title: Stability of markers used for real-time tumor tracking after percutaneous intrapulmonary placement.
abstract: OBJECTIVE
  To determine the stability of markers used for real-time tumor tracking after percutaneous intrapulmonary placement.
  
  
  METHODS
  A total of 42 patients with 44 lesions, 111 markers, and ≥2 repeat computed tomography (CT) scans were studied. The tumor on the repeat CT scans was registered with the tumor on the planning CT scan. Next, the three-dimensional marker coordinates were determined on the planning CT scan and repeat CT scans. Marker stability was analyzed by the displacement of the markers and the displacement of the center of mass (COM) of the marker configurations. In addition, we assessed the reliability of using the intermarker distance as a check for displacements in the COM of the marker configurations.
  
  
  RESULTS
  The median marker displacement was 1.3 mm (range, 0.1-53.6). The marker displacement was >5 mm in 12% of the markers and >10 mm in 5% of the markers. The causes of marker displacement >5 mm included marker migration (2 of 13) and target volume changes (5 of 13). Nonsynchronous tumor and marker movement during breathing might have been responsible for the displacements >5 mm in the other 6 of 13 markers. The median displacement in the COM of the marker configurations was 1.0 mm (range, 0.1-23.3). Displacements in the COM of the marker configurations of ≥2.0 mm were detected by changes in the intermarker distance of >1.5 mm in 96% of the treatment fractions.
  
  
  CONCLUSIONS
  The median marker displacement was small (1.3 mm). Nevertheless, displacements >5 mm occurred in 12% of the markers. Therefore, we recommend the implantation of multiple markers because multiple markers will enable a quick and reliable check of marker displacement by determining the change in the intermarker distance. A displacement in the COM of the marker configuration of ≥2.0 mm was almost always detected (96%) by a change in the distance between the markers of >1.5 mm. This enabled the displaced marker to be disabled, such that tumor localization was not compromised.
authors.affiliation: Department of Radiation Oncology, Erasmus Medical Center-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands. n.vandervoortvanzyp@erasmusmc.nl
authors.forename: Noëlle C
authors.initials: NC
authors.lastname: van der Voort van Zyp
authors.forename: Mischa S
authors.initials: MS
authors.lastname: Hoogeman
authors.forename: Steven
authors.initials: S
authors.lastname: van de Water
authors.forename: Peter C
authors.initials: PC
authors.lastname: Levendag
authors.forename: Bronno
authors.initials: B
authors.lastname: van der Holt
authors.forename: Ben J M
authors.initials: BJ
authors.lastname: Heijmen
authors.forename: Joost J
authors.initials: JJ
authors.lastname: Nuyttens
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D045853:Exhalation; D005260:Female; D057918:Fiducial Markers; D005548:Foreign-Body Migration / Q000000981:diagnostic imaging*; D006801:Humans; D016014:Linear Models; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D008297:Male; D010984:Platinum; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden
chemical_list: D010984:Platinum