Organ and Effective Doses in the Male Phantom Adam Exposed in AP Direction to Broad Unidirectional Beams of Monoenergetic Electrons

Abstract

Organ and effective doses per unit of fluence are calculated through Monte Carlo simulation of radiation transport (MCNP code, version 4) for the mathematical adult male phantom, ADAM, placed in vacuum and irradiated in the AP direction with broad unidirectional electron beams. The electrons are monoenergetic in the energy range of 0.1 to 10 MeV. Effective dose per unit of fluence increases with increasing electron energy from 8 × 10⁻¹⁴ to 2 × 10⁻¹⁰ Sv cm⁻². Corresponding effective dose equivalents are also calculated. At the high end of the energy range considered, the present values agree reasonably well with the results of a series of calculations performed with the MIRD-5 male phantom in the 5 to 46 MeV electron energy range, as published in ICRU Report 43 (1988). The difference between effective dose and effective dose equivalent is relatively small for electron energies between 1.5 and 10 MeV. However, the difference increases rapidly if the electron energy decreases. Below 0.5 MeV, effective dose equivalent is about a factor of 100 less than effective dose. In this low energy range, annual dose limits are reached sooner if effective dose instead of effective dose equivalent is used as parameter of risk assessment. Taking the directional dose equivalent as a substitute for effective dose introduces an unnecessarily large safety factor.