Biological Effects of High-Energy Neutrons MeasuredIn VivoUsing a Vertebrate Model

Abstract

Interaction of solar protons and galactic cosmic radiation with the atmosphere and other materials produces high-energy secondary neutrons from below 1 to 1000 MeV and higher. Although secondary neutrons may provide an appreciable component of the radiation dose equivalent received by space and high-altitude air travelers, the biological effects remain poorly defined, particularly in vivo in intact organisms. Here we describe the acute response of Japanese medaka (Oryzias latipes) embryos to a beam of high-energy spallation neutrons that mimics the energy spectrum of secondary neutrons encountered aboard spacecraft and high-altitude aircraft. To determine RBE, embryos were exposed to 0-0.5 Gy of high-energy neutron radiation or 0-15 Gy of reference γ radiation. The radiation response was measured by imaging apoptotic cells in situ in defined volumes of the embryo, an assay that provides a quantifiable, linear dose response. The slope of the dose response in the developing head, relative to reference γ radiation, indicates an RBE of 24.9 (95% CI 13.6-40.7). A higher RBE of 48.1 (95% CI 30.0-66.4) was obtained based on overall survival. A separate analysis of apoptosis in muscle showed an overall nonlinear response, with the greatest effects at doses of less than 0.3 Gy. Results of this experiment indicate that medaka are a useful model for investigating biological damage associated with high-energy neutron exposure.

Assessing the risk of second malignancies after modern radiotherapy

“…2b) and in spacecraft 31 . A recent experiment in Medaka fish embryos exposed to a high-energy neutron source at the Los Alamos Neutron Science Center reported an RBE ranging between 25 and 48 relative to γ-rays for apoptosis in cells of the developing brain 81 .…”

Genotoxicity of acute and chronic gamma‐irradiation on zebrafish cells and consequences for embryo development

“…Furthermore, little is known about the effects of acute and chronic exposure to ionizing radiation on DNA repair mechanisms in fish [13]. Most studies examined the effects of irradiation exposure on survival and embryo development in fish exposed to radionuclides acutely or chronically [14][15][16][17][18][19][20]. Acute and chronic exposures do not lead to the same effects at the organism level: multiple development abnormalities were shown in acute irradiated embryos in medaka (Oryzias latipes) [18,20], whereas few morphologic abnormalities were observed on chronic irradiated embryos [21].…”

Neurocytotoxic effects of iron-ions on the developing brain measured in vivo using medaka (Oryzias latipes), a vertebrate model

“…Moreover, medaka have been used to estimate the relative biological effectiveness (RBE) of high-LET radiation based on germ cell mutations (Shimada et al 2005) and high-energy neutrons measured using apoptotic endpoints in the developing brain and muscle tissue (Kuhne et al 2009). Based on these findings, we examined the apoptosis in the developing OT of medaka embryos after exposure to high-LET iron-ions using an AO-staining assay.…”