Patient-specific biomechanical model of the respiratory system for radiation therapy ; Modèle biomécanique patient-spécifique pour la prédiction du mouvement respiratoire pour la radiothérapie

The 4D computational patient specic of the respiratory system could be potentially used in various medical contexts; for diagnosis, treatment planning, laparoscopic, dose computation or the registration between online imaging systems such as positron emission tomography (PET), computed-tomography (CT) as well as high delity and precise computer-based training simulators. The main novelty of this PhD project lies in the context of radiation therapy; we have developed a patient-specic biomechanical model of the respiratory system enabling the correlation of the internal organs motion with respiratory surrogate signal(s) during the treatment. This permits to take into account the respiratory motion variabilities. The deformation of the dierent structures is controlled and driven by simulated rib cage (mimic the external intercostal muscles) and diaphragm actions. For the diaphragm, we have applied the radial direction of muscle forces, and simple homogeneous dirichlet boundary condition is applied to the lower part of the diaphragm, which is attached to the rib cage. For each rib a rigid transformation is calculated automatically by nite helical axis method (rigid translation and rotation) and used to dene displacement boundary conditions. The resulting widening of the thoracic cavity forces the lungs to expand due to an applied negative pressure in the pleural cavity. Other novelty of the PhD project, that the amplitude of the lung pressure and diaphragm force are patient-specic, and determined at dierent respiratory states by an optimization framework based on inverse FE analysis methodology, by minimizing the volume lungs errors, between the respiratory volume (calculated from CT scan images at each state) and the simulated volume (calculated by biomechanical simulation). All other structures are linked to each other, but feature dierent deformation behavior due to the assigned material properties. Our results are quite realistic compared to the 4D CT scan images and the proposed physically-based FE model is ...