title: Interfractional prostate shifts: review of 1870 computed tomography (CT) scans obtained during image-guided radiotherapy using CT-on-rails for the treatment of prostate cancer.
abstract: OBJECTIVE
  To review 1870 CT scans of interfractional prostate shift obtained during image-guided radiotherapy.
  
  
  METHODS
  A total of 1870 pretreatment CT scans were acquired with CT-on-rails, and the corresponding shift data for 329 patients with prostate cancer were analyzed.
  
  
  RESULTS
  Of the 1870 scans reviewed, 44% required no setup adjustments in the anterior-posterior (AP) direction, 14% had shifts of 3-5 mm, 29% had shifts of 6-10 mm, and 13% had shifts of >10 mm. In the superior-inferior direction, 81% had no adjustments, 2% had shifts of 3-5 mm, 15% had shifts of 6-10 mm, and 2% had shifts of >10 mm. In the left-right direction, 65% had no adjustment, 13% had shifts of 3-5 mm, 17% had shifts of 6-10 mm, and 5% had shifts of >10 mm. Further analysis of the first 66 consecutive patients divided into three groups according to body mass index indicates that the shift in the AP direction for the overweight subgroup was statistically larger than those for the control and obese subgroups (p < 0.05). The interfractional shift in the lateral direction for the obese group (1 SD, 5.5 mm) was significantly larger than those for the overweight and control groups (4.1 and 2.9 mm, respectively) (p < 0.001).
  
  
  CONCLUSIONS
  These data demonstrate that there is a significantly greater shift in the AP direction than in the lateral and superior-inferior directions for the entire patient group. Overweight and obese patient groups show a significant difference from the control group in terms of prostate shift.
authors.affiliation: Department of Radiation Oncology, The Carol G. Simon Cancer Center, Morristown Memorial Hospital, Morristown, NJ, USA.
authors.forename: James R
authors.initials: JR
authors.lastname: Wong
authors.forename: Zhanrong
authors.initials: Z
authors.lastname: Gao
authors.forename: Minoru
authors.initials: M
authors.lastname: Uematsu
authors.forename: Scott
authors.initials: S
authors.lastname: Merrick
authors.forename: Nolan P
authors.initials: NP
authors.lastname: Machernis
authors.forename: Timothy
authors.initials: T
authors.lastname: Chen
authors.forename: Chee Wai
authors.initials: CW
authors.lastname: Cheng
mesh_terms: D015992:Body Mass Index; D001835:Body Weight; D004307:Dose-Response Relationship, Radiation; D017709:Fractals; D006801:Humans; D008297:Male; D009765:Obesity; D050177:Overweight; D011467:Prostate / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011877:Radionuclide Imaging; D011878:Radiotherapy / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods