title: Reaction mechanism interplay in determining the biological effectiveness of neutrons as a function of energy.
abstract: Neutron relative biological effectiveness (RBE) is found to be energy dependent, being maximal for energies ∼1 MeV. This is reflected in the choice of radiation weighting factors wR for radiation protection purposes. In order to trace back the physical origin of this behaviour, a detailed study of energy deposition processes with their full dependences is necessary. In this work, the Monte Carlo transport code PHITS was used to characterise main secondary products responsible for energy deposition in a 'human-sized' soft tissue spherical phantom, irradiated by monoenergetic neutrons with energies around the maximal RBE/wR. Thereafter, results on the microdosimetric characterisation of secondary protons were used as an input to track structure calculations performed with PARTRAC, thus evaluating the corresponding DNA damage induction. Within the proposed simplified approach, evidence is suggested for a relevant role of secondary protons in inducing the maximal biological effectiveness for 1 MeV neutrons.
authors.affiliation: Department of Physics, University of Pavia, Pavia, Italy INFN, National Institute of Nuclear Physics, Sezione di Pavia, Pavia, Italy giorgio.baiocco@unipv.it.
authors.forename: G
authors.initials: G
authors.lastname: Baiocco
authors.affiliation: Department of Physics, University of Pavia, Pavia, Italy INFN, National Institute of Nuclear Physics, Sezione di Pavia, Pavia, Italy LENA, Laboratory of Applied Nuclear Energy, University of Pavia, Pavia, Italy.
authors.forename: D
authors.initials: D
authors.lastname: Alloni
authors.affiliation: Department of Physics, University of Pavia, Pavia, Italy INFN, National Institute of Nuclear Physics, Sezione di Pavia, Pavia, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Babini
authors.affiliation: Department of Physics, University of Pavia, Pavia, Italy INFN, National Institute of Nuclear Physics, Sezione di Pavia, Pavia, Italy Department of Oncology, Gray Institute, University of Oxford, Old Road Campus, Oxford OX3 7DQ, UK.
authors.forename: L
authors.initials: L
authors.lastname: Mariotti
authors.affiliation: Department of Physics, University of Pavia, Pavia, Italy INFN, National Institute of Nuclear Physics, Sezione di Pavia, Pavia, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Ottolenghi
mesh_terms: D003198:Computer Simulation; D004249:DNA Damage / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D009010:Monte Carlo Method; D009502:Neutrons; D011522:Protons; D011835:Radiation Protection / Q000592:standards*; D011874:Radiometry / Q000379:methods*; D012062:Relative Biological Effectiveness
chemical_list: D011522:Protons