Création et utilisation d'atlas anatomiques numériques pour la radiothérapie. (Design and Use of Anatomical Atlases for Radiotherapy)

The main objective of this thesis is to provide radio-oncology specia-lists with automatic tools for delineating organs at risk of a patient undergoing aradiotherapy treatment of cerebral or head and neck tumors.To achieve this goal, we use an anatomical atlas, i.e. a representative anatomyassociated to a clinical image representing it. The registration of this atlas allowsto segment automatically the patient structures and to accelerate this process.Contributions in this method are presented on three axes.First, we want to obtain a registration method which is as independent as possiblew.r.t. the setting of its parameters. This setting, done by the clinician, indeedneeds to be minimal while guaranteeing a robust result. We therefore proposeregistration methods allowing to better control the obtained transformation, usingoutlier rejection techniques or locally a ne transformations.The second axis is dedicated to the consideration of structures associated withthe presence of the tumor. These structures, not present in the atlas, indeed leadto local errors in the atlas-based segmentation. We therefore propose methods todelineate these structures and take them into account in the registration.Finally, we present the construction of an anatomical atlas of the head and neckregion and its evaluation on a database of patients. We show in this part thefeasibility of the use of an atlas for this region, as well as a simple method toevaluate the registration methods used to build an atlas.All this research work has been implemented in a commercial software (Imago fromDOSIsoft), allowing us to validate our results in clinical conditions.