Dosimetric study in the human head for CT investigation of the inner ear using the Geant4 toolkit

This work is a status report of the job in progress finalized to the estimation of the dose distribution inside the head of a patient undergoing a high resolution CT (Computed Tomography) for the diagnosis of pathologies related to the inner ear. Geant4 (GEometry ANd Tracking) has been used to simulate the head and propagate the particles in the human tissues. The ear has a very complex structure, in particular the inner section includes many very small structures, which are located in a very compact region (a few square centimeters), and many of them have dimensions below the millimeter. The semicircular canals and vestibule are part of the Vestibular Complex that provides the feeling of balance, rotation, gravity and linear acceleration. Otoliths, receptors in the vestibule, are small groups of calcium carbonate by the maximum diameter of 200 micrometers. Two different approaches have been checked for the representation of the human head. The first phantom has been constructed using a vector graphics approach through the geometric solids provided by Geant4. The second phantom has been constructed using an anatomical division into voxels. In particular, we achieved a volumetric model definition very close to the division into axial layers. In this approach the simulation may be customized by using DICOM CT images. In this work we will present the results obtained using the Geant4 toolkit and the suggestions we find to proceed.