title: Iterative metal artifact reduction improves dose calculation accuracy : Phantom study with dental implants.
abstract: OBJECTIVE
  Metallic dental implants cause severe streaking artifacts in computed tomography (CT) data, which affect the accuracy of dose calculations in radiation therapy. The aim of this study was to investigate the benefit of the metal artifact reduction algorithm iterative metal artifact reduction (iMAR) in terms of correct representation of Hounsfield units (HU) and dose calculation accuracy.
  
  
  METHODS
  Heterogeneous phantoms consisting of different types of tissue equivalent material surrounding metallic dental implants were designed. Artifact-containing CT data of the phantoms were corrected using iMAR. Corrected and uncorrected CT data were compared to synthetic CT data to evaluate accuracy of HU reproduction. Intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans were calculated in Oncentra v4.3 on corrected and uncorrected CT data and compared to Gafchromic™ EBT3 films to assess accuracy of dose calculation.
  
  
  RESULTS
  The use of iMAR increased the accuracy of HU reproduction. The average deviation of HU decreased from 1006 HU to 408 HU in areas including metal and from 283 HU to 33 HU in tissue areas excluding metal. Dose calculation accuracy could be significantly improved for all phantoms and plans: The mean passing rate for gamma evaluation with 3 % dose tolerance and 3 mm distance to agreement increased from 90.6 % to 96.2 % if artifacts were corrected by iMAR.
  
  
  CONCLUSIONS
  The application of iMAR allows metal artifacts to be removed to a great extent which leads to a significant increase in dose calculation accuracy.
authors.affiliation: Department of Radiotherapy, Regensburg University Medical Center, 93042, Regensburg, Germany. manuel.maerz@klinik.uni-regensburg.de.
authors.forename: Manuel
authors.initials: M
authors.lastname: Maerz
authors.affiliation: Department of Radiotherapy, Regensburg University Medical Center, 93042, Regensburg, Germany.
authors.forename: Pia
authors.initials: P
authors.lastname: Mittermair
authors.affiliation: Siemens Healthcare GmbH, Forchheim, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Krauss
authors.affiliation: Department of Radiotherapy, Regensburg University Medical Center, 93042, Regensburg, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Koelbl
authors.affiliation: Department of Radiotherapy, Regensburg University Medical Center, 93042, Regensburg, Germany.
authors.forename: Barbara
authors.initials: B
authors.lastname: Dobler
mesh_terms: D016477:Artifacts; D015921:Dental Implants; D006801:Humans; D008670:Metals; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement / Q000379:methods*; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*
chemical_list: D015921:Dental Implants; D008670:Metals
keywords: Dental implants; Dose calculation; Gafchromic; MAR; Metal artifact reduction; Metal artifacts; Radiation therapy