The feasibility of in-beam PET for therapeutic beams of 3He

At the experimental carbon ion treatment facility at the Gesellschaft fur Schwerionenforschung (GSI) Darmstadt the clinical benefit of the in-beam PET method has been proven. It led to a significant improvement of the quality of patient treatment. Several heavy ion treatment facilities, which will provide in the near future a large variety of ions, are in planning or even under construction. The deduction of clinically relevant parameters from in-beam PET data requires a precise knowledge of the spatial distribution of beam induced positron emitters in the irradiated volume. Therefore, the beta+-activity induced by He-3 has been studied for the first time at the Gesellschaft fur Schwerionenforschung with three mono-energetic He-3 beams of 130.03 AMeV to 207.92 AMeV and mean intensities varying from 2.0 (.) 10(8) to 3.5 (.) 10(8) ions/s. The beams were stopped in homogeneous thick targets consisting of PMMA, graphite and water, which were placed in the center of the field of view of the PET-scanner at the experimental carbon ion therapy at GSI. Results on the production rate and the spatial distribution of He-3 ion induced positron activity is presented and compared with data from C-12-irradiation. The accuracy and resolution for determining the range of the He-3 primary beams is deduced. Furthermore, energy dependent thick target cross sections for different reaction channels leading to positron emitters are estimated from the experimental data.