title: Four-Dimensional Dose Reconstruction for Scanned Proton Therapy Using Liver 4DCT-MRI.
abstract: OBJECTIVE
  Four-dimensional computed tomography-magnetic resonance imaging (4DCT-MRI) is an image-processing technique for simulating many 4DCT data sets from a static reference CT and motions extracted from 4DMRI studies performed using either volunteers or patients. In this work, different motion extraction approaches were tested using 6 liver cases, and a detailed comparison between 4DCT-MRI and 4DCT was performed.
  
  
  METHODS
  4DCT-MRI has been generated using 2 approaches. The first approach used motion extracted from 4DMRI as being "most similar" to that of 4DCT from the same patient (subject-specific), and the second approach used the most similar motion obtained from a motion library derived from 4DMRI liver studies of 13 healthy volunteers (population-based). The resulting 4DCT-MRI and 4DCTs were compared using scanned proton 4D dose calculations (4DDC).
  
  
  RESULTS
  Dosimetric analysis showed that 93% ± 8% of points inside the clinical target volume (CTV) agreed between 4DCT and subject-specific 4DCT-MRI (gamma analysis: 3%/3 mm). The population-based approach however showed lower dosimetric agreement with only 79% ± 14% points in the CTV reaching the 3%/3 mm criteria.
  
  
  CONCLUSIONS
  4D CT-MRI extends the capabilities of motion modeling for dose calculations by accounting for realistic and variable motion patterns, which can be directly employed in clinical research studies. We have found that the subject-specific liver modeling appears more accurate than the population-based approach. The former is particularly interesting for clinical applications, such as improved target delineation and 4D dose reconstruction for patient-specific QA to allow for inter- and/or intra-fractional plan corrections.
authors.affiliation: Department of Physics, Swiss Federal Institute of Technology, Zürich, Switzerland; Proton Therapy Center, Paul Scherrer Institute, PSI Villigen, Switzerland. Electronic address: kinga.bernatowicz@psi.ch.
authors.forename: Kinga
authors.initials: K
authors.lastname: Bernatowicz
authors.affiliation: Proton Therapy Center, Paul Scherrer Institute, PSI Villigen, Switzerland.
authors.forename: Marta
authors.initials: M
authors.lastname: Peroni
authors.affiliation: Proton Therapy Center, Paul Scherrer Institute, PSI Villigen, Switzerland.
authors.forename: Rosalind
authors.initials: R
authors.lastname: Perrin
authors.affiliation: Department of Physics, Swiss Federal Institute of Technology, Zürich, Switzerland; Department of Radiation Oncology, University Hospital of Zürich, Zürich, Switzerland.
authors.forename: Damien C
authors.initials: DC
authors.lastname: Weber
authors.affiliation: Department of Physics, Swiss Federal Institute of Technology, Zürich, Switzerland; Proton Therapy Center, Paul Scherrer Institute, PSI Villigen, Switzerland.
authors.forename: Antony
authors.initials: A
authors.lastname: Lomax
mesh_terms: D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008099:Liver / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009068:Movement; D064847:Multimodal Imaging / Q000379:methods*; D061766:Proton Therapy / Q000379:methods*; D011829:Radiation Dosage; D061089:Radiotherapy, Image-Guided / Q000379:methods; D012119:Respiration