ABSTRACT
Most researchers choose the diffusion approximation to the transport equation as the model to describe photon migration in biological tissues. However, the applicability of this approximation is limited and, in certain cases, invalid. In this paper we introduce a two-dimensional, finite element-spherical harmonics (FE-P(N)) radiation transport method for the simulation of light propagation in tissue. The propagation of light is investigated first in a layered cylinder, which can be seen as a very simplistic approximation of a human head. Effects of the anisotropy factor g on the photon migration is then examined in homogeneous and heterogeneous media for different values of g and mu(s). The influence of void-like heterogeneities and channels in which absorption and scattering are very small compared with the surrounding medium on the transport of photons is also investigated. Significant differences between transport and diffusion calculations are shown to occur in all cases.
Subject(s)
Computer Simulation , Head/anatomy & histology , Head/radiation effects , Image Enhancement/methods , Models, Biological , Photons , Anisotropy , Brain/anatomy & histology , Brain/radiation effects , Brain Neoplasms/diagnosis , Cerebrospinal Fluid/radiation effects , Diffusion , Diffusion Magnetic Resonance Imaging/methods , Finite Element Analysis , Humans , Light , Phantoms, Imaging , Scattering, Radiation , Skin/anatomy & histology , Skin/radiation effects , Subarachnoid Space/anatomy & histology , Subarachnoid Space/radiation effectsABSTRACT
In nuclear accident consequence assessment, dose contributions from radionuclide deposition on the human body have in the past generally been either ignored or estimated on the basis of rather simple models. Recent experimental work has improved the state of knowledge of relevant processes and parameter ranges. The results presented in this paper represent a first approach to a detailed assessment of doses from radiopollutant deposition on the human body, based on contaminant-specific data. Both the dose to skin from beta-emitters and the whole-body dose from gamma-emitters on body surfaces were found to give potentially significant contributions to dose. Further, skin penetration of some contaminants could lead to significant internal doses.
Subject(s)
Air Pollutants, Radioactive , Models, Theoretical , Radioactive Hazard Release , Radiometry , Beta Particles , Gamma Rays , Humans , Skin/radiation effectsABSTRACT
A procedure has been developed for the calculation of absorbed doses to human tissues or organs, due to external y-activity from an atmospheric release of radio-isotopes in the form of a finite plume. The procedure is based upon the moments method, which yields a solution of the photon transport equation for infinite air. Analytical expression have been derived which are applied to these infinite air y-fluxes to allow for the presence of the ground. Photon spectra and exposures may be calculated for any type of plume composition, release, height and atmospheric stability. By combining the computed spectra with published human organ doses due to external irradiation, absorbed doses to various human tissues have been evaluated. Calculations have also been carried out, on the basis of ICRP recommendations, to predict effective dose-equivalent and effective dose equivalent per unit exposure (rem/R) factors. As examples, of the application of the method in safety assessment one hypothetical monoenergetic emitter release and one notional MAGNOX reactor release have been considered. The annihilation radiation contribution to exposure is also discussed (AU)
