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#### Erscheinungsjahr

- 2019 (8) (entfernen)

#### Dokumenttyp

- Zeitschriftenartikel (3)
- Posterpräsentation (3)
- Vortrag (2)

#### Schlagworte

- Dosimetry (5)
- Geant4 (5)
- Microdosimetry (5)
- DNA (4)
- Simulation (4)
- AuNP (3)
- Geant4-DNA (3)
- LLG (3)
- MCS (3)
- Micromagnetism (3)
- Monte-Carlo simulation (3)
- Nanoparticle (3)
- OOMMF (3)
- DNA damage (2)
- Electron irradiation (2)
- Energy deposit (2)
- Exchange interaction (2)
- Ferromagnetism (2)
- LEE (2)
- Landau Lifshitz equation (2)
- Magnetic moment (2)
- Monte-Carlo Simulation (2)
- OH radicals (2)
- Object oriented micromagnetic framework (2)
- Radiation damage (2)
- Radiationtherapy (2)
- Radioactive decay (2)
- Stochastic Landau Lifshitz Gilbert equation (2)
- Temeprature scaling (2)
- low energy electrons (2)
- particle scattering (2)
- Alpha (1)
- Beta decay (1)
- Bloch wall (1)
- Brachytherapy (1)
- Cancer (1)
- Cancer treatment (1)
- Cell size (1)
- Cluster (1)
- Co (1)
- Cobalt (1)
- Computer simulation (1)
- Curie temperature (1)
- Damping factor (1)
- Domain wall (1)
- Exchange length (1)
- Fe (1)
- Gamma (1)
- Gold (1)
- Gold Nanoparticle (1)
- Gold Nanoparticles (1)
- Iron (1)
- LL equation (1)
- Landau Lifshitz Gilbert equation (1)
- Magnet coupling (1)
- Magnetic Nanoparticles (1)
- Magnetic anisotropy (1)
- Magnetic interacion (1)
- Magnetic nanoparticle (1)
- Magnetic nanoparticles (1)
- Magnetization dynamics (1)
- Monte Carlo (1)
- Monte-Carlo (1)
- Monte-Carlo Simulations (1)
- NP (1)
- Neel wall (1)
- Ni (1)
- Nickel (1)
- Paramagnetism (1)
- Phase transition (1)
- Radioactive NP (1)
- Spin (1)
- Steel (1)
- Stochastic Landau Lifshitz equation (1)
- Superparamagnetism (1)
- Temperature effects (1)
- Thin film systems (1)
- beta particle (1)
- clustered nanoparticles (1)
- gamma ray (1)
- radiolysis (1)
- temeprature dependent exchange length (1)

#### Organisationseinheit der BAM

Dose enhancement by gold nanoparticles (AuNP) was shown to increase the biological effectiveness of radiation damage in biomolecules and tissue. Most of the current studies focus on external beam therapy on combination with AuNP. Here we present a Monte-Carlo study (Geant4) to characterise radioactive AuNP. Radioactive ¹⁹⁸Au emits beta and gamma rays and is considered for applications with solid tumours. To effectively apply ¹⁹⁸AuNP their energy deposit characteristics have to be determined in terms of intrinsic and extrinsic properties e.g. AuNP diameter, AuNP density, and their clustering behaviour. After each decay process, the energy deposit, inelastic scattering events, kinetic energy spectrum of secondary particles within the AuNP themselves and in a spherical target volume of water up to 1 μm radius were determined. Simulations were performed for AuNP radii ranging from 2.5 nm to 20 nm radius, different cluster sizes and densities. The results show an increase of the energy deposit in the vicinity of the AuNP up to 150 nm. This effect nearly vanishes for distances up to one micron. For the case of AuNP clusters and the same activity, the enhancement of the energy deposit increases with the relative gold mass percentage and therefore can be adjusted by changing AuNP radius or clustering behaviour.

The movement of the macroscopic magnetic moment in ferromagnetic systems can be described by the Landau-Lifshitz (LL) or Landau-Lifshitz-Gilbert (LLG) equation. These equations are strictly valid only at absolute zero temperature. To include temperature effects a stochastic version of the LL or LLG equation for a spin density of one per unit cell can be used instead. To apply the stochastic LL to micromagnetic simulations, where the spin density per unit cell is generally higher, a conversion regarding simulation cell size and temperature has to be established. Based on energetic considerations, a conversion for ferromagnetic bulk and thin film systems is proposed. The conversion is tested in micromagnetic simulations which are performed with the Object Oriented Micromagnetic Framework (OOMMF). The Curie temperatures of bulk Nickel, Cobalt and Iron systems as well as Nickel thin-film systems with thicknesses between 6.3 mono layer (ML) and 31ML are determined from micromagnetic simulations. The results show a good agreement with experimentally determined Curie temperatures of bulk and thin film systems when temperature scaling is performed according to the presented model.

Dose enhancement by gold nanoparticles (AuNP) was shown to increase the biological effectiveness of radiation damage in biomolecules and tissue. Most of the current studies focus on external beam therapy on combination with AuNP. Here we present a Monte-Carlo study (Geant4) to characterise radioactive AuNP. Radioactive 198 Au emits beta and gamma rays and is considered for applications with solid tumours. To effectively apply 198 AuNP their energy deposit characteristics have to be determined in terms of intrinsic and extrinsic properties e.g. AuNP diameter, AuNP density, and their clustering behaviour. After each decay process, the energy deposit, inelastic scattering events, kinetic energy spectrum of secondary particles within the AuNP themselves and in a spherical target volume of water up to 1 μm radius were determined. Simulations were performed for AuNP radii ranging from 2.5 nm to 20 nm radius, different cluster sizes and densities. The results show an increase of the energy deposit in the vicinity of the AuNP up to 150 nm. This effect nearly vanishes for distances up to one micron. For the case of AuNP clusters and the same activity, the enhancement of the energy deposit increases with the relative gold mass percentage and therefore can be adjusted by changing AuNP radius or clustering behaviour.

Particle scattering simulations are an useful tool to plan experiments, design detectors, estimate doses in irradiated materials and medical treatment planning.
Geant4 is a Monte-Carlo toolkit for the simulation of of particles scattering in matter. Photons, electrons, ions etc can be simulated with energies in the eV to GeV range. Their interactions with matter in arbitrary scattering geometries be studied. Scattering models, cross sections and material parameters can be set to cover interactions in gas, liquid and solid state. The import of geometries from computer aided design files or the protein data base is possible.
It is currently being applied in high energy and nuclear physics, accelerator and detector design, space application, dosimetry and medical sciences.
In this first part of the talk a brief overview over the structure, functionality and possible applications of Geant4 will be given. In the second part an example application will be presented: The determination of the microscopic dose-damage relations in aqueous environment for electron irradiated plasmid DNA will be explained. Therefore, we combine electron scattering simulations in water with calculations concerning the movement of biomolecules to obtain the energy deposit in the biologically relevant nanoscopic volume. We present, how to combine these simulational results and experimental data via a generalized damage model to determine the microscopic dose-damage relation at a molecular level.

The determination of microscopic dose-damage relations in aqueous environment is of fundamental interest for dosimetry and its application in radiation-therapy and protection. We present a combined experimental and simulational approach to quantify the microscopic energy deposit at biomolecules in liquid environment which is applicable to a wide range of primary radiation sources, e.g. photons, electrons or ions, and targets, such as DNA, proteins or cells.Therefore, we combine Geant4 particle-scattering simulations in water with calculations concerning the movement of biomolecules to obtain the energy deposit in the biologically relevant nanoscopic volume. We present, how to combine these simulational results and experimental data via a generalised damage model to determine the microscopic dose-damage relation at a molecular level.
To show the viability of this approach, we apply this method to an experimentally challenging system, the direct irradiation of plasmid DNA (pUC19) in water with electrons as primary particles. Here we combine electron-scattering simulations with calculations concerning the diffusion and convection induced movement of the DNA, within a coarse-grained model of the irradiated liquid. Additionally a microscopic target model for DNA molecules based on the relation of lineal energy and radiation quality is used to calculate their effective target volume.
It was found that on average fewer than two ionisations within a 7.5\,nm radius around the sugar-phosphate backbone are sufficient to cause a single strand break, with a corresponding median lethal energy deposit being E\textsubscript{1/2}=6+-4\,eV. The presented method is applicable for all types of ionising radiation and a broad variety of biological targets.

Simulational tools are applied to investigate the physical properties of nanoparticles.
For the description of radioactive gold nanoparticles, particles scattering simulations are performed with the Geant4 monte carlo simulation toolkit.
The temperature dependent behaviour of the magnetization dynamics of different magnetic nanoparticles are simulated with the object oriented micormagnetic framework (OOMMF).