Modern Applied Science www.ccsenet.org/mas 26 Estimation of the Radioactivity Produced in Patient Tissue during Carbon Ion Therapy Dariush Sardari Faculty of Engineering, Islamic Azad University, Science and Research Branch P.O. Box 14515-775, Tehran - IRAN Tel: 98-21-4481-7007 E-mail: sardari@srbiau.ac.ir Nicolae Verga Department of Oncology, Faculty of General Medicine Carol Davila University of Medicine and Pharmacy, Bucharest, Romania Pooneh Saidi Faculty of Engineering, Islamic Azad University, Science and Research Branch P.O. Box 14515-775, Tehran - IRAN Abstract Nuclear interactions of the projectile carbon ion in biological soft tissue for cancer treatment purpose are studied. Elastic interaction of carbon ion with carbon, oxygen and nitrogen nuclei existing in soft tissue leads to beam divergence especially in Bragg peak region, where the carbon ion is slowing down. Monte Carlo simulation shows the amount of carbon ion beam divergence in soft tissue. For carbon ion beam with 2.4 GeV energy and 2mm diameter, at 85mm penetration depth the beam spreads out to 4mm diameter. Non-elastic interactions are modeled as well. Such interactions are important due to secondary radiation produced in patient’s body. The product particles include positrons and neutrons, being important in therapeutic dose verification with PET imaging and extra dose in the hospital ambient, respectively. Computer code ALICE produces reaction cross sections that might be used to roughly estimate the neutron and positron yield. Computer code ALICE was used to assess the cross section and yield of products from carbon nuclei interaction with soft tissue. Keywords: Carbon ion therapy, Induced activity, Nuclear reaction 1. Introduction Application of charged particle such as proton and carbon ion is being developed for treatment of cancerous tumors (Khoroshkov & Minakova, 1998). This is due to eligibility of such particles in tailoring radiation dose distribution to geometrical shape of tumor and capability of carbon ion in damage of radio-resistant tumors (Schardt 2007). Unlike photons, charged particles have a finite range in matter with little scattering. The increase of energy loss with decreasing velocity is characteristic of all ions. Charged particles slow down as they travel through matter as a result of electromagnetic interactions, including Coulomb scattering. The slower they move, the more efficient they are at ionizing atoms in their path and more likely they are to interact with atomic nuclei. It means that the highest radiation dose is delivered at points in the body at which the charged particles stop, while the dose elsewhere is low. Hence the rate of energy loss increases sharply near the end of its range, culminating in a peak, the so called Bragg peak. The depth of the Bragg peak in the body depends precisely on the initial energy of charged particles. Carbon ion with higher LET than proton is more efficient in destroying tumors resisting against radiation therapy. Thus carbon ion therapy has become a matter of interest over past few years (Khoroshkov & Minakova 1998, Schardt 2007). Verification of dose delivery to the tumor is possible by taking advantage of the property of positrons in producing 511 keV annihilation gamma photons (Parodi 2008). A similar technique as PET imaging might be utilized to track the charged particle beam down to the tumor by making the image of its trail of positron emitters. Nuclear interactions along the track of charged particles in the patients body leads to production of sufficient amount of positrons, which makes possible the use of PET imaging technique for the purpose of tracking the