Study on advancement of in vivo counting using mathematical simulation (in Japanese)

Abstract

To estimate intakes of radionuclides, individual monitoring is required. For the individual monitoring, direct measurement of radionuclides in the body—in vivo counting—is very useful. To develop a precision in vivo counting technique that fulfills the requirements of the International Commission on Radiological Protection (ICRP) 1990, which recommends that “uncertainties by a factor of at least 3 may well have to be recognized and are acceptable in the estimation of intakes and associated committed equivalent and effective doses,” some problems such as the investigation of uncertainties in estimates of body burdens by in vivo counting and the selection of the way to improve the precision, have been studied. In the present study, a calibration technique for in vivo counting using Monte Carlo simulation was developed. The advantage of this technique is that counting efficiency can be obtained for various shapes and sizes that are very difficult to change for phantoms. To validate the calibration technique by calculations, the response functions and counting efficiencies of a whole-body counter installed in the Japan Atomic Energy Research Institute were evaluated using the simulation and compared with measurements. The calculations were found to be in good agreement with the measurements. The method for the determination of counting efficiency curves as a function of energy was developed using the present technique and a physical correction equation was derived from the relationship between parameters of correction factor: surface area of total body and counting efficiencies of the whole-body counter. The uncertainties in body burdens of [formula omitted] estimated with the whole-body counter were also investigated using the Monte Carlo simulation and measurements. It was found that the uncertainties of body burdens are strongly dependent on various sources of uncertainty such as radioactivity distribution within the body and counting statistics. Furthermore, the evaluation method of the peak efficiencies of a Ge semiconductor detector was developed by the Monte Carlo simulation for optimum arrangement of Ge semiconductor detectors for designing a precision whole-body counter. © 2003, American Association of Physicists in Medicine. All rights reserved.