Biological Effectiveness of Accelerated Protons for Chromosome Exchanges

• Main Author: Kerry eGeorge
• Format: Article
• Language: English
• Published: Frontiers Media S.A. 2015-10-01
• Series: Frontiers in Oncology
• Subjects: Protons; Radiation Effects; Chromosome damage; RBE; Space radiobiology
• Online Access: http://journal.frontiersin.org/Journal/10.3389/fonc.2015.00226/full

We have investigated chromosome exchanges induced in human cells by 7 different energies of protons (5 MeV to 2.5 GeV) with LET values ranging from 0.2 to 8 keV/m. Human lymphocytes were irradiated in vitro and chromosome damage was assessed using three-color fluorescence in situ hybridization (FISH) chromosome painting in chemically-condensed chromosomes collected during the first cell division post-irradiation. The relative biological effectiveness (RBE) was calculated from the initial slope of the dose response curve for chromosome exchanges with respect to low dose and low dose-rate -rays (denoted as RBEmax), and relative to acute doses of -rays (denoted as RBEγAcute). The linear dose response term was similar for all energies of protons, suggesting that the decrease in LET with increasing proton energy was balanced by the increase in dose from the production of nuclear secondaries. Secondary particles increase slowly above energies of a few hundred MeV. Additional studies of 50 g/cm2 aluminum-shielded, high-energy-proton beams showed minor differences compared to the unshielded protons and lower RBE values found for shielded in comparison to unshielded beams of 2 or 2.5 GeV. All energies of protons produced a much higher percentage of complex-type chromosome exchanges when compared to acute doses of γ-rays. The implications of these results for space radiation protection and proton therapy are discussed.