The Experts below are selected from a list of 14094 Experts worldwide ranked by ideXlab platform
Oliver Jakel - One of the best experts on this subject based on the ideXlab platform.
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experimental verification of ion Stopping Power prediction from dual energy ct data in tissue surrogates
Physics in Medicine and Biology, 2014Co-Authors: Nora Hunemohr, Oliver Jakel, Bernhard Krauss, Christoph Tremmel, Benjamin Ackermann, Steffen GreilichAbstract:We present an experimental verification of Stopping-Power-ratio (SPR) prediction from dual energy CT (DECT) with potential use for dose planning in proton and ion therapy. The approach is based on DECT images converted to electron density relative to water ϱe/ϱe, w and effective atomic number Zeff. To establish a parameterization of the I-value by Zeff, 71 tabulated tissue compositions were used. For the experimental assessment of the method we scanned 20 materials (tissue surrogates, polymers, aluminum, titanium) at 80/140Sn kVp and 100/140Sn kVp (Sn: additional tin filtration) and computed the ϱe/ϱe, w and Zeff with a purely image based algorithm. Thereby, we found that ϱe/ϱe, w (Zeff) could be determined with an accuracy of 0.4% (1.7%) for the tissue surrogates with known elemental compositions. SPRs were predicted from DECT images for all 20 materials using the presented approach and were compared to measured water-equivalent path lengths (closely related to SPR). For the tissue surrogates the presented DECT approach was found to predict the experimental values within 0.6%, for aluminum and titanium within an accuracy of 1.7% and 9.4% (from 16-bit reconstructed DECT images).
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influence of the delta ray production threshold on water to air Stopping Power ratio calculations for carbon ion beam radiotherapy
Physics in Medicine and Biology, 2013Co-Authors: D Sanchezparcerisa, Oliver Jakel, Alexander Gemmel, Eike Rietzel, Katia ParodiAbstract:Previous calculations of the water-to-air Stopping Power ratio (sw,air) for carbon ion beams did not involve tracking of delta ray electrons, even though previous calculations with protons predict an effect up to 1%. We investigate the effect of the delta ray production threshold insw,air calculations and propose an empirical expression which takes into account the effect of the delta ray threshold as well as the uncertainty in the mean ionization potentials (I-values) of air and water. The formula is derived from the results of Monte Carlo calculations using the most up-to-date experimental data for I-values and a delta ray production threshold of 10 keV. It allows us to reduce the standard uncertainty insw,air below 0.8%, instead of the current 2% given in international protocols, which results in a reduction of the overall uncertainty for absolute dosimetry based on air-filled ionization chambers. (Some figures may appear in colour only in the online journal)
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monte carlo simulations on the water to air Stopping Power ratio for carbon ion dosimetry
Medical Physics, 2009Co-Authors: K Henkner, Niels Bassler, Nikolai Sobolevsky, Oliver JakelAbstract:Many papers discussed the I value for water given by the ICRU, concluding that a value of about 80 +/- 2 eV instead of 67.2 eV would reproduce measured ion depth-dose curves. A change in the I value for water would have an effect on the Stopping Power and, hence, on the water-to-air Stopping Power ratio, which is important in clinical dosimetry of proton and ion beams. For energies ranging from 50 to 330 MeV/u and for one spread out Bragg peak, the authors compare the impact of the I value on the water-to-air Stopping Power ratio. The authors calculate ratios from different ICRU Stopping Power tables and ICRU reports. The Stopping Power ratio is calculated via track-length dose calculation with SHIELD-HIT07. In the calculations, the Stopping Power ratio is reduced to a value of 1.119 in the plateau region as compared to the cited value of 1.13 in IAEA TRS-398. At low energies the Stopping Power ratio increases by up to 6% in the last few tenths of a mm toward the Bragg peak. For a spread out Bragg peak of 13.5 mm width at 130 mm depth, the Stopping Power ratio increases by about 1% toward the distal end.
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calculation of Stopping Power ratios for carbon ion dosimetry
Physics in Medicine and Biology, 2006Co-Authors: Oksana Geithner, Nikolai Sobolevsky, Pedro Andreo, Gunther H Hartmann, Oliver JakelAbstract:Water-to-air Stopping Power ratio calculations for the ionization chamber dosimetry of clinical carbon ion beams with initial energies from 50 to 450 MeV/u have been performed using the Monte Carlo technique. To simulate the transport of a particle in water the computer code SHIELD-HIT v2 was used, which is a newly developed version where substantial modifications were implemented on its predecessor SHIELD-HIT v1 (Gudowska et al 2004 Phys. Med. Biol. 49 1933-58). The code was completely rewritten replacing formerly used single precision variables with double precision variables. The lowest particle transport specific energy was decreased from 1 MeV/u down to 10 keV/u by modifying the Bethe-Bloch formula, thus widening its range for medical dosimetry applications. In addition, the code includes optionally MSTAR and ICRU-73 Stopping Power data. The fragmentation model was verified and its parameters were also adjusted. The present code version shows excellent agreement with experimental data. It has been used to compute the physical quantities needed for the calculation of Stopping Power ratios, s(water,air), of carbon beams. Compared with the recommended constant value given in the IAEA Code of Practice, the differences found in the present investigations varied between 0.5% and 1% at the plateau region, respectively for 400 MeV/u and 50 MeV/u beams, and up to 2.3% in the vicinity of the Bragg peak for 50 MeV/u.
L A Collins - One of the best experts on this subject based on the ideXlab platform.
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ab initio studies on the Stopping Power of warm dense matter with time dependent orbital free density functional theory
Physical Review Letters, 2018Co-Authors: Y H Ding, Alexander J White, Ondřej Certik, L A CollinsAbstract:Electronic transport properties of warm dense matter, such as electrical or thermal conductivities and nonadiabatic Stopping Power, are of particular interest to geophysics, planetary science, astrophysics, and inertial confinement fusion (ICF). One example is the α-particle Stopping Power of dense deuterium-tritium (DT) plasmas, which must be precisely known for current small-margin ICF target designs to ignite. We have developed a time-dependent orbital-free density functional theory (TD-OF-DFT) method for ab initio investigations of the charged-particle Stopping Power of warm dense matter. Our current dependent TD-OF-DFT calculations have reproduced the recently well-characterized Stopping Power experiment in warm dense beryllium. For α-particle Stopping in warm and solid-density DT plasmas, the ab initio TD-OF-DFT simulations show a lower Stopping Power up to ∼25% in comparison with three Stopping-Power models often used in the high-energy-density physics community.
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ab initio studies on the Stopping Power of warm dense matter with time dependent orbital free density functional theory
Physical Review Letters, 2018Co-Authors: Y H Ding, Alexander J White, Ondřej Certik, L A CollinsAbstract:Electronic transport properties of warm dense matter, such as electrical or thermal conductivities and nonadiabatic Stopping Power, are of particular interest to geophysics, planetary science, astrophysics, and inertial confinement fusion (ICF). One example is the $\ensuremath{\alpha}$-particle Stopping Power of dense deuterium-tritium (DT) plasmas, which must be precisely known for current small-margin ICF target designs to ignite. We have developed a time-dependent orbital-free density functional theory (TD-OF-DFT) method for ab initio investigations of the charged-particle Stopping Power of warm dense matter. Our current dependent TD-OF-DFT calculations have reproduced the recently well-characterized Stopping Power experiment in warm dense beryllium. For $\ensuremath{\alpha}$-particle Stopping in warm and solid-density DT plasmas, the ab initio TD-OF-DFT simulations show a lower Stopping Power up to $\ensuremath{\sim}25%$ in comparison with three Stopping-Power models often used in the high-energy-density physics community.
Pedro Andreo - One of the best experts on this subject based on the ideXlab platform.
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calculation of Stopping Power ratios for carbon ion dosimetry
Physics in Medicine and Biology, 2006Co-Authors: Oksana Geithner, Nikolai Sobolevsky, Pedro Andreo, Gunther H Hartmann, Oliver JakelAbstract:Water-to-air Stopping Power ratio calculations for the ionization chamber dosimetry of clinical carbon ion beams with initial energies from 50 to 450 MeV/u have been performed using the Monte Carlo technique. To simulate the transport of a particle in water the computer code SHIELD-HIT v2 was used, which is a newly developed version where substantial modifications were implemented on its predecessor SHIELD-HIT v1 (Gudowska et al 2004 Phys. Med. Biol. 49 1933-58). The code was completely rewritten replacing formerly used single precision variables with double precision variables. The lowest particle transport specific energy was decreased from 1 MeV/u down to 10 keV/u by modifying the Bethe-Bloch formula, thus widening its range for medical dosimetry applications. In addition, the code includes optionally MSTAR and ICRU-73 Stopping Power data. The fragmentation model was verified and its parameters were also adjusted. The present code version shows excellent agreement with experimental data. It has been used to compute the physical quantities needed for the calculation of Stopping Power ratios, s(water,air), of carbon beams. Compared with the recommended constant value given in the IAEA Code of Practice, the differences found in the present investigations varied between 0.5% and 1% at the plateau region, respectively for 400 MeV/u and 50 MeV/u beams, and up to 2.3% in the vicinity of the Bragg peak for 50 MeV/u.
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ionization chamber dosimetry of small photon fields a monte carlo study on Stopping Power ratios for radiosurgery and imrt beams
Physics in Medicine and Biology, 2003Co-Authors: F Sanchezdoblado, Pedro Andreo, R Capote, Antonio Leal, M Perucha, R Arrans, L Nunez, Ernesto Mainegra, J I Lagares, E CarrascoAbstract:Absolute dosimetry with ionization chambers of the narrow photon fields used in stereotactic techniques and IMRT beamlets is constrained by lack of electron equilibrium in the radiation field. It is questionable that Stopping-Power ratio in dosimetry protocols, obtained for broad photon beams and quasi-electron equilibrium conditions, can be used in the dosimetry of narrow fields while keeping the uncertainty at the same level as for the broad beams used in accelerator calibrations. Monte Carlo simulations have been performed for two 6 MV clinical accelerators (Elekta SL-18 and Siemens Mevatron Primus), equipped with radiosurgery applicators and MLC. Narrow circular and Z-shaped on-axis and off-axis fields, as well as broad IMRT configured beams, have been simulated together with reference 10 x 10 cm2 beams. Phase-space data have been used to generate 3D dose distributions which have been compared satisfactorily with experimental profiles (ion chamber, diodes and film). Photon and electron spectra at various depths in water have been calculated, followed by Spencer-Attix (delta = 10 keV) Stopping-Power ratio calculations which have been compared to those used in the IAEA TRS-398 code of practice. For water/air and PMMA/air Stopping-Power ratios, agreements within 0.1% have been obtained for the 10 x 10 cm2 fields. For radiosurgery applicators and narrow MLC beams, the calculated s(w,air) values agree with the reference within +/-0.3%, well within the estimated standard uncertainty of the reference Stopping-Power ratios (0.5%). Ionization chamber dosimetry of narrow beams at the photon qualities used in this work (6 MV) can therefore be based on Stopping-Power ratios data in dosimetry protocols. For a modulated 6 MV broad beam used in clinical IMRT, s(w,air) agrees within 0.1% with the value for 10 x 10 cm2, confirming that at low energies IMRT absolute dosimetry can also be based on data for open reference fields. At higher energies (24 MV) the difference in s(w,air) was up to 1.1%, indicating that the use of protocol data for narrow beams in such cases is less accurate than at low energies, and detailed calculations of the dosimetry parameters involved should be performed if similar accuracy to that of 6 MV is sought.
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monte carlo calculated Stopping Power ratios water air for clinical proton dosimetry 50 250 mev
Physics in Medicine and Biology, 1997Co-Authors: Pedro Andreo, Joakim MedinAbstract:Calculations of Stopping Power ratios, water to air, for the determination of absorbed dose to water in clinical proton beams using ionization chamber measurements have been undertaken using the Monte Carlo method. A computer code to simulate the transport of protons in water (PETRA) has been used to calculate sw.air-data under different degrees of complexity, ranging from values based on primary protons only to data including secondary electrons and high-energy secondary protons produced in nonelastic nuclear collisions. All numerical data are based on ICRU 49 proton Stopping Powers. Calculations using primary protons have been compared to the simple continuous slowing-down approximation (c.s.d.a.) analytical technique used in proton dosimetry protocols, not finding significant differences that justify elaborate Monte Carlo simulations except beyond the mean range of the protons (the far side of the Bragg peak). The influence of nuclear nonelastic processes, through the detailed generation and transport of secondary protons, on the calculated Stopping-Power ratios has been found to be negligible. The effect of alpha particles has also been analysed, finding differences smaller than 0.1% from the results excluding them. Discrepancies of up to 0.6% in the plateau region have been found, however, when the production and transport of secondary electrons are taken into account. The large influence of nonelastic nuclear interactions on proton depth-dose distributions shows that the removal of primary protons from the incident beam decreases the peak-to-plateau ratio by a large factor, up to 40% at 250 MeV. It is therefore emphasized that nonelastic nuclear reactions should be included in Monte Carlo simulations of proton beam depth-dose distributions.
Y H Ding - One of the best experts on this subject based on the ideXlab platform.
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ab initio studies on the Stopping Power of warm dense matter with time dependent orbital free density functional theory
Physical Review Letters, 2018Co-Authors: Y H Ding, Alexander J White, Ondřej Certik, L A CollinsAbstract:Electronic transport properties of warm dense matter, such as electrical or thermal conductivities and nonadiabatic Stopping Power, are of particular interest to geophysics, planetary science, astrophysics, and inertial confinement fusion (ICF). One example is the α-particle Stopping Power of dense deuterium-tritium (DT) plasmas, which must be precisely known for current small-margin ICF target designs to ignite. We have developed a time-dependent orbital-free density functional theory (TD-OF-DFT) method for ab initio investigations of the charged-particle Stopping Power of warm dense matter. Our current dependent TD-OF-DFT calculations have reproduced the recently well-characterized Stopping Power experiment in warm dense beryllium. For α-particle Stopping in warm and solid-density DT plasmas, the ab initio TD-OF-DFT simulations show a lower Stopping Power up to ∼25% in comparison with three Stopping-Power models often used in the high-energy-density physics community.
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ab initio studies on the Stopping Power of warm dense matter with time dependent orbital free density functional theory
Physical Review Letters, 2018Co-Authors: Y H Ding, Alexander J White, Ondřej Certik, L A CollinsAbstract:Electronic transport properties of warm dense matter, such as electrical or thermal conductivities and nonadiabatic Stopping Power, are of particular interest to geophysics, planetary science, astrophysics, and inertial confinement fusion (ICF). One example is the $\ensuremath{\alpha}$-particle Stopping Power of dense deuterium-tritium (DT) plasmas, which must be precisely known for current small-margin ICF target designs to ignite. We have developed a time-dependent orbital-free density functional theory (TD-OF-DFT) method for ab initio investigations of the charged-particle Stopping Power of warm dense matter. Our current dependent TD-OF-DFT calculations have reproduced the recently well-characterized Stopping Power experiment in warm dense beryllium. For $\ensuremath{\alpha}$-particle Stopping in warm and solid-density DT plasmas, the ab initio TD-OF-DFT simulations show a lower Stopping Power up to $\ensuremath{\sim}25%$ in comparison with three Stopping-Power models often used in the high-energy-density physics community.
Frank Graziani - One of the best experts on this subject based on the ideXlab platform.
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Stopping Power enhancement from discrete particle wake correlations in high energy density plasmas
Physical Review E, 2021Co-Authors: Ian Ellis, D J Strozzi, W B Mori, Frank GrazianiAbstract:Three-dimensional (3D) simulations of electron beams propagating in high-energy-density plasmas using the quasistatic Particle-in-Cell (PIC) code QuickPIC demonstrate a significant increase in Stopping Power when beam electrons mutually interact via their wakes. Each beam electron excites a plasma wave wake of wavelength $\ensuremath{\sim}2\ensuremath{\pi}c/{\ensuremath{\omega}}_{pe}$, where $c$ is the speed of light and ${\ensuremath{\omega}}_{pe}$ is the background plasma frequency. We show that a discrete collection of electrons undergoes a beam-plasma-like instability caused by mutual particle-wake interactions that causes electrons to bunch in the beam, even for beam densities ${n}_{b}$ for which fluid theory breaks down. This bunching enhances the beam's Stopping Power, which we call ``correlated Stopping,'' and the effect increases with the ``correlation number'' ${N}_{b}\ensuremath{\equiv}{n}_{b}{(c/{\ensuremath{\omega}}_{pe})}^{3}$. For example, a beam of monoenergetic 9.7 MeV electrons with ${N}_{b}=1/8$, in a cold background plasma with ${n}_{e}={10}^{26}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ (450 g ${\mathrm{cm}}^{\ensuremath{-}3}$ DT), has a Stopping Power of $2.28\ifmmode\pm\else\textpm\fi{}0.04$ times the single-electron value, which increases to $1220\ifmmode\pm\else\textpm\fi{}5$ for ${N}_{b}=64$. The beam also experiences transverse filamentation, which eventually limits the Stopping enhancement.
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molecular dynamics simulations of classical Stopping Power
Physical Review Letters, 2013Co-Authors: Paul E Grabowski, Frank Graziani, Michael P Surh, David F Richards, Michael S MurilloAbstract:Molecular dynamics can provide very accurate tests of classical kinetic theory; for example, unambiguous comparisons can be made for classical particles interacting via a repulsive $1/r$ potential. The plasma Stopping Power problem, of great interest in its own right, provides an especially stringent test of a velocity-dependent transport property. We have performed large-scale ($\ensuremath{\sim}{10}^{4}--{10}^{6}$ particles) molecular dynamics simulations of charged-particle Stopping in a classical electron gas that span the weak to moderately strong intratarget coupling regimes. Projectile-target coupling is varied with projectile charge and velocity. Comparisons are made with disparate kinetic theories (both Boltzmann and Lenard-Balescu classes) and fully convergent theories to establish regimes of validity. We extend these various Stopping models to improve agreement with the MD data and provide a useful fit to our results.
