title: Impact of probe pressure variability on prostate localization for ultrasound-based image-guided radiotherapy.
abstract: OBJECTIVE
  To evaluate the impact of transabdominal probe pressure on prostate positioning with an intramodality ultrasound (US) image-guided-radiotherapy system and to quantify pressure variability over the treatment course.
  
  
  METHODS
  8 prostate cancer patients (group A) and 17 healthy volunteers underwent 3 consecutive US images with increasing probe pressure levels, and 1 CT acquisition for the group A only. Prostate positions were compared after manual registration of the first US image contour projected on 2 others. Group A's pressure levels were quantified by measuring skin-to-skin distances between corresponding CT-US images. The same methodology was used on paired CT/CBCT-US images acquired during treatments of 18 prostate cancer patients to determine whether the different pressure levels applied to the group A were close to the clinical practices and to quantify pressure variability along the treatment course.
  
  
  RESULTS
  84% of 3D prostate displacements were above 2mm for at least one pressure level. Probe pressures deliberately applied were similar to the ones observed clinically. The latter drastically varied between sessions.
  
  
  CONCLUSIONS
  Even with an intramodality system, probe pressure can impact prostate localization because of the pressure variability along the treatment course. Therefore, margins should be expanded from 0.5 to 1.2mm to ensure treatment accuracy.
authors.affiliation: CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France.
authors.forename: Marie
authors.initials: M
authors.lastname: Fargier-Voiron
authors.affiliation: CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France; Léon Bérard Cancer Center, University of Lyon, France.
authors.forename: Benoît
authors.initials: B
authors.lastname: Presles
authors.affiliation: Léon Bérard Cancer Center, University of Lyon, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Pommier
authors.affiliation: CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France; Léon Bérard Cancer Center, University of Lyon, France.
authors.forename: Simon
authors.initials: S
authors.lastname: Rit
authors.affiliation: Léon Bérard Cancer Center, University of Lyon, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Munoz
authors.affiliation: CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Liebgott
authors.affiliation: CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France; Léon Bérard Cancer Center, University of Lyon, France.
authors.forename: David
authors.initials: D
authors.lastname: Sarrut
authors.affiliation: CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France; Léon Bérard Cancer Center, University of Lyon, France. Electronic address: marie-claude.biston@lyon.unicancer.fr.
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Biston
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D056888:Patient Positioning; D011312:Pressure; D011467:Prostate / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods; D014463:Ultrasonography
keywords: IGRT; Probe pressure; Prostate; Ultrasound