An improved dosimetric model of the head and brain

Abstract

During the last decade, various brain imaging methods using radionuclides have become available. Due to the introduction of new techniques, a small-scale dosimetry study of the brain, and more specifically the organs of the head (brain, eyes thyroid, skull, skin) was needed. However, the brain and head models developed in the past were crude representations of the human. In this research, a new brain model has been developed which includes eight subregions. This head model was included in a revised head model developed by Posion et al. in 1984. Some corrections and improvements were added to this head model such as the development of a new spinal region and a new cranium region in order to incorporate the cerebrospinal fluid. This model was used with a Monte Carlo code, EGS4, to calculate absorbed fraction of energy and specific absorbed fraction of energy for photon and electron sources located in one of thirteen chosen source regions. These calculations were made for radiations in the energy range 10 keV to 4 MeV. All twenty-three regions included in the revised head and brain model were taken as target regions. S-values were also calculated for several radionuclides used in brain imaging, and also deposited in the thyroid, the skull or the spinal skeleton. The S-values were calculated using discrete energy points on the beta emission spectrum of the radionuclides.