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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

Abstract

Purpose

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.

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.

Conclusion

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

Zusammenfassung

Zielsetzung

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.

Ergebnisse

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.

Schlussfolgerung

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

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Acknowledgments

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). https://doi.org/10.1007/s00066-016-0958-z

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  • DOI: https://doi.org/10.1007/s00066-016-0958-z

Keywords

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

Schlüsselwörter

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