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Article ; Online: Monte Carlo simulation of the ionization and uptake behavior of cationic oligomers into pH-responsive polyelectrolyte microgels of opposite charge - a model for oligopeptide uptake and release.

Strauch, Christian / Schneider, Stefanie

2024 Volume 20, Issue 6, Page(s) 1263–1274

Abstract: ... since the ionization depends on many parameters. In this work, we performed Metropolis Monte Carlo simulations ...

Abstract	External stimuli can tune the uptake and release of guest molecules in microgels. Especially their pH responsiveness makes microgels exciting candidates for drug delivery systems. When both microgel and guest molecules are pH-responsive, predicting the electrostatically driven uptake can be complex since the ionization depends on many parameters. In this work, we performed Metropolis Monte Carlo simulations while systematically varying the p
MeSH term(s)	Microgels ; Polyelectrolytes ; Monte Carlo Method ; Oligopeptides ; Hydrogen-Ion Concentration
Chemical Substances	Microgels ; Polyelectrolytes ; Oligopeptides
Language	English
Publishing date	2024-02-07
Publishing country	England
Document type	Journal Article
ZDB-ID	2191476-X
ISSN	1744-6848 ; 1744-683X
ISSN (online)	1744-6848
ISSN	1744-683X
DOI	10.1039/d3sm01426f
Database	MEDical Literature Analysis and Retrieval System OnLINE

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Article: Validation of a Monte Carlo Framework for Out-of-Field Dose Calculations in Proton Therapy.

De Saint-Hubert, Marijke / Verbeek, Nico / Bäumer, Christian / Esser, Johannes / Wulff, Jörg / Nabha, Racell / Van Hoey, Olivier / Dabin, Jérémie / Stuckmann, Florian / Vasi, Fabiano / Radonic, Stephan / Boissonnat, Guillaume / Schneider, Uwe / Rodriguez, Miguel / Timmermann, Beate / Thierry-Chef, Isabelle / Brualla, Lorenzo

Frontiers in oncology

2022 Volume 12, Page(s) 882489

Abstract: ... been developed based on the Monte Carlo code TOPAS. The purpose of this work is to evaluate ... beam to report on neutron dose equivalent dose data. The Monte Carlo code TOPAS (version 3.6) was run ...

Abstract	Proton therapy enables to deliver highly conformed dose distributions owing to the characteristic Bragg peak and the finite range of protons. However, during proton therapy, secondary neutrons are created, which can travel long distances and deposit dose in out-of-field volumes. This out-of-field absorbed dose needs to be considered for radiation-induced secondary cancers, which are particularly relevant in the case of pediatric treatments. Unfortunately, no method exists in clinics for the computation of the out-of-field dose distributions in proton therapy. To help overcome this limitation, a computational tool has been developed based on the Monte Carlo code TOPAS. The purpose of this work is to evaluate the accuracy of this tool in comparison to experimental data obtained from an anthropomorphic phantom irradiation. An anthropomorphic phantom of a 5-year-old child (ATOM, CIRS) was irradiated for a brain tumor treatment in an IBA Proteus Plus facility using a pencil beam dedicated nozzle. The treatment consisted of three pencil beam scanning fields employing a lucite range shifter. Proton energies ranged from 100 to 165 MeV. A median dose of 50.4 Gy(RBE) with 1.8 Gy(RBE) per fraction was prescribed to the initial planning target volume (PTV), which was located in the cerebellum. Thermoluminescent detectors (TLDs), namely, Li-7-enriched LiF : Mg, Ti (MTS-7) type, were used to detect gamma radiation, which is produced by nuclear reactions, and secondary as well as recoil protons created out-of-field by secondary neutrons. Li-6-enriched LiF : Mg,Cu,P (MCP-6) was combined with Li-7-enriched MCP-7 to measure thermal neutrons. TLDs were calibrated in Co-60 and reported on absorbed dose in water per target dose (μGy/Gy) as well as thermal neutron dose equivalent per target dose (μSv/Gy). Additionally, bubble detectors for personal neutron dosimetry (BD-PND) were used for measuring neutrons (>50 keV), which were calibrated in a Cf-252 neutron beam to report on neutron dose equivalent dose data. The Monte Carlo code TOPAS (version 3.6) was run using a phase-space file containing 10
Language	English
Publishing date	2022-06-08
Publishing country	Switzerland
Document type	Journal Article
ZDB-ID	2649216-7
ISSN	2234-943X
ISSN	2234-943X
DOI	10.3389/fonc.2022.882489
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Article ; Online: Monte Carlo model for ion mobility and diffusion for characteristic electric fields in nanodosimetry.

Kempf, Irina / Schneider, Uwe

Zeitschrift fur medizinische Physik

2023 Volume 34, Issue 1, Page(s) 140–152

Abstract: ... by nanodosimetric measurements. For the development of nanodosimetric detectors, a Monte Carlo model for ion ... for helium, nitrogen, neon, argon, and propane gas. With the Monte Carlo code and resonant charge exchange ...

Abstract	The quantification of the effects of space radiation for manned spaceflight can be approximated by nanodosimetric measurements. For the development of nanodosimetric detectors, a Monte Carlo model for ion mobility and diffusion for characteristic electric fields is presented. This model can be used to describe the interactions of ions in their parent gas based solely on commonly known input parameters, such as the ionization potential, kinetic diameter, molar mass, and polarizability of the gas. A model for approximating the resonant charge exchange cross section has been proposed, requiring only the ionization energy and mass of the parent gas as input parameters. The method proposed in this work was tested against experimental drift velocity data for a wide range of gases (helium, neon, nitrogen, argon, krypton, carbon monoxide, carbon dioxide, oxygen, propane). The transverse diffusion coefficients were compared to experimental values for helium, nitrogen, neon, argon, and propane gas. With the Monte Carlo code and resonant charge exchange cross section approximation model presented in this work, it is now possible to calculate an estimate of the drift velocities, transverse diffusion, and thus the ion mobility of ions in their parent gas. This is essential for further nanodosimetric detector development, as those parameters are often not well known for the gas mixtures used in nanodosimetry.
MeSH term(s)	Neon ; Argon ; Helium ; Propane ; Ions ; Nitrogen ; Monte Carlo Method
Chemical Substances	Neon (4VB4Y46AHD) ; Argon (67XQY1V3KH) ; Helium (206GF3GB41) ; Propane (T75W9911L6) ; Ions ; Nitrogen (N762921K75)
Language	English
Publishing date	2023-02-15
Publishing country	Germany
Document type	Journal Article
ZDB-ID	1104517-6
ISSN	1876-4436 ; 0939-3889 ; 0040-5973
ISSN (online)	1876-4436
ISSN	0939-3889 ; 0040-5973
DOI	10.1016/j.zemedi.2022.12.006
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Article ; Online: Ionisation and swelling behaviour of weak polyampholyte core-shell networks - a Monte Carlo study.

Strauch, Christian / Schneider, Stefanie

Soft matter

2023 Volume 19, Issue 5, Page(s) 938–950

Abstract: ... in the network, whereas using Metropolis Monte Carlo simulations, both the degree of ionisation and ... we performed Metropolis Monte Carlo simulations for a bead-spring model using the constant-pH method ...

Abstract	The network charge of polyampholyte microgels can be tuned by varying the pH of the surrounding solution, and a charge reversal from a positively charged microgel at low pH to a negatively charged microgel at high pH can be achieved. In a titration experiment, it is difficult to tell apart the ionisation of the acidic and basic monomers in the network and to determine the distribution of charges in the network, whereas using Metropolis Monte Carlo simulations, both the degree of ionisation and the distribution of ionised monomers can be determined separately for both species. Building on our earlier work on alternating polyampholyte microgels, we now investigated the pH-dependent ionisation and the swelling behaviour of polyampholyte core-shell microgels under good solvent conditions. For this purpose, we performed Metropolis Monte Carlo simulations for a bead-spring model using the constant-pH method. As in our previous study on alternating microgels, the width of the U-shaped curve of the microgels volume as a function of pH depends on the relative dissociation constants of acid and base, and the microgel volume can be approximated by a linear function of the total network charge. Due to the spatial separation of acid and base in core-shell systems, the ionisation is less enhanced compared to a microgel with an alternating distribution of the two species. Nevertheless, we still see an influence of the presence of one species on the ionisation behaviour of the other species under good solvent conditions. Furthermore, the isoelectric point is shifted towards higher pH, which is caused by a higher charge density in the core compared to that in the shell. Added salt changes the Donnan equilibrium, which determines the counterion distribution within and outside of the microgel. At the same time, it contributes to the electrostatic screening of the network charges, leading to a narrowing of the U-shaped volume transition curve.
Language	English
Publishing date	2023-02-01
Publishing country	England
Document type	Journal Article
ZDB-ID	2191476-X
ISSN	1744-6848 ; 1744-683X
ISSN (online)	1744-6848
ISSN	1744-683X
DOI	10.1039/d2sm01301k
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Article ; Online: Organ absorbed doses in the IORT treatment of breast cancer with the INTRABEAM device: a Monte-Carlo study.

Nasir, Zulfa / Probst, Luis / Schneider, Frank / Clausen, Sven / Bürgy, Daniel / Glatting, Gerhard / Nwankwo, Obioma

Biomedical physics & engineering express

2023 Volume 9, Issue 2

Abstract: ... ...

Abstract	Purpose
MeSH term(s)	Humans ; Female ; Radiotherapy Dosage ; Breast Neoplasms/radiotherapy ; Radiotherapy Planning, Computer-Assisted ; Organs at Risk ; Monte Carlo Method
Language	English
Publishing date	2023-02-22
Publishing country	England
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ISSN	2057-1976
ISSN (online)	2057-1976
DOI	10.1088/2057-1976/acb941
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Article ; Online: Monte Carlo simulations of weak polyampholyte microgels: pH-dependence of conformation and ionization.

Hofzumahaus, C / Strauch, C / Schneider, S

Soft matter

2021 Volume 17, Issue 24, Page(s) 6029–6043

Abstract: We performed Metropolis Monte Carlo simulations to investigate the impact of varying acid and base ...

Abstract	We performed Metropolis Monte Carlo simulations to investigate the impact of varying acid and base dissociation constants on the pH-dependent ionization and conformation of weak polyampholyte microgels under salt-free conditions and under explicit consideration of the chemical ionization equilibria of the acidic and basic groups and their electrostatic interaction. Irrespective of their relative acid and base dissociation constant, all of the microgels undergo a pH-dependent charge reversal from positive to negative with a neutral charge at the isoelectric point. This charge reversal is accompanied by a U-shaped swelling transition of the microgels with a minimum of their size at the point of charge neutrality. The width of the U-shaped swelling transition, however, is found to depend on the chosen relative acid and base dissociation constants through which the extent of the favorable electrostatic intramolecular interaction of the ionized acidic and basic groups is altered. The pH-dependent swelling transition of the microgels is found to become broader, the stronger the intramolecular electrostatic interaction of the oppositely charged ionized species is. In addition, the intramolecular charge compensation of the acidic and basic groups of the microgels allows their counterions to abandon the microgel and the associated gain in translational entropy further amplifies the broadening of the pH-dependent swelling transition. The analysis of the radial ionization profiles of the acidic and basic groups of the differently composed microgels reveals a variety of radial ionization patterns with a dependence on the overall charge of the microgels.
Language	English
Publishing date	2021-06-02
Publishing country	England
Document type	Journal Article
ZDB-ID	2191476-X
ISSN	1744-6848 ; 1744-683X
ISSN (online)	1744-6848
ISSN	1744-683X
DOI	10.1039/d1sm00433f
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Article ; Online: A Monte Carlo technique to model performance of streak camera-based time-resolving x-ray spectrometers.

Stoupin, S / MacPhee, A G / Ose, N / MacDonald, M J / Masse, L / Rusby, D / Schneider, M B

The Review of scientific instruments

2021 Volume 93, Issue 9, Page(s) 93510

Abstract: A Monte Carlo technique has been developed to simulate the expected signal and the statistical ...

Abstract	A Monte Carlo technique has been developed to simulate the expected signal and the statistical noise of x-ray spectrometers that use streak cameras to achieve the time resolution required for ultrafast diagnostics of laser-generated plasmas. The technique accounts for statistics from both the photons incident on the streak camera's photocathode and the electrons emitted by the photocathode travelling through the camera's electron optics to the sensor. We use the technique to optimize the design of a spectrometer, which deduces the temporal history of electron temperature of the hotspot in an inertial confinement fusion implosion from its hard x-ray continuum emission spectra. The technique is general enough to be applied to any instrument using an x-ray streak camera.
Language	English
Publishing date	2021-10-04
Publishing country	United States
Document type	Journal Article
ZDB-ID	209865-9
ISSN	1089-7623 ; 0034-6748
ISSN (online)	1089-7623
ISSN	0034-6748
DOI	10.1063/5.0101705
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Article: Experimental Validation of an Analytical Program and a Monte Carlo Simulation for the Computation of the Far Out-of-Field Dose in External Beam Photon Therapy Applied to Pediatric Patients.

De Saint-Hubert, Marijke / Suesselbeck, Finja / Vasi, Fabiano / Stuckmann, Florian / Rodriguez, Miguel / Dabin, Jérémie / Timmermann, Beate / Thierry-Chef, Isabelle / Schneider, Uwe / Brualla, Lorenzo

Frontiers in oncology

2022 Volume 12, Page(s) 882506

Abstract: ... Monte Carlo algorithm. The purpose of this work is to evaluate the accuracy of these approaches ... Monte Carlo code dose planning method was also used for computing the out-of-field dose. It was executed ... the Monte Carlo data yielded differences which are, in general, smaller than 20%. It was observed ...

Abstract	Background: The out-of-the-field absorbed dose affects the probability of primary second radiation-induced cancers. This is particularly relevant in the case of pediatric treatments. There are currently no methods employed in the clinical routine for the computation of dose distributions from stray radiation in radiotherapy. To overcome this limitation in the framework of conventional teletherapy with photon beams, two computational tools have been developed-one based on an analytical approach and another depending on a fast Monte Carlo algorithm. The purpose of this work is to evaluate the accuracy of these approaches by comparison with experimental data obtained from anthropomorphic phantom irradiations. Materials and methods: An anthropomorphic phantom representing a 5-year-old child (ATOM, CIRS) was irradiated considering a brain tumor using a Varian TrueBeam linac. Two treatments for the same planned target volume (PTV) were considered, namely, intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT). In all cases, the irradiation was conducted with a 6-MV energy beam using the flattening filter for a prescribed dose of 3.6 Gy to the PTV. The phantom had natLiF : Mg, Cu, P (MCP-N) thermoluminescent dosimeters (TLDs) in its 180 holes. The uncertainty of the experimental data was around 20%, which was mostly attributed to the MCP-N energy dependence. To calculate the out-of-field dose, an analytical algorithm was implemented to be run from a Varian Eclipse TPS. This algorithm considers that all anatomical structures are filled with water, with the exception of the lungs which are made of air. The fast Monte Carlo code dose planning method was also used for computing the out-of-field dose. It was executed from the dose verification system PRIMO using a phase-space file containing 3x10 Results: In the out-of-the-field region, the absorbed dose was on average four orders of magnitude lower than the dose at the PTV. For the two modalities employed, the discrepancy between the central values of the TLDs located in the out-of-the-field region and the corresponding positions in the analytic model were in general less than 40%. The discrepancy in the lung doses was more pronounced for IMRT. The same comparison between the experimental and the Monte Carlo data yielded differences which are, in general, smaller than 20%. It was observed that the VMAT irradiation produces the smallest out-of-the-field dose when compared to IMRT. Conclusions: The proposed computational methods for the routine calculation of the out-of-the-field dose produce results that are similar, in most cases, with the experimental data. It has been experimentally found that the VMAT irradiation produces the smallest out-of-the-field dose when compared to IMRT for a given PTV.
Language	English
Publishing date	2022-07-07
Publishing country	Switzerland
Document type	Journal Article
ZDB-ID	2649216-7
ISSN	2234-943X
ISSN	2234-943X
DOI	10.3389/fonc.2022.882506
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Book ; Online: Monte Carlo simulation of ultrafast nonequilibrium spin and charge transport in iron

Briones, J. / Schneider, H. C. / Rethfeld, B.

2021

Abstract: ... using a kinetic Monte Carlo model. This model simulates spin dependent dynamics by taking into account ...

Abstract	Spin transport and spin dynamics after femtosecond laser pulse irradiation of iron (Fe) are studied using a kinetic Monte Carlo model. This model simulates spin dependent dynamics by taking into account two interaction processes during nonequilibrium: Elastic electron - lattice scattering, where only the direction of the excited electrons changes neglecting the energy loss, and inelastic electron - electron interaction, where secondary electrons are generated. An analysis of the particle kinetics inside the material shows that a smaller elastic scattering time affects the spin dynamics by leading to a larger spatial spread of electrons in the material, whereas generation of secondary electrons affects the spin transport with a larger time of propagation of homogeneous spin polarization.
Keywords	Condensed Matter - Materials Science
Publishing date	2021-09-26
Publishing country	us
Document type	Book ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Optimal Displacement Parameters in Monte Carlo Simulations.

Hebbeker, Pascal / Linse, Per / Schneider, Stefanie

Journal of chemical theory and computation

2016 Volume 12, Issue 4, Page(s) 1459–1465

Abstract: ... in Metropolis Monte Carlo simulations is presented. The optimization is based on maximizing the mean square ...

Abstract	An adaptive algorithm optimizing single-particle translational displacement parameters in Metropolis Monte Carlo simulations is presented. The optimization is based on maximizing the mean square displacement of a trial move. It is shown that a large mean square displacement is strongly correlated with a high precision of average potential energy. The method is here demonstrated on model systems representing a Lennard-Jones fluid and a dilute polymer solution at poor solvent conditions. Our adaptive algorithm removes the need to provide values of displacement parameters in simulations, and it is easily extendable to optimize parameters of other types of trial moves.
Language	English
Publishing date	2016-04-12
Publishing country	United States
Document type	Journal Article ; Research Support, Non-U.S. Gov't
ISSN	1549-9626
ISSN (online)	1549-9626
DOI	10.1021/acs.jctc.5b00797
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