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Quasi-IMAT Study with Conventional Equipment to Show High Plan Quality with a Single Gantry Arc

Quasi-IMAT-Studie zur Untersuchung der Planqualität mit einer einzigen Gantryrotation mit konventioneller Ausrüstung

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Background and Purpose:

Nowadays, intensity-modulated arc therapy (IMAT) for clinical use is mostly based on forward planning. The aim of this work is to investigate the potential of a step-and-shoot quasi-IMAT (qIMAT) technique to improve plan quality.

Material and Method:

qIMAT plans with 18 and 36 beams were generated with a total number of 36 segments. Additionally, the number of segments was increased to 72, in order to investigate if the quality of the plans improves with the number of beams and segments. A conventional six-field intensity-modulated radiation therapy (IMRT) plan was used as a reference. The beam setup was applied to the CarPet phantom and to five prostate cancer patients.

Results:

In the phantom case, the dose received by the organ at risk (OAR) decreased considerably by using qIMAT. At the same time, coverage and homogeneity of planning target volume (PTV) remained unaffected. For the prostate cases, a good dose coverage was accomplished inside the PTV. Rectum and bladder were better spared with qIMAT. When increasing the number of segments, only a slight improvement of the plan quality was observed.

Conclusion:

The study showed that qIMAT improves the sparing of OARs while keeping the uniformity within the PTV, when compared with conventional IMRT. The more concave the PTV, the more noticeable is this behavior. The qIMAT technique has the advantage that it can be realized with a conventional equipment. The plan quality is high even with a single gantry arc and one segment per beam direction.

Hintergrund und Ziel:

Die klinische Anwendung der intensitätsmodulierten Arc-Therapie (IMAT) erfolgt derzeit hauptsächlich durch Vorwärtsplanung. Das Ziel dieser Studie ist, das Potential einer „step-and-shoot“-Quasi-IMAT-(qIMAT-)Technik zur Erhöhung der Planqualität zu untersuchen.

Material und Methodik:

qIMAT-Pläne mit 18 und 36 Feldern und maximal 36 Segmenten wurden erzeugt. Zusätzlich wurde die Segmentzahl auf 72 erhöht, um eine potentielle Verbesserung in Abhängigkeit von der Felder- und Segmentzahl zu untersuchen. Ein konventioneller IMRT-Plan (intensitätsmodulierte Strahlentherapie) mit sechs Feldern wurde als Referenz benutzt. Die Konfiguration der Felder wurde am CarPet-Phantom und an fünf Prostatakrebsfällen angewendet.

Ergebnisse:

Beim Phantom nahm die deponierte Dosis im Risikoorgan (OAR) deutlich ab, wenn qIMAT angewendet wurde. Gleichzeitig blieben die Abdeckung des Zielvolumens und Homogenität des Planungszielvolumens (PTV) unverändert. Bei den Prostatafällen konnte eine gute Abdeckung des Zielvolumens erreicht werden. Rektum und Blase wurden mit qIMAT besser geschont. Bei Erhöhung der Segmentzahl wurde eine leichte Verbesserung beobachtet.

Schlussfolgerung:

Die Untersuchung zeigte, dass qIMAT weniger Dosis im OAR deponierte, während die Homogenität im PTV im Vergleich zur konventionellen IMRT gleich blieb. Dieses Verhalten wird ausgeprägter, wenn der Grad der Konkavität des PTVs zunimmt. Der Vorteil der qIMAT-Methode besteht darin, dass eine Verbesserung der Planqualität mit konventioneller Ausrüstung erreicht werden kann. Die Planqualität ist bereits mit einer Quasirotation bei einem Segment pro Einstrahlrichtung hoch.

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Authors and Affiliations

  1. Department of Radiotherapy, University of Regensburg, Regensburg, Germany

    Ludwig Bogner

  2. Department of Radiotherapy, University of Regensburg, Franz-Josef-Strauß-Allee 11, 93053, Regensburg, Germany

    Judith Alvarez Moret

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  1. Judith Alvarez Moret
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  2. Oliver Kölbl
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  3. Ludwig Bogner
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Correspondence to Judith Alvarez Moret.

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Alvarez Moret, J., Kölbl, O. & Bogner, L. Quasi-IMAT Study with Conventional Equipment to Show High Plan Quality with a Single Gantry Arc. Strahlenther Onkol 185, 41–48 (2009). https://doi.org/10.1007/s00066-009-1890-2

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  • DOI: https://doi.org/10.1007/s00066-009-1890-2

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