. m ed - p h ] 6 O ct 2 00 6 Distributions of positron - emitting nuclei in proton and carbon - ion therapy studied with GEANT 4

Depth distributions of positron-emitting nuclei in PMMA phantoms are calculated within a Monte Carlo model for Heavy-Ion Therapy (MCHIT) based on the GEANT4 toolkit (version 8.0). The calculated total production rates of C, C and O nuclei are compared with experimental data and with corresponding results of the FLUKA and POSGEN codes. The distributions of e annihilation points are obtained by simulating radioactive decay of unstable nuclei and transporting positrons in surrounding medium. A finite spatial resolution of the Positron Emission Tomography (PET) is taken into account in a simplified way. Depth distributions of β-activity as seen by a PET scanner are calculated and compared to available data for PMMA phantoms. The calculated β-activity profiles are in good agreement with PET data for proton and C beams at energies suitable for particle therapy. The MCHIT capability to predict the β-activity and dose distributions in tissue-like materials of different chemical composition is demonstrated. Submitted to: Phys. Med. Biol. PACS numbers: 87.53.Pb, 87.53.Wz, 87.53.Vb E-mail: [email protected]