title: Quantification of prostate and seminal vesicle interfraction variation during IMRT.
abstract: OBJECTIVE
  To quantify the interfraction variability in prostate and seminal vesicle (SV) positions during a course of intensity-modulated radiotherapy (IMRT) using an integrated computed tomography (CT)-linear accelerator system and to assess the impact of rectal and bladder volume changes.
  
  
  METHODS
  We studied 15 patients who had undergone IMRT for prostate carcinoma. Patients had one pretreatment planning CT scan followed by three in-room CT scans per week using a CT-on-rails system. The prostate, bladder, rectum, and pelvic bony anatomy were contoured in 369 CT scans. Using the planning CT scan as a reference, the volumetric and positional changes were analyzed in the subsequent CT scans.
  
  
  RESULTS
  For all 15 patients, the mean systematic internal prostate and SV variation was 0.1 +/- 4.1 mm and 1.2 +/- 7.3 mm in the anteroposterior axis, -0.5 +/- 2.9 mm and -0.7 +/- 4.5 mm in the superoinferior axis, and 0.2 +/- 0.9 mm and -0.9 +/- 1.9 mm in the lateral axis, respectively. The mean magnitude of the three-dimensional displacement vector was 4.6 +/- 3.5 mm for the prostate and 7.6 +/- 4.7 mm for the SVs. The rectal and bladder volume changes during treatment correlated with the anterior and superior displacement of the prostate and SVs.
  
  
  CONCLUSIONS
  The dominant prostate and SV variations occurred in the anteroposterior and superoinferior directions. The systematic prostate and SV variation between the treatment planning CT and daily therapy as a result of the rectal and bladder volume changes emphasizes the need for daily directed target localization and/or immobilization techniques.
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA. sjfrank@mdanderson.org
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Frank
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
authors.forename: Rajat J
authors.initials: RJ
authors.lastname: Kudchadker
authors.forename: Renaud
authors.initials: R
authors.lastname: De Crevoisier
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Lee
authors.forename: Rex
authors.initials: R
authors.lastname: Cheung
authors.forename: Seungtaek
authors.initials: S
authors.lastname: Choi
authors.forename: Jennifer
authors.initials: J
authors.lastname: O'Daniel
authors.forename: Susan L
authors.initials: SL
authors.lastname: Tucker
authors.forename: He
authors.initials: H
authors.lastname: Wang
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Kuban
mesh_terms: D000328:Adult; D001822:Body Burden; D006801:Humans; D008297:Male; D008875:Middle Aged; D009928:Organ Specificity; D011467:Prostate; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D015203:Reproducibility of Results; D012669:Seminal Vesicles; D012680:Sensitivity and Specificity