title: Assessment of organ motion in postoperative endometrial and cervical cancer patients treated with intensity-modulated radiation therapy.
abstract: OBJECTIVE
  Intensity-modulated radiation therapy (IMRT) may be useful to reduce toxicity in gynecologic cancer patients requiring postoperative pelvic irradiation. This study was undertaken to quantify vaginal wall organ motion during the course of postoperative pelvic irradiation using pelvic IMRT.
  
  
  METHODS
  Twenty-two consecutive patients treated with postoperative pelvic IMRT on helical tomotherapy had fiducial markers placed at the vaginal apex prior to simulation then daily megavoltage computed tomography (CT) scans for positioning. The daily positions of the fiducials were registered and measured in reference to the initial CT scan to quantify the degree of vaginal wall organ motion during the entire course of therapy.
  
  
  RESULTS
  The total motion of the fiducials center of mass (COM) was a median of 5.8 mm (range, 0.6-20.2 mm), and 95% of all COM positions fell within 15.7 mm of their original position. Directional margins of 3.1 mm along the right-left axis, 9.5 mm along the superoinferior axis, and of 12.1 mm along the anteroposterior axis encompassed the vaginal fiducials in 95% of treatments. Mean organ deformation for all patients was 3.9 mm, (range, 0-27.5 mm; standard deviation, 3.1 mm), with significant distortions of greater than 10 mm in 17% of secondary image sets.
  
  
  CONCLUSIONS
  These data suggest a planning target volume margin of 16 mm will account for maximal organ motion in the majority of gynecologic patients undergoing postoperative pelvic IMRT, and it may be possible to incorporate directional motion into the planning target volume margin.
authors.affiliation: Department of Radiation Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL 33612, USA. Eleanor.harris@moffitt.org
authors.forename: Eleanor E R
authors.initials: EE
authors.lastname: Harris
authors.forename: Kujtim
authors.initials: K
authors.lastname: Latifi
authors.forename: Chad
authors.initials: C
authors.lastname: Rusthoven
authors.forename: Ken
authors.initials: K
authors.lastname: Javedan
authors.forename: Kenneth
authors.initials: K
authors.lastname: Forster
mesh_terms: D016889:Endometrial Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D005260:Female; D057918:Fiducial Markers; D006801:Humans; D009068:Movement; D011859:Radiography; D061089:Radiotherapy, Image-Guided / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D047368:Tumor Burden; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D014621:Vagina / Q000000981:diagnostic imaging*