title: Daily bone alignment with limited repeat CT correction rivals daily ultrasound alignment for prostate radiotherapy.
abstract: OBJECTIVE
  To compare the effectiveness of daily ultrasound (US)- and computed tomography (CT)-guided alignments with an off-line correction protocol using daily bone alignment plus a correction factor for systematic internal prostate displacement (CF(ID)).
  
  
  METHODS
  Ten prostate cancer patients underwent CT scans three times weekly using an integrated CT-linear accelerator system, followed by alignment using US for daily radiotherapy. Intensity-modulated radiotherapy plans were designed with our current clinical margins. The treatment plan was copied onto the repeat CT images and aligned using several methods: (1) bone alignment plus CF(ID) after three off-line CT scans (bone+3CT), (2) bone alignment plus CF(ID) after six off-line CT scans (bone+6CT), (3) US alignment, and (4) CT alignment. The accuracy of the repeated US and CT measurements to determine the CF(ID) was compared. The target dosimetric effect was quantified.
  
  
  RESULTS
  The CF(ID) for internal systematic prostate displacements was more accurately measured with limited repeat CT scans than with US (residual error, 0.0 +/- 0.7 mm vs. 2.0 +/- 3.2 mm). Bone+3CT, bone+6CT, and US provided equivalent prostate and seminal vesicle dose coverage, but bone+3CT and bone+6CT produced more precise daily alignments. Daily CT alignment provided the greatest target dose coverage.
  
  
  CONCLUSIONS
  Daily bone alignment plus CF(ID) for internal systematic prostate displacement provided better daily alignment precision and equivalent dose coverage compared with daily US alignment. The CF(ID) should be based on at least three repeat CT scans, which could be collected before the start of treatment or during the first 3 treatment days. Daily bone alignment plus CF(ID) provides another option for accurate prostate cancer patient positioning.
authors.affiliation: Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: O'Daniel
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
authors.forename: Lifei
authors.initials: L
authors.lastname: Zhang
authors.forename: He
authors.initials: H
authors.lastname: Wang
authors.forename: Susan L
authors.initials: SL
authors.lastname: Tucker
authors.forename: Rajat J
authors.initials: RJ
authors.lastname: Kudchadker
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Lee
authors.forename: Rex
authors.initials: R
authors.lastname: Cheung
authors.forename: James D
authors.initials: JD
authors.lastname: Cox
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Kuban
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
mesh_terms: D000465:Algorithms; D002138:Calibration; D002985:Clinical Protocols; D006801:Humans; D008297:Male; D009068:Movement; D010384:Pelvic Bones / Q000000981:diagnostic imaging; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012015:Reference Standards; D014057:Tomography, X-Ray Computed / Q000379:methods; D014463:Ultrasonography