Investigation of Irregular Motion Influence for Future 4D In-Beam PET Imaging

Particle therapy PET (PT-PET) has been established for dose monitoring and particle range assessment in hadron therapy. Imaging is up to now restricted to static organs. However, by means of phantom irradiation it has been shown that a 4D maximum likelihood expectation maximization (4D MLEM) reconstruction method is able to compensate for blurring artefacts of regular motion in in-beam PET images. Nevertheless, respiratory curves often show inconsistent amplitude variation, frequency modulation and baseline drift during radiotherapy. Since the anatomical information is not updated by a CT scanner during treatment, transformation of data from each phase could only rely on the 4D CT obtained prior to irradiation, which might be incorrectly transformed. Based on that clinical situation, this study aims to investigate the effect of irregularity in motion on 4D PET image reconstruction.