Technical Note: Effect of explicit M and N‐shell atomic transitions on a low‐energy x‐ray source

Abstract

The EGSnrc default of using averaged M and N-shell binding energies has an observable effect on the HVL and RDD of a low energy x-ray source with high-Z target. For accurate modeling of this class of devices, explicit atomic transitions should be included.

On the capabilities of conventional x‐ray tubes to deliver ultra‐high (FLASH) dose rates

“…The x-ray beams contained low-energy tungsten L-shell x rays that are simulated with a~4% accuracy in the EGSnrc code * . 27 The experimental validation showed that outside of the heel effect region, measured doses at 15 and 18 mm depth in phantom agreed with MC simulations to within 3.6%, which was an acceptable level of agreement for our work and demonstrates the capacity for conventional x-ray tubes to deliver FLASH therapy. It is interesting to note that the MC dose was underestimated at both depths, which could potentially be attributed to the x-ray tube end-effect not accounted for in the MC simulations.…”

“…It was indirectly determined that the dose rates generated by both x‐ray tubes were FLASH capable, exceeding 100 Gy/s on the surface of the phantom. The x‐ray beams contained low‐energy tungsten L‐shell x rays that are simulated with a ~4% accuracy in the EGSnrc code . The experimental validation showed that outside of the heel effect region, measured doses at 15 and 18 mm depth in phantom agreed with MC simulations to within 3.6%, which was an acceptable level of agreement for our work and demonstrates the capacity for conventional x‐ray tubes to deliver FLASH therapy.…”

On the use of the absorbed depth‐dose measurements in the beam calibration of a surface electronic high‐dose‐rate brachytherapy unit, a Monte Carlo‐based study

“…Compton interactions use the relativistic impulse approximation, which takes into account both binding effects and Doppler broadening . Furthermore, PENELOPE2014 simulates explicitly the emission of characteristic x rays, Auger and Coster‐Kronig electrons that result from vacancies produced in K, L, M and N shells, using transition probabilities extracted from the evaluated atomic data library (EADL) . The energy of the x rays published in the EADL was updated, when available, being the K and L shell transitions from Deslattes et al and the M lines from Bearden .…”

Heterogeneous multiscale Monte Carlo simulations for gold nanoparticle radiosensitization

“…Transport parameters are generally EGSnrc defaults with the following exceptions: pair angular sampling is turned off, Rayleigh scattering and electron impact ionization are turned on, NRC cross section data are used for bremsstrahlung events and XCOM cross section data are used for photon interactions. Explicit M ‐ and N ‐shell transitions are modeled to account for the dosimetric effects of these atomic relaxations (EGSnrc default is to treat M ‐ and N ‐shell transitions in an average way); note that K ‐ and L ‐shells are considered explicitly by default. Photons and electrons are simulated down to 1 keV kinetic energy.…”