AbstractID: 9660 Title: Three Dimensional Lung Respiratory Motion Study Using Finite Element Analysis Target respiratory motion is a considerable challenge for the IMRT treatment of lung cancer. 3D displacement information of the tumor and surrounding tissue during respiration provides the ground for future verification and treatment techniques. We have used finite element (FE) contact-impact analysis to simulate lung respiratory motion. Respiratory motion is driven by a negative surface pressure from the diaphragm and the chest wall. This process was simulated with FE methods. In this pilot study, the FE model was done under the assumption that the lung tissue is a uniform isotropic elastic material, a restriction that can in principle be relieved. At least two CT scans at two different breathing phases are required to establish the model. A 3D mesh of the lung is created given the lung surface in the expiration phase. A contact target surface is created from the lung surface in the inspiration phase. Starting from an equilibrium state, negative surface pressure load is gradually added onto the solid lung model. The lung volume expands step by step until it contacts with the target surface. Frictionless sliding is allowed after contact happens. This process is finished when the two surfaces are completely closed. The validation of this FE model is done in two and three dimensions using fluoroscopic videos acquired during breathing which are compared to an image sequence derived from the FE model.