title: Issues in respiratory motion compensation during external-beam radiotherapy.
abstract: OBJECTIVE
  To investigate how respiration influences the motion of lung and pancreas tumors and to relate the observations to treatment procedures intended to improve dose alignment by predicting the moving tumor's position from external breathing indicators.
  
  
  METHODS
  Breathing characteristics for five healthy subjects were observed by optically tracking the displacement of the chest and abdomen, and by measuring tidal air volume with a spirometer. Fluoroscopic imaging of five radiotherapy patients detected the motion of lung and pancreas tumors synchronously with external breathing indicators.
  
  
  RESULTS
  The external and fluoroscopic data showed a wide range of behavior in the normal breathing pattern and its effects on the position of lung and pancreas tumors. This included transient phase shifts between two different external measures of breathing that diminished to zero over a period of minutes, modulated phase shifts between tumor and chest wall motion, and other complex phenomena.
  
  
  CONCLUSIONS
  Respiratory compensation strategies that infer tumor position from external breathing signals, including methods of beam gating and dynamic beam tracking, require three-dimensional knowledge of the tumor's motion trajectory as well as the ability to detect and adapt to transient and continuously changing characteristics of respiratory motion during treatment.
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Cihat
authors.initials: C
authors.lastname: Ozhasoglu
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Murphy
mesh_terms: D000005:Abdomen; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D009068:Movement; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D055585:Physical Phenomena; D010825:Physics; D011859:Radiography; D012119:Respiration; D013909:Thorax