The Experts below are selected from a list of 69 Experts worldwide ranked by ideXlab platform
Oleg Shcherbakov - One of the best experts on this subject based on the ideXlab platform.
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angular distributions and anisotropy of fission fragments from neutron induced fission in intermediate energy range 1 200 mev
European Physical Journal Web of Conferences, 2017Co-Authors: Alexander Vorobyev, Alexei M Gagarski, Oleg Shcherbakov, Larisa A Vaishnene, Alexei L BarabanovAbstract:Angular distributions of fission fragments from the neutron-induced fission of 232 Th, 233 U, 235 U, 238 U and 209 Bi have been measured in the energy range 1–200 MeV at the neutron TOF spectrometer GNEIS based on the spallation neutron source at 1 GeV proton synchrocyclotron of the PNPI (Gatchina, Russia). The multiwire proportional counters have been used as a position sensitive fission fragment detector. A description of the experimental equipment and measurement procedure is given. The anisotropy of fission fragments deduced from the data on measured angular distributions is presented in comparison with experimental data of other authors, first of all, the recent data from WNR at LANSCE (Los Alamos, USA) and n_TOF(CERN).
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neutron induced fission of 233u 238u 232th 239pu 237np natpb and 209bi relative to 235u in the energy range 1 200 mev
Journal of Nuclear Science and Technology, 2002Co-Authors: Oleg Shcherbakov, Andrei Donets, Alexander Evdokimov, Alexander Fomichev, Tokio Fukahori, Akira Hasegawa, Alexander Laptev, Vladimir Maslov, Guennady Petrov, Sergei SolovievAbstract:Fission cross section ratios of 233U, 238U, 232Th, 239Pu, 237Np, natural Pb and 209Bi to 235U have been measured in a wide energy range of incident neutrons from 1 MeV to 200 MeV using a time-of-flight technique at the neutron spectrometer GNEIS based on the 1-GeV proton synchrocyclotron of PNPI. For actinide targets, the threshold cross section method and evaluated data below 14 MeV were used for normalization of the shape measurement data, while the evaluated and recommended fission cross sections of 235U were used to convert the ratio data to absolute fission cross sections. For Pb and Bi targets, an absolute normalization of the measured cross section ratios has been done using the thickness of the targets and detection efficiencies.
Sergei Soloviev - One of the best experts on this subject based on the ideXlab platform.
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neutron induced fission of 233u 238u 232th 239pu 237np natpb and 209bi relative to 235u in the energy range 1 200 mev
Journal of Nuclear Science and Technology, 2002Co-Authors: Oleg Shcherbakov, Andrei Donets, Alexander Evdokimov, Alexander Fomichev, Tokio Fukahori, Akira Hasegawa, Alexander Laptev, Vladimir Maslov, Guennady Petrov, Sergei SolovievAbstract:Fission cross section ratios of 233U, 238U, 232Th, 239Pu, 237Np, natural Pb and 209Bi to 235U have been measured in a wide energy range of incident neutrons from 1 MeV to 200 MeV using a time-of-flight technique at the neutron spectrometer GNEIS based on the 1-GeV proton synchrocyclotron of PNPI. For actinide targets, the threshold cross section method and evaluated data below 14 MeV were used for normalization of the shape measurement data, while the evaluated and recommended fission cross sections of 235U were used to convert the ratio data to absolute fission cross sections. For Pb and Bi targets, an absolute normalization of the measured cross section ratios has been done using the thickness of the targets and detection efficiencies.
Alexei L Barabanov - One of the best experts on this subject based on the ideXlab platform.
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angular distributions and anisotropy of fission fragments from neutron induced fission in intermediate energy range 1 200 mev
European Physical Journal Web of Conferences, 2017Co-Authors: Alexander Vorobyev, Alexei M Gagarski, Oleg Shcherbakov, Larisa A Vaishnene, Alexei L BarabanovAbstract:Angular distributions of fission fragments from the neutron-induced fission of 232 Th, 233 U, 235 U, 238 U and 209 Bi have been measured in the energy range 1–200 MeV at the neutron TOF spectrometer GNEIS based on the spallation neutron source at 1 GeV proton synchrocyclotron of the PNPI (Gatchina, Russia). The multiwire proportional counters have been used as a position sensitive fission fragment detector. A description of the experimental equipment and measurement procedure is given. The anisotropy of fission fragments deduced from the data on measured angular distributions is presented in comparison with experimental data of other authors, first of all, the recent data from WNR at LANSCE (Los Alamos, USA) and n_TOF(CERN).
Tianyu Zhao - One of the best experts on this subject based on the ideXlab platform.
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Feasibility of proton FLASH irradiation using a synchrocyclotron for preclinical studies
Medical physics, 2020Co-Authors: Arash Darafsheh, Y. Hao, Townsend Zwart, Miles Wagner, Daniel Catanzano, Jeffrey F. Williamson, Nels C. Knutson, Baozhou Sun, Sasa Mutic, Tianyu ZhaoAbstract:PURPOSE It has been recently shown that radiotherapy at ultrahigh dose rates (>40 Gy/s, FLASH) has a potential advantage in sparing healthy organs compared to that at conventional dose rates. The purpose of this work is to show the feasibility of proton FLASH irradiation using a gantry-mounted synchrocyclotron as a first step toward implementing an experimental setup for preclinical studies. METHODS A clinical Mevion HYPERSCAN® synchrocyclotron was modified to deliver ultrahigh dose rates. Pulse widths of protons with 230 MeV energy were manipulated from 1 to 20 μs to deliver in conventional and ultrahigh dose rate. A boron carbide absorber was placed in the beam for range modulation. A Faraday cup was used to determine the number of protons per pulse at various dose rates. Dose rate was determined by the dose measured with a plane-parallel ionization chamber with respect to the actual delivery time. The integral depth dose (IDD) was measured with a Bragg ionization chamber. Monte Carlo simulation was performed in TOPAS as the secondary check for the measurements. RESULTS Maximum protons charge per pulse, measured with the Faraday cup, was 54.6 pC at 20 μs pulse width. The measured IDD agreed well with the Monte Carlo simulation. The average dose rate measured using the ionization chamber showed 101 Gy/s at the entrance and 216 Gy/s at the Bragg peak with a full width at half maximum field size of 1.2 cm. CONCLUSIONS It is feasible to deliver protons at 100 and 200 Gy/s average dose rate at the plateau and the Bragg peak, respectively, in a small ~1 cm2 field using a gantry-mounted synchrocyclotron.
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two stage ionoacoustic range verification leveraging monte carlo and acoustic simulations to stably account for tissue inhomogeneity and accelerator specific time structure a simulation study
Medical Physics, 2018Co-Authors: S K Patch, D E M Hoff, T B Webb, L G Sobotka, Tianyu ZhaoAbstract:PURPOSE Range errors constrain treatment planning by limiting choice of ion beam angles and requiring large margins. Ionoacoustic range verification requires recovering the location of an acoustic source from low frequency signals. A priori information is applied to stably overcome resolution limits of inverse acoustic source imaging in this simulation study. In particular, the accuracy and robustness of ionoacoustic range verification for lateral and oblique delivery of high-energy protons to the prostate is examined. METHODS Dose maps were computed using GEANT4 Monte Carlo simulations via the TOPAS user interface. Thermoacoustic pulses were propagated using k-Wave software, with initial pressures corresponding to instantaneous dose deposition and piecewise constant maps of tissue properties derived from the planning CT. A database of dose maps with corresponding thermoacoustic emissions and Bragg peak locations, referred to as "control points," were precomputed. Corresponding thermoacoustic emissions were also precomputed. Pulses were recorded at four coplanar locations corresponding to the outer surface of a virtual transrectal array. To model experimental beam delivery, k-Wave results were convolved in time with a Gaussian envelope to account for noninstantaneous proton delivery by a synchrocyclotron. Thermoacoustic pulses were bandlimited below 150 kHz, and amplitudes were directly proportional to charge delivered. To test robustness of our method, white noise was added. Range was estimated in a two-step process. The first step obtained a preliminary range estimate by one-way beamforming. The second step was taken using data corresponding to the "control point" nearest to the preliminary range estimate. For each receiver, the time of flight difference, ∆t, between the measured and control thermoacoustic signals were accurately estimated by applying the Fourier shift theorem. Receiver-Bragg peak distance was then estimated by adding vs ∆t to the known distance of the control point, where vs is soundspeed. A linear system of equations based upon all receiver locations and distances was solved to recover the Bragg peak location. All simulations were performed relative to the planning CT. Because ultrasound (US) images were not available, results were overlaid onto the planning CT. RESULTS Beamformed estimates from noise-free data tracked all beam locations within 1 cm. Final estimates for oblique and lateral beams were accurate to within 1.0 and 1.6 mm respectively. Average errors of final range estimates for oblique beams from data with SNR = 0 dB were no greater than 2.0 mm. CONCLUSIONS Ionoacoustic range verification may improve current practice. Ionoacoustic range estimates can be inherently co-registered to ultrasound images of underlying anatomy. To ensure estimates are robust in clinical practice, dose maps based upon the planning CT should be overlaid onto ultrasound volumes acquired at time of treatment and acoustic simulations re-computed to provide a database of control points and corresponding thermoacoustic emissions. Computation times for beamformed estimates are already fast enough for online range verification, but are not accurate enough for a measurement aperture limited to the surface of a transrectal ultrasound probe. Accelerated acoustic simulations will be required to enable online two-stage correction, but offline calculation is already suitable for adaptive planning.
S K Patch - One of the best experts on this subject based on the ideXlab platform.
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thermoacoustic range verification during pencil beam delivery of a clinical plan to an abdominal imaging phantom
Radiotherapy and Oncology, 2021Co-Authors: S K Patch, Chinh Nguyen, Diego Dominguezramirez, Rudi Labarbe, Guillaume Janssens, Diego Cammarano, Jake Lister, Christopher Finch, Jamil Lambert, Jeevan PandeyAbstract:Abstract Purpose The purpose of this phantom study is to demonstrate that thermoacoustic range verification could be performed clinically. Thermoacoustic emissions generated in an anatomical multimodality imaging phantom during delivery of a clinical plan are compared to simulated emissions to estimate range shifts compared to the treatment plan. Methods A single-field 12-layer proton pencil beam scanning (PBS) treatment plan created in Pinnacle prescribing 6 Gy/fraction was delivered by a superconducting synchrocyclotron to a triple modality (CT, MRI, and US) abdominal imaging phantom. Data was acquired by four acoustic receivers rigidly affixed to a linear ultrasound array. Receivers 1-2 were located distal to the treatment volume, whereas 3-4 were lateral. Receivers’ room coordinates were computed relative to the ultrasound image plane after co-registration to the planning CT volume. For each prescribed beamlet, a set of thermoacoustic emissions corresponding to varied beam energies were computed. Simulated emissions were compared to measured emissions to estimate shifts of the Bragg peak. Results Shifts were small for high-dose beamlets that stopped in soft tissue. Signals acquired by channels 1-2 yielded shifts of - 0.2 ± 0.7 m m relative to Monte Carlo simulations for high dose spots (∼40 cGy) in the second layer. Additionally, for beam energy ≥ 125 MeV, thermoacoustic emissions qualitatively tracked lateral motion of pristine beams in a layered gelatin phantom, and time shifts induced by changing phantom layers were self-consistent within nanoseconds. Conclusions Acoustic receivers tuned to spectra of thermoacoustic emissions may enable range verification during proton therapy.
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two stage ionoacoustic range verification leveraging monte carlo and acoustic simulations to stably account for tissue inhomogeneity and accelerator specific time structure a simulation study
Medical Physics, 2018Co-Authors: S K Patch, D E M Hoff, T B Webb, L G Sobotka, Tianyu ZhaoAbstract:PURPOSE Range errors constrain treatment planning by limiting choice of ion beam angles and requiring large margins. Ionoacoustic range verification requires recovering the location of an acoustic source from low frequency signals. A priori information is applied to stably overcome resolution limits of inverse acoustic source imaging in this simulation study. In particular, the accuracy and robustness of ionoacoustic range verification for lateral and oblique delivery of high-energy protons to the prostate is examined. METHODS Dose maps were computed using GEANT4 Monte Carlo simulations via the TOPAS user interface. Thermoacoustic pulses were propagated using k-Wave software, with initial pressures corresponding to instantaneous dose deposition and piecewise constant maps of tissue properties derived from the planning CT. A database of dose maps with corresponding thermoacoustic emissions and Bragg peak locations, referred to as "control points," were precomputed. Corresponding thermoacoustic emissions were also precomputed. Pulses were recorded at four coplanar locations corresponding to the outer surface of a virtual transrectal array. To model experimental beam delivery, k-Wave results were convolved in time with a Gaussian envelope to account for noninstantaneous proton delivery by a synchrocyclotron. Thermoacoustic pulses were bandlimited below 150 kHz, and amplitudes were directly proportional to charge delivered. To test robustness of our method, white noise was added. Range was estimated in a two-step process. The first step obtained a preliminary range estimate by one-way beamforming. The second step was taken using data corresponding to the "control point" nearest to the preliminary range estimate. For each receiver, the time of flight difference, ∆t, between the measured and control thermoacoustic signals were accurately estimated by applying the Fourier shift theorem. Receiver-Bragg peak distance was then estimated by adding vs ∆t to the known distance of the control point, where vs is soundspeed. A linear system of equations based upon all receiver locations and distances was solved to recover the Bragg peak location. All simulations were performed relative to the planning CT. Because ultrasound (US) images were not available, results were overlaid onto the planning CT. RESULTS Beamformed estimates from noise-free data tracked all beam locations within 1 cm. Final estimates for oblique and lateral beams were accurate to within 1.0 and 1.6 mm respectively. Average errors of final range estimates for oblique beams from data with SNR = 0 dB were no greater than 2.0 mm. CONCLUSIONS Ionoacoustic range verification may improve current practice. Ionoacoustic range estimates can be inherently co-registered to ultrasound images of underlying anatomy. To ensure estimates are robust in clinical practice, dose maps based upon the planning CT should be overlaid onto ultrasound volumes acquired at time of treatment and acoustic simulations re-computed to provide a database of control points and corresponding thermoacoustic emissions. Computation times for beamformed estimates are already fast enough for online range verification, but are not accurate enough for a measurement aperture limited to the surface of a transrectal ultrasound probe. Accelerated acoustic simulations will be required to enable online two-stage correction, but offline calculation is already suitable for adaptive planning.
