Increasing organ dose accuracy through voxel phantom organ matching with individual patient anatomy

Abstract

PurposeGiven the large use of computed tomography (CT) worldwide, the potential harmful effects and the radiation dose delivered to the patient have become high-interest topics among the scientific community. The main objective of this work was to modify existing three-dimensional (3D) voxel phantom models to resemble real patients as much as possible, thus trying to give a contribute towards the concept of a more personalized patient dosimetry. Moreover, comparisons were made of organ dose computed in the standard reference phantom and phantoms modified to match patient body size and organ size. This study focused essentially on one of the biggest and most radiosensitive organs in the thorax, the lungs. MethodsIn order to accomplish this objective a FORTRAN-based program was developed, which is able to semi-automatically modify the volumetric information of organs of interest in a standard voxel phantom (Female ICRP Adult Reference). Monte Carlo (MC) PENELOPE simulation code was used to mimic CT previews and, therefore, generate 2D projections, used for visual organ matching with clinical patient CT images, and calculate organ dose in both phantoms (ICRP standard and ICRP modified). Two CT scan irradiation setups were considered, namely Fan Beam CT (FBCT) and Cone Beam CT (CBCT) geometries. Validation of the implemented MC model (voxel phantom plus X-ray sources in diagnostic energy range) was accomplished through the calculation of lung-absorbed dose per fluence conversion coefficients for the Anterior-Posterior (AP) geometry setup with subsequent comparison with ICRP 116 tabulated values. ResultsThe main results reported that matching the voxel phantom's size and lungs provides organ dose values substantially different from the ones calculated in the ICRP reference phantom. According to the data presented in this study, organ dose can be up to 20% underestimated and 40% overestimated when compared to organ dose in the reference phantom, considering both irradiation setups. ConclusionsThis study demonstrates that voxel phantoms developed using single patient data could provide a better and more precise organ dose assessment by MC methods with respect to a standard phantom.