Evaluation of DNA damage induced by Auger electrons from Cs

Watanabe, Ritsuko; Hattori, Yuya; Kai, Takeshi

International Journal of Radiation Biology, 92(11), p.660 - 664, 2016/11

https://doi.org/10.3109/09553002.2015.1136853

To understand the effect of internal exposure of Cs, we focus on estimation of microscopic energy deposition pattern and DNA damage induced by directly emitted electrons (beta-rays, internal conversion electrons, Auger electrons) from Cs. Monte Carlo track simulation method was used to calculate the microscopic energy deposition pattern. To simulate the energy deposition by directly emitted electrons, we considered the multiple ejections of electrons after internal conversion. Induction process of DNA strand breaks and base lesions was modeled and simulated using Monte Carlo methods for cell mimetic condition. The yield and spatial distribution of simple and complex DNA damage were calculated for the cases of -rays and electrons from Cs. The simulation showed that significant difference of DNA damage spectrum was not caused by the difference between secondary electron spectrum by -rays and directly ejected electron spectrum. The result support that the existing evaluation that internal exposure and external exposure are almost equivalent.

Recent progress of radiation physicochemical process (first part)

Kai, Takeshi; Yokoya, Akinari; Fujii, Kentaro; Watanabe, Ritsuko

Hoshasen Kagaku (Internet), (101), p.3 - 11, 2016/04

Behavior analysis of low energy electrons in liquid water provides the fundamentals for successive radiation chemistry, and it makes analysis of DNA damage implication involved in the electrons possible. We have progressed theoretical studies for radiation physicochemical process of liquid water to clear the role of low-energy secondary electrons damage to DNA. The process has included many unknown factors for the DNA damage so far. Based on the results, we implied a newly formation process of unrepair DNA damage produced by the secondary electrons assumed that it was ejected from DNA by impact of a high energy electron. We report our outcomes separately in three manuscripts entitled "Recent progress of radiation physicochemical process (first, second, third parts)" to journal of radiation chemistry. In this first part, we outline recent status of studies for the DNA damage and the radiation physicochemical process, we also show calculation method of electron impact cross sections involved strongly in electron deceleration in liquid water in the topics of our outcomes. From the calculated results, we also report our prediction, which are different from previous one, for electron thermalization.

Thermal equilibrium and prehydration processes of electrons injected into liquid water calculated by dynamic Monte Carlo method

Kai, Takeshi; Yokoya, Akinari; Ukai, Masatoshi*; Fujii, Kentaro; Watanabe, Ritsuko

Radiation Physics and Chemistry, 115, p.1 - 5, 2015/10

https://doi.org/10.1016/j.radphyschem.2015.05.021

Role of secondary electrons on DNA damage have not been understood sufficiently because there still exists a lack of study for thermalization process of an electron in liquid phase. We calculated thermalization lengths and spatial distributions of an electron in liquid water using cross sections for rotation and phonon excitations in a liquid phase. Obtained thermalization lengths are in good agreement with experimental results reported by literatures. Thermalization time was also estimated from time evolution of spatial distributions of the incident electron to be hundreds femtoseconds. From these results, we predict that thermalization and pre-hydration of electron might progress simultaneously. These electrons possibly cause damage in biological molecules in a cell. Particularly severe types of DNA damage consisting of proximately located multiple lesions are potentially induced by reaction of DNA with the thermalized electrons by dissociative electron transfer.

Spectrum of radiation-induced clustered non-DSB damage; A Monte Carlo track structure modelling and calculations

Watanabe, Ritsuko; Rahmanian, S.*; Nikjoo, H.*

Radiation Research, 183(5), p.525 - 540, 2015/05

https://doi.org/10.1667/RR13902.1

To calculate the spectrum of initial base damage induced by selected electrons and ions, Monte Carlo track structure method was used to simulate the radiation induced DNA damage in a cell mimetic condition based on a single track action. We present relative yield of strand breaks and base damage for selected monoenergetic electrons 100 eV - 100 keV, photons C, Al and Ti; and some selected ions (3.2 MeV/u proton; 0.74 and 2.4 MeV/u He; 29 MeV/u N, and 950 MeV/u Fe). Data are presented for simple and complex types of DNA damage. The ratios of yields of base damage to SSBs were estimated to be about 2-4 independent on the LETs examined. The contribution of base damage to the complexity of damage site was shown to be significant. The data can be used for testing mechanistic models of DNA repair kinetics and in particular the base excision repair.

Radial dependence of lineal energy distribution of 290-MeV/u carbon and 500-MeV/u iron ion beams using a wall-less tissue-equivalent proportional counter

Tsuda, Shuichi; Sato, Tatsuhiko; Watanabe, Ritsuko; Takada, Masashi*

Journal of Radiation Research, 56(1), p.197 - 204, 2015/01

https://doi.org/10.1093/jrr/rru076

Radial dependence of lineal energy distribution, yf(y), have been experimentally evaluated for a 0.72 micrometer site in tissue using 290 MeV/u carbon and 500 MeV/u iron ion beams using a wall-less tissue equivalent proportional counter. The yf(y) distributions and dose-mean of y, are compared with the calculation by a track structure simulation code TRACION and a microdosimetric function of the PHITS code. The values of the measured agree with those of the calculation within 20% but differences in the shape of yf(y) were found in the case of the iron ion irradiation. The result indicates that further improvement of the calculation model for yf(y) distribution in PHITS is needed in terms of the analytical function that reproduce energy deposition by delta rays, in the case that primary ions have LET more than a few hundred keV/micrometer.

Dependence of the yields of AP sites and AP clusters produced in plasmid DNA on scavenging capacity and LET

Shiina, Takuya*; Watanabe, Ritsuko; Suzuki, Masao*; Yokoya, Akinari

Journal of Radiation Research, 55(Suppl.1), p.i15 - i16, 2014/03

BB2013-0476.pdf:0.21MB

https://doi.org/10.1093/jrr/rrt160

Visualization of H2AX foci caused by heavy ion particle traversal; Distribution between core track versus non-track damage

Nakajima, Nakako*; Brunton, H.*; Watanabe, Ritsuko; Shrikhande, A.*; Hirayama, Ryoichi*; Matsufuji, Naruhiro*; Fujimori, Akira*; Murakami, Takeshi*; Okayasu, Ryuichi*; Jeggo, P.*; et al.

PLOS ONE (Internet), 8(8), p.e70107_1 - e70107_14, 2013/08

https://doi.org/10.1371/journal.pone.0070107

Heavy particle irradiation can produce complex DNA double strand breaks (DSBs) within the particle trajectory. Additionally, secondary electrons, termed delta-electrons, can create low linear energy transfer (LET) damage distant from the track. Using imaging with deconvolution, we show that at 8 hours after exposure to Fe ions, H2AX foci forming at DSBs within the particle track are large and encompass multiple smaller and closely localised foci, which we designate as clustered H2AX foci. We also identified simple H2AX foci distant from the track. They are rapidly repaired. Clustered H2AX foci induced by heavy particle radiation cause prolonged checkpoint arrest compared to simple H2AX foci. However, mitotic entry was observed when 10 clustered foci remain. Thus, cells can progress into mitosis with multiple clusters of DSBs following the traversal of a heavy particle.

Microscopic energy distribution of low-dose radiation

Watanabe, Ritsuko

Hoshasen Seibutsu Kenkyu, 47(4), p.335 - 346, 2012/12

http://ci.nii.ac.jp/naid/40019554636

To comprehend the low-dose radiation induced biological effect from the initial process, the microscopic dose distribution needs to be considered because of its strong ununiformity. In this article, distribution of energy deposition by low-dose Cs -rays calculated using Monte Carlo track structure simulation is presented. Also, the concept of low-dose radiation from a standpoint of microdosimetry is overviewed. This review is a part of special articles on radiation biological effect induced by low-dose and low-dose rate radiation.

Spectroscopic approaches to study DNA damage induced in genome exposed to ionizing radiation and its enzymatic repair

Yokoya, Akinari; Fujii, Kentaro; Oka, Toshitaka; Watanabe, Ritsuko

Hoshasen, 38(2), p.55 - 60, 2012/08

http://ci.nii.ac.jp/naid/40019426916

Applications of the microdosimetric function implemented in the macroscopic particle transport simulation code PHITS

Sato, Tatsuhiko; Watanabe, Ritsuko; Sihver, L.*; Niita, Koji*

International Journal of Radiation Biology, 88(1-2), p.143 - 150, 2012/01

https://doi.org/10.3109/09553002.2011.611216

The microdosimetric function of PHITS has been applied to the biological dose estimation for charged-particle therapy and the risk estimation for astronauts. The former application was performed in combination with the microdosimetric kinetic model, while the latter was done with the radiation quality factor expressed as a function of lineal energy. Owing to the unique features of the microdosimetric function, the improved PHITS has a potential to establish more sophisticated systems for the radiological protection in space as well as the treatment planning of charged-particle therapy.