Bremsstrahlung Yield Research Articles

Characteristics of Bremsstrahlung emissions of 177Lu, 188Re, and 90Y for SPECT/CT quantification in radionuclide therapy

PurposeBeta particles emitted by radioisotopes used in targeted radionuclide therapies (TRT) create Bremsstrahlung (BRS) which may affect SPECT quantification when imaging these isotopes. The purpose of the current study was to investigate the characteristics of Bremsstrahlung produced in tissue by three β-emitting radioisotopes used in TRT. MethodsMonte Carlo simulations of 177Lu, 188Re, and 90Y sources placed in water filled cylinders were performed. BRS yields, mean energies and energy spectra for (a) all photons generated in the decays, (b) photons that were not absorbed and leave the cylinder, and (c) photons detected by the camera were analyzed. Next, the results of simulations were compared with those from experiments performed on a clinical SPECT camera using same acquisition conditions and phantom configurations as in simulations. ResultsSimulations reproduced relatively well the shapes of the measured spectra, except for 90Y which showed an overestimation in the low energy range. Detailed analysis of the results allowed us to suggest best collimators and imaging conditions for each of the investigated isotopes. Finally, our simulations confirmed that the BRS contribution to the energy spectra in quantitative imaging of 177Lu and 188Re could be ignored. ConclusionsFor 177Lu and 188Re, BRS contributes only marginally to the total spectra recorded by the camera. Our analysis shows that MELP and HE collimators are the best for imaging these two isotopes. For 90Y, HE collimator should be used.

Optimum target source term estimation for high energy electron accelerators

Abstract Optimum target for bremsstrahlung emission is defined as the thickness of the target material, which produces maximum bremsstrahlung yield, on interaction of electron with the target. The bremsstrahlung dose rate per unit electron beam power at a distance of 1 m from the target material gives the optimum target source term. In the present work, simulations were performed for three different electron energies, 450, 1000 and 2500 MeV using EGSnrc Monte-Carlo code to determine the optimum thickness. An empirical relation for optimum target as a function of electron energy and atomic number of the target materials is found out from results. Using the simulated optimum target thickness, experiments are conducted to determine the optimum target source term. For the experimental determination, two available electron energies, 450 MeV and 550 MeV from booster synchrotron of Indus facility is used. The optimum target source term for these two energies are also simulated. The experimental and simulated source term are found to be in very good agreement within ±3%. Based on the agreement of the simulated source term with the experimental source term at 450 MeV and 550 MeV, the same simulation methodology is used to simulate optimum target source term up to 2500 MeV. The paper describes the simulations and experiments carried out on optimum target bremsstrahlung source term and the results obtained.

Ag K-shell ionization by electron impact: New cross-section measurements between 50 and 100keV and review of previous experimental data

Abstract We report the measurement of Ag K-shell ionization cross-section by electron impact in the range 50–100 keV and review the experimental data found in the literature. The sample consisted in a thin film of Ag evaporated on a thin C backing. The x-ray spectra generated by electron bombardment in the Sao Paulo Microtron were observed with a planar HPGe detector. The ratios between characteristic and bremsstrahlung x-ray yields were transformed to ionization cross sections with the help of theoretical atomic-field bremsstrahlung cross sections. The measured cross sections are compared with existing experimental values and calculations based on the semi-relativistic distorted-wave Born approximation. According to our experiment, the ratio of Ag K β to K α x-ray intensities is 0.2018(24).

A dosimetric study of Beta induced bremsstrahlung in bone

A dosimetric study of beta-induced bremsstrahlung in bone is important in the field of radiation protection. The beta-induced bremsstrahlung spectra produced by 113 pure beta nuclides in the bone are computed. The spectral shapes are primarily responsible for variations in the shapes by depth-dose distributions. They are intended to provide a quick and convenient reference for spectral shapes and to give an indication of the wide variation in these shapes. The computed bremsstrahlung spectrum is used in the evaluation of bremsstrahlung dose in bone. The evaluated beta bremsstrahlung dose as a function of distance for the studied nuclides is also presented. The beta bremsstrahlung dose decreases with the increase in distance. Present work also estimates the dosimetric parameters of bremsstrahlung such as yield, intensity and dose rate of bremsstrahlung by various pure beta nuclides in tissues of human skeleton such as cortical bone, red marrow, yellow marrow, spongiosa and cartilage. The yield, intensity and dose rate of bremsstrahlung in the cortical bone are higher than that of red marrow, yellow marrow, spongiosa and cartilage. Hence cortical bone is more beta/bremsstrahlung radiosensitive than that of other tissues of human skeleton. The estimated bremsstrahlung efficiency, intensity, photon spectra and photon track-length distributions determine the quality and quantity of the radiation. Precise estimation of this source term is very important in planning for radiotherapy and diagnosis.

Kα and bremsstrahlung x-ray radiation backlighter sources from short pulse laser driven silver targets as a function of laser pre-pulse energy

Measurements of silver K-shell and bremsstrahlung emission from thin-foil laser targets as a function of laser prepulse energy are presented. The silver targets were chosen as a potential 22 keV backlighter source for the National Ignition Facility Experiments. The targets were irradiated by the Titan laser with an intensity of 8 × 1017 W/cm2 with 40 ps pulse length. A secondary nanosecond timescale laser pulse with controlled, variable energy was used to emulate the laser prepulse. Results show a decrease in both Kα and bremsstrahlung yield with increasing artificial prepulse. Radiation hydrodynamic modeling of the prepulse interaction determined that the preplasma and intact target fraction were different in the three prepulse energies investigated. Interaction of the short pulse laser with the resulting preplasma and target was then modeled using a particle-in-cell code PSC which explained the experimental results. The relevance of this work to future Advanced Radiographic Capability laser x-ray backlighter sources is discussed.

Gamma-ray Cherenkov-transition radiation

The spectral and angular distributions as well as the total number of photons of gamma-ray Cherenkov-transition radiation (GCTR) produced by charged particles in the photon energy region are calculated. For this purpose we used the experimental results of the recent discovery according to which in the above-mentioned region the measured refractive index of silicon as well as the theoretically calculated refractive index of gold are greater than 1. Using the results of the carried out numerical calculations an experimental arrangement is discussed for the observation and experimental study of the GCTR. As our results show the GCTR photon yield is about one order of magnitude higher than the background bremsstrahlung yield. Some applications of GCTR, in particular, for comparatively easy search of new materials with refractive index , are proposed.

Creation of High Energy/Intensity Bremsstrahlung by a Multi-Target and Focusing of the Scattered Electrons by Small-Angle Backscatter at a Cone Wall and a Magnetic Field—Enhancement of the Outcome of Linear Accelerators in Radiotherapy

The yield of bremsstrahlung (BS) from collisions of fast electrons (energy at least 6 MeV) with a Tungsten target can be significantly improved by exploitation of Tungsten wall scatter in a multi-layered target. A simplified version of a previously developed principle is also able to focus on small angle scattered electrons by a Tungsten wall. It is necessary that the thickness of each Tungsten layer does not exceed 0.04 mm—a thickness of 0.03 mm is suitable for accelerators in medical physics. Further focusing of electrons results from suitable magnetic fields with field strength between 0.5 Tesla and 1.2 Tesla (if the cone with multi-layered targets is rather narrow). Linear accelerators in radiation therapy only need to be focused by wall scatter without further magnetic fields (a standard case: 31 plates with 0.03 mm thickness and 1 mm distance between the plates). We considered three cases with importance in medical physics: A very small cone with an additional magnetic field for focusing (the field diameter at 90 cm depth: 6 cm), a medium cone with an optional magnetic field (field diameter at 90 cm depth: 13 cm) and a broad cone without a magnetic field (the field diameter at 90 cm depth: 30 cm). All these cases can be positioned in a carousel. Measurements have been performed in the existing carousel positioned in the plane of the flattening filter and scatter foils for electrons.

Bremsstrahlung dose of therapeutic beta nuclides in bone and muscle

In the nuclear medicine, beta nuclides are released during the treatment. This beta interacts with bone and muscle and produces external Bremsstrahlung (EB) radiation. Present work formulated a new method to evaluate the EB spectrum and hence the Bremsstrahlung dose of therapeutic beta nuclides (Lu-177, Sr-90, Sm-153, I-153, Cs-137, Au-201, Dy-165, Mo-99, Sr-89, Fe-59, P-32, Ho-166, Sr-92, Re-188, Y-90, Pr-147, Co-60, K-42) in bone and muscle. The Bremsstrahlung yields of these beta nuclides are also estimated. Bremsstrahlung production is higher in bone than that of muscle. Presented data provides a quick and convenient reference for radiation protection and it can be quickly employed to give a first pass dose estimate prior to a more detailed experimental study.

External bremsstrahlung of 90Sr–90Y, 147Pm and 204Tl in detector compounds

External Bremsstrahlung spectra produced by the complete absorption of beta particles from 90Sr to 90Y, 147Pm and 204Tl in nuclear radiation detection compounds like Cesium iodide (CsI) and Sodium Iodide (NaI) has been measured using 0.038m×0.038m NaI(Tl) crystal and is compared with Tseng–Pratt theory. The Bremsstrahlung yields are calculated using the unfolded spectra. This paper also describes a new procedure for the calculation of effective absorption coefficient of Bremsstrahlung from the Bremsstrahlung spectra. The measured spectra show fairly good agreement at low energy end of spectrum and some deviation at higher energy end of spectrum with the theory. The measured Bremsstrahlung yields may be useful to apply corrections, whenever beta particle passes through CsI and NaI detectors.

Estimation of microblock sizes in mosaic crystals according to fast electron radiation characteristics

The possibilities of a previously proposed technique for determining the characteristic sizes of microblocks in mosaic aα-class crystals have been analyzed. Determination is performed according to the ratio between the measured and calculated values for the diffraction suppression of the fixed-energy bremsstrahlung yield. The limits of applicability of the technique have been revealed. It is demonstrated that the technique can be implemented in an electron accelerator with the average energy Ee ∼ 30–40 MeV and long baselines making it possible to use crystal-diffraction spectrometers. The influence of microblock sizes on coherent electromagnetic processes in real crystals is discussed.

Characteristic and non-characteristic X-ray yields produced from thick Ti element by sub-relativistic electrons

Measurements are performed to study the electron impact energy dependence of doubly differential bremsstrahlung yields (DDBY) and of characteristic Ti Kα line yields produced from sub-relativistic electrons (10–25keV) colliding with a thick Ti (Z=22) target. The emitted radiation is detected by a Si-PIN photo-diode detector with energy resolution (FWHM) of 180eV at 5.9keV. The measured data of DDBY are compared with the results predicted by Monte-Carlo (MC) simulations using the general purpose PENELOPE code. A reasonable agreement is found between experimental and simulation results within the experimental uncertainty of measurements of 12%. Characteristic Ti Kα yields are obtained for the considered impact energy range and they are compared with the existing theoretical results. A good agreement is found between the present measurements and the theoretical calculations. Furthermore, data are presented for impact energy dependence of the ratio Kα/(Kα+Kβ) of a thick Ti target under impact of 10–25keV electrons. The ratio shows a very weak dependence on impact energy in the studied range. The average value of the ratio is found to be 0.881±0.003.

Beta Bremsstrahlung dose in concrete shielding

In a nuclear reactor, beta nuclides are released during nuclear reactions. These betas interact with shielding concrete and produces external Bremsstrahlung (EB) radiation. To estimate Bremsstrahlung dose and shield efficiency in concrete, it is essential to know Bremsstrahlung distribution or spectra. The present work formulated a new method to evaluate the EB spectrum and hence Bremsstrahlung dose of beta nuclides (32P, 89Sr, 90Sr–90Y, 90Y, 91Y, 208Tl, 210Bi, 234Pa and 40K) in concrete. The Bremsstrahlung yield of these beta nuclides in concrete is also estimated. The Bremsstrahlung yield in concrete due to 90Sr–90Y is higher than those of other given nuclides. This estimated spectrum is accurate because it is based on more accurate modified atomic number (Zmod) and Seltzer's data, where an electron–electron interaction is also included. Presented data in concrete provide a quick and convenient reference for radiation protection. The present methodology can be used to calculate the Bremsstrahlung dose in nuclear shielding materials. It can be quickly employed to give a first pass dose estimate prior to a more detailed experimental study.

On the creation of high energy bremsstrahlung and intensity by a multitarget and repeated focusing of the scattered electrons by small-angle backscatter at the wall of a cone and magnetic fields—A possible way to improve linear accelerators in radiotherapy and to verify Heisenberg–Euler scatter

The yield of bremsstrahlung from collisions of fast electrons (energy at least 6MeV) with a Tungsten target can be significantly improved by exploitation of Tungsten wall scatter in a multi-layered target. The Tungsten wall can serve to refocuse small angle scattered electrons. It is necessary that the thickness of one Tungsten layer does not exceed 0.02mm. Further repeated focusing of electrons results from suitable magnetic fields with field strength between 0.5T and 6T (if the cone with multi-layered targets is rather narrow). Linear accelerators in radiation therapy only need repeated focusing by wall scatter without further magnetic fields (standard case: ca. 100–000 plates with 0.01mm thickness and 1mm distance between the plates). The construction of a very narrow bremsstrahlung beam with extremely high photon intensity requires an additional strong magnetic field (order 1–6T), which provides the possibility to check Heisenberg–Euler scatter of high energy photons.

Determination of RW3-to-water mass-energy absorption coefficient ratio for absolute dosimetry

The measurement of absorbed dose to water in a solid-phantom may require a conversion factor because it may not be radiologically equivalent to water. One phantom developed for the use of dosimetry is a solid water, RW3 white-polystyrene material by IBA. This has a lower mass-energy absorption coefficient than water due to high bremsstrahlung yield, which affects the accuracy of absolute dosimetry measurements. In this paper, we demonstrate the calculation of mass-energy absorption coefficient ratios, relative to water, from measurements in plastic water and RW3 with an Elekta Synergy linear accelerator (6 and 10 MV photon beams) as well as Monte Carlo modeling in BEAMnrc and DOSXYZnrc. From this, the solid-phantom-to-water correction factor was determined for plastic water and RW3.

Beta induced Bremsstrahlung exposure in DNA and RNA

The Bremsstrahlung exposure induced by some of the therapeutic beta nuclides ( 90Y, 143Pm, 169Er, 204Tl, 210Bi, 89Sr, 45Ca and 131I) in DNA and RNA has been calculated by extending the national council for radiation protection model. It has estimated the specific Bremsstrahlung constant (Γ Br), Probability of energy loss by beta during Bremsstrahlung emission ( P Br ) and Bremsstrahlung activity ( A release ) Br . The estimated Bremsstrahlung activities of pure beta nuclides in DNA and RNA are extremely large (10 2 GBq–10 6 GBq). The patients receiving such nuclides would never receive that much activity because of prohibitive radiation toxicity (few 100 MBq). Thus the patients receiving these pure beta emitting nuclides do not have to be hospitalized for radiation precautions. It is also estimated the Bremsstrahlung yield ( I Br ) for wide energy range (0.01 MeV–100 MeV) using the tabulated values given for elements by Lucien pages. The variation of I Br as a function of incident electron energy is shown graphically. This data may be useful in the analysis of Bremsstrahlung dose where beta emitting nuclide is involved in medical therapy.

Yield constants of external Bremsstrahlung excited by 90Sr– 90Y, 147Pm and 204Tl in CdO and lead compounds

Bremsstrahlung yield of 90Sr– 90Y, 147Pm and 204Tl in CdO, PbF 2, Pb(NO 3) 2 and PbCl 2 has been measured using 3.8 cm×3.8 cm NaI(Tl) crystal and is compared with Tseng and Pratt theory. The Z dependence of external Bremsstrahlung (EB) is also measured and compared with the theory. The Bremsstrahlung photon yield and energy yield constants ( K′ and K) are evaluated from the measured and theoretical yields. These values decrease with the increase in E max of beta. The evaluated K′ and K may be useful to calculate the photon yield and the energy yield, when these beta particles interact with the compounds of modified atomic number ranging from 42 to 73.

X‐ray spectra by means of Monte Carlo simulations for imaging applications

AbstractX‐ray tubes have a broad range of applications worldwide, including several techniques for atomic physics, like X‐ray fluorescence, as well as for medical imaging, like computed tomography. The performances of X‐ray imaging detectors have shown to be significantly sensitive to the incident beam spectrum. Therefore, an accurate knowledge of the X‐ray beam becomes necessary for the emission source characterization and the whole imaging process comprehension. Direct measurements and suitable Monte Carlo simulations may be used to establish the X‐ray spectra. Dedicated Monte Carlo simulation routines, based on the PENELOPE code, have been developed to determine the Bremsstrahlung X‐ray spectra generated by conventional X‐ray tubes. The simulated spectra have been validated by comparison with the corresponding experimental data showing an overall good agreement. The incorporation of a suitably designed virtual grid allowed to assess the angular distribution of Bremsstrahlung yield, showing a remarkable anisotropy. In addition, a dedicated program has been developed for virtual imaging, which enables to perform suitable X‐ray absorption contrast images. Also, the developed program includes a user‐friendly graphic interface to allow the upload of required input parameters, which include setup arrangement, beam characteristics, sample properties and image simulation parameters (spatial resolution, tracks per run, etc.). The software includes dedicated subroutines which handle the physical process from X‐ray generation up to detector signal acquisition. The aim of the developed program is to perform virtual imaging by means of absorption contrast and using conventional X‐ray sources, which may be a useful tool for the study the X‐ray imaging techniques in several research fields as well as for educational purposes. The performed comparisons with experimental data have shown good agreement. The obtained results for X‐ray imaging may constitute useful information for the comprehension and improvement of X‐ray image quality, like absorption contrast optimization, detail visualization, definition and detectability. Copyright © 2010 John Wiley & Sons, Ltd.

Bremsstrahlung exposure of tissues from beta-therapeutic nuclides

The Bremsstrahlung exposure rate from beta point source, probability of energy loss by beta during the Bremsstrahlung emission and the Bremsstrahlung activity of tissues have been calculated. The Bremsstrahlung yield for tissues in the wide energy range is also estimated from 0.01 to 100MeV using the tabulated values given for elements by Lucien pages. The estimated Bremsstrahlung activities of pure beta nuclides in all types of tissues are extremely large (102–106GBq). The patients receiving such nuclides would never receive that much activity because of prohibitive radiation toxicity (few 100MBq). Thus the patients receiving these pure beta emitting nuclides do not have to be hospitalized for radiation precautions.

Plastic materials as a radiation shield forβ− sources: a comparative study through Monte Carlo calculation

We have developed a Monte Carlo simulation in Geant4 to compare the attenuation properties andthe bremsstrahlung radiation yield of different types of plastic materials employed as shields forβ− radioactivesources. Code validation results against Sandia and NIST data are presented. For polypropylene (C3H6), polystyrene (C2H3), polyamide nylon-6 (C6H11ON), poly-methyl methacrylate(C5H8O2), polycarbonate(C16H6O3), polyethyleneterephthalate (C10H8O4),polyvinyl chloride (C2H3Cl) andpolytetrafluoroethylene (C2F4) we evaluated the mean and maximum ranges for electrons originating from 90Sr and 90Y, as well as the number and spectrum of the bremsstrahlung x-rays produced. Significantdifferences appear between the various materials, and the choice of the best onealso depends on the physical properties requested for each specific application.

Theoretical study on bremsstrahlung of high energy electrons

Bremsstrahlung will be produced when the metal target is bombarded by high energy electrons. Bremsstrahlung characteristics is discussed under the condition of optimal bremsstrahlung efficiency for the purpose of improving its quality. This paper simulates the bremsstrahlung characteristics, combining theoretical analysis with MCNP/4C program. Electron yield characteristics, photon yield of conic collimator, angular distributions and energy spectrum distributions are simulated for targets of different thickness and materials for 10 and 20?MeV electrons. The simulation results show that photon efficiency, emitted electron and photon flux distribution is related to material and thickness of the target. And the maximum photon yield of bremsstrahlung is mainly dependent on the electron energe range, and related to atomic number. Thus the relevant boundary conditions and characteristics are obtained under the optimal bremsstrahlung efficiency of different targets for 10 and 20?MeV electrons.