title: Semiautomatic registration of 3D transabdominal ultrasound images for patient repositioning during postprostatectomy radiotherapy.
abstract: OBJECTIVE
  The aim of the present work is to propose and evaluate registration algorithms of three-dimensional (3D) transabdominal (TA) ultrasound (US) images to setup postprostatectomy patients during radiation therapy.
  
  
  METHODS
  Three registration methods have been developed and evaluated to register a reference 3D-TA-US image acquired during the planning CT session and a 3D-TA-US image acquired before each treatment session. The first method (method A) uses only gray value information, whereas the second one (method B) uses only gradient information. The third one (method C) combines both sets of information. All methods restrict the comparison to a region of interest computed from the dilated reference positioning volume drawn on the reference image and use mutual information as a similarity measure. The considered geometric transformations are translations and have been optimized by using the adaptive stochastic gradient descent algorithm. Validation has been carried out using manual registration by three operators of the same set of image pairs as the algorithms. Sixty-two treatment US images of seven patients irradiated after a prostatectomy have been registered to their corresponding reference US image. The reference registration has been defined as the average of the manual registration values. Registration error has been calculated by subtracting the reference registration from the algorithm result. For each session, the method has been considered a failure if the registration error was above both the interoperator variability of the session and a global threshold of 3.0 mm.
  
  
  RESULTS
  All proposed registration algorithms have no systematic bias. Method B leads to the best results with mean errors of -0.6, 0.7, and -0.2 mm in left-right (LR), superior-inferior (SI), and anterior-posterior (AP) directions, respectively. With this method, the standard deviations of the mean error are of 1.7, 2.4, and 2.6 mm in LR, SI, and AP directions, respectively. The latter are inferior to the interoperator registration variabilities which are of 2.5, 2.5, and 3.5 mm in LR, SI, and AP directions, respectively. Failures occur in 5%, 18%, and 10% of cases in LR, SI, and AP directions, respectively. 69% of the sessions have no failure.
  
  
  CONCLUSIONS
  Results of the best proposed registration algorithm of 3D-TA-US images for postprostatectomy treatment have no bias and are in the same variability range as manual registration. As the algorithm requires a short computation time, it could be used in clinical practice provided that a visual review is performed.
authors.affiliation: Université de Lyon, CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Lyon F-69621, France and Léon Bérard Cancer Center, Université de Lyon, Lyon F-69373, France.
authors.forename: Benoît
authors.initials: B
authors.lastname: Presles
authors.affiliation: Université de Lyon, CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Lyon F-69621, France.
authors.forename: Marie
authors.initials: M
authors.lastname: Fargier-Voiron
authors.affiliation: Léon Bérard Cancer Center, Université de Lyon, Lyon F-69373, France.
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Biston
authors.affiliation: The Andrew Love Cancer Centre, University Hospital Geelong, Geelong 3220, Australia.
authors.forename: Rod
authors.initials: R
authors.lastname: Lynch
authors.affiliation: Léon Bérard Cancer Center, Université de Lyon, Lyon F-69373, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Munoz
authors.affiliation: Université de Lyon, CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Lyon F-69621, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Liebgott
authors.affiliation: Léon Bérard Cancer Center, Université de Lyon, Lyon F-69373, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Pommier
authors.affiliation: Université de Lyon, CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Lyon F-69621, France and Léon Bérard Cancer Center, Université de Lyon, Lyon F-69373, France.
authors.forename: Simon
authors.initials: S
authors.lastname: Rit
authors.affiliation: Université de Lyon, CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Lyon F-69621, France and Léon Bérard Cancer Center, Université de Lyon, Lyon F-69373, France.
authors.forename: David
authors.initials: D
authors.lastname: Sarrut
mesh_terms: D000465:Algorithms; D003131:Combined Modality Therapy; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D056888:Patient Positioning / Q000379:methods* / Q000706:statistics & numerical data; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy* / Q000601:surgery; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D013269:Stochastic Processes; D014463:Ultrasonography / Q000706:statistics & numerical data*