Biological Effectiveness of High-Energy Protons: Target Fragmentation

Authors

Francis A. Cucinotta, Space Transportation Systems Division, Rockwell International, Houston, TexasFollow
Robert Katz, University of Nebraska-LincolnFollow
John W. Wilson, NASA Langley Research Center, Hampton, Virginia
Lawrence W. Townsend, NASA Langley Research Center, Hampton, Virginia
Judy Shinn, NASA Langley Research Center, Hampton, Virginia
Ferenc Hajnal, Environmental Measurements Laboratory, U.S. Department of Energy. New York, New York

Date of this Version

April 1991

Comments

Published in Radiation Research 127, 130-137 (1991).

Abstract

High-energy protons traversing tissue produce local sources of high-linear-energy-transfer (LET) ions through nuclear fragmentation. We examine the contribution of these target fragments to the biological effectiveness of high-energy protons using the cellular track model. The effects of secondary ions are treated in terms of the production collision density using energy-dependent parameters from a high-energy fragmentation model. Calculations for mammalian cell cultures show that at high dose, at which intertrack effects become important, protons deliver damage similar to that produced by γ rays, and with fragmentation the relative biological effectiveness (RBE) of protons increases moderately from unity. At low dose, where sublethal damage is unimportant, the contribution from target fragments dominates, causing the proton effectiveness to be very different from that of γ rays with a strongly fluence-dependent RBE. At high energies, the nuclear fragmentation cross sections become independent of energy. This leads to a plateau in the proton single-particle-action cross section, below 1 keV/pm, since the target fragments dominate.