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Wayne D Newhauser - One of the best experts on this subject based on the ideXlab platform.
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neutron production from Beam modifying devices in a modern double scattering proton therapy Beam delivery system
Physics in Medicine and Biology, 2009Co-Authors: A Perezandujar, Wayne D Newhauser, P M DelucaAbstract:In this work the neutron production in a passive Beam delivery system was investigated. Secondary particles including neutrons are created as the proton Beam interacts with Beam shaping devices in the treatment head. Stray neutron exposure to the whole body may increase the risk that the patient develops a radiogenic cancer years or decades after radiotherapy. We simulated a passive proton Beam delivery system with double scattering technology to determine the neutron production and energy distribution at 200 MeV proton energy. Specifically, we studied the neutron absorbed dose per therapeutic absorbed dose, the neutron absorbed dose per source particle and the neutron energy spectrum at various locations around the nozzle. We also investigated the neutron production along the nozzle's central axis. The absorbed doses and neutron spectra were simulated with the MCNPX Monte Carlo code. The simulations revealed that the range modulation wheel (RMW) is the most intense neutron source of any of the Beam Spreading devices within the nozzle. This finding suggests that it may be helpful to refine the design of the RMW assembly, e.g., by adding local shielding, to suppress neutron-induced damage to components in the nozzle and to reduce the shielding thickness of the treatment vault. The simulations also revealed that the neutron dose to the patient is predominated by neutrons produced in the field defining collimator assembly, located just upstream of the patient.
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calculations of neutron dose equivalent exposures from range modulated proton therapy Beams
Physics in Medicine and Biology, 2005Co-Authors: J Polf, Wayne D NewhauserAbstract:Passive Beam Spreading techniques have been used for most proton therapy treatments worldwide. This delivery method employs static scattering foils to spread the Beam laterally and a range modulating wheel or ridge filter to spread the high dose region in depth to provide a uniform radiation dose to the treatment volume. Neutrons produced by interactions of the treatment Beam with nozzle components, such as the range modulation wheel, can account for a large portion of the secondary dose delivered to healthy tissue outside the treatment volume. Despite this fact, little is known about the effects of range modulation on the secondary neutron exposures around passively scattered proton treatment nozzles. In this work, the neutron dose equivalent spectra per incident proton (H(E)/p) and total neutron dose equivalent per therapeutic absorbed dose (H/D) were studied using Monte Carlo techniques for various values of range modulation at 54 locations around a passive scattering proton therapy treatment nozzle. As the range modulator wheel step thickness increased from 1.0 to 11.5 cm, the peak values of H(E)/p decreased from approximately 1 × 10−17 mSv Gy−1 to approximately 2 × 10−18 mSv Gy−1 at 50 cm from isocentre along the Beam's central axis. In general, H/D increased with increasing range modulation at all locations studied, and the maximum H/D exposures shifted away from isocentre.
Bernard Gottschalk - One of the best experts on this subject based on the ideXlab platform.
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comparison of geant4 multiple coulomb scattering models with theory for radiotherapy protons
Physics in Medicine and Biology, 2017Co-Authors: Anastasia Makarova, Bernard Gottschalk, W SauerweinAbstract:Usually, Monte Carlo models are validated against experimental data. However, models of multiple Coulomb scattering (MCS) in the Gaussian approximation are exceptional in that we have theories which are probably more accurate than the experiments which have, so far, been done to test them. In problems directly sensitive to the distribution of angles leaving the target, the relevant theory is the Moliere/Fano/Hanson variant of Moliere theory (Gottschalk et al 1993 Nucl. Instrum. Methods Phys. Res. B 74 467-90). For transverse Spreading of the Beam in the target itself, the theory of Preston and Koehler (Gottschalk (2012 arXiv:1204.4470)) holds. Therefore, in this paper we compare Geant4 simulations, using the Urban and Wentzel models of MCS, with theory rather than experiment, revealing trends which would otherwise be obscured by experimental scatter. For medium-energy (radiotherapy) protons, and low-Z (water-like) target materials, Wentzel appears to be better than Urban in simulating the distribution of outgoing angles. For Beam Spreading in the target itself, the two models are essentially equal.
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comparison of geant4 multiple coulomb scattering models with theory for radiotherapy protons
arXiv: Medical Physics, 2016Co-Authors: Anastasia Makarova, Bernard Gottschalk, W SauerweinAbstract:Usually, Monte Carlo models are validated against experimental data. However, models of multiple Coulomb scattering (MCS) in the Gaussian approximation are exceptional in that we have theories which are probably more accurate than the experiments which have, so far, been done to test them. In problems directly sensitive to the distribution of angles leaving the target, the relevant theory is the Moliere/Fano/Hanson variant of Moliere theory. For transverse Spreading of the Beam in the target itself, the theory of Preston and Koehler holds. Therefore, in this paper we compare Geant4 simulations, using the Urban and Wentzel models of MCS, with theory rather than experiment, revealing trends which would otherwise be obscured by experimental scatter. For medium-energy (radiotherapy) protons, and low-Z (water-like) target materials, Wentzel appears to be better than Urban in simulating the distribution of outgoing angles. For Beam Spreading in the target itself, the two models are essentially equal.
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techniques of proton radiotherapy transport theory
arXiv: Medical Physics, 2012Co-Authors: Bernard GottschalkAbstract:These are notes for the lecture on Transport Theory in a one-week intensive course, "Techniques of Proton Radiotherapy". Topics are: Phase space diagrams: model Beam line-effect of a scatterer-effect of a drift-the Beam ellipse-phase space diagrams for the model Beam line-emittance change in a drift-emittance change in a scatterer-phase space for a more realistic Beam line-summary Miscellaneous topics: review of Gaussians-the Gaussian approximation to multiple Coulomb scattering (MCS)-relativistic single particle kinematics-completing the square-scattering power Fermi-Eyges theory: history-the basic theory-the Beam ellipse-drawing the ellipse given the moments-ellipse examples-transporting the Beam ellipse through a slab-emittance change in a drift-emittance change in a scatterer-differential form of the transport equations-equivalent sources-Beam contained in the Beam ellipse-summary Beam Spreading in matter: theory of Preston and Koehler-generalization to heavy ions-experimental tests (Preston and Koehler, Phillips, Wong et al.)-summary Analytical geometry of the ellipse (appendix): tilted ellipse-transformation to principal frame-summary and explicit procedures-area enclosed by the ellipse
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on the scattering power of radiotherapy protons
Medical Physics, 2009Co-Authors: Bernard GottschalkAbstract:Purpose: First, to show that accurate formulas for scattering power T must take into account the competition between the Gaussian core and the single scattering tail of the angular distribution, which affects the rate of change in the Gaussian width and leads to the single scattering correction (SSC). Second, to show that the SSC requires that T(x) be nonlocal: Besides material properties and energy at the point of interest, it must depend in some fashion on how much multiple scattering has already taken place. Third, after reviewing five previous formulas (three local and two nonlocal), to derive an improved ''differential Moliere'' formula T{sub dM}. Last, to investigate, by studying some practical cases, when an accurate formula for T is actually needed. Methods: We first take the numerical derivative of the Moliere/Fano/Hanson in order to find the true SSC. We simplify the formula for T{sub IC} (ICRU Report 35) for protons, introducing a new material dependent property, the ''scattering length''X{sub S}, analogous to radiation length X{sub 0}. We then use T{sub IC} as a basis for T{sub dM} by including a nonlocal correction factor f{sub dM} which, by virtue of the Oeveraas approximation, parametrizes the single scattering correction. Results:more » The improved scattering power is T{sub dM}{identical_to}f{sub dM}(pv,p{sub 1}v{sub 1})x(E{sub s}/pv){sup 2}1/X{sub S} where f{sub dM}{identical_to}0.5244+0.1975 lg(1-(pv/p{sub 1}v{sub 1}){sup 2})+0.2320 lg(pv)-0.0098 lg(pv)lg(1-(pv/p{sub 1}v{sub 1}){sup 2}), p{sub 1}v{sub 1} (MeV) is the initial product of proton momentum and speed, pv is the same at the point of interest, and E{sub s}=15.0 MeV. T{sub dM} is easily computed and generalizes readily to mixed slabs because f{sub dM} is not material dependent. Conclusions: Whether an accurate formula for T is required depends very much on the problem at hand. For Beam Spreading in water, five of the six formulas for T give almost identical results, suggesting that patient dose calculations are insensitive to T. That is not true, however, of Beam Spreading in Pb. At the opposite extreme, the projected rms Beam width at the end of a Pb/Lexan/air stack, analogous to the upstream modulator in a passive Beam Spreading system, is sensitive to T. In this case a simple experiment would discriminate between all but two of the six formulas discussed. Scattering power applies as much to Monte Carlo as to deterministic transport calculations. Using T in any of its forms will avoid step size dependence. Using the best available T could be important in general purpose Monte Carlo codes, which are expected to give the correct answer to many different problems.« less
Norman S. Kopeika - One of the best experts on this subject based on the ideXlab platform.
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Adaptive suboptimum detection of an optical pulse-position-modulation signal with a detection matrix and centroid tracking
Journal of the Optical Society of America A, 1998Co-Authors: Norman S. Kopeika, Shlomi ArnonAbstract:In some applications of optical communication systems, such as satellite optical communication and atmospheric optical communication, the optical Beam wanders on the detector surface as a result of vibration and turbulence effects, respectively. The wandering of the Beam degrades the communication system performance. In this research, we derive a mathematical model of an optical communication system with a detection matrix to improve the system performance for direct-detection pulse-position modulation. We include a centroid tracker in the communication system model. The centroid tracker tracks the center of the Beam. Using the position of the Beam center and an a priori model of the Beam Spreading, we estimate the optical power on each pixel (element) in the detection matrix. Using knowledge of the amplitudes of signal and noise in each pixel, we tune adaptively and separately the gain of each individual pixel in the detection matrix for communication signals. Tuning the gain is based on the mathematical model derived in this research. This model is defined as suboptimal, owing to some approximations in the development and is a suboptimum solution to the optimization problem of n multiplied by m free variables, where n, m are the dimensions of the detection matrix. Comparison is made between the adaptive suboptimum model and the standard model. From the mathematical analysis and the results of the comparison it is clear that this model significantly improves communication system performance.
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Adaptive suboptimum detection of optical PPM signal with detection matrix and centroid tracking
Photonics for Space Environments V, 1997Co-Authors: Arnon Shlomi, Norman S. KopeikaAbstract:In some applications of optical communication systems, such as satellite optical communication and atmospheric optical communication, the optical Beam wanders on the detector surface due to vibration and turbulence effects, respectively. The wandering of the Beam degrades the communication system performance. In this research, we derive a mathematical model of an optical communication system with a detection matrix to improve the system performance for direct detection pulse position modulation (PPM) We include a centroid tracker in the communication system model. The centroid tracker tracks the center of the Beam. Using the position of Beam center and an apriori model of Beam Spreading we estimate the optical power on each pixel (element) in the detection matrix. Based on knowledge of the amplitudes of signal and noise in each pixel, we tune adaptively and separately the gain of each individual pixel in the detection matrix for communication signals. Tuning the gain is based on the mathematical model derived in this research. This model is defined as suboptimal due to some approximations in the development and is a suboptimum solution to the optimization problem of n multiplied by m free variables, where U,mare the dimensions of the detection matrix. Comparison is made between the adaptive suboptimum model and the standard model. From the mathematical analysis and the results of the comparison it is clear that this model improves significantly communication system performance.
W Sauerwein - One of the best experts on this subject based on the ideXlab platform.
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comparison of geant4 multiple coulomb scattering models with theory for radiotherapy protons
Physics in Medicine and Biology, 2017Co-Authors: Anastasia Makarova, Bernard Gottschalk, W SauerweinAbstract:Usually, Monte Carlo models are validated against experimental data. However, models of multiple Coulomb scattering (MCS) in the Gaussian approximation are exceptional in that we have theories which are probably more accurate than the experiments which have, so far, been done to test them. In problems directly sensitive to the distribution of angles leaving the target, the relevant theory is the Moliere/Fano/Hanson variant of Moliere theory (Gottschalk et al 1993 Nucl. Instrum. Methods Phys. Res. B 74 467-90). For transverse Spreading of the Beam in the target itself, the theory of Preston and Koehler (Gottschalk (2012 arXiv:1204.4470)) holds. Therefore, in this paper we compare Geant4 simulations, using the Urban and Wentzel models of MCS, with theory rather than experiment, revealing trends which would otherwise be obscured by experimental scatter. For medium-energy (radiotherapy) protons, and low-Z (water-like) target materials, Wentzel appears to be better than Urban in simulating the distribution of outgoing angles. For Beam Spreading in the target itself, the two models are essentially equal.
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comparison of geant4 multiple coulomb scattering models with theory for radiotherapy protons
arXiv: Medical Physics, 2016Co-Authors: Anastasia Makarova, Bernard Gottschalk, W SauerweinAbstract:Usually, Monte Carlo models are validated against experimental data. However, models of multiple Coulomb scattering (MCS) in the Gaussian approximation are exceptional in that we have theories which are probably more accurate than the experiments which have, so far, been done to test them. In problems directly sensitive to the distribution of angles leaving the target, the relevant theory is the Moliere/Fano/Hanson variant of Moliere theory. For transverse Spreading of the Beam in the target itself, the theory of Preston and Koehler holds. Therefore, in this paper we compare Geant4 simulations, using the Urban and Wentzel models of MCS, with theory rather than experiment, revealing trends which would otherwise be obscured by experimental scatter. For medium-energy (radiotherapy) protons, and low-Z (water-like) target materials, Wentzel appears to be better than Urban in simulating the distribution of outgoing angles. For Beam Spreading in the target itself, the two models are essentially equal.
P M Deluca - One of the best experts on this subject based on the ideXlab platform.
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neutron production from Beam modifying devices in a modern double scattering proton therapy Beam delivery system
Physics in Medicine and Biology, 2009Co-Authors: A Perezandujar, Wayne D Newhauser, P M DelucaAbstract:In this work the neutron production in a passive Beam delivery system was investigated. Secondary particles including neutrons are created as the proton Beam interacts with Beam shaping devices in the treatment head. Stray neutron exposure to the whole body may increase the risk that the patient develops a radiogenic cancer years or decades after radiotherapy. We simulated a passive proton Beam delivery system with double scattering technology to determine the neutron production and energy distribution at 200 MeV proton energy. Specifically, we studied the neutron absorbed dose per therapeutic absorbed dose, the neutron absorbed dose per source particle and the neutron energy spectrum at various locations around the nozzle. We also investigated the neutron production along the nozzle's central axis. The absorbed doses and neutron spectra were simulated with the MCNPX Monte Carlo code. The simulations revealed that the range modulation wheel (RMW) is the most intense neutron source of any of the Beam Spreading devices within the nozzle. This finding suggests that it may be helpful to refine the design of the RMW assembly, e.g., by adding local shielding, to suppress neutron-induced damage to components in the nozzle and to reduce the shielding thickness of the treatment vault. The simulations also revealed that the neutron dose to the patient is predominated by neutrons produced in the field defining collimator assembly, located just upstream of the patient.
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a prototype Beam delivery system for the proton medical accelerator at loma linda
Medical Physics, 1991Co-Authors: George Coutrakon, M Bauman, David A Lesyna, Daniel W Miller, J Nusbaum, Jon W Slater, J Johanning, J Miranda, P M Deluca, J SiebersAbstract:A variable energy proton accelerator was commissioned at Fermi National Accelerator Laboratory for use in cancer treatment at the Loma Linda University Medical Center. The advantages of precise dose localization by proton therapy, while sparing nearby healthy tissue, are well documented [R. R. Wilson, Radiology 47, 487 (1946); M. Wagner, Med. Phys. 9, 749 (1982); M. Goitein and F. Chen, Med. Phys. 10, 831 (1983)]. One of the components of the proton therapy facility is a Beam delivery system capable of delivering precise dose distributions to the target volume in the patient. To this end, a prototype Beam delivery system was tested during the accelerator's commissioning period. The Beam delivery system consisted of a Beam Spreading device to produce a large, uniform field, a range modulator to generate a spread out Bragg peak (SOBP), and various Beam detectors to measure intensity, Beam centering, and dose distributions. The Beam delivery system provided a uniform proton dose distribution in a cylindrical volume of 20-cm-diam area and 9-cm depth. The dose variations throughout the target volume were found to be less than +/- 5%. Modifications in the range modulator should reduce this considerably. The central axis dose rate in the region of the SOBP was found to be 0.4 cGy/spill with an incident Beam intensity of 6.7 x 10(9) protons/spill. With an accelerator repetition rate of 30 spills/min and expected intensity of 2.5 x 10(10) protons/spill for patient treatment, this system can provide 50 cGy/min for a 20-cm-diam field and 9-cm range modulation.(ABSTRACT TRUNCATED AT 250 WORDS)