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Influence of metallic dental implants and metal artefacts on dose calculation accuracy

Einfluss von metallischen Zahnimplantaten und Metallartefakten auf die Genauigkeit der Dosisberechnung

Abstract

Purpose

Metallic dental implants cause severe streaking artefacts in computed tomography (CT) data, which inhibit the correct representation of shape and density of the metal and the surrounding tissue. The aim of this study was to investigate the impact of dental implants on the accuracy of dose calculations in radiation therapy planning and the benefit of metal artefact reduction (MAR). A second aim was to determine the treatment technique which is less sensitive to the presence of metallic implants in terms of dose calculation accuracy.

Materials and methods

Phantoms consisting of homogeneous water equivalent material surrounding dental implants were designed. Artefact-containing CT data were corrected using the correct density information. Intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans were calculated on corrected and uncorrected CT data and compared to 2-dimensional dose measurements using GafChromic™ EBT2 films.

Results

For all plans the accuracy of dose calculations is significantly higher if performed on corrected CT data (p = 0.015). The agreement of calculated and measured dose distributions is significantly higher for VMAT than for IMRT plans for calculations on uncorrected CT data (p = 0.011) as well as on corrected CT data (p = 0.029).

Conclusion

For IMRT and VMAT the application of metal artefact reduction significantly increases the agreement of dose calculations with film measurements. VMAT was found to provide the highest accuracy on corrected as well as on uncorrected CT data. VMAT is therefore preferable over IMRT for patients with metallic implants, if plan quality is comparable for the two techniques.

Zusammenfassung

Ziel

Zahnimplantate aus Metall verursachen in Computertomographiedaten (CT) streifenförmige Artefakte. Diese verhindern eine korrekte Zuordnung von Form und Dichteeigenschaften des Metalls und des umgebenden Gewebes. Ziel dieser Studie war es, den Einfluss von Zahnimplantaten auf die Genauigkeit der Dosisberechnung in der Strahlentherapie zu untersuchen und zu überprüfen, ob eine reine Reduktion der Metallartefakte ohne Korrektur der Form und der Dichtewerte des Metallimplantats eine genauere Dosisberechnung ermöglicht. Als zweites Ziel sollte die Bestrahlungstechnik bestimmt werden, welche bei vorhandenen metallischen Implantaten, in Bezug auf die Dosisberechnungsgenauigkeit am wenigsten fehleranfällig ist.

Methoden und Material

Es wurden Phantome aus homogenem wasseräquivalentem Material mit Zahnimplantaten entworfen. CT-Daten welche Artefakte enthielten wurden mit den richtigen Dichtewerten korrigiert. Auf korrigierten und nichtkorrigierten CT-Daten wurden IMRT (intensity-modulated radiation therapy) und VMAT (volumetric modulated arc therapy)-Pläne berechnet und mit 2-dimensionalen Dosismessungen, welche mit GafChromic™-EBT2-Filmen durchgeführt wurden, verglichen.

Ergebnisse

Die Dosisberechnungsgenauigkeit ist für alle Pläne signifikant besser, wenn die Berechnungen auf korrigierten Daten durchgeführt wurden (p = 0,015). Berechnete und gemessene Dosisverteilungen stimmen für VMAT-Pläne signifikant besser überein als für IMRT-Pläne, sowohl bei Rechnungen auf nichtkorrigierten (p = 0,011) als auch auf korrigierten (p = 0,029) CT-Daten.

Schlussfolgerung

Für IMRT und VMAT wird die Übereinstimmung von berechneten und gemessenen Dosisverteilungen signifikant erhöht. Es wurde gezeigt, dass VMAT sowohl auf korrigierten als auch auf nichtkorrigierten CT-Daten die höchste Genauigkeit liefert. Wenn die Planqualität für beide Techniken vergleichbar ist, sollte bei Patienten mit Metallimplantaten die VMAT der IMRT vorgezogen werden.

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Notes

  1. NucletronTM, “Oncentra External Beam v4.0 – Physics and Algorithms.”

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Compliance with ethical guidelines

Acknowledgements

The work was supported by the Wilhelm Sander Foundation. We want to thank Walter Schäffer for providing the teeth implant material.

Conflict of interest

M. März, O. Kölbl and B. Dobler state the following: the department has a research cooperation with Elekta GmbH Hamburg. The accompanying manuscript does not include studies on humans or animals.

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Correspondence to Manuel Maerz M.Sc..

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Maerz, M., Koelbl, O. & Dobler, B. Influence of metallic dental implants and metal artefacts on dose calculation accuracy. Strahlenther Onkol 191, 234–241 (2015). https://doi.org/10.1007/s00066-014-0774-2

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  • DOI: https://doi.org/10.1007/s00066-014-0774-2

Keywords

  • Computed tomography
  • Metal artifacts
  • Dental implants
  • Radiotherapy
  • Intensity modulated radiation therapy
  • GafChromic

Schlüsselwörter

  • Computertomographie
  • Metallartefakte
  • Zahnimplantate
  • Strahlentherapie
  • Intensitätsmodulierte Strahlentherapie
  • GafChromic