Application Technique of Computational Phantoms from Photographic Images for Patient-tailored Whole Body Counting

In the direct bioassay method for internal exposure monitoring, the radioactivities in the body are measured by detectors placed around the body and hence the counting geometry including body size of the subject significantly affects the counting efficiencies. To take into account the body size, a set of standardidized BOMAB phantoms, usually consists of 4 or 5 phantoms, is used for calibration of the body counter but the body size or shape of a real subject still could significantly deviate from one of the standard phantom selected. This study attempted to develop a new method to apply subject-tailored efficiency data. Since the number of standard phantoms are very limited, a digital calibration which determines the counting efficiencies by Monte Carlo simulations of body counting was introduced. Validity of this approach was examined by comparing the simulation results to the measured values for the standard BOMAB phantoms. The computational voxel phantoms were constructed by reconstruction technique from photographic images, in AP and lateral directions, of the BOMAB phantoms instead using the given specifications. Although discrepancies of certain degree between the calculated and measured efficiencies, the results support the new approach to be developed further. Finally, the computational phantom reconstruction technique was testified for real human subject. Because of very simple algorithm applied, there were some distortions in parts of the body, specifically arms, but the resulting voxel phantom is of quality enough to be used in calculation of efficiencies for subject-tailored body counting