Nanodosimetry in biological tissue interacting with ion beams

M.A. QUINTO; O. A. FÓJON; R. D. RIVAROLA; PHILIPPE F. WECK; C. CHAMPION; J.M. MONTI; J. HANSSEN

Moscow

Conferencia; The International Conference on Many Particle Spectroscopy of Atoms, Molecules, Clusters and Surfaces MPS-2016; 2016

The understandingof the physicalmechanisms producing energy deposition onbiological matter, under ion beam irradiation, isa subject of principal interest in radiotherapyand, in particular in hadrontherapy.Modeling the radiobiological damagesinduced by the ionizing particles traversing theliving matter requires a precise knowledge ofthe full radiation history:Different electronic reactions involvingelectron ionization and charge exchange appearas main candidates to give an appropriatedescription of the process.By using quantum-mechanical models,different molecular targets irradiated with singleand multiple charged ions impacting atintermediate and high collision velocities areinvestigated.Among them, we must mention the fournucleobases (adenine, cytosine, thymine andguanine) as well as the sugar-phosphatebackbone of DNA and also the RNA uracil.Electron emission multiple differential,single differential and total cross sections arecompared with recent experimental data. Forelectron capture, measurements are muchscarcer and only a few values of total crosssections can be contrasted with theoreticalpredictions. We focus also our interest in the case of water molecules, considering that it isthe main compound of the biological tissue. Therole of Auger emission in electron capture andionization reactions is evaluated.In order to gain insight into the real energydeposit cartography induced by ion impact in thebiological medium, we have compared the meanenergy deposit in water to its homologous in a?realistic? DNA medium. Consequently, weconsidered a biological medium composed byhydrated DNA here simulated by adding 18 watermolecules per nucleotide in order to contrast withthe case of dry DNA [1].A fine description of the various energy transfersinduced by proton impact during both ionizationand capture points out strong discrepancies betweenwater and DNA revealing also the crucial role ofthe sugar-phosphate backbone in particular whenthe electron capture process is considered.The results are incorporated in a MonteCarlo code to determine the energy depositionpatterns at nanometer scale in a simplifieddescription of the cellular nucleus.