title: The analysis of respiration-induced pancreatic tumor motion based on reference measurement.
abstract: BACKGROUND
  To evaluate pancreatic tumor motion and its dynamics during respiration.
  
  
  METHODS
  This retrospective study includes 20 patients with unresectable pancreatic cancer who were treated with stereotactic ablative radiotherapy. An online respiratory tumor tracking system was used. Periodical maximum and minimum tumor positions with respiration in superior-inferior (SI), latero-lateral (LL), and anterior-posterior (AP) directions were collected for tumor motion evaluation. The predictability of tumor motion in each axis, based on reference measurement, was analyzed.
  
  
  RESULTS
  The use of a 20-mm and 5-mm constant margins for SI and LL/AP directions, avoids target underdosage, without the need for reference measurement. Pearson's correlation coefficient indicated only a modest correlation between reference and subsequent measurements in the SI direction (r = 0.50) and no correlation in LL (r = 0.17) and AP (r = 0.35) directions. When margins based on the reference measurement of respiratory tumor motion are used, then 30% of patients have a risk zone of underdosage >3 mm (in average). ITV (internal target volume) optimization based on the reference measurement is possible, but allows only modest margin reduction (approximately from 20 mm to 16-17 mm) in SI direction and no reduction in AP and LL directions.
  
  
  CONCLUSIONS
  Our results support the use of 20-mm margin in the SI direction and 5-mm margins in the LL and AP directions to account for respiratory motion without reference measurement. Single measurement of tumor motion allows only modest margin reduction. Further margin reduction is only possible when there is on-line tumor motion control according to internal markers.
authors.affiliation: Department of Oncology, University Hospital Ostrava, 17, listopadu 1790, 708 52 Ostrava, Czech Republic. lukas.knybel@fno.cz.
authors.forename: Lukas
authors.initials: L
authors.lastname: Knybel
authors.forename: Jakub
authors.initials: J
authors.lastname: Cvek
authors.forename: Bretislav
authors.initials: B
authors.lastname: Otahal
authors.forename: Tomas
authors.initials: T
authors.lastname: Jonszta
authors.forename: Lukas
authors.initials: L
authors.lastname: Molenda
authors.forename: Daniel
authors.initials: D
authors.lastname: Czerny
authors.forename: Eva
authors.initials: E
authors.lastname: Skacelikova
authors.forename: Marian
authors.initials: M
authors.lastname: Rybar
authors.forename: Pavel
authors.initials: P
authors.lastname: Dvorak
authors.forename: David
authors.initials: D
authors.lastname: Feltl
mesh_terms: D016477:Artifacts; D002277:Carcinoma / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D009038:Motion; D010190:Pancreatic Neoplasms / Q000601:surgery*; D016634:Radiosurgery; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D012189:Retrospective Studies