A medical data processing method, performed by a computer, for determining error analysis data describing the registration accuracy of a first elastic registration between first and second image data A, B describing images of an anatomical structure of a patient, comprising the steps of: - acquiring the first image data A describing a first image of the anatomical structure, - acquiring the second image data B describing a second image of the anatomical structure, - determining first registration data describing a first elastic registration of the first image data A to the second image data B by mapping the first image data A to the second image data B using a registration algorithm, - determining second registration data describing a second elastic registration of the second image data B to the first image data A by mapping the second image data B to the first image data A using the registration algorithm, - determining error analysis data describing the registration accuracy of the first elastic registration based on the first registration data and the second registration data, wherein determining error analysis data comprises: - transforming the original position of a data point P A within the first image data A using the first registration data, - transforming the transformed position using the second registration data to obtain a new position of the data point P A', - calculating the distance between the original position and the new position of the data point P A, P A' to obtain an observed error E M, wherein determining error analysis data comprises determining observed errors E M for a plurality of data points P A within the first image data A, wherein determining error analysis data comprises determining at least one statistical parameter from the plurality of observed errors E M, wherein determining error analysis data comprises defining at least one data area within the first image data A, characterized by determining at least one local statistical parameter for the observed errors E M obtained for data points within the at least one data area, the method comprises the step of acquiring critical structure data describing the position of at least one critical structure corresponding to a region of interest within the anatomical structure in the first image data A and calculating the distance between the position of the critical structure and the position of at least one data area within the first image data A, wherein by calculating the distance between the position of the critical structure and the position of the at least one data area within the first image data, the local statistical parameter for the observed errors within the at least one data area is related to the critical structure. - acquiring the first image data A describing a first image of the anatomical structure, - acquiring the second image data B describing a second image of the anatomical structure, - determining first registration data describing a first elastic registration of the first image data A to the second image data B by mapping the first image data A to the second image data B using a registration algorithm, - determining second registration data describing a second elastic registration of the second image data B to the first image data A by mapping the second image data B to the first image data A using the registration algorithm, - determining error analysis data describing the registration accuracy of the first elastic registration based on the first registration data and the second registration data, wherein determining error analysis data comprises: - transforming the original position of a data point P A within the first image data A using the first registration data, - transforming the transformed position using the second registration data to obtain a new position of the data point P A', - calculating the distance between the original position and the new position of the data point P A, P A' to obtain an observed error E M,