PET monitoring of cancer therapy with3He and12C beams: a study with the GEANT4 toolkit
Physics in Medicine and Biology
We study the spatial distributions of β^+-activity produced by therapeutic beams of ^3He and ^12C ions in various tissue-like materials. The calculations were performed within a Monte Carlo model for Heavy-Ion Therapy (MCHIT) based on the GEANT4 toolkit. The contributions from ^10,11C, ^13N, ^14,15O, ^17,18F and ^30P positron-emitting nuclei were calculated and compared with experimental data obtained during and after irradiation. Positron emitting nuclei are created by ^12C beam in
... n reactions of projectile and target nuclei. This leads to a β^+-activity profile characterised by a noticeable peak located close to the Bragg peak in the corresponding depth-dose distribution. On the contrary, as the most of positron-emitting nuclei are produced by ^3He beam in target fragmentation reactions, the calculated total β^+-activity during or soon after the irradiation period is evenly distributed within the projectile range. However, we predict also the presence of ^13N, ^14O, ^17,18F created in charge-transfer reactions by low-energy ^3He ions close to the end of their range in several tissue-like media. The time evolution of β^+-activity profiles was investigated for both kinds of beams. Due to the production of ^18F nuclide the β^+-activity profile measured 2 or 3 hours after irradiation with ^3He ions will have a distinct peak correlated with the maximum of depth-dose distribution. We found certain advantages of low-energy ^3He beams over low-energy proton beams for reliable PET monitoring during particle therapy of shallow located tumours. In this case the distal edge of β^+-activity distribution from ^17F nuclei clearly marks the range of ^3He in tissues.