An ab-initio approach to trace back the physical origin of neutron biological effectiveness as a function of energy

New experimental and theoretical efforts have been recently undertaken in the framework of the European project ANDANTE, with the overarching objective of determining values of RBE (Relative Biological Effectiveness) for neutrons for specific tissues and neutron energies. The context of the project is specifically the possible role of secondary neutrons in the induction of second primary neoplasms following particle therapy, especially for pediatric patients. Because of the great attention demanded by this issue, and since the understanding of the impact of radiation quality in early and late responses of biological targets to ionizing radiation exposure necessarily grounds on the results of mechanistic studies starting from physical interactions, a theoretical effort to trace back neutron biological effectiveness to first principles (as much as this is possible) seems highly desirable. In this work we coupled the potential of two different modeling approaches, namely radiation transport and track structure calculations, in order to evaluate the biological effects of neutron exposures of tissue targets at cellular/sub-cellular level, as a function of neutron energy and target geometry. Two different energy dependent neutron RBE models are proposed: the first is phenomenological and based only on the characterization of linear energy transfer on a microscopic scale; the second is purely ab-initio and based on the induction of complex DNA damage. Results for the two models are compared and found in good qualitative agreement with current standards for radiation protection factors, which are agreed upon on the basis of RBE data.