Elektronenemissionsspektren von Goldnanopartikeln zur Dosisberechnung in der Strahlentherapie

Die Strahlentherapie ist eine der drei Standardmethoden zur Behandlung von Krebserkrankungen und basiert auf der zellschädigenden Wirkung ionisierender Strahlung und der durch sie freigesetzten Sekundärelektronen. Da die Wechselwirkungen jedoch nicht zellspezifisch sind, werden neben dem tumorösen Gewebe auch gesunde Zellen geschädigt. Um dies zu verringern, sollen sogenannte Radiosensitizer, wie beispielsweise Goldnanopartikel (AuNP), in das Tumorgewebe eingebracht werden, welche die Dosisverteilung stärker auf das Tumorvolumen beschränken. In der modernen Therapieplanung spielen Strahlentransportrechnungen mittels Monte-Carlo (MC) Simulationen eine wichtige Rolle. Diese Rechnungen basieren derzeit auf physikalischen Modellen, die insbesondere bei Elektronenenergien unterhalb einiger keV nur eine grobe Näherung darstellen. MC Simulationen unterschiedlicher Studien weisen dabei oft eine große Bandbreite von Ergebnissen auf. Ziel der Arbeit war es, die Elektronenemissionsspektren von AuNP für Elektronen-, Protonen- und Photonenstrahlung zu bestimmen und dadurch einen ersten Datensatz zum Benchmarken von MC Simulationen zur Verfügung zu stellen. Hierfür mussten in einem ersten Schritt ein geeignetes Trägermaterial sowie eine optimale Depositionstechnik für die verwendeten AuNP gefunden werden. Als das geeignetste Substrat für die Deposition der AuNP konnte eine freitragende Kohlenstofffolie ausgemacht werden. Bei der Deposition erwies sich das Drop-Casting als die beste Methode. Die Deposition mit einem Spin-Coater lieferte ebenfalls gute Resultate, mit einem Microdrop konnte dagegen keine ausreichend homogene Probe hergestellt werden. Nach der Präparation wurden die Proben mittels Rasterelektronenmikroskopie sowie Rastertransmissionselektronenmikroskopie hinsichtlich ihrer Größe, räumlichen Verteilung und Flächenbelegung charakterisiert. Hieraus ergab sich, dass die AuNP sowohl Monolagen als auch Cluster bilden, welche in Multilagen übergehen. Die Proben wurden anschließend mittels Röntgenphotoelektronenspektroskopie hinsichtlich ihrer chemischen Struktur analysiert. Dabei konnten Kohlenstoff- und Sauerstoffkontaminationen nachgewiesen werden. Ein Sputtern der Probe mit Argon entfernte zwar die Kontaminationen, aber auch das Coating der AuNP, sodass ein Sputtern nur in begrenztem Umfang möglich ist. Für die auf der Kohlenstofffolie deponierten AuNP konnte aufgrund ihres Coatings sowie von Kontaminationen nahezu keine Zunahme der Elektronenausbeute bei Messungen mit einem Elektronenstrahl im Vergleich zu Messungen der Kohlenstofffolie ohne AuNP festgestellt werden. Die in dieser Arbeit durchgeführten Messungen mit Protonenstrahlung zeigen zum ersten Mal doppelt differentielle Elektronenemissionsspektren von AuNP und Gold. Hierbei konnte ein deutlicher Anstieg der Elektronenausbeute durch die Verwendung von AuNP im Vergleich zur reinen Kohlenstofffolie beobachtet werden. Die mit Photonenstrahlung an der Beamline P22 bei PETRA III am DESY in Hamburg gemessenen Elektronenemissionsspektren zeigten ebenfalls eine erhöhte Elektronenausbeute durch den Einsatz von AuNP im Vergleich zur Kohlenstofffolie ohne AuNP. Sie liefern erste wertvolle Benchmark-Daten für Photonen- und Elektronentransportprozesse in AuNP für Energien bis etwa 10 keV

Combined experimental and theoretical study on the elastic electron scattering cross sections of ethanol

Combined theoretical and experimental studies on the elastic scattering of electrons on ethanol were performed in the energy range of 30–800 eV. The differential elastic electron scattering cross sections (DCS) of ethanol were measured for scattering angles of 30° to 150° using the relative flow technique and nitrogen (N2) as the reference gas. From these experimental DCS, integral elastic and momentum transfer cross sections were estimated. The comparison of the experimental results from the present work to those of other groups showed good agreement within the experimental uncertainty. In addition to the experimental determination, the DCS of ethanol were calculated by applying the independent atomic model with screening-corrected additivity rule and the modified independent atomic model. These theoretical calculations reproduced the experimental data well within the experimental uncertainty, with agreement better at high electron energies as was expected. Graphical abstract: [Figure not available: see fulltext.

Experimental benchmark data for Monte Carlo simulated radiation effects of gold nanoparticles. Part I: Experiment and raw data analysis

Electron emission spectra of gold nanoparticles (AuNPs) after photon interaction were measured over the energy range between 50 eV and 9500 eV to provide reference data for Monte Carlo radiation-transport simulations. Experiments were performed with the HAXPES spectrometer at the PETRA III high-brilliance beamline P22 at DESY (Hamburg, Germany) for photon energies below and above each of the gold L-edges, i.e., at 11.9 keV, 12.0 keV, 13.7 keV, 13.8 keV, 14.3 keV, and 14.4 keV. The study focused on a sample with gold nanoparticles with an average diameter of 11.0 nm on a thin carbon foil. Additional measurements were performed on a sample with 5.3 nm gold nanoparticles and on reference samples of gold and carbon foils. Further measurements were made to calibrate the photon flux monitor, to characterize the transmission function of the electron spectrometer and to determine the size of the photon beam. This allowed the determination of the absolute values of the spectral particle radiance of secondary electrons per incident photon flux. The paper presents the experimental and raw data analysis procedures, reviews the data obtained for the nanoparticle samples and discusses their limitations.Comment: 18 pages, 13 Figures, 6 Tables plus 4 Supplements with altogether 14 pages, 16 figures, 2 table

Experimental benchmark data for Monte Carlo simulated radiation effects of gold nanoparticles. Part II: comparison of measured and simulated electron spectra from gold nanofoils

Electron emission spectra of a thin gold foil after photon interaction were measured over the energy range between 50 eV and 9500 eV to provide reference data for Monte Carlo radiation-transport simulations. Experiments were performed with the HAXPES spectrometer at the PETRA III high-brilliance beamline P22 at DESY (Hamburg, Germany) for photon energies just below and above each of the gold L-edges, that is, at 11.9 keV, 12.0 keV, 13.7 keV, 13.8 keV, 14.3 keV, and 14.4 keV. The data were analyzed to obtain the absolute values of the particle radiance of the emitted electrons per incident photon flux. Simulations of the experiment were performed using the Penelope and Geant4 Monte Carlo radiation-transport codes. Comparison of the measured and simulated results shows good qualitative agreement. On an absolute scale, the experiments tend to produce higher electron radiance values at the lower photon energies studied as well as at the higher photon energies for electron energies below the energy of the Au L3 photoelectron. This is attributed to the linear polarization of the photon beam in the experiments, something which is not considered in the simulation codes

Experimental benchmark data for Monte Carlo simulated radiation effects of gold nanoparticles. Part II: Comparison of measured and simulated electron spectra from gold nanofoils

Electron emission spectra of a thin gold foil after photon interaction were measured over the energy range between 50 eV and 9500 eV to provide reference data for Monte Carlo radiation-transport simulations. Experiments were performed with the HAXPES spectrometer at the PETRA III high-brilliance beamline P22 at DESY (Hamburg, Germany) for photon energies just below and above each of the gold L-edges, i.e., at 11.9 keV, 12.0 keV, 13.7 keV, 13.8 keV, 14.3 keV, and 14.4 keV. The data were analyzed to obtain the absolute values of the particle radiance of the emitted electrons per incident photon flux. Simulations of the experiment were performed using the Monte Carlo radiation-transport codes Penelope and Geant4. Comparison of the measured and simulated results shows good qualitative agreement. When simulation results are convolved with curves that take into account the effect of lifetime broadening, line shapes of photoelectron and Auger peaks similar to those observed experimentally are obtained. On an absolute scale, the experiments tend to give higher electron radiance values at the lower photon energies studied as well as at the higher photon energies for electron energies below the energy of the Au L3 photoelectron. This is attributed to the linear polarization of the photon beam in the experiments which is not considered in the simulation codes.Comment: Revised manuscript after peer review, 13 pages, 9 figure

Deposition of Gold Nanoparticles on a Self‐Supporting Carbon Foil

Electron emission cross sections of gold nanoparticles (AuNPs) are important for assessing their radiosensitizing effects from ionizing radiation using Monte Carlo simulations. Measurements of these data require samples of sufficiently large area density, homogeneous nanoparticle distribution, and a mechanically stable sample holder to ensure a low background signal. While several methods exist for the deposition of nanoparticles, there is little information regarding the deposition of AuNPs in an aqueous solution onto a self-supporting film. The aim of this is to find suitable preparation techniques for AuNP samples which fulfill the above requirements. AuNP samples are produced using different deposition techniques and a 50 nm-thick carbon foil as the substrate. These samples are characterized with respect to the size and spatial distribution of AuNPs using a scanning electron microscope. The drop-casting technique yields the best results, while those obtained with the spin-coater technique are less reproducible regarding sample stability. The microdrop method is deemed unsuitable due to its tendency to form AuNP clusters. Measurements conducted with a synchrotron radiation source, as well as with protons and electrons, confirm the suitability of these samples for studying electron emission spectra of AuNPs for different radiation types