Simulation of micro- nanodosimetry spectra and free radicals with Geant4-DNA, LQD, PHYCHEML, CHEM for ion beams

International audience ; IntroductionHadrontherapy treatments rely on the estimation of the relative biological effectiveness (RBE). Biophysical models, such as the Microdosimetric Kinetic Model (MKM) [1] and the Nanodosimetry Oxidative stress model (NanOx) [2], evaluate the RBE using the calculation of specific energy spectra at micrometric scale (MKM, Nanox) and/or nanometric scale (LEM, Nanox). For the NanOx formalism, the chemical energy based on free radical production during irradiation is also considered. This study aims at benchmarking GEANT4-DNA and LQD/PHYCHEML/CHEM for the simulation of specific and lineal energy spectra and radiolysis species. Physical and chemical data are estimated for electron [1-100 keV], proton [1-250 MeV] and carbone ion [1 MeV/n- 400 MeV/n] monoenergetic beams. Material and Methods.Geant4-DNA physics lists are tested with the different options available. These options are recommended for discrete particle interactions and use different electron elastic and inelastic models. LQD [3] uses CDW-EIS calculation for ionizations induced by ions. Three-dimensional energy transfer points are calculated in thin liquid water slices. Transfer points are analyzed with the TED code to calculate, in micrometric and nanometric targets, the specific and the lineal energy. Radiochemical species (e^(-aq), OH., H_2 O_2.,O_2.), are calculated with the Geant4-DNA chemistry module and with PHYCHEML/CHEM modules associated to LQD. Results are then extrapolated to SOBP by superposing appropriate monoenergetic ion tracks.Results.The comparison of the results obtained with Geant4-DNA and LQD will be presented for monoenergetic beams as well as for SOBP. This study is preliminary to a full implementation of MKM and NanOx biophysical models into the GATE platform and the associated physical and chemical databases.Bibliography1. Hawkins RB. Med Phys. 1998;25: 1157–1170.2. Cunha M, et al. PMB, 2017;62:1248-1268.3. Gervais B, et al. RPC, 2005 ;75: 493-513.