Energy deposition of H and He ion beams in hydroxyapatite films: A study with implications for ion-beam cancer therapy

Abstract

Ion-beam cancer therapy is a promising technique to treat deep-seated tumors; however, for an accurate treatment planning, the energy deposition by the ions must be well known both in soft and hard human tissues. Although the energy loss of ions in water and other organic and biological materials is fairly well known, scarce information is available for the hard tissues (i.e., bone), for which the current stopping power information relies on the application of simple additivity rules to atomic data. Especially, more knowledge is needed for the main constituent of human bone, calcium hydroxyapatite (HAp), which constitutes 58% of its mass composition. In this work the energy loss of H and He ion beams in HAp films has been obtained experimentally. The experiments have been performed using the Rutherford backscattering technique in an energy range of 450-2000 keV for H and 400-5000 keV for He ions. These measurements are used as a benchmark for theoretical calculations (stopping power and mean excitation energy) based on the dielectric formalism together with the MELF-GOS (Mermin energy loss function-generalized oscillator strength) method to describe the electronic excitation spectrum of HAp. The stopping power calculations are in good agreement with the experiments. Even though these experimental data are obtained for low projectile energies compared with the ones used in hadron therapy, they validate the mean excitation energy obtained theoretically, which is the fundamental quantity to accurately assess energy deposition and depth-dose curves of ion beams at clinically relevant high energies. The effect of the mean excitation energy choice on the depth-dose profile is discussed on the basis of detailed simulations. Finally, implications of the present work on the energy loss of charged particles in human cortical bone are remarked.

On the Z1-dependence of electronic stopping in TiN

“…The mechanisms involved in these energy transfer processes are of great interest in many research fields as e.g. ion implantation 1 , medicine 2 and materials science 3 . The mean energy loss of the ion per unit path length when travelling in a material is usually expressed by the force the medium exerts on the ion, known as the stopping power, S , or more conveniently by the stopping cross section (SCS), ε = S/n , where n is the atomic density.…”

Simulation of the energy spectra of swift light ion beams after traversing cylindrical targets: a consistent interpretation of experimental data relevant for hadron therapy

“…Taking into account that most of the organic materials evaluated have a similar excitation spectrum with a maximum around 20 eV, they proposed that the experimental optical ELF of the outermost electrons of organic compounds can be parameterised with a single Drude-type function, with parameters that are obtained as a function of the mean atomic number of the target (i.e., the number of electrons per formula divided by the number of atoms) [47]. This approach has been applied to obtain electronic cross sections and stopping power of relevant biological materials for different ions [9,11,48]. Once the optical ELF of liquid ethanol is obtained, we applied the MELF-GOS method to find the Bethe surface, which allows calculating quantities such as the electronic stopping power and the energy-loss straggling.…”

Vicinage effect in the energy loss of H2 dimers: Experiment and calculations based on time-dependent density-functional theory

“…The study of the stopping processes of light projectiles in matter is essential not only for a basic understanding of particle-solid interactions but also for many applied fields of research, such as plasma physics [1,2], medical therapies [3][4][5], and radiation damage [6]. The transfer of energy from the incident projectile to the electrons of the target is a very complex problem in which phenomena such as dynamic screening and charge transfer processes have to be considered.…”