title: A new lung stent tested as fiducial marker in a porcine model.
abstract: BACKGROUND
  The aim of the present study was to test the feasibility of a Nickel-Titanium (Ni-Ti) stent technique (Memocore™) in a porcine model. The stent is intended as a new fiducial for gated image guided radiotherapy in the lung. The study included test of an improved insertion system and respiratory gated treatments with this new technique.
  
  
  METHODS
  Tests were carried out in a porcine model using Göttingen mini-pigs. The study included 10 animals. Planning CT was performed as 4 dimensional CT (4DCT) using the Varian RPM system. Respiratory gated radiotherapy treatments were simulated using the Brainlab ExacTrac system. Reproducibility of stent position during treatment was analyzed off-line using an experimental version of the ExacTrac software. The experimental version has a dedicated algorithm for segmentation of the stent in the planning CT and subsequent registration to X-ray position images.
  
  
  RESULTS
  A total of 23 stents were inserted in the 10 animals. Stents could be placed in all parts of the lungs. No stent migrated within the four weeks the experiment lasted. Stent trajectories in the lung were not reproducible, even though respiration was highly standardized using a respirator. The best accuracy of stent position in the gating window was obtained using gating at the half_max amplitude as reference level. The smallest stent movement within the gating window was observed in the exhale phase. Further success of human application will depend on the possibility to insert the stent within or close to lung tumors.
  
  
  CONCLUSIONS
  This new technique based on the Memocore™ lung stent used in connection with respiratory gated radiotherapy was demonstrated to be feasible in a porcine model. The study demonstrated lack of reproducibility in lung trajectories of inserted stents. The technique gave the best accuracy when applied to the exhale phase of respiration.
authors.affiliation: Dept. of Medical Physics, Oncology, Aalborg Hospital, Aarhus University Hospital, Denmark. jhc@rn.dk
authors.forename: Jesper
authors.initials: J
authors.lastname: Carl
authors.forename: Jane
authors.initials: J
authors.lastname: Nielsen
authors.forename: Martin Skovmos
authors.initials: MS
authors.lastname: Nielsen
authors.forename: Peter Rose
authors.initials: PR
authors.lastname: Zepernick
authors.forename: Benedict
authors.initials: B
authors.lastname: Kjaergaard
authors.forename: Henrik Kirstein
authors.initials: HK
authors.lastname: Jensen
mesh_terms: D000465:Algorithms; D000818:Animals; D005240:Feasibility Studies; D057918:Fiducial Markers; D008168:Lung; D008175:Lung Neoplasms / Q000532:radiotherapy; D023421:Models, Animal; D009532:Nickel; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012119:Respiration; D015607:Stents; D013552:Swine; D013556:Swine, Miniature; D014025:Titanium; D014057:Tomography, X-Ray Computed
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium