title: Impact of respiratory-correlated CT sorting algorithms on the choice of margin definition for free-breathing lung radiotherapy treatments.
abstract: To investigate the impact of Toshiba phase- and amplitude-sorting algorithms on the margin strategies for free-breathing lung radiotherapy treatments in the presence of breathing variations.
  
  
  
  4D CT of a sphere inside a dynamic thorax phantom was acquired. The 4D CT was reconstructed according to the phase- and amplitude-sorting algorithms. The phantom was moved by reproducing amplitude, frequency, and a mix of amplitude and frequency variations. Artefact analysis was performed for Mid-Ventilation and ITV-based strategies on the images reconstructed by phase- and amplitude-sorting algorithms. The target volume deviation was assessed by comparing the target volume acquired during irregular motion to the volume acquired during regular motion.
  
  
  
  The amplitude-sorting algorithm shows reduced artefacts for only amplitude variations while the phase-sorting algorithm for only frequency variations. For amplitude and frequency variations, both algorithms perform similarly. Most of the artefacts are blurring and incomplete structures. We found larger artefacts and volume differences for the Mid-Ventilation with respect to the ITV strategy, resulting in a higher relative difference of the surface distortion value which ranges between maximum 14.6% and minimum 4.1%.
  
  
  
  The amplitude- is superior to the phase-sorting algorithm in the reduction of motion artefacts for amplitude variations while phase-sorting for frequency variations. A proper choice of 4D CT sorting algorithm is important in order to reduce motion artefacts, especially if Mid-Ventilation strategy is used.
authors.affiliation: Institute of Radiation Physics, Lausanne University Hospital, Switzerland.
authors.forename: Sheeba
authors.initials: S
authors.lastname: Thengumpallil
authors.affiliation: Institute of Radiation Physics, Lausanne University Hospital, Switzerland.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Germond
authors.affiliation: Radio-Oncology Department, Lausanne University Hospital, Switzerland.
authors.forename: Jean
authors.initials: J
authors.lastname: Bourhis
authors.affiliation: Institute of Radiation Physics, Lausanne University Hospital, Switzerland.
authors.forename: François
authors.initials: F
authors.lastname: Bochud
authors.affiliation: Institute of Radiation Physics, Lausanne University Hospital, Switzerland.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Moeckli
mesh_terms: D000465:Algorithms; D016477:Artifacts; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D009038:Motion; D019047:Phantoms, Imaging; D012119:Respiration; D047368:Tumor Burden
keywords: 4D CT; Artefacts; Breathing variations; ITV; MidV; Sorting algorithms