Stopping power study of H and He in Hydropaxyapatite films: A study with implications in ion-beam therapy

(1) IF. Universidade Federal Rio Grande do Sul, Av. Bento Gonçalves 9500, 91501-970, Brazil
(2) Departamento de Fisica, Universidad de Murcia, 30100, Spain
(3) Department de Fisica Aplicada, Universidad dÁlacant Apartat 99, 030080 Spain
(4) Centro Atomico Bariloche, RA-8400, San Carlos de Bariloche, Argentina
(5) IF, Universidade Federal Rio Grande do Sul, Av. B. Gonçalves 9500-970, Brazil

Ion-beam 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 tissues. Although the energy deposition in soft tissues is well determinate the same is not true concerning hard tissues (i.e., bones). In particular more knowledge is needed for the main constituent of the human bone, calcium hydroxyapatite (HAp) which constitutes 58% of its mass composition. Moreover the HAp is considered as a biomaterial because it forms a strong bond with the human bone. In the present work, the energy loss of H and He in those films was determined experimentally for the first time. The experiments were performed using the Rutherford backscattering technique in an energy range of 250-2000 keV for H and 300-5000 keV for He. The corresponding theoretical calculations derived from the dielectric formalism [1] and a proper description of the HAp electronic excitation spectrum shows a nice agreement with the experimental data. Even though the experimental results were obtained at rather low energies as compared with the ones used for ion-therapy, they validate the mean excitation energy I obtained theoretically. This parameter is the fundamental quantity to accurately asses the 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 shown by the SEICS code [2], which is based on molecular dynamics and Monte Carlo techniques. This program shows that there is a significant difference between the present results and the theoretical ones obtained by using the Bragg rule. Finally in this presentation we show how the fundamental physics inspired studies, such as the present one, have implications in the field of ion-beam cancer therapy where an accurate knowledge of the energy by swift ions is required by a proper treatment planning.  

[1] M. Behar, R. C. Fadanelli, I. Abril,  R.  Garcia-Molina, L. C. C. Nagamine, and N. R. Arista, Phys. Rev. A 80, 062901 (2009).
[2] R. Garcia-Molina, I. Abril, S. Heredia-Avalos, I. Kriakou, D. Enfietzoglou, Phys. Med. Biol. 56, 6475 ( 2011).