In-beam PET monitoring of mono-energetic 16O and 12C beams: experiments and FLUKA simulations for homogeneous targets

O-16 and C-12 ion beams will be used-besides lighter ions-for cancer treatment at the Heidelberg Ion Therapy Center (HIT), Germany. It is planned to monitor the treatment by means of in-beam positron emission tomography (PET) as it is done for therapy with C-12 beams at the experimental facility at the Gesellschaft fur Schwerionenforschung (GSI), Darmstadt, Germany. To enable PET also for O-16 beams, experimental data of the beta(+)-activity created by these beams are needed. Therefore, in-beam PET measurements of the activity created by O-16 beams of various energies on targets of PMMA, water and graphite were performed at GSI for the first time. Additionally reference measurements of C-12 beams on the same target materials were done. The results of the measurements are presented. The deduction of clinically relevant results from in-beam PET data requires reliable simulations of the beta(+)-activity production, which is done presently by a dedicated code limited to C-12 beams. Because this code is not extendable to other ions in an easy way, a new code, capable of simulating the production of the beta(+)-activity by all ions of interest, is needed. Our choice is the general purpose Monte Carlo code FLUKA which was used to simulate the ion transport, the beta(+)-active isotope production, the decay, the positron annihilation and the transport of the annihilation photons. The detector response was simulated with an established software that gives the output in the same list-mode data format as in the experiment. This allows us to use the same software to reconstruct measured and simulated data, which makes comparisons easier and more reliable. The calculated activity distribution shows general good agreement with the measurements.