Noriko Usami

Mutagenic and transforming effects of soft-X-rays with resonance energy of phosphorus K-absorption edge.

Syrian golden hamster embryo (SHE) cells were exposed to synchrotron-produced monochromatic X-rays at 5.747 (2.159 keV), 5.763 (2.153 keV) and 5.779 A (2.147 keV). Although X-rays of all wavelengths induced mutations and chromatid aberrations in a dose-dependent manner, when cells were irradiated with 2.153 keV X-rays, which correspond to the resonance energy of the phosphorus K-absorption edge, the frequencies of mutation and chromatid aberration at equal dose levels were higher than for X-rays of the other wavelengths. At equal survival levels, however, there was no difference in the frequencies of mutations and chromatid aberrations in cells irradiated with soft X-rays. On the other hand, the frequency of morphological transformation in cells irradiated with 2.147 keV X-rays was higher than those irradiated with 2.153 keV and 2.159 keV X-rays. The relative biological effectiveness compared to cobalt-60 gamma-rays in morphological transformation was 2.8 for 2.147 keV, 1.1 for 2.159 keV and 1.0 for 2.153 keV at a 37% survival level.

Biological effects of Auger processes of bromine on yeast cells induced by monochromatic synchrotron X-rays.

The biological effects of inner-shell ionization in bromine atoms incorporated into DNA in the form of bromodeoxyuridine monophosphate (BrdUMP), induced by monochromatized synchrotron X-rays, were studied using a deoxythymidine monophosphate (dTMP)-permeable mutant of yeast, Saccharomyces cerevisiae. The BrdUMP-incorporated yeast cells were irradiated with monochromatic X-rays of 13.51 or 13.45 keV, between which the bromine K-absorption edge (13.47 keV) is located. The cells were 1.07 times more sensitive to irradiation by 13.51 keV X-rays than at 13.45 keV, while dTMP-incorporated cells did not show any difference in sensitivity. In the presence of a radioprotector during irradiation, BrdUMP-incorporated cells showed a larger enhancement (1.20). These enhancements observed in the bromine-incorporated cells cannot be explained only by an increase of the absorbed dose due to a substitution of CH3 group of thymine by bromine. It may be concluded that a major part of the enhancement was caused by inner-shell photoionization, followed by an Auger cascade of the bromine in the DNA. The quantum yield of lethality caused by the photoabsorption of bromine K-shell is not affected by the presence of cysteamine, suggesting the biological enhancement by the Auger processes may not be influenced by chemical protection.

Hadrontherapy enhanced by combination with heavy atoms: Role of Auger effect in nanoparticles

Abstract This chapter is dedicated to the possibility of augmenting the radiobiological effects when irradiated tissues are loaded with high-Z atoms contained in molecules or nanoparticles by fast atomic ions. A preliminary quantitative study of DNA break induction by monochromatic photons tuned to the resonant photoabsorption energy of LIII shell of platinum suggests that secondary electrons emitted by the incident ionizing particles can trigger the Auger effect in the high-Z atom by inelastic collision. Imaging by nano secondary ion mass spectrometry experiments of cells loaded with platinum salt has revealed that the high-Z atoms need not be located in the nucleus to increase the cell death rate. This finding opens the possibility of using nanoparticles made of high-Z atoms in combination with atomic ion irradiation to augment the cell death rate. Experiments made with HeLa and U87 glioblastoma cell lines, in combination with platinum or gold salt, and also nanoparticles, show a neat enhancement of the cancerous cell line death rate.This chapter is dedicated to the possibility of augmenting the radiobiological effects when irradiated tissues are loaded with high-Z atoms contained in molecules or nanoparticles by fast atomic ions. A preliminary quantitative study of DNA break induction by monochromatic photons tuned to the resonant photoabsorption energy of LIII shell of platinum suggests that secondary electrons emitted by the incident ionizing particles can trigger the Auger effect in the high-Z atom by inelastic collision. Imaging by nano secondary ion mass spectrometry experiments of cells loaded with platinum salt has revealed that the high-Z atoms need not be located in the nucleus to increase the cell death rate. This finding opens the possibility of using nanoparticles made of high-Z atoms in combination with atomic ion irradiation to augment the cell death rate. Experiments made with HeLa and U87 glioblastoma cell lines, in combination with platinum or gold salt, and also nanoparticles, show a neat enhancement of the cancerous cell line death rate.