Monte Carlo calculations of nano- and microdosimetric quantities for relative biological effectiveness in radiation protection and radiotherapy
Absorbed dose is a well-established quantity for relating biological response to the physical impact of ionizing radiation. Detailed protocols for quantitative determination of its magnitude have been determined for several radiation qualities in different areas such as radiology, nuclear medicine, radiotherapy and radiation protection. The variation of the biological response per dose between different radiation qualities (RQ) are described by empirical factors such as the Relative Biological Effectiveness (RBE) in radiotherapy, or the radiation weighting factor (wR) common in radiation protection applications. Besides RQ these data depends both on dose level, chosen biological endpoint, biological target, and dose rate. The Linear Energy Transfer is usually used as RQ qualifier for presentation of RBE data, but lacks in prediction power. Monte Carlo simulation of particle tracks is increasingly used to produce other quantities for RQ characterization data, and further applied in modelling attempts to predict radiation responses including the RBE. Among such data are e.g. cluster formation frequencies, distance distributions between ionizing events, etc. Although these quantities may have increased prediction power in radiobiological modelling, they are not readily measurable with established microdosimetry methods, and their relations to standard microdosimetry quantities such as the dose weighted lineal energy y_D are poorly known. In view of the increased establishment of new proton clinical facilities such as Skandionkliniken, the use of particle therapy protons will increase. The project aims at achieving the following goals: Produce an open accessible data base of Monte Carlo simulated track structure data for radiation qualities of interest with Geant4 DNA Analyze track data and provide relevant data of e.g. cluster frequency distributions and other quantities of interest for microdosimetry and modelling of relative biological effectiveness Measure and reproduce by Monte Carlo simulations micro and nanodosimetric data for selected detectors and radiation qualities Study RBE modelling based on the aforementioned data and find relations between measured data and radiation quality descriptors aiming for accurate, traceable quantities Investigate feasibility of RBE model applications in treatment planning of radiotherapy and possible usage in clinical treatment planning systems Tracks for the particles of interest (primarily protons and carbon ions but also conventional photons and brachytherapy sources for which relevant published radiobiological data exist) will be simulated to establish a data base covering the energy range of interest in radiotherapy. In collaboration with the radiation measurement laboratory at the Swedish Radiation Safety Authority the geometry of different detectors will be implemented and measurement results simulated for selected particle energies. The laboratory will take responsibility for performing measurements, for which specifications will be jointly developed. Analysis of measured and simulated data will aim for relating measurable, radiation quality dependent quantities with simulated quantities used in RBE modelling, with an overall goal of both refining modelling frameworks and work out simple on site experimental procedures for RQ verification.