title: Incidence of changes in respiration-induced tumor motion and its relationship with respiratory surrogates during individual treatment fractions.
abstract: OBJECTIVE
  To determine how frequently (1) tumor motion and (2) the spatial relationship between tumor and respiratory surrogate markers change during a treatment fraction in lung and pancreas cancer patients.
  
  
  METHODS
  A Cyberknife Synchrony system radiographically localized the tumor and simultaneously tracked three respiratory surrogate markers fixed to a form-fitting vest. Data in 55 lung and 29 pancreas fractions were divided into successive 10-min blocks. Mean tumor positions and tumor position distributions were compared across 10-min blocks of data. Treatment margins were calculated from both 10 and 30 min of data. Partial least squares (PLS) regression models of tumor positions as a function of external surrogate marker positions were created from the first 10 min of data in each fraction; the incidence of significant PLS model degradation was used to assess changes in the spatial relationship between tumors and surrogate markers.
  
  
  RESULTS
  The absolute change in mean tumor position from first to third 10-min blocks was >5 mm in 13% and 7% of lung and pancreas cases, respectively. Superior-inferior and medial-lateral differences in mean tumor position were significantly associated with the lobe of lung. In 61% and 54% of lung and pancreas fractions, respectively, margins calculated from 30 min of data were larger than margins calculated from 10 min of data. The change in treatment margin magnitude for superior-inferior motion was >1 mm in 42% of lung and 45% of pancreas fractions. Significantly increasing tumor position prediction model error (mean ± standard deviation rates of change of 1.6 ± 2.5 mm per 10 min) over 30 min indicated tumor-surrogate relationship changes in 63% of fractions.
  
  
  CONCLUSIONS
  Both tumor motion and the relationship between tumor and respiratory surrogate displacements change in most treatment fractions for patient in-room time of 30 min.
authors.affiliation: Department of Bioengineering, A. James Clark School of Engineering, University of Maryland, College Park, MD, USA.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Malinowski
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: McAvoy
authors.forename: Rohini
authors.initials: R
authors.lastname: George
authors.forename: Sonja
authors.initials: S
authors.lastname: Dietrich
authors.forename: Warren D
authors.initials: WD
authors.lastname: D'Souza
mesh_terms: D000704:Analysis of Variance; D019583:Dose Fractionation, Radiation; D057918:Fiducial Markers; D006801:Humans; D016018:Least-Squares Analysis; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D009068:Movement; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D011859:Radiography; D016634:Radiosurgery / Q000379:methods*; D012119:Respiration; D012189:Retrospective Studies; D013997:Time Factors