i) a direction guideline, which direction guideline is a user drawn line superimposed over the first volumetric image data and ii) an intensity gradient in the second volumetric image; and generating a signal indicative of the registration transformation.