title: Daily variations in the position of the prostate bed in patients with prostate cancer receiving postoperative external beam radiation therapy.
abstract: OBJECTIVE
  The aim of this study was to evaluate the extent of the variation in the position of the prostate bed with respect to the bony anatomy.
  
  
  METHODS
  Four patients were treated to 70 Gy in 35 fractions. Before each fraction, a megavoltage computed tomography (CT) of the prostate bed was obtained, resulting in a total of 140 CT studies. Retrospectively, each CT scan was aligned to the simulation kilovoltage scan based on bony anatomy and the prostate bed. The difference between the 2 alignments was calculated for each scan.
  
  
  RESULTS
  The average differences (+/-1 SD) between the two alignments were 0.06+/-0.37, 0.10+/-0.86, and 0.39+/-1.27 mm in the lateral, longitudinal (SI), and vertical (AP) directions, respectively. Laterally, there was no difference>or=3 mm. The cumulative frequency of SI differences were as follows; >or=3 mm: 3%, >or=4 mm: 1%, and >or=5 mm: 1% (maximum: 5 mm). The cumulative frequency of AP differences were as follows; >or=3 mm: 7%, and >or=4 mm: 3% (maximum: 4 mm).
  
  
  CONCLUSIONS
  In patients with prostate cancer receiving postoperative radiotherapy, the prostate bed motion relative to the pelvic bony anatomy is of a relatively small magnitude. Significant motion (>or=3 mm) is infrequent. However, small differences between the prostate bed and the bony anatomy still exist. This might have implications on treatment margins when daily alignment on bony anatomy is performed.
authors.affiliation: Department of Radiation Oncology, M. D. Anderson Cancer Center Orlando, Orlando, FL 32806, USA. patrick.kupelian@orhs.org
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Kupelian
authors.forename: Katja M
authors.initials: KM
authors.lastname: Langen
authors.forename: Twyla R
authors.initials: TR
authors.lastname: Willoughby
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Wagner
authors.forename: Omar A
authors.initials: OA
authors.lastname: Zeidan
authors.forename: Sanford L
authors.initials: SL
authors.lastname: Meeks
mesh_terms: D006801:Humans; D008297:Male; D009068:Movement; D011184:Postoperative Period; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000601:surgery; D012669:Seminal Vesicles; D013997:Time Factors; D036542:Tomography, Spiral Computed