title: Quantification and comparison of visibility and image artifacts of a new liquid fiducial marker in a lung phantom for image-guided radiation therapy.
abstract: OBJECTIVE
  A new biodegradable liquid fiducial marker was devised to allow for easy insertion in lung tumors using thin needles. The purpose of this study was to evaluate the visibility of the liquid fiducial markers for image-guided radiation therapy and compare to existing solid fiducial markers and to one existing liquid fiducial marker currently commercially available.
  
  
  METHODS
  Fiducial marker visibility was quantified in terms of contrast to noise ratio (CNR) on planar kilovoltage x-ray images in a thorax phantom for different concentrations of the radio-opaque component of the new liquid fiducial marker, four solid fiducial markers, and one existing liquid fiducial marker. Additionally, the image artifacts produced on computer tomography (CT) and cone-beam CT (CBCT) of all fiducial markers were quantified.
  
  
  RESULTS
  The authors found that the new liquid fiducial marker with the highest concentration of the radio-opaque component had a CNR > 2.05 for 62/63 exposures, which compared favorably to the existing solid fiducial markers and to the existing liquid fiducial marker evaluated. On CT and CBCT, the new liquid fiducial marker with the highest concentration produced lower streaking index artifact (30 and 14, respectively) than the solid gold markers (113 and 20, respectively) and the existing liquid fiducial marker (39 and 20, respectively). The size of the image artifact was larger for all of the liquid fiducial markers compared to the solid fiducial markers because of their larger physical size.
  
  
  CONCLUSIONS
  The visibility and the image artifacts produced by the new liquid fiducial markers were comparable to existing solid fiducial markers and the existing liquid fiducial marker. The authors conclude that the new liquid fiducial marker represents an alternative to the fiducial markers tested.
authors.affiliation: Department of Oncology, Section of Radiotherapy, 3994, Rigshospitalet, Blegdamsvej 9, Copenhagen 2100, Denmark and Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen 2100, Denmark.
authors.forename: Jonas
authors.initials: J
authors.lastname: Scherman Rydhög
authors.affiliation: DTU Nanotech, Department of Micro- and Nanotechnology, Center for Nanomedicine and Theranostics, Technical University of Denmark, Building 423, Kongens Lyngby 2800, Denmark.
authors.forename: Rasmus
authors.initials: R
authors.lastname: Irming Jølck
authors.affiliation: DTU Nanotech, Department of Micro- and Nanotechnology, Center for Nanomedicine and Theranostics, Technical University of Denmark, Building 423, Kongens Lyngby 2800, Denmark.
authors.forename: Thomas Lars
authors.initials: TL
authors.lastname: Andresen
authors.affiliation: Department of Oncology, Section of Radiotherapy, 3994, Rigshospitalet, Blegdamsvej 9, Copenhagen 2100, Denmark and Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, Copenhagen 2100, Denmark.
authors.forename: Per
authors.initials: P
authors.lastname: Munck Af Rosenschöld
mesh_terms: D016477:Artifacts; D054893:Cone-Beam Computed Tomography; D057918:Fiducial Markers; D008168:Lung / Q000000981:diagnostic imaging* / Q000528:radiation effects*; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation* / Q000592:standards*; D059629:Signal-To-Noise Ratio