title: Clinical evaluation of normalized metal artifact reduction in kVCT using MVCT prior images (MVCT-NMAR) for radiation therapy treatment planning.
abstract: OBJECTIVE
  To evaluate the metal artifacts in diagnostic kilovoltage computed tomography (kVCT) images of patients that are corrected by use of a normalized metal artifact reduction (NMAR) method with megavoltage CT (MVCT) prior images: MVCT-NMAR.
  
  
  METHODS
  MVCT-NMAR was applied to images from 5 patients: 3 with dual hip prostheses, 1 with a single hip prosthesis, and 1 with dental fillings. The corrected images were evaluated for visualization of tissue structures and their interfaces and for radiation therapy dose calculations. They were compared against the corresponding images corrected by the commercial orthopedic metal artifact reduction algorithm in a Phillips CT scanner.
  
  
  RESULTS
  The use of MVCT images for correcting kVCT images in the MVCT-NMAR technique greatly reduces metal artifacts, avoids secondary artifacts, and makes patient images more useful for correct dose calculation in radiation therapy. These improvements are significant, provided the MVCT and kVCT images are correctly registered. The remaining and the secondary artifacts (soft tissue blurring, eroded bones, false bones or air pockets, CT number cupping within the metal) present in orthopedic metal artifact reduction corrected images are removed in the MVCT-NMAR corrected images. A large dose reduction was possible outside the planning target volume (eg, 59.2 Gy to 52.5 Gy in pubic bone) when these MVCT-NMAR corrected images were used in TomoTherapy treatment plans without directional blocks for a prostate cancer patient.
  
  
  CONCLUSIONS
  The use of MVCT-NMAR corrected images in radiation therapy treatment planning could improve the treatment plan quality for patients with metallic implants.
authors.affiliation: Department of Oncology, University of Alberta, Edmonton, AB, Canada. Electronic address: mpaudel@ualberta.ca.
authors.forename: Moti Raj
authors.initials: MR
authors.lastname: Paudel
authors.affiliation: Department of Oncology, University of Alberta, Edmonton, AB, Canada.
authors.forename: Marc
authors.initials: M
authors.lastname: Mackenzie
authors.affiliation: Department of Oncology, University of Alberta, Edmonton, AB, Canada; Department of Physics, University of Alberta, Edmonton, AB, Canada; Department of Medical Physics, Cross Cancer Institute, Edmonton, AB, Canada.
authors.forename: B Gino
authors.initials: BG
authors.lastname: Fallone
authors.affiliation: Department of Oncology, University of Alberta, Edmonton, AB, Canada; Department of Medical Physics, Cross Cancer Institute, Edmonton, AB, Canada.
authors.forename: Satyapal
authors.initials: S
authors.lastname: Rathee
mesh_terms: D016477:Artifacts; D003764:Dental Materials; D003793:Dental Restoration, Permanent; D005260:Female; D005833:Genital Neoplasms, Female / Q000000981:diagnostic imaging*; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging*; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008670:Metals; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003764:Dental Materials; D008670:Metals