Absolute Biological Effectiveness of Neutrons and Photons

Publisher Website
Google Scholar
Abstract
The cause of inactivation, chromosome aberrations and mutations in mammalian cells by the direct action of all types of ionising radiation is attributed to the, statistically determined, spatial correlation of pairs of interactions along single charged particle tracks with the mean chord separation (~2 nm) of the strands in the intranuclear DNA segments to induce double strand breaks. Energy deposition parameters such as absorbed dose, and therefore RBE, are not relevant to the description of the process. A unified scheme for the direct action of all radiations on various cell types can be obtained by expressing the inactivation probability or intrinsic efficiency for damage as a function of the mean free path for ionisation by the relevant charged particles at depth in the medium. In this way the quality of the radiation can be expressed absolutely. When expressed mathematically, this mechanism can account for the various shapes of observed dose-effect curves which, for direct action, are predicted to be independent of dose rate but dependent on the irradiation time. Damage is predicted to increase for prolonged exposures by heavy particles in a manner which could be consistent with the observed reverse dose rate effect. The most damaging neutrons are intrinsically three times less damaging than the most damaging heavy ions implying that there are no physical reasons for doubling the quality factor of neutrons with respect to heavy ions. On the basis of these findings the absolute biological effectiveness (ABE) for direct action can be quantified. Illustrative ABE factors for low dose chronic exposures are calculated for neutrons and photons.

This publication has 0 references indexed in Scilit: