title: 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.
authors.affiliation: Centro Atómico Bariloche, RA-8400 San Carlos de Bariloche, Argentina.
authors.forename: Silvina
authors.initials: S
authors.lastname: Limandri
authors.affiliation: Departament de Física Aplicada, Universitat d'Alacant, E-03080 Alacant, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: de Vera
authors.affiliation: Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, 91501-970, Brazil.
authors.forename: Raul C
authors.initials: RC
authors.lastname: Fadanelli
authors.affiliation: Instituto de Física, Universidade de São Paulo, 05508-090, São Paulo, Brazil.
authors.forename: Luiz C C M
authors.initials: LC
authors.lastname: Nagamine
authors.affiliation: Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud, 150, Rio de Janeiro, 22290-180, RJ, Brazil.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Mello
authors.affiliation: Departamento de Física, Centro de Investigación en Óptica y Nanofísica, Regional Campus of International Excellence "Campus Mare Nostrum," Universidad de Murcia, E-30100 Murcia, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Garcia-Molina
authors.affiliation: Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, 91501-970, Brazil.
authors.forename: Moni
authors.initials: M
authors.lastname: Behar
authors.affiliation: Departament de Física Aplicada, Universitat d'Alacant, E-03080 Alacant, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Abril
mesh_terms: D018786:Bone Substitutes / Q000737:chemistry / Q000528:radiation effects; D003198:Computer Simulation; D017886:Durapatite / Q000737:chemistry* / Q000528:radiation effects*; D004735:Energy Transfer; D020450:Heavy Ions; D006371:Helium / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D008422:Materials Testing; D008956:Models, Chemical; D011882:Radiotherapy, High-Energy / Q000379:methods
chemical_list: D018786:Bone Substitutes; D006371:Helium; D006859:Hydrogen; D017886:Durapatite