title: Are fiducial markers useful surrogates when using respiratory gating to reduce motion of gastroesophageal junction tumors?
abstract: BACKGROUND
  Radiation therapy (RT) is an integral component of the management of gastroesophageal junction (GEJ) tumors. We evaluated the use of implanted radiopaque fiducials as tumor surrogates to allow for more focal delivery of RT to these mobile tumors when using respiratory gating (RG) to reduce motion.
  
  
  METHODS
  We analyzed four-dimensional computed tomography scans of 20 GEJ patients treated with RG and assessed correlation between tumor and implanted fiducial motion over the whole respiratory cycle and within a clinically realistic gate around end-exhalation. We evaluated fiducial motion concordance in 11 patients with multiple fiducials.
  
  
  RESULTS
  Gating reduced anterior-posterior (AP) and superior-inferior (SI) mean tumor and fiducial motions by over 50%. Fiducials and primary tumor motions were moderately correlated: R(2) for AP and SI linear fits to the entire group were 0.54 and 0.68, respectively, but the correlation had strong inter-patient variation. For all patients with multiple fiducials, relative in-gate displacements were below 3 mm; results were similar for eight of 11 patients over the whole cycle.
  
  
  CONCLUSIONS
  Implanted fiducial and gross tumor volume (GTV) motions correlate well but the correlation is patient-specific and may be dependent on the location of the fiducials with respect to the GTV.
authors.affiliation: a Department of Medical Physics , Memorial Sloan Kettering Cancer Center , New York , New York , USA ;
authors.forename: Fenghong
authors.initials: F
authors.lastname: Liu
authors.affiliation: b Department of Radiation Oncology , Memorial Sloan Kettering Cancer Center , New York , New York , USA ;
authors.forename: Shu
authors.initials: S
authors.lastname: Ng
authors.affiliation: c Department of Radiation Oncology , Hôpital Tenon , Paris , France.
authors.forename: Florence
authors.initials: F
authors.lastname: Huguet
authors.affiliation: a Department of Medical Physics , Memorial Sloan Kettering Cancer Center , New York , New York , USA ;
authors.forename: Ellen D
authors.initials: ED
authors.lastname: Yorke
authors.affiliation: a Department of Medical Physics , Memorial Sloan Kettering Cancer Center , New York , New York , USA ;
authors.forename: Gikas S
authors.initials: GS
authors.lastname: Mageras
authors.affiliation: b Department of Radiation Oncology , Memorial Sloan Kettering Cancer Center , New York , New York , USA ;
authors.forename: Karyn A
authors.initials: KA
authors.lastname: Goodman
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology / Q000532:radiotherapy*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004938:Esophageal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D004943:Esophagogastric Junction / Q000473:pathology; D005260:Female; D057918:Fiducial Markers; D056973:Four-Dimensional Computed Tomography / Q000379:methods; D006801:Humans; D008297:Male; D008875:Middle Aged; D009038:Motion; D010190:Pancreatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration