title: A randomized comparison of interfraction and intrafraction prostate motion with and without abdominal compression.
abstract: OBJECTIVE
  To quantify inter- and intrafraction prostate motion in a standard VacLok (VL) immobilization device or in the BodyFix (BF) system incorporating a compression element which may reduce abdominal movement.
  
  
  METHODS
  Thirty-two patients were randomly assigned to VL or BF. Interfraction prostate motion >3 mm was corrected pre-treatment. EPIs were taken daily at the start and end of the first and last treatment beams. Interfraction and intrafraction prostate motion were measured for centre of mass (COM) and individual markers.
  
  
  RESULTS
  There were no significant differences in interfraction (p0.002) or intrafraction (p0.16) prostate motion with or without abdominal compression. Median intrafraction motion was slightly smaller than interfraction motion in the AP (7.0 mm vs. 7.6 mm) and SI direction (3.2 mm vs. 4.7 mm). The final image captured the maximal intrafraction displacement in only 40% of fractions. Our PTV incorporated >95% of total prostate motion.
  
  
  CONCLUSIONS
  Intrafraction motion became the major source of error during radiotherapy after online correction of interfraction prostate motion. The addition of 120 mbar abdominal compression to custom pelvic immobilization influenced neither interfraction nor intrafraction prostate motion.
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital, Toronto, Ont., Canada. Tara.Rosewall@rmp.uhn.on.ca
authors.forename: Tara
authors.initials: T
authors.lastname: Rosewall
authors.forename: Peter
authors.initials: P
authors.lastname: Chung
authors.forename: Andrew
authors.initials: A
authors.lastname: Bayley
authors.forename: Gina
authors.initials: G
authors.lastname: Lockwood
authors.forename: Hamideh
authors.initials: H
authors.lastname: Alasti
authors.forename: Robert
authors.initials: R
authors.lastname: Bristow
authors.forename: Vickie
authors.initials: V
authors.lastname: Kong
authors.forename: Michael
authors.initials: M
authors.lastname: Milosevic
authors.forename: Charles
authors.initials: C
authors.lastname: Catton
mesh_terms: D000005:Abdomen; D019583:Dose Fractionation, Radiation; D006801:Humans; D007103:Immobilization / Q000379:methods*; D008297:Male; D009068:Movement; D011312:Pressure; D011467:Prostate; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D019736:Prostheses and Implants; D015641:Radiography, Interventional; D018709:Statistics, Nonparametric; D016683:Supine Position; D014057:Tomography, X-Ray Computed