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Iterative metal artifact reduction improves dose calculation accuracy

Phantom study with dental implants

Iterative Metallartefakt Reduktion verbessert die Genauigkeit der Dosisberechnung

Phantomstudie mit Zahnimplantaten



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.

Materials and 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.


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.


The application of iMAR allows metal artifacts to be removed to a great extent which leads to a significant increase in dose calculation accuracy.



Metallische Implantate verursachen streifenförmige Artefakte in CT-Bildern, welche die Dosisberechnung beeinflussen. In dieser Studie soll der Nutzen des iterativen Metall-Artefakt-Reduktions-Algorithmus iMAR hinsichtlich der Wiedergabetreue von Hounsfield-Werten (HU) und der Genauigkeit von Dosisberechnungen untersucht werden.

Material und Methoden

Es wurden heterogene Phantome aus verschiedenen Arten gewebeäquivalenten Materials mit Zahnimplantaten entworfen. Von den Phantomen wurden CT-Scans angefertigt und mittels des iMAR-Algorithmus korrigiert. Um die Wiedergabetreue der Hounsfield-Einheiten zu testen, wurden die korrigierten und nichtkorrigierten CT-Daten gegen synthetische CT-Daten verglichen. IMRT- und VMAT-Pläne wurden in Oncentra v4.3 berechnet und zur Beurteilung der Genauigkeit der Dosisberechnung mit Gafchromic™-EBT3-Filmmessungen verglichen.


Die Anwendung von iMAR erhöht die Wiedergabetreue der Hounsfield-Einheiten. Die durchschnittliche Abweichung zu den synthetischen Daten fällt in Gewebebereichen ohne Metall von 283 HU auf 33 HU und in Metallbereichen von 1006 HU auf 408 HU. Die Genauigkeit der Dosisberechnungen konnte für alle Phantome und Pläne signifikant verbessert werden. Die mittlere Akzeptanzrate der Gammaevaluation mit 3 % Dosistoleranz und 3 mm Ortstoleranz steigt von 90,6 auf 96,2%, wenn Artefakte mittels iMAR korrigiert werden.


Mit Hilfe von iMAR konnten die Artefakte zu großen Teilen entfernt werden, was zu einer signifikanten Erhöhung der Dosisberechnungsgenauigkeit führt.

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  1. Maerz M, Koelbl O, Dobler B (2015) Influence of metallic dental implants and metal artefacts on dose calculation accuracy. Strahlenther Onkol 191:234–241

    Article  PubMed  Google Scholar 

  2. Glide-Hurst C, Chen D, Zhong H et al (2013) Changes realized from extended bit-depth and metal artifact reduction in CT. Med Phys 40:061711

    CAS  Article  PubMed  Google Scholar 

  3. Li H, Noel C, Chen H et al (2012) Clinical evaluation of a commercial orthopedic metal artifact reduction tool for CT simulations in radiation therapy. Med Phys 39:7507–7517

    Article  PubMed  PubMed Central  Google Scholar 

  4. Mail N, Albarakati Y, Ahmad Khan M et al (2013) The impacts of dental filling materials on RapidArc treatment planning and dose delivery: challenges and solution. Med Phys 40:081714

    Article  PubMed  Google Scholar 

  5. Paudel MR, Mackenzie M, Fallone BG et al (2013) Evaluation of normalized metal artifact reduction (NMAR) in kVCT using MVCT prior images for radiotherapy treatment planning. Med Phys 40:081701

    CAS  Article  PubMed  Google Scholar 

  6. Paudel MR, Mackenzie M, Fallone BG et al (2014) Clinical evaluation of normalized metal artifact reduction in kVCT using MVCT prior images (MVCT-NMAR) for radiation therapy treatment planning. Int J Radiat Oncol Biol Phys 89:682–689

    Article  PubMed  Google Scholar 

  7. Spadea MF, Verburg J, Baroni G et al (2013) Dosimetric assessment of a novel metal artifact reduction method in CT images. J Appl Clin Med Phys 14:4027

    PubMed  Google Scholar 

  8. Spadea MF, Verburg JM, Baroni G et al (2014) The impact of low-Z and high-Z metal implants in IMRT: a Monte Carlo study of dose inaccuracies in commercial dose algorithms. Med Phys 41:011702

    Article  PubMed  Google Scholar 

  9. Axente M, Paidi A, Von Eyben R et al (2015) Clinical evaluation of the iterative metal artifact reduction algorithm for CT simulation in radiotherapy. Med Phys 42:1170–1183

    Article  PubMed  Google Scholar 

  10. Morsbach F, Bickelhaupt S, Wanner GA et al (2013) Reduction of metal artifacts from hip prostheses on CT images of the pelvis: value of iterative reconstructions. Radiology 268:237–244

    Article  PubMed  Google Scholar 

  11. Morsbach F, Wurnig M, Kunz DM et al (2013) Metal artefact reduction from dental hardware in carotid CT angiography using iterative reconstructions. Eur Radiol 23:2687–2694

    Article  PubMed  Google Scholar 

  12. Subhas N, Primak AN, Obuchowski NA et al (2014) Iterative metal artifact reduction: evaluation and optimization of technique. Skeletal Radiol 43:1729–1735

    Article  PubMed  Google Scholar 

  13. Yohannes I, Kolditz D, Langner O et al (2012) A formulation of tissue- and water-equivalent materials using the stoichiometric analysis method for CT-number calibration in radiotherapy treatment planning. Phys Med Biol 57:1173–1190

    Article  PubMed  Google Scholar 

  14. Meyer E, Raupach R, Lell M et al (2010) Normalized metal artifact reduction (NMAR) in computed tomography. Med Phys 37:5482–5493

    Article  PubMed  Google Scholar 

  15. Meyer E, Raupach R, Lell M et al (2012) Frequency split metal artifact reduction (FSMAR) in computed tomography. Med Phys 39:1904–1916

    Article  PubMed  Google Scholar 

  16. Alvarez-Moret J, Pohl F, Koelbl O et al (2010) Evaluation of volumetric modulated arc therapy (VMAT) with Oncentra MasterPlan(R) for the treatment of head and neck cancer. Radiat Oncol 5:110

    Article  PubMed  PubMed Central  Google Scholar 

  17. Dobler B, Pohl F, Bogner L et al (2007) Comparison of direct machine parameter optimization versus fluence optimization with sequential sequencing in IMRT of hypopharyngeal carcinoma. Radiat Oncol 2:33

    Article  PubMed  PubMed Central  Google Scholar 

  18. Dobler B, Weidner K, Koelbl O (2010) Application of volumetric modulated arc therapy (VMAT) in a dual-vendor environment. Radiat Oncol 5:95

    Article  PubMed  PubMed Central  Google Scholar 

  19. International Commission on Radiological Protection (1975) Report of the task group on reference man. ICRP 23

  20. International Commission on Radiation Units and Measurements (1989) Tissue substitutes in radiation dosimetry and measurement. ICRU 44

  21. Crijns W, Maes F, Van Der Heide UA et al (2013) Calibrating page sized Gafchromic EBT3 films. Med Phys 40:012102

    CAS  Article  PubMed  Google Scholar 

  22. Siebers JV, Keall PJ, Nahum AE et al (2000) Converting absorbed dose to medium to absorbed dose to water for Monte Carlo based photon beam dose calculations. Phys Med Biol 45:983–995

    CAS  Article  PubMed  Google Scholar 

  23. Low DA, Harms WB, Mutic S et al (1998) A technique for the quantitative evaluation of dose distributions. Med Phys 25:656–661

    CAS  Article  PubMed  Google Scholar 

  24. Ezzell GA, Burmeister JW, Dogan N et al (2009) IMRT commissioning: multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119. Med Phys 36:5359–5373

    Article  PubMed  Google Scholar 

  25. Hayashi N, Watanabe Y, Malmin R et al (2012) Evaluation of triple channel correction acquisition method for radiochromic film dosimetry. J Radiat Res 53:930–935

    Article  PubMed  PubMed Central  Google Scholar 

  26. Micke A, Lewis DF, Yu X (2011) Multichannel film dosimetry with nonuniformity correction. Med Phys 38:2523–2534

    Article  PubMed  Google Scholar 

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The work was supported by the Wilhelm Sander Foundation. We want to thank Walter Schäffer for providing the teeth implant material. We want to thank Elmar Lang for support in applying for third-party funding.

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Correspondence to Manuel Maerz M.Sc..

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Conflict of interest

The department of M. Maerz, P. Mittermair, O. Koelbl and B. Dobler has a research cooperation with Elekta GmbH Hamburg.

M. Maerz, P. Mittermair, O. Koelbl and B. Dobler state that there are no conflicts of interest. A. Krauss is employee of Siemens Healthcare GmbH.

The accompanying manuscript does not include studies on humans or animals.

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Maerz, M., Mittermair, P., Krauss, A. et al. Iterative metal artifact reduction improves dose calculation accuracy. Strahlenther Onkol 192, 403–413 (2016).

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  • Metal artifact reduction
  • Metal artifacts
  • MAR
  • Dental implants
  • Dose calculation
  • Gafchromic
  • Radiation therapy


  • Metallartefaktreduktion
  • Metallartefakte
  • MAR
  • Zahnimplantate
  • Dosisberechnung
  • Gafchromic
  • Strahlentherapie