Hauptautor*innen: Katrin Saße

Co-Autor*innen: Karina Albers, Peter Douglas Klassen, Neelan J. Marianyagam, Georg Weidlich, M. Bret Schneider, Steven Chang, John Adler, Björn Poppe, Hui Khee Looe, Daniela Eulenstein

Abstract:

Introduction: When treating clinical lesions, collimator dimensions matching the anatomical targets are highly beneficial to spare surrounding tissues. Therefore, a novel 3 mm cone, for targets smaller than the current smallest collimator diameter of 4 mm, for the ZAP-X was commissioned in this work.

Material and Methods: Profile and output factor measurements were performed using a microSilicon detector (PTW, Germany) and radiochromic films (Ashland, USA). For the microSilicon perturbation effects were quantified and output correction factors (OCF) derived using Monte Carlo simulations.

Results: A small broadening of the microSilicon’s profile of the 3 mm cone can be asserted both in measurements and Monte Carlo simulations. The output ratio of the 3 mm cone, normalized to the reference 25 mm cone, amounts to 0.4466 +/- 0.0224 (microSilicon) respectively 0.4434 +/- 0.0222 (film), which agrees within the measurement uncertainty. The material of the microSilicon components causes a small over-response, while the dominating volume-averaging effect gives rise to an under-response. The effects are partially compensated resulting in an OFC of 1.0333 for the 3 mm cone.

Summary: The commissioning of the 3 mm cone can be performed using the microSilicon. The required correction (3.3%) lies below the 5% limit recommended in the TRS-483.

Hauptautor*innen: Isabel Blum

Co-Autor*innen: Jing Syuen Wong, Krishna Godino Padre, Jessica Stolzenberg, Hermann Fuchs, Kilian-Simon Baumann, Björn Poppe, Hui Khee Looe

Abstract:

Purpose: The aim of this work is to investigate the response of the Roos chamber irradiated by clinical proton beams in magnetic fields.

Material and Methods: Monte Carlo simulations were performed in GATE version 9.2 (based on Geant4 version 11.0.2). The correction factors kB,M,Q of the Roos chamber were determined at different energies up to 252 MeV and magnetic field strengths up to 1 T, by simulating the ratios of chamber signals MQ/MB,Q, without and with magnetic field. Additionally, detailed simulations were carried out to understand the observed magnetic field dependence.

Results: The ratios of the chamber signals show both, energy and magnetic field dependence. They increase initially with the applied magnetic field and decrease again after reaching a maximum at around 0.5 T; the lowest 97.4 MeV beam shows no observable magnetic field dependence. The deviation from unity of the factors is also larger for higher proton energies.

Conclusion: Detailed Monte Carlo studies showed that the observed effect can be mainly attributed to the differences in the transport of electrons produced both outside and inside of the air cavity in the presence of a magnetic field.

Hauptautor*innen: Lukas Gabrisch

Co-Autor*innen: Matteo Cechetto, Björn Delfs, Hui Khee Looe, Jan Budroweit, Rubén García Alía, Björn Poppe and Vanessa Wyrwoll

Abstract:

This study explores the use of a SRAM memory to measure the neutron fluence in a radiotherapy facility using a high-energy 15 MV photon beam from a clinical linear accelerator. By varying the photon beam's field size and positioning the SRAM memory at three different locations relative to the beam's isocenter, the research examined neutron-induced single event upsets (SEUs) in the SRAM memory. Results showed that neutrons produced from photonuclear interactions between high-energy photons and high-Z materials in the accelerator induced SEUs. The measured SEU rate depends on the location of the measurement. Monte Carlo simulations were conducted to determine the neutron fluence under each measurement condition. Using the simulated neutron fluence differential in energy and the previously determined interaction cross sections, the expected SEUs were calculated. Comparison between measured and simulated SEUs, normalized to the linear accelerator output, showed good agreement within experimental uncertainties. Since secondary neutron exposure poses risks to all patients, especially to those with pacemakers or electronic aids, using SEU quantification in SRAM devices to estimate the neutron fluence offers new opportunities to assess clinical risks.

Hauptautor*innen: Pascal Saße

Co-Autor*innen: Björn Poppe

Abstract:

Neben der konventionellen Strahlentherapie mit Gammastrahlung oder der Protonentherapie, hebt sich die Schwerionen-Teletherapie mit C12 als klinisch relevante Alternative hervor. Die Bestrahlung von Tumoren mit Kohlenstoffionen verspricht durch schärfe Dosisgradienten eine bessere Verträglichkeit und gesteigerte Wirksamkeit der Therapie für bestimmte Entitäten. Jedoch geht der potentielle klinische Nutzen mit einer höheren Komplexität einher. Durch Fragmentierungsprozesse wird der Dosisübertrag durch bis zu 60 verschiedene Teilchen mit verschiedenen biologischen Wirksamkeiten bedingt. In diesem Projekt wurden hochpräzise Monte Carlo Simulationen durchgeführt, um die exakte Zusammensetzung klinisch relevanter Bestrahlungsfelder zu analysieren. Für Primärenergie zwischen 100 MeV/u und 430 MeV/u konnten die dosimetrisch relevanten Teilchenarten bestimmt und genauer eingegrenzt werden. Dies ermöglicht eine einfachere Beschreibung und damit bedeutsamere Vergleiche verschiedener Strahlungsfelder aus physikalischer Perspektive. Primäre Metriken in diesem Projekt waren die Wasserenergiedosis und das Verhältnis der Massenstoßbremsvermögen für die jeweiligen Felder. Die Ergebnisse wurden bereits angewendet, um Messungen in einer Ionentherapieanlage durchzuführen. Im weiteren Verlauf des Projektes werden die Ergebnisse auf energiemodulierte Felder ausgeweitet. Die Ergebnisse dieser Arbeit ermöglichten es einen standardisierten Workflow für weitere Computersimulationen zu definieren. Darüber hinaus sind die Ergebnisse dieser Arbeit eine Voraussetzung für eine bessere radiobiologische Charakterisierung moderner Bestrahlungsmodalitäten.

Hauptautor*innen: Karin Klink

Co-Autor*innen: Volker Hohmann, Jörn Anemüller

Abstract:

Human communication frequently takes place in complex acoustic environments. These can include background noise, difficult room acoustics or changing speech clarity due to movement of the speaker and/or the listener. In these conditions, the performance of electroacoustic devices like hearing aids is often very limited. The perception of the subject depends not only on the performance of the device in the sound field. By changing the behavior (e.g., moving the head or body towards a speaker), the subject can influence the sound field and improve perception. Unfortunately, such closed-loop methods are not often used in hearing acoustics. To improve the function of hearing devices, the communication loop needs to be incorporated into the device function. The CRC HAPPAA uses simulations (model-in the-loop), algorithms (model-of-the-loop) and experiments (subject-in-the-loop) to develop such an immersive hearing device. The immersive hearing device includes behavior-controlled spatial filtering and can then be tested both in the real lab and in a corresponding audio-visual virtual reality with telepresence. This leads to the development of a versatile and scalable audio-visual virtual reality for further testing. This project is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project ID 352015383 – SFB 1330.