Determining the effective dose equivalent and effective dose for anthropomorphic phantoms with different torso thicknesses for broad parallel beams of external photon radiation

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references (leaves 62-69).Issued also on microfiche from Lange Micrographics.The hazard from different sources of radiation can be evaluated using the concept of effective dose and effective dose equivalent defined in ICRP Publications 60 and 26, respectively. The Code of Federal regulations (Statndards 1991) sets limits for effective dose equivalent both for radiation workers and for members of the general public. Computer codes utilizing Monte Carlo methods can be used to assess organ doses for known source geometries and appropriate phantoms. Most of the calculations have been performed for the reference person described in ICRP Publication 23 (1975). The mathematical model of the human body - anthropomorphic phantom - corresponding to this description has been designed and widely used for determining the effective dose and effective dose equivalent. However, when considering the human body, the dimensions of the body and organs vary widely. This study determined the effective dose equivalent and effective dose for anthropomorphic phantoms with differing torso thicknesses for broad parallel beams of external photon radiation. The mathematical model of the human body that was used for this study was a hermaphroditic phantom developed at the Oak Ridge National Laboratory (Eckerman et at. 1996). Adding a layer of soft tissue around the phantom's torso modeled the change in the adipose tissue thickness. Phantoms with 0, 1, 2, 3, 4, 5, 6, and 7 cm of extra torso thickness were included in calculations. The studied irradiation geometries were anterior-posterior (AP), posterior-anterior (PA), lateral (LAT), and overhead (OH) beams. The phantom was irradiated with a broad parallel beam of monoenergetic photons of 80 keV, 300 keV, and 1 MeV, which cover the most typical photon energies for nuclear power facilities. Photon transport was modeled with the Monte Carlo Nuclear Particle transport code MCNP 4A (Briesmeister 1993). Calculated results for the standard Oak Ridge phantom correlated well with published results of other studies (ICRP 1987, ICRP 1991b, and Reece et al. 1994). Both effective dose equivalent and effective dose decreased linearly with phantom's torso thickness increase for anterior-posterior (AP), posterior-anterior (PA), and lateral (LAT) irradiation geometries. But these quantities increased linearly with increase of adipose tissue thickness for overhead (OH) irradiation