1. A method, comprising: generating with a processor a three-dimensional subject specific model of a structure of interest of a subject to be scanned by fitting a forward projection of an anatomical three-dimensional model to a forward projection of pre-scan image data from a low-dose helical three-dimensional scan acquired by an imaging system based on: I = ∑ j = 1 N ⁢ ∑ k = 1 D ⁢  p jk - p jk sim ⁡ ( M )  2 , wherein I is an objective function, p jk sim (M) represents the forward projection of the anatomical three-dimensional model M onto a k th detector element, k =1,. .. , D of projection view number j, j=1,. .. , N, and p jk represents the forward projection of the low-dose helical three-dimensional pre-scan image data, which iteratively minimizes differences between the forward projection of the low-dose helical three-dimensional pre-scan image data and the forward projection of the anatomical three-dimensional model onto detector elements of projection views; and generating with the processor an imaging plan for the subject based on the three-dimensional subject specific model.