Transfer of information between angiographic films and CT images: a technique to control the drawing of target volumes

Background and purpose: This work was undertaken to improve the definition of target volumes for radiosurgery using the angiographic and CT data. Materials and methods: The basis of this new method is to combine both imaging modalities and to compare them in each representation, i.e. to plot the volume obtained by angiography on CT images and also the contours defined by the CT on angiographic films. To obtain the angiographic volume, the radiographs are taken at several incidence angles. The X-ray sources position and the position of the films are determined using rectangular markers, then the intersection of all the loci of the target volume are calculated. Results: Verifications with a phantom show the accuracy of the procedure and the benefit obtained by increasing the number of angles of incidence in the angiographic imaging. The centre of gravity of the experimental target could be localized to an accuracy of better than 0.4 mm. The method was used in 11 clinical cases with excellent clinical results. Conclusions: The method can be easily applied and improves the delineation of target volumes in radiosurgery. CT data counterbalances the relative weakness of angiography concerning the three-dimensional geometry. Angiography adds useful information on the blood flow that is not shown in CT. Almost all the presented clinical cases benefit from the technique described here.