title: Ultrasound-based image guided radiotherapy for prostate cancer: comparison of cross-modality and intramodality methods for daily localization during external beam radiotherapy.
abstract: OBJECTIVE
  To compare two different ultrasound-based verification systems for prostate alignment during daily external beam radiation therapy (EBRT) for localized prostate cancer.
  
  
  METHODS
  Prostate displacements were measured prospectively in 40 patients undergoing daily EBRT. Comparison was made between a system based on the cross-modality verification method (CMVM), which uses two different imaging modalities to assess organ motion, and a system based on the intramodality verification method (IMVM), which uses only one imaging modality for such assessment. A total of 217 CMVM and 217 IMVM displacements were collected within a minute of each other. In 10 patients, IMVM displacements were also compared with those measured by sequential CT scans.
  
  
  RESULTS
  Analysis in the paired CMVM and IMVM displacements shows a significant mean difference of 0.9 +/- 3.3 mm in the lateral and 6.0 +/- 5.1 mm in the superoinferior directions (p < 0.0001), whereas no significant difference was detected in the anteroposterior direction between the two methods. Comparison of the computed tomography scan and IMVM measured displacements shows no significant difference between the two methods, with mean values of 0.2 +/- 1.7 mm in the lateral, -0.3 +/- 1.6 mm in the anteroposterior, and 0.1 +/- 1.4 mm in the superoinferior directions.
  
  
  CONCLUSIONS
  A significant systematic difference exists between cross-modality and intramodality methods when assessing prostate alignment during daily EBRT. Because displacements assessed by IMVM are consistent with those assessed by computed tomography scan, a more accurate prostate alignment appears to be obtained when the IMVM method is used.
authors.affiliation: Department of Oncology, Division of Radiation Oncology, McGill University, Montreal, Quebec, Canada.
authors.forename: Fabio L B
authors.initials: FL
authors.lastname: Cury
authors.forename: George
authors.initials: G
authors.lastname: Shenouda
authors.forename: Luis
authors.initials: L
authors.lastname: Souhami
authors.forename: Marie
authors.initials: M
authors.lastname: Duclos
authors.forename: Sergio L
authors.initials: SL
authors.lastname: Faria
authors.forename: Marc
authors.initials: M
authors.lastname: David
authors.forename: Frank
authors.initials: F
authors.lastname: Verhaegen
authors.forename: Robert
authors.initials: R
authors.lastname: Corns
authors.forename: Tony
authors.initials: T
authors.lastname: Falco
mesh_terms: D006801:Humans; D008297:Male; D009068:Movement; D011446:Prospective Studies; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D014057:Tomography, X-Ray Computed; D018084:Ultrasonography, Interventional / Q000379:methods*