Using ASM in CT Data Segmentaion for Prostate Radiotherapy

A novel method of prostate segmentation in a new CT data making use of explicit knowledge about the prostate is proposed. The segmentation procedure is based on active shape statistical model (ASM) of the prostate, calculated using available data base of CTs annotated by medical doctors. In the paper the problem of automatic calculation of

corresponding

prostate landmarks in

different

CTs, which are absolutely necessary for the ASM, is solved in a new manner by: 1) finding parameters of affine and B-spline transformations in groupwise registration framework ensuring pixel-based registration of all available CTs in one common co-ordinate system, 2) performing forward affine and B-spline transformation of the annotated prostate contours into this co-ordinate system, 3) averaging them - interpolation & re-sampling, 4) propagation (projection) of mean landmarks, obtained in common co-ordinate system, to the training CTs using the backward transformation. Having the same prostate landmarks in set of CTs, the ASM of the prostate is calculated (its mean shape and tendencies to its direction variations). The result of matching ASM to the data is treated as the prostate segmentation result. Obtained results are presented and discussed in the paper.