title: Real-time tumor tracking in the lung using an electromagnetic tracking system.
abstract: OBJECTIVE
  To describe the first use of the commercially available Calypso 4D Localization System in the lung.
  
  
  METHODS
  Under an institutional review board-approved protocol and an investigational device exemption from the US Food and Drug Administration, the Calypso system was used with nonclinical methods to acquire real-time 4-dimensional lung tumor tracks for 7 lung cancer patients. The aims of the study were to investigate (1) the potential for bronchoscopic implantation; (2) the stability of smooth-surface beacon transponders (transponders) after implantation; and (3) the ability to acquire tracking information within the lung. Electromagnetic tracking was not used for any clinical decision making and could only be performed before any radiation delivery in a research setting. All motion tracks for each patient were reviewed, and values of the average displacement, amplitude of motion, period, and associated correlation to a sinusoidal model (R(2)) were tabulated for all 42 tracks.
  
  
  RESULTS
  For all 7 patients at least 1 transponder was successfully implanted. To assist in securing the transponder at the tumor site, it was necessary to implant a secondary fiducial for most transponders owing to the transponder's smooth surface. For 3 patients, insertion into the lung proved difficult, with only 1 transponder remaining fixed during implantation. One patient developed a pneumothorax after implantation of the secondary fiducial. Once implanted, 13 of 14 transponders remained stable within the lung and were successfully tracked with the tracking system.
  
  
  CONCLUSIONS
  Our initial experience with electromagnetic guidance within the lung demonstrates that transponder implantation and tracking is achievable though not clinically available. This research investigation proved that lung tumor motion exhibits large variations from fraction to fraction within a single patient and that improvements to both transponder and tracking system are still necessary to create a clinical daily-use system to assist with actual lung radiation therapy.
authors.affiliation: Department of Radiation Oncology, MD Anderson Cancer Center Orlando, Orlando, FL 32806, USA. Amish.Shah@orlandohealth.com
authors.forename: Amish P
authors.initials: AP
authors.lastname: Shah
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Kupelian
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Waghorn
authors.forename: Twyla R
authors.initials: TR
authors.lastname: Willoughby
authors.forename: Justin M
authors.initials: JM
authors.lastname: Rineer
authors.forename: Rafael R
authors.initials: RR
authors.lastname: Mañon
authors.forename: Mark A
authors.initials: MA
authors.lastname: Vollenweider
authors.forename: Sanford L
authors.initials: SL
authors.lastname: Meeks
mesh_terms: D001999:Bronchoscopy; D004574:Electromagnetic Fields; D057918:Fiducial Markers / Q000009:adverse effects; D006801:Humans; D020007:Implants, Experimental; D008168:Lung / Q000000981:diagnostic imaging; D008175:Lung Neoplasms / Q000000981:diagnostic imaging; D009068:Movement; D011030:Pneumothorax / Q000209:etiology; D019736:Prostheses and Implants; D011859:Radiography; D012371:Robotics / Q000379:methods*