Abstract
The BioQuaRT project within the European Metrology Research Programme aims at correlating ion track structure characteristics with the biological effects of radiation and develops measurement and simulation techniques for determining ion track structure on different length scales from about 2 nm to about 10 μm. Within this framework, we investigate methods to translate track-structure quantities derived on a nanometre scale to macroscopic dimensions. Input data sets were generated by simulations of ion tracks of protons and carbon ions in liquid water using the Geant 4 Monte Carlo toolkit with the Geant4-DNA processes. Based on the energy transfer points — recorded with nanometre resolution — we investigated parametrisations of overall properties of ion track structure. Three different track structure parametrisations have been developed using the distances to the 10 next neighbouring ionisations, the radial energy distribution and ionisation cluster size distributions. These parametrisations of nanometric track structure build a basis for deriving biologically relevant mean values which are essential in the clinical situation where each voxel is exposed to a mixed radiation field.
Highlights
High energy ion beams are progressively used for the treatment of cancer patients, as the tumor can be targeted with higher accuracy and organs at risk can be spared more effectively compared to conventional photon therapy [1]
Input data sets were generated by simulations of ion tracks of protons and carbon ions in liquid water using the Geant 4 Monte Carlo toolkit with the Geant4-DNA processes
Benefiting from a multi-scale approach, the BioQuaRT1 project [2,3] aims at creating a new dosimetric quantity to define the local radiation quality, which strongly influences the biological response. This quantity should be integrated into clinical treatment planning systems which simulate and optimise the treatment for each individual patient. Within this framework we studied the spatial distribution of energy depositions on the nanometer scale
Summary
High energy ion beams are progressively used for the treatment of cancer patients, as the tumor can be targeted with higher accuracy and organs at risk can be spared more effectively compared to conventional photon therapy [1]. We present here three parametrisations which can be used to extract track structure properties for each desired energy in a clinical energy range without the need to perform a full nanometric Monte Carlo simulation for each patient These parametrisations may be useful for treatment planning, where the three-dimensional patient geometry is represented by voxels with a size of ≈1 mm. The methods presented in this paper can be the basis for the development of a data base of parametrisations that enables a fast computation of the relevant track structure parameters for different particle types and energies present in a mixed radiation field This is crucial as treatment planning typically involves the evaluation of various possible treatment plans, and it would not be feasible to perform a full track structure simulation with nanometre resolution for each particle type and energy present in each voxel. The third model concentrates on ionisation cluster size distributions and is based on the fact that a higher number of ionisations in a small volume results in a higher number of lesions on the DNA and an increased yield of double strand breaks [8,9]
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