Secondary beam fragments produced by 200 MeV u⁻¹¹²C ions in water and their dose contributions in carbon ion radiotherapy

For applications in heavy-ion radiotherapy, the emission of secondary fragments from 200 MeV u -1 carbon ions was investigated using a 12.78 cm thick water absorber as a tissue-equivalent beam stopping target. Secondary light particles (n, p, d, t, 3 He and 4 He) produced by nuclear fragmentation and emerging from the target in forward direction were detected with a E -E-telescope consisting of NE102 and BaF 2 scintillation detectors. Energy spectra of the fragments at angles of 0 , 5 , 10 , 20 and 30 to the beam axis were obtained from time-of-flight measurements. They show a broad maximum at about half of the projectiles energy per nucleon, the shape at high energies is exponential and extends up to the projectiles initial energy per nucleon-for neutrons and protons to about twice the energy of the projectile per nucleon. Comparison of the experimental data with calculations performed with the Monte-Carlo code (partide and heavy ion transport code system (PHITS)) shows fairly good agreement for neutrons, protons and deuterons, but some deviations for tritons and helium fragments. The neutron dose in patient treatments with carbon ions was estimated to be 8 mGy per treatment-Gy based on the measured neutron yield.