Isabel Abril

Ionization of biomolecular targets by ion impact: input data for radiobiological applications

In this work we review and further develop a semiempirical model recently proposed for the ion impact ionization of complex biological media. The model is based on the dielectric formalism, and makes use of a semiempirical parametrization of the optical energy-loss function of bioorganic compounds, allowing the calculation of single and total ionization cross sections and related quantities for condensed biological targets, such as liquid water, DNA and its components, proteins, lipids, carbohydrates or cell constituents. The model shows a very good agreement with experimental data for water, adenine and uracil, and allows the comparison of the ionization efficiency of different biological targets, and also the average kinetic energy of the ejected secondary electrons.

Propagation of Swift Protons in Liquid Water and Generation of Secondary Electrons in Biomaterials

A proper description of the propagation of a swift proton beam through biomaterials, accounting for the energy deposited as well as the geometrical evolution of the beam as a function of the target depth and nature, is a crucial issue in proton therapy. For this purpose, simulation is a very adequate tool, since the most relevant interactions that take place between the projectile and the target constituents (electrons and nuclei) can be conveniently accounted for in a controlled manner. In this chapter an overview and relevant results for hadron therapy are presented of the simulations we have developed using the code SEICS (Simulation of Energetic Ions and Clusters through Solids), which combines Monte Carlo and Molecular Dynamics, to follow in detail the motion and energy deposition of swift protons through targets of hadron therapeutic interest, mainly liquid water. The main interactions considered in our study are of elastic nature (affecting mainly the projectile’s direction) and inelastic processes (leading to either nuclear reactions or electronic energy loss). The performance of the code, as well as the quality of its main input, namely the stopping force for proton beams in liquid water (which is the main tissue constituent), are benchmarked by comparing the results of the simulations with available experimental proton energy spectra as a function of the detection angle after traversing a micrometric liquid water jet. The excellent agreement with experiments validates the SEICS code, which we can use then to study several problems of interest for proton therapy, including the calculation of depth-dose curves and lateral dose profiles, the energy evolution of the proton beam along the target, as well as the production of secondary electrons at the Bragg peak in relevant biomaterials.

Simulation of the energy loss of proton beams interacting with few layer graphene foils

Synopsis We have simulated the passage of proton beams, having energies E < 10 keV, through graphene targets, considering the case of few layer foils. For this purpose and for comparison, we implement Monte Carlo and deterministic semi-classical approaches to describe the interaction of protons with carbon atoms in graphene structures. Our results show that the energy loss through a single layer graphene foil is smaller than recent ab initio calculations based on time dependent density functional theory (TD-DFT). Besides, for E > 6 keV the energy loss into a graphene target composed of n layers is n times the energy loss through a single layer graphene foil.

Energy deposition around swift proton and carbon ion tracks in biomaterials

* Departamento de Física CIOyN, Universidad de Murcia, E-30100 Murcia, Spain. † European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*), Bruno Kessler Foundation, and Trento Institute for Fundamental Physics and Applications (INFN-TIFPA), I-38123 Trento, Italy. ‡ School of Mathematics and Physics, Queen’s University Belfast, BT7 1NN Belfast, Northern Ireland, UK. § Departament de Física Aplicada, Universitat d’Alacant, E-03080 Alacant, Spain