Abstract
Existing radiation codes for biomedical applications face the challenge of dealing with largely different spatial scales, from nanometer scales governing individual energy deposits to macroscopic scales of dose distributions in organs and tissues in radiotherapy. Event-by-event track-structure codes are needed to model energy deposition patterns at cellular and subcellular levels. In conjunction with DNA and chromatin models, they predict radiation-induced DNA damage and subsequent biological effects. Describing larger-scale effects is the realm of radiation transport codes and dose calculation algorithms. A coupling approach with a great potential consists in implementing into radiation transport codes the results of track-structure simulations captured by analytical formulas. This strategy allows extending existing transport codes to biologically relevant endpoints, without the need of developing dedicated modules and running new computationally expensive simulations. Depending on the codes used and questions addressed, alternative strategies can be adopted, reproducing DNA damage in dependence on different parameters extracted from the transport code, e.g., microdosimetric quantities, average linear energy transfer (LET), or particle energy. Recently, a comprehensive database on DNA damage induced by ions from hydrogen to neon, at energies from 0.5 GeV/u down to their stopping, has been created with PARTRAC biophysical simulations. The results have been captured as a function of average LET in the cell nucleus. However, the formulas are not applicable to slow particles beyond the Bragg peak, since these can have the same LET as faster particles but in narrower tracks, thus inducing different DNA damage patterns. Particle energy distinguishes these two cases. It is also more readily available than LET from some transport codes. Therefore, a set of new analytical functions are provided, describing how DNA damage depends on particle energy. The results complement the analysis of the PARTRAC database, widening its potential of application and use for implementation in transport codes.
Highlights
Radiation transport codes are a key tool for many research and practical applications dealing with radiation-matter interactions
It could be argued that they are ideal to characterize the radiation field in a single cell nucleus that can be assumed as a quasi-spherical volume with a linear dimension of ∼10 μm. These considerations are at the basis of our previous works, in which we proposed a full coupling between PHITS and PARTRAC to derive the RBE of neutrons of different energy [14, 15], as well as a full set of analytical functions [16] reproducing PARTRAC results on different types of DNA damage as a function of an linear energy transfer (LET) estimate, when the cell nucleus is irradiated with a variety of light ions at radiotherapy-relevant energies down to stopping
It has the advantage that particle energy distributions can be extracted from transport codes. Starting from these considerations, we provide in this work a set of new analytical functions exploring how PARTRAC results on DNA damage depend on particle energy, for light ions up to Ne, with energies per nucleon from 0.5 GeV/u down to stopping
Summary
Radiation transport codes are a key tool for many research and practical applications dealing with radiation-matter interactions. Radiation action proceeds through energy deposition events (mainly ionizations and excitations of target atoms) that are spatially distributed with a ∼nm spacing. Coupling these spatial scales and dealing with them in a common simulation framework is, without a doubt, a challenge. Concerning different target materials, radiation transport with a condensed-history approach mainly requires the knowledge of particle stopping power (as well as cross-section data for nuclear reactions), while an event-byevent simulation requires accurate knowledge of all interaction cross sections with atomic electrons [10]. Track-structure calculations are mostly performed in water only
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