The effectiveness of the high-LET radiations from the boron neutron capture [10B(n,α) 7Li] reaction determined for induction of chromosome aberrations and apoptosis in lymphocytes of human blood samples.

Abstract

Provided that a selective accumulation of (10)B-containing compounds is introduced in tumor cells, following irradiation by thermal neutrons produces high-LET alpha-particles ((4)He) and recoiling lithium-7 ((7)Li) nuclei emitted during the capture of thermalized neutrons (0.025eV) from (10)B. To estimate the biological effectiveness of this boron neutron capture [(10)B(n,α)(7)Li] reaction, the chromosome aberration assay and the flow cytometry apoptosis assay were applied. At the presence of the clinically used compounds BSH (sodium borocaptate) and BPA (p-boronophenylalanine), human lymphocytes were irradiated by sub-thermal neutrons. For analyzing chromosome aberrations, human lymphocytes were exposed to thermally equivalent neutron fluences of 1.82×10(11) cm(-2) or 7.30×10(11) cm(-2) (corresponding to thermal neutron doses of 0.062 and 0.248Gy, respectively) in the presence of 0, 10, 20, and 30ppm of BSH or BPA. Since the kerma coefficient of blood increased by 0.864×10(-12)Gycm(2) per 10ppm of (10)B, the kerma coefficients in blood increase from 0.34×10(-12) cm(2) (blood without BSH or BPA) up to 2.93×10(-12) Gycm(2) in the presence of 30ppm of (10)B. For the (10)B(n, α)(7)Li reaction, linear dose-response relations for dicentrics with coefficients α=0.0546±0.0081Gy(-1) for BSH and α=0.0654±0.0075Gy(-1) for BPA were obtained at 0.062Gy as well as α=0.0985±0.0284Gy(-1) for BSH and α=0.1293±0.0419Gy(-1) for BPA at 0.248Gy. At both doses, the corresponding (10)B(n, α)(7)Li reactions from BSH and BPA are not significantly different. A linear dose-response relation for dicentrics also was obtained for the induction of apoptosis by the (10)B(n, α)(7)Li reaction at 0.248Gy. The linear coefficients α=0.0249±0.0119Gy(-1) for BSH and α=0.0334±0.0064Gy(-1) for BPA are not significantly different. Independently of the applied thermal neutron doses of 0.062Gy or 0.248Gy, the (10)B(n, α)(7)Li reaction from 30ppm BSH or BPA induced an apparent RBE of about 2.2 for the production of dicentrics as compared to exposure to thermal neutrons alone. Since the apparent RBE value is defined as the product of the RBE of a thermal neutron dose alone times a boron localization factor which depends on the concentration of a (10)B-containing compound, this localization factor determines the biological effectiveness of the (10)B(n, α)(7)Li reaction.