Energy Deposition around Swift Carbon-Ion Tracks in Liquid Water

Abstract

Energetic carbon ions are promising projectiles used for cancer radiotherapy. A thorough knowledge of how the energy of these ions is deposited in biological media (mainly composed of liquid water) is required. This can be attained by means of detailed computer simulations, both macroscopically (relevant for appropriately delivering the dose) and at the nanoscale (important for determining the inflicted radiobiological damage). The energy lost per unit path length (i.e., the so-called stopping power) of carbon ions is here theoretically calculated within the dielectric formalism from the excitation spectrum of liquid water obtained from two complementary approaches (one relying on an optical-data model and the other exclusively on ab initio calculations). In addition, the energy carried at the nanometre scale by the generated secondary electrons around the ion’s path is simulated by means of a detailed Monte Carlo code. For this purpose, we use the ion and electron cross sections calculated by means of state-of-the art approaches suited to take into account the condensed-phase nature of the liquid water target. As a result of these simulations, the radial dose around the ion’s path is obtained, as well as the distributions of clustered events in nanometric volumes similar to the dimensions of DNA convolutions, contributing to the biological damage for carbon ions in a wide energy range, covering from the plateau to the maximum of the Bragg peak.

Electron tracks simulation in water: Performance comparison between GPU CPU and the EUMED grid installation

“…However, both the inelastic and the elastic cross sections models become inaccurate for low energies, thus increasing the results uncertainty. In the future, the Rutherford model can be replaced with the partial wave expansion to improve the elastic scattering collisions, in fact recent studies showed the importance of elastic scattering models and their effect on numerical simulations [41,42].…”

Ion-Type Dependence of DNA Electronic Excitation in Water under Proton, α-Particle, and Carbon Ion Irradiation: A First-Principles Simulation Study

“…The positions of all DNA and water atoms are held constant, as the time scales for these simulations (0.27–3.38 fs, depending on projectile ion velocity) are too short for any notable nuclear motion . The projectile ion is moved at a constant velocity of interest for obtaining the velocity-dependent electronic stopping power curve. , The electronic stopping power, or the energy transfer rate from the projectile ion to target, is a crucial property for many applications, including beam cancer therapy. − As the projectile ion travels through the simulation cell, the electron density changes in response to the time-dependent potential generated by the projectile ion until the ion reaches the end of its trajectory, and the simulation is stopped. By moving the projectile at a constant velocity, while all other atoms are held in place, the total energy of the nonequilibrium simulation is not conserved, as work is done throughout by the projectile ion. ,, Therefore, changes in the total energy of the system can be used to calculate the electronic stopping power as a function of the projectile ion velocity (see Figures S4 and S5 for details) …”

Transient absorption measurement of laser-accelerated ion bunch radiolysis on sub-ps timescales

“…22 Additionally, the water-ions generated by the interaction processes cause an additive charged background that polarizes the neutral water molecules within the ion track. There is no detailed study about proton tracks in liquid water regarding free charge concentrations, but similar studies about carbon-tracks in liquid water, 23 ion tracks in various solids 24 and models like the thermal spike model for protons in liquid water 25 suggest that this charge background is present as long as the radical dissipation time of ≈ 10 ps. Therefore, an electron ionized in the ion track could not encounter a neutral water background in its vicinity, showing an energy structure as in seen figure 1, but rather a highly polarised medium.…”