title: Evaluation of a multi-atlas CT synthesis approach for MRI-only radiotherapy treatment planning.
abstract: OBJECTIVE
  Computed tomography (CT) imaging is the current gold standard for radiotherapy treatment planning (RTP). The establishment of a magnetic resonance imaging (MRI) only RTP workflow requires the generation of a synthetic CT (sCT) for dose calculation. This study evaluates the feasibility of using a multi-atlas sCT synthesis approach (sCTa) for head and neck and prostate patients.
  
  
  METHODS
  The multi-atlas method was based on pairs of non-rigidly aligned MR and CT images. The sCTawas obtained by registering the MRI atlases to the patient's MRI and by fusing the mapped atlases according to morphological similarity to the patient. For comparison, a bulk density assignment approach (sCTbda) was also evaluated. The sCTbdawas obtained by assigning density values to MRI tissue classes (air, bone and soft-tissue). After evaluating the synthesis accuracy of the sCTs (mean absolute error), sCT-based delineations were geometrically compared to the CT-based delineations. Clinical plans were re-calculated on both sCTs and a dose-volume histogram and a gamma analysis was performed using the CT dose as ground truth.
  
  
  RESULTS
  Results showed that both sCTs were suitable to perform clinical dose calculations with mean dose differences less than 1% for both the planning target volume and the organs at risk. However, only the sCTaprovided an accurate and automatic delineation of bone.
  
  
  CONCLUSIONS
  Combining MR delineations with our multi-atlas CT synthesis method could enable MRI-only treatment planning and thus improve the dosimetric and geometric accuracy of the treatment, and reduce the number of imaging procedures.
authors.affiliation: Faculty of Sciences, University of Lisbon, Campo Grande, Portugal; Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom. Electronic address: filipaguerreiro23@gmail.com.
authors.forename: F
authors.initials: F
authors.lastname: Guerreiro
authors.affiliation: Translational Imaging Group, Centre for Medical Imaging Computing, University College London, London, United Kingdom. Electronic address: n.burgos@ucl.ac.uk.
authors.forename: N
authors.initials: N
authors.lastname: Burgos
authors.affiliation: Royal Marsden Hospital, London, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Dunlop
authors.affiliation: Royal Marsden Hospital, London, United Kingdom.
authors.forename: K
authors.initials: K
authors.lastname: Wong
authors.affiliation: Royal Marsden Hospital, London, United Kingdom.
authors.forename: I
authors.initials: I
authors.lastname: Petkar
authors.affiliation: Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom; Royal Marsden Hospital, London, United Kingdom.
authors.forename: C
authors.initials: C
authors.lastname: Nutting
authors.affiliation: Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom; Royal Marsden Hospital, London, United Kingdom.
authors.forename: K
authors.initials: K
authors.lastname: Harrington
authors.affiliation: Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom; Royal Marsden Hospital, London, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Bhide
authors.affiliation: Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom; Royal Marsden Hospital, London, United Kingdom.
authors.forename: K
authors.initials: K
authors.lastname: Newbold
authors.affiliation: Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom; Royal Marsden Hospital, London, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Dearnaley
authors.affiliation: Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom; Royal Marsden Hospital, London, United Kingdom.
authors.forename: N M
authors.initials: NM
authors.lastname: deSouza
authors.affiliation: Royal Marsden Hospital, London, United Kingdom.
authors.forename: V A
authors.initials: VA
authors.lastname: Morgan
authors.affiliation: Centre for Medical Image Computing, Dept. Medical Physics and Biomedical Engineering, University College London, London, United Kingdom.
authors.forename: J
authors.initials: J
authors.lastname: McClelland
authors.affiliation: Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Nill
authors.affiliation: Translational Imaging Group, Centre for Medical Imaging Computing, University College London, London, United Kingdom.
authors.forename: M J
authors.initials: MJ
authors.lastname: Cardoso
authors.affiliation: Translational Imaging Group, Centre for Medical Imaging Computing, University College London, London, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Ourselin
authors.affiliation: Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom; Royal Marsden Hospital, London, United Kingdom.
authors.forename: U
authors.initials: U
authors.lastname: Oelfke
authors.affiliation: Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom.
authors.forename: A C
authors.initials: AC
authors.lastname: Knopf
mesh_terms: D000465:Algorithms; D001271:Atlases as Topic; D005240:Feasibility Studies; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009959:Oropharyngeal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: MRI-only radiotherapy workflow; Multi-atlas approach; Synthetic CT