Estimation of the counting efficiencies for individual subjects in Cs-137 whole-body counting, using voxel phantoms

A method is described to estimate the counting efficiency appropriate to the body size of each individual subject in Cs-137 whole-body counting, using voxel phantoms. Individual voxel phantoms approximate to the body sizes of subjects were prepared by expanding and contracting the standard voxel phantom that corresponds to a Japanese standard adult male. The individual phantom was made to have the same body height and weight as those of each individual subject. For a whole-body counter at NIRS (Japan), the counting efficiencies for ten subjects were calculated, using the voxel phantoms and a Monte Carlo simulation code. The differences in the counting efficiency between each individual phantom and a conventional phantom ranged from -5 to +12%. The counting efficiency is larger in small body sizes than in large body sizes. The results indicate that body burdens tended to be overestimated in subjects of small body sizes.