title: Rectal motion in patients receiving preoperative radiotherapy for carcinoma of the rectum.
abstract: OBJECTIVE
  To assess the movement of rectum, mesorectum, and rectal primary during a course of preoperative chemoradiotherapy.
  
  
  METHODS
  Seventeen patients with Stage II or III rectal cancer had a planning CT scan with rectal contrast before commencement of preoperative chemoradiation. The scan was repeated during Weeks 1, 3, and 5 of chemoradiation. The rectal primary (gross tumor volume), rectum, mesorectum, and bladder were contoured on all four scans. An in-house biomechanical model-based deformable image registration technique, Morfeus, was used to measure the three-dimensional spatial change in these structures after bony alignment. The required planning target volume margin for this spatial change, after bone alignment, was also calculated.
  
  
  RESULTS
  Rectal contrast was found to introduce a systematic error in the position of all organs compared with the noncontrast state. The largest change in structures during radiotherapy was in the anterior and posterior directions for the mesorectum and rectum and in the superior and inferior directions for the gross tumor volume. The planning target volume margins required for internal movement for the mesorectum based on the three scans acquired during treatment are 4 mm right, 5 mm left, 7 mm anterior, and 6 mm posterior. For the rectum, values were 8 mm right, 8 mm left, 8 mm anterior, and 9 mm posterior. The greatest movement of the rectum occurred in the upper third.
  
  
  CONCLUSIONS
  Contrast is no longer used in CT simulation. Assuming bony alignment, a nonuniform margin of 8 mm anteriorly, 9 mm posteriorly, and 8 mm left and right is recommended.
authors.affiliation: Department of Radiation Medicine, Princess Margaret Hospital, University Health Network, Toronto, ON, Canada. james.brierley@rmp.uhn.on.ca
authors.forename: James D
authors.initials: JD
authors.lastname: Brierley
authors.forename: Laura A
authors.initials: LA
authors.lastname: Dawson
authors.forename: Elliott
authors.initials: E
authors.lastname: Sampson
authors.forename: Andrew
authors.initials: A
authors.lastname: Bayley
authors.forename: Sandra
authors.initials: S
authors.lastname: Scott
authors.forename: Joanne L
authors.initials: JL
authors.lastname: Moseley
authors.forename: Timothy
authors.initials: T
authors.lastname: Craig
authors.forename: Bernard
authors.initials: B
authors.lastname: Cummings
authors.forename: Robert
authors.initials: R
authors.lastname: Dinniwell
authors.forename: John J
authors.initials: JJ
authors.lastname: Kim
authors.forename: Jolie
authors.initials: J
authors.lastname: Ringash
authors.forename: Rebecca
authors.initials: R
authors.lastname: Wong
authors.forename: Kristy K
authors.initials: KK
authors.lastname: Brock
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000627:therapeutic use; D003131:Combined Modality Therapy / Q000379:methods; D003287:Contrast Media; D005472:Fluorouracil / Q000627:therapeutic use; D006801:Humans; D009068:Movement; D056888:Patient Positioning; D010384:Pelvic Bones / Q000000981:diagnostic imaging; D011300:Preoperative Care; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy / Q000601:surgery; D012007:Rectum / Q000000981:diagnostic imaging*; D047368:Tumor Burden; D001743:Urinary Bladder / Q000000981:diagnostic imaging
chemical_list: D000964:Antimetabolites, Antineoplastic; D003287:Contrast Media; D005472:Fluorouracil