Secondary doses delivered to an anthropomorphic male phantom under prostate irradiation with proton and carbon ion beams

Secondary radiation exposure of patients undergoing radiation therapy with light ions is of great concern due to possible tissue damage and risk of induction of secondary cancers. Secondary particles such as neutrons, protons and heavier ions are produced when the primary ions interact through nuclear inelastic reactions with the beam-line components, and with the tissues of the patient. Evaluations of secondary doses delivered to an anthropomorphic male phantom under prostate irradiation with (1)H and (12)C ion beams with energies 172 MeV and 330 MeV/u, respectively, have been performed with the Monte Carlo code SHIELD-HIT. Fluences of secondary particles with atomic mass A = 1-7 and energies up to 200-600 MeV/u are observed in organs even at larger distances (40-50 cm) from the irradiated volume. The secondary absorbed doses in selected organs are discussed taking into account the dose contribution from secondary neutrons, and the contribution from charged fragments that are not the products of neutron interactions. For (12)C ion irradiation, a substantial contribution to the absorbed organ dose is due to charged fragments. This contribution decreases from 81% in the organs close to the irradiated volume to 35-40% in the organs at larger distances. (C) 2010 Elsevier Ltd. All rights reserved.