Abstract
Purpose
To compare a quasi-volumetric modulated arc therapy (qVMAT) with three-dimensional conformal radiation therapy (3D-CRT) and intensity-modulated radiation therapy (IMRT) for the treatment of high-grade gliomas. The qVMAT technique is a fast method of radiation therapy in which multiple equispaced beams analogous to those in rotation therapy are radiated in succession.
Patients and methods
This study included 12 patients with a planning target volume (PTV) that overlapped at least one organ at risk (OAR). 3D-CRT was planned using 2–3 non-coplanar beams, whereby the field-in-field technique (FIF) was used to divide each field into 1–3 subfields to shield the OAR. The qVMAT strategy was planned with 15 equispaced beams and IMRT was planned using 9 beams with a total of 80 segments. Inverse planning for qVMAT and IMRT was performed by direct machine parameter optimization (DMPO) to deliver a homogenous dose distribution of 60 Gy within the PTV and simultaneously limit the dose received by the OARs to the recommended values. Finally, the effect of introducing a maximum dose objective (max. dose < 54 Gy) for a virtual OAR in the form of a 0.5 cm ring around the PTV was investigated.
Results
The qVMAT method gave rise to significantly improved PTV95% and conformity index (CI) values in comparison to 3D-CRT (PTV95% = 90.7 % vs. 82.0 %; CI = 0.79 vs. 0.74, respectively). A further improvement was achieved by IMRT (PTV95% = 94.4 %, CI = 0.78). In qVMAT and IMRT, the addition of a 0.5 cm ring around the PTV produced a significant increase in CI (0.87 and 0.88, respectively), but dosage homogeneity within the PTV was considerably reduced (PTV95% = 88.5 % and 92.3 %, respectively). The time required for qVMAT dose delivery was similar to that required using 3D-CRT.
Conclusion
These findings suggest that qVMAT should be preferred to 3D-CRT for the treatment of high-grade gliomas. The qVMAT method could be applied in hospitals, for example, which have limited departmental resources and are not equipped with systems capable of VMAT delivery.
Zusammenfassung
Ziel
Ziel war es, eine sog. quasi volumetrisch modulierte Rotationsbestrahlung (qVMAT) mit einer konformalen 3-D-Bestrahlung (3D-CRT) und einer intensitätsmodulierten Bestrahlung (IMRT) bei der Behandlung von massiven Gliomen zu vergleichen. Die qVMAT ist eine schnelle Bestrahlungstechnik, bei der viele äquidistante Stehfelder analog einer Rotationsbestrahlung nacheinander bestrahlt werden.
Patienten und Methoden
In die Studie waren 12 Patienten eingeschlossen, bei denen das Planungszielvolumen (PTV) mindestens in einem Risikoorgan (OAR) teilweise enthalten war. Die 3D-CRT-Bestrahlungsplanung erfolgte über 2–3 nichtkoplanare Felder, wobei zur Schonung des Risikoorgans bei jedem Feld eine Feld-in-Feld-Technik mit 1–3 Subfeldern angewendet wurde. Die qVMAT wurde mit 15 äquidistanten Feldern realisiert, die IMRT mit 9 Feldern mit insgesamt 80 Segmenten. Um eine homogene Dosisverteilung im PTV von 60 Gy bei gleichzeitiger Schonung des Risikoorgans zu erreichen, wurde die Bestrahlungsplanung für die Techniken qVMAT und IMRT mit der „direct machine parameter optimization“ (DMPO) durchgeführt. Zusätzlich wurde die Auswirkung eines „maximum constraint“ (< 54 Gy) für ein virtuelles Risikoorgan (0,5-cm-Schalenstruktur um das PTV) auf die Planqualität untersucht.
Ergebnisse
Im Vergleich zur 3D-CRT-Methode ergab sich für die qVMAT eine signifikante Verbesserung der PTV95% (90,7 % vs. 82,0 %) und des Conformity-Indexes (CI; 0,79 vs. 0,74). Eine weitere Verbesserung wurde durch die IMRT erreicht (PTV95 %: 94,4 %; CI: 0,78). Wird bei der Planung ein virtuelles Risikoorgan in Form einer 0,5 cm dicken Schale um das PTV berücksichtigt, wird zwar der CI bei qVMAT und IMRT signifikant verbessert (0,87 bzw. 0,88), allerdings nimmt die Dosishomogenität im Zielvolumen deutlich ab (PTV95%: 88,5 % bzw. 92,3 %). Die Bestrahlungszeiten bei Anwendung der qVMAT sind mit denen der 3D-CRT vergleichbar.
Schlussfolgerung
Die Ergebnisse lassen darauf schließen, dass die qVMAT in der Behandlung massiver Gliome gegenüber der 3D-CRT zu bevorzugen ist. Die qVMAT kann beispielsweise in Krankenhäusern eingesetzt werden, die nur über begrenzte Mittel verfügen und nicht mit VMAT-fähigen Systemen ausgestattet sind.
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On behalf of all authors, the corresponding author states that there is no conflict of interest.
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Fadda, G., Massazza, G., Zucca, S. et al. Quasi-VMAT in high-grade glioma radiation therapy. Strahlenther Onkol 189, 367–371 (2013). https://doi.org/10.1007/s00066-012-0296-8
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DOI: https://doi.org/10.1007/s00066-012-0296-8