Three-dimensional localisation based on projectional and tomographic image correlation: an application for digital tomosynthesis.

Accurate three-dimensional tumor localisation in Radiotherapy, is critical to the treatment outcome, particularly when high dose gradients are present. A number of techniques have been proposed for the localisation of anatomical structures or markers. The present study proposes an approach to a concurrent maximisation of localisation accuracy and efficiency by correlation of tomographic and projectional images. The method introduces an element of direct verification and interactive optimisation of the process. Tomographic images are used for the identification of a point of interest. Its position is computed within the treatment co-ordinate system and verification of this position is achieved by obtaining the beam's eye view of the identified point on two projection radiographs. The key element of the approach is that all images used should be part of one single image data set. The implementation of this localisation method, as part of the functionality of a Digital Tomosynthesis prototype, has provided an integrated facility for localisation, of optimised accuracy and precision, while easy and efficient to use. The considerations are general and apply in principle to any imaging system that can augment tomographic images with projections.