Abstract
We evaluate the track segment yield G′ of typical water radiolysis products (eaq−, ·OH and H2O2) under heavy ions (He, C and Fe ions) using a Monte Carlo simulation code in the Geant4-DNA. Furthermore, we reproduce experimental results of ·OH of He and C ions around the Bragg peak energies (< 6 MeV/u). In the relatively high energy region (e.g., > 10 MeV/u), the simulation results using Geant4-DNA have agreed with experimental results. However, the G-values of water radiolysis species have not been properly evaluated around the Bragg peak energies, at which high ionizing density can be expected. Around the Bragg peak energy, dense continuous secondary products are generated, so that it is necessary to simulate the radical–radical reaction more accurately. To do so, we added the role of secondary products formed by irradiation. Consequently, our simulation results are in good agreement with experimental results and previous simulations not only in the high-energy region but also around the Bragg peak. Several future issues are also discussed regarding the roles of fragmentation and multi-ionization to realize more realistic simulations.
Highlights
Cancer patients can nowadays select several modalities in radiotherapy such as conventional X-ray therapy and particle therapies
The linear energy transfer (LET) dependence of G-values of typical water radiolysis products in the high energy region (> 100 MeV/u) was evaluated using Geant4-DNA15,16 The simulation results were in agreement with experimental results
The first issue is roles played by secondary products generated by water radiolysis
Summary
Cancer patients can nowadays select several modalities in radiotherapy such as conventional X-ray therapy and particle therapies (e.g., proton therapy, heavy ion therapy and boron neutron capture therapy). While primary energy transfer induced by ionizing radiation in media occurring in the extremely fast stage (typically 10–18 s)[5] can be accurately calculated using a Monte Carlo simulation toolkit, it is tough to simulate the following secondary reactions in the “physicochemical phase”. Many researchers have experimentally evaluated radiation chemical yields (G-values), the number of entities formed or destroyed by unit energy (conventionally 100 eV), of ·OH, hydrated electrons (e−aq) and hydrogen peroxide (H2O2), all of them are typical water radiolysis products under ionizing radiation[6,7,8,9,10], using radical scavengers (e.g., coumarin-3-carboxylic acid (C3CA) and phenol). The LET dependence of G-values of typical water radiolysis products in the high energy region (> 100 MeV/u) was evaluated using Geant4-DNA15,16 The simulation results were in agreement with experimental results. The obtained simulation results are compared to the experimental results around Bragg peak energies and previously obtained ones in the high energy region
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