Impact of Target Oxygenation on the Chemical Track Evolution of Ion and Electron Radiation

Abstract

The radiosensitivity of biological systems is strongly affected by the system oxygenation. On the nanoscopic scale and molecular level, this effect is considered to be strongly related to the indirect damage of radiation. Even though particle track radiolysis has been the object of several studies, still little is known about the nanoscopic impact of target oxygenation on the radical yields. Here we present an extension of the chemical module of the Monte Carlo particle track structure code TRAX, taking into account the presence of dissolved molecular oxygen in the target material. The impact of the target oxygenation level on the chemical track evolution and the yields of all the relevant chemical species are studied in water under different irradiation conditions: different linear energy transfer (LET) values, different oxygenation levels, and different particle types. Especially for low LET radiation, a large production of two highly toxic species ( HO 2 • and O 2 • − ), which is not produced in anoxic conditions, is predicted and quantified in oxygenated solutions. The remarkable correlation between the HO 2 • and O 2 • − production yield and the oxygen enhancement ratio observed in biological systems suggests a direct or indirect involvement of HO 2 • and O 2 • − in the oxygen sensitization effect. The results are in agreement with available experimental data and previous computational approaches. An analysis of the oxygen depletion rate in different radiation conditions is also reported. The radiosensitivity of biological systems is strongly affected by the system oxygenation. On the nanoscopic scale and molecular level, this effect is considered to be strongly related to the indirect damage of radiation. Even though particle track radiolysis has been the object of several studies, still little is known about the nanoscopic impact of target oxygenation on the radical yields. Here we present an extension of the chemical module of the Monte Carlo particle track structure code TRAX, taking into account the presence of dissolved molecular oxygen in the target material. The impact of the target oxygenation level on the chemical track evolution and the yields of all the relevant chemical species are studied in water under different irradiation conditions: different linear energy transfer (LET) values, different oxygenation levels, and different particle types. Especially for low LET radiation, a large production of two highly toxic species ( HO 2 • and O 2 • − ), which is not produced in anoxic conditions, is predicted and quantified in oxygenated solutions. The remarkable correlation between the HO 2 • and O 2 • − production yield and the oxygen enhancement ratio observed in biological systems suggests a direct or indirect involvement of HO 2 • and O 2 • − in the oxygen sensitization effect. The results are in agreement with available experimental data and previous computational approaches. An analysis of the oxygen depletion rate in different radiation conditions is also reported.

A Quantitative Analysis of the Role of Oxygen Tension in FLASH Radiation Therapy

“…A number of models of oxygen kinetics in irradiated systems have been proposed, including depletion which is linear in dose, or through first-or second-order reactions with radiation products (12,14,16,24). For exposures carried out in pure water or dilute solutions, experimental measurements and computational models of dissolved oxygen suggest oxygen depletion is independent of O2 concentration down to very low concentrations (14,25). However, within cells and tissues, a large number of other molecules are present which can interact with radiolysis products, potentially altering these kinetics by introducing competition for reactions with dissolved oxygen.…”

Significant changes in yields of 7-hydroxy-coumarin-3-carboxylic acid produced under FLASH radiotherapy conditions

“…1 and 5]. Furthermore, some important studies were done using a computer simulation 8,9 and a kinetic model was developed to understand the mechanism of the FLASH effect. 10 However, the mechanism of the FLASH effect has not been experimentally investigated.…”

Quantitative estimation of track segment yields of water radiolysis species under heavy ions around Bragg peak energies using Geant4-DNA

“…This reaction is a competing process with the interaction of e aq − with the O 2 · − . However, for the high LET region, · OH react more efficiently with e aq − 48 . In brief, · OH are diminished by reactions with e aq − in the track core.…”