Experimental verification of a 4D MLEM reconstruction algorithm used for in-beam PET measurements in particle therapy

Abstract. In-beam positron emission tomography (PET) had been proven to be a reliable technique in ion beam radiotherapy for the in situ and non-invasive evaluation of the correct dose deposition in static tumour entities. In the presence of intra-fractional target motion an appropriate time-resolved (4D) reconstruction algorithm has to be used to avoid reconstructed activity distributions suffering from motion-related blurring artefacts and to allow for a dedicated dose monitoring. 4D reconstruction algorithms from diagnostic PET imaging that can properly handle the typically low counting statistics of in-beam PET data have been adapted and optimized for the characteristics of the double-head PET scanner BASTEI installed at GSI Helmholtzzentrum Darmstadt, Germany (GSI). Systematic investigations of the reconstructed images have been performed by means of real measurements from moving radioactive sources and irradiation of moving phantoms. From in-beam PET listmode data sets acquired together with a motion surrogate signal valuable images can be generated for different motion patterns and motion-compensated beam delivery techniques.