title: Experimental investigation of irregular motion impact on 4D PET-based particle therapy monitoring.
abstract: Particle therapy positron emission tomography (PT-PET) is an in vivo and non-invasive imaging technique to monitor treatment delivery in particle therapy. The inevitable patient respiratory motion during irradiation causes artefacts and inaccurate activity distribution in PET images. Four-dimensional (4D) maximum likelihood expectation maximisation (4D MLEM) allows for a compensation of these effects, but has up to now been restricted to regular motion for PT-PET investigations. However, intra-fractional motion during treatment might differ from that during acquisition of the 4D-planning CT (e.g. amplitude variation, baseline drift) and therefore might induce inaccurate 4D PET reconstruction results. This study investigates the impact of different irregular analytical one-dimensional (1D) motion patterns on PT-PET imaging by means of experiments with a radioactive source and irradiated moving phantoms. Three sorting methods, namely phase sorting, equal amplitude sorting and event-based amplitude sorting, were applied to manage the PET list-mode data. The influence of these sorting methods on the motion compensating algorithm has been analysed. The event-based amplitude sorting showed a superior performance and it is applicable for irregular motions with ⩽ 4 mm amplitude elongation and drift. For motion with 10 mm baseline drift, the normalised root mean square error was as high as 10.5% and a 10 mm range deviation was observed.
authors.affiliation: OncoRay-National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden-Rossendorf, Fetscherstraße 74, 01307 Dresden, Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Tian
authors.forename: K
authors.initials: K
authors.lastname: Stützer
authors.forename: W
authors.initials: W
authors.lastname: Enghardt
authors.forename: M
authors.initials: M
authors.lastname: Priegnitz
authors.forename: S
authors.initials: S
authors.lastname: Helmbrecht
authors.forename: C
authors.initials: C
authors.lastname: Bert
authors.forename: F
authors.initials: F
authors.lastname: Fiedler
mesh_terms: D000465:Algorithms; D016477:Artifacts; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D009038:Motion; D019047:Phantoms, Imaging; D061766:Proton Therapy / Q000379:methods