3D numerical test objects for the evaluation of a software used for an automatic analysis of a Linear Accelerator mechanical stability

Mechanical stability of a medical LINear Accelerator (LINAC), particularly the quality of the gantry, collimator and table rotations and the accuracy of the isocenter position, are crucial for the radiation therapy process, especially in stereotactic radio surgery 1, 2 and in Image Guided Radiation Therapy 3, 4, 5 (IGRT) where this mechanical stability is perturbed due to the additional weight the kV x-ray tube and detector. In this paper, we present a new method to evaluate a software 6, 7, 8 which is used to perform an automatic measurement of the "size" (flex map) and the location of the kV and the MV isocenters of the linear accelerator. The method consists of developing a complete numerical 3D simulation of a LINAC and physical phantoms in order to produce Electronic Portal Imaging Device (EPID) images including calibrated distortions of the mechanical movement of the gantry and isocenter misalignments 2, 9 .