Atlas based identification of targets for functional radiosurgery

Switching off hyperactive nuclei is a widely used approach for selected patients with movement disorders (such as Parkinson’s disease and dystonia) and is now being considered as a possible treatment for epilepsy and psychiatric disorders. Besides deep brain stimulation (DBS), another possible therapeutic solution consists of producing a lesion in the target nucleus, for example by means of radiosurgery. For that, the need to have an accurate, non-invasive localization of the target arises and the aim of our work consists of developing atlas-based identifications. Subthalamic and centromedian nuclei coordinates were obtained from the Talairach atlas. They were transformed into the coordinates of the Montreal Neurological Institute (MNI) atlas by means of linear piecewise transformation, creating a mask representative of these structures. The MNI atlas volume was registered onto the patient MRI by a global affine transformation followed by a local nonrigid. This deformation field was therefore applied to the masks of the structure to be targeted, providing the location of that structure on the patient MRI. Five patients undergoing DBS implantation (four within the subthalamic nucleus to treat Parkinson’s disease, one within the centromedian nucleus to treat central pain) were examined by this technique. The distance between the implanted pacemaker and the surface of the registered structure mask provided an idea of the quality of this technique. It was less than 1 mm for those patients who had a very satisfactory outcome (UPDRS scale improvement equal or superior to 50% in 2 patients with Parkinson’s disease; more than 50% pain reduction in one patient with central pain). It was about 1 mm for the patient with a less satisfactory outcome (30 to 40% UPDRS improvement in the remaining parkinsonian patient). It was much larger than 1 mm for the patient with a complete unsatisfactory outcome.