title: Initial clinical evaluation of PET-based ion beam therapy monitoring under consideration of organ motion.
abstract: OBJECTIVE
  Intrafractional organ motion imposes considerable challenges to scanned ion beam therapy and demands for a thorough verification of the applied treatment. At the Heidelberg Ion-Beam Therapy Center (HIT), the scanned ion beam delivery is verified by means of postirradiation positron-emission-tomography (PET) imaging. This work presents a first clinical evaluation of PET-based treatment monitoring in ion beam therapy under consideration of target motion.
  
  
  METHODS
  Three patients with mobile liver lesions underwent scanned carbon ion irradiation at HIT and postirradiation PET/CT (x-ray-computed-tomography) imaging with a commercial scanner. Respiratory motion was recorded during irradiation and subsequent image acquisition. This enabled a time-resolved (4D) calculation of the expected irradiation-induced activity pattern and, for one patient where an additional 4D CT was acquired at the PET/CT scanner after treatment, a motion-compensated PET image reconstruction. For the other patients, PET data were reconstructed statically. To verify the treatment, calculated prediction and reconstructed measurement were compared with a focus on the ion beam range.
  
  
  RESULTS
  Results in the current three patients suggest that for motion amplitudes in the order of 2 mm there is no benefit from incorporating respiratory motion information into PET-based treatment monitoring. For a target motion in the order of 10 mm, motion-related effects become more severe and a time-resolved modeling of the expected activity distribution can lead to an improved data interpretation if a sufficient number of true coincidences is detected. Benefits from motion-compensated PET image reconstruction could not be shown conclusively at the current stage.
  
  
  CONCLUSIONS
  The feasibility of clinical PET-based treatment verification under consideration of organ motion has been shown for the first time. Improvements in noise-robust 4D PET image reconstruction are deemed necessary to enhance the clinical potential.
authors: Heidelberg Ion-Beam Therapy Center and Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg 69120, Germany.
authors: Christopher
authors: C
authors: Kurz
authors: Heidelberg Ion-Beam Therapy Center and Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg 69120, Germany.
authors: Julia
authors: J
authors: Bauer
authors: Heidelberg Ion-Beam Therapy Center and Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg 69120, Germany.
authors: Daniel
authors: D
authors: Unholtz
authors: GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt 64291, GermanyStrahlenklinik, Universitätsklinikum Erlangen, Erlangen 91054, Germany.
authors: Daniel
authors: D
authors: Richter
authors: Heidelberg Ion-Beam Therapy Center and Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg 69120, Germany.
authors: Klaus
authors: K
authors: Herfarth
authors: Heidelberg Ion-Beam Therapy Center and Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg 69120, Germany.
authors: Jürgen
authors: J
authors: Debus
authors: Heidelberg Ion-Beam Therapy Center and Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg 69120, GermanyDepartment of Medical Physics, Ludwig-Maximilians-University, Munich 85748, Germany.
authors: Katia
authors: K
authors: Parodi
mesh_terms: D063193:Heavy Ion Radiotherapy / Q000379:methods*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000532:radiotherapy; D009068:Movement; D049268:Positron-Emission Tomography; D061089:Radiotherapy, Image-Guided / Q000379:methods*