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

PurposeMetallic 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 methodsPhantoms 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.ResultsFor 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).ConclusionFor 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.ZusammenfassungZielZahnimplantate 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 MaterialEs 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.ErgebnisseDie 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.SchlussfolgerungFür 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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