Design and evaluation of electron beam energy degraders for breast boost irradiation

BACKGROUND: For breast cancer patients who require electron boost energies between 6 and 9 MeV, an energy degraders (ED) in the 9 MeV beamline was specially designed and manufactured to increase the skin dose of 6 MeV and to reduce the penetration depth of 9 MeV beams. METHODS: We used Monte Carlo (MC) techniques as a guide in the design of ED for use with linear accelerators. In order to satisfy percent depth dose (PDD) characteristics and dose profile uniformity in water, the shape and thickness of Lucite® ED in the 9 MeV beamline was iteratively optimized and then manufactured. The ED geometry consists of a truncated cone attached on top of a plane plate, with total central thickness of 1.0 cm. The ED was placed on the lower most scraper of the electron applicator. The PDDs, profiles, and output factors were measured in water to validate the MC-based design. RESULTS: Skin doses with the EDs increased by 8–9 %, compared to those of the 9 MeV beam. The outputs with the EDs were 0.882 and 0.972 for 10 × 10 and 15 × 15 cm(2) cones, respectively, as compared to that of a conventional 9 MeV beam for a 10 × 10 cm(2) cone. The X-ray contamination remained less than 1.5 %. In-vivo measurements were also performed for three breast boost patients and showed close agreement with expected values. CONCLUSIONS: The optimally designed ED in the 9 MeV beamline provides breast conserving patients with a new energy option of 7 MeV for boost of the shallow tumor bed. It would be an alternative to bolus and thus eliminate inconvenience and concern about the daily variation of bolus setup

Fano cavity test for electron Monte Carlo transport algorithms in magnetic fields: comparison between EGSnrc, PENELOPE, MCNP6 and Geant4

A Fano cavity test was performed for four general-purpose Monte Carlo codes, EGSnrc, PENELOPE, MCNP6 and Geant4 to evaluate the accuracy of their electron transport algorithms in magnetic fields. In the simulations, a plane-parallel ionization chamber was modelled as a circular gas disk sandwiched between two circular solid wall disks. It was assumed that an isotropic and uniform line source per unit mass along the central axis of the gas and solid emits mono-energetic electrons with energies 0.01, 0.1,1.0 and 3.0 MeV at different magnetic field strengths 0, 0.35,1.0,1.5 and 3.0 Tin the electron transport mode (no Bremsstrahlung). The relative difference between the calculated dose to the gas region and the initial total energy of emitted electrons per unit mass was defined as the accuracy of Monte Carlo codes. In all results, EGSnrc with the enhanced electric and magnetic field (EEMF) macros was not considerably sensitive to the step size parameters and showed accuracy less than 0.18% +/- 0.06% with a coverage factor k = 2. The other codes could not achieve competent accuracy with their default settings of step size parameters, compared to EGSnrc with the EEMF macros. With the step size parameters carefully selected, the accuracy of PENELOPE and MCNP6 was within 1.0% and 0.4%, respectively. However, Geant4 showed accuracy within 1.7% except in 3.0 T. EGSnrc with the EEMF macros achieved the best accuracy for the Fano test at the electron energies and the magnetic field strengths investigated in this study and thus, would be recommended to simulate dose responses of ionization chambers in the presence of magnetic fields

Improved electrochemical properties of linear carbonate-containing electrolytes using fluoroethylene carbonate in Na4Fe3(PO4)2(P2O7)/Na cells

Sodium-ion batteries (NIBs) have attracted considerable attention as promising next-generation rechargeable batteries, especially for large-scale energy storage systems (ESS), because of the natural abundance of Na and the similarities of these batteries to lithium-ion batteries (LIBs). Much effort has been made to improve the electrochemical performances of NIBs through the development of high-performance cathodes, anodes, and electrolytes. One efficient and desirable strategy for practical applications of NIBs is to utilize materials that are adopted in commercialized LIBs. Electrolytes in most studies are composed of polar solvents such as ethylene carbonate (EC) and propylene carbonate (PC). Accordingly, instead of conventional polyethylene (PE) membranes, glass fiber filters (GFF), which easily uptake polar solvents, have been used as separators. However, the too thick, mechanically weak, and porous GFF is not suitable as a separator because it can reduce the volumetric energy density and cannot guarantee the safety of batteries. In this study, for the introduction ofa PE separator into NIBs, the inclusion of linear carbonate as a cosolvent was attempted, motivated by the fact that this material has been widely used owing to its low viscosity and good compatibility with conventional PE separators. However, due to their high reactivity toward Na metal electrodes in half cells, linear carbonate-containing electrolytes are not electrochemically stable at Na4Fe3(PO4)2(P2O7) cathodes during cycling. Undesirable reactions between linear carbonates and Na metal electrodes are examined using 13C nuclear magnetic resonance (NMR) and possible mechanisms for the detrimental effect of byproducts formed by linear carbonate decomposition at the Na metal electrode on the cathode are proposed. To alleviate severe decomposition of linear carbonates at the Na metal electrode, fluoroethylene carbonate (FEC) has been exploited as a functional additive. Our investigation reveals that remarkable enhancement in electrochemical properties of electrolytes with linear carbonates in Na4Fe3(PO4)2(P2O7)/Na half cells is achieved in the presence of FEC additive

Performance evaluation of a beta-spectrometer comprising a plastic scintillator and multi-wire chamber using a coincidence method

This paper describes an experimental setup developed to measure the beta-ray energy spectrum as well as a Geant4 simulation study conducted to characterize the properties of a beta-spectrometer. The beta-spectrometer comprises a multi-wire chamber to generate signals to indicate the incidence of beta rays and a plastic scintillation detector to measure its energy. The coincidence method of the detector signals was used to remove high gamma-ray interference. To evaluate the performance of the developed spectrometer, the energy spectra were measured with the radionuclide sources (Cs-137 and Bi-207) emitting internal conversion electrons and gamma rays. The gamma-ray interference removal rate of the spectrometer using the coincidence method was 99.12 +/- 0.09%. To reconstruct the beta spectrum from the measured spectrum, Monte Carlo simulations using the Geant4 toolkit were performed to calculate the coefficient related to the effect of gamma rays. The obtained spectrum confirmed that the energy resolution and intrinsic internal conversion peak detection efficiency of the beta-spectrometer were 10.2% at 1 MeV and 91.6%, respectively

Design and evaluation of electron beam energy degraders for breast boost irradiation

Background For breast cancer patients who require electron boost energies between 6 and 9 MeV, an energy degraders (ED) in the 9 MeV beamline was specially designed and manufactured to increase the skin dose of 6 MeV and to reduce the penetration depth of 9 MeV beams. Methods We used Monte Carlo (MC) techniques as a guide in the design of ED for use with linear accelerators. In order to satisfy percent depth dose (PDD) characteristics and dose profile uniformity in water, the shape and thickness of Lucite® ED in the 9 MeV beamline was iteratively optimized and then manufactured. The ED geometry consists of a truncated cone attached on top of a plane plate, with total central thickness of 1.0 cm. The ED was placed on the lower most scraper of the electron applicator. The PDDs, profiles, and output factors were measured in water to validate the MC-based design. Results Skin doses with the EDs increased by 8–9 %, compared to those of the 9 MeV beam. The outputs with the EDs were 0.882 and 0.972 for 10 × 10 and 15 × 15 cm2 cones, respectively, as compared to that of a conventional 9 MeV beam for a 10 × 10 cm2 cone. The X-ray contamination remained less than 1.5 %. In-vivo measurements were also performed for three breast boost patients and showed close agreement with expected values. Conclusions The optimally designed ED in the 9 MeV beamline provides breast conserving patients with a new energy option of 7 MeV for boost of the shallow tumor bed. It would be an alternative to bolus and thus eliminate inconvenience and concern about the daily variation of bolus setup

Stable and Dense Sodium Metal Deposition Using a Fluorination Solvent Containing Electrolyte with a 1 M Salt Concentration

Extensive academic and industrial efforts have been dedicated to developing battery-based energy storage technologies with high energy density, low cost, long cycle life, high energy efficiency, and ease of deployment in daily life. In particular, for large-scale electrical energy storage, attention has shifted to sodium (Na) metal batteries owing to the highest specific capacity and the lowest redox potential of metallic Na and the natural abundance of Na resources. Nevertheless, the exceedingly high electrochemical and chemical reactivity of Na metal electrodes toward organic liquid electrolytes and severe Na dendrite formation limit their commercialization. Since most Na deposition occurs at the interface between the anode (or the current collector) and the electrolyte, the discovery of a stable electrolyte is essential for utilizing Na metal anodes in practical applications. In this study, we demonstrate that fluorination solvent containing electrolyte dramatically enhances the reversibility of Na plating and stripping reactions in Na/Cu cells, realizes dense Na deposition, and leads to improved cycling stability at high current densities. By examining the detailed mechanism of the novel electrolyte system, we have found that the interfacial layer contains NaF, which has a high shear modulus and enhances the mechanical integrity of the interlayer by the attractive interaction between the F- ions and Na+ ions of ionic compounds such as Na2CO3 and sodium alkylcarbonates (NaO2CO-R-), resulting in the formation of mechanically strong and ion-permeable interlayers that suppress uncontrolled Na metal plating. The discovery of this work represents a step forward in the electrolyte design of Na metal anodes

Ultraconcentrated sodium bis(fluorosulfonyl)imide-based electrolytes for high-performance sodium metal batteries

We present an ultraconcentrated electrolyte composed of 5 M sodium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane for Na metal anodes coupled with high-voltage cathodes. Using this electrolyte, a very high Coulombic efficiency of 99.3% at the 120th cycle for Na plating/stripping is obtained in Na/stainless steel (SS) cells with highly reduced corrosivity toward Na metal and high oxidation durability (over 4.9 V versus Na/Na+) without corrosion of the aluminum cathode current collector. Importantly, the use of this ultraconcentrated electrolyte results in substantially improved rate capability in Na/SS cells and excellent cycling performance in Na/Na symmetric cells without the increase of polarization. Moreover, this ultraconcentrated electrolyte exhibits good compatibility with high-voltage Na4Fe3(PO4)2(P2Ov7) and Na0.7(Fe0.5Mn0.5)O2 cathodes charged to high voltages (>4.2 V versus Na/Na+), resulting in outstanding cycling stability (high reversible capacity of 109 mAh g-1 over 300 cycles for the Na/Na4Fe3(PO4)2(P2O7) cell) compared with the conventional dilute electrolyte, 1 M NaPF6 in ethylene carbonate/propylene carbonate (5/5, v/v).clos

Fluoroethylene Carbonate-Based Electrolyte with 1 M Sodium Bis(fluorosulfonyl)imide Enables High-Performance Sodium Metal Electrodes

Sodium (Na) metal anodes with stable electro-chemical cycling have attracted widespread attention because of their highest specific capacity and lowest potential among anode materials for Na batteries. The main challenges associated with Na metal anodes are dendritic formation and the low density of deposited Na during electrochemical plating. Here, we demonstrate a fluoroethylene carbonate (FEC)-based electrolyte with 1 M sodium bis(fluorosulfonyl)imide (NaFSI) salt for the stable and dense deposition of the Na metal during electrochemical cycling. The novel electrolyte combination developed here circumvents the dendritic Na deposition that is one of the primary concerns for battery safety and constructs the uniform ionic interlayer achieving highly reversible Na plating/stripping reactions. The FEC NaFSI constructs the mechanically strong and ion-permeable interlayer containing NaF and ionic compounds such as Na2CO3 and sodium alkylcarbonates