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Overestimation of Low-Dose Radiation in Intensity-Modulated Radiotherapy with Sliding-Window Technique

Überschätzung des applizierten Dosis in Niedrigdosisbereichen bei intensitätsmodulierter Radiotherapie mit Sliding-Window-Technik

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Strahlentherapie und Onkologie Aims and scope Submit manuscript

Purpose:

To analyze different control-system limitations on the measured dose distributions in low-dose regions of simplified intensity fields with an electronic portal imaging device to ascertain the optimal settings for the control-system limitations in the planning system.

Material and Methods:

The authors created one field with an "optimal fluence" of intensity 1.0 (full dose) and one field with intensity 0.0 (no dose) in the central part of the field. The influence of different dose rates (DRs) and maximum leaf speeds (LS) on the calculated and measured dose and dose profiles were analyzed.

Results:

Good agreement between calculated and measured dose in the case of a field of intensity 1.0 was found. For the field with intensity 0.0, the measured dose was 20–60% lower than the dose calculated by the "actual fluence". The results were found dependent on the DR and LS.

Conclusion:

The overestimation in regions of optimal intensity 0.0 by the planning system cannot be resolved by the user. Taking the measured dose in the region of desired intensity 1.0 and other technical limitations (like beam hold interrupts or spikes in the cross and longitudinal profiles) into consideration, the application of an LS of 2.5 cm/s and a DR of 500 MU/min is recommended in order to minimize radiation dose applied to organs at risk, which are located in regions of low intensity, like, for example, the spinal cord.

Ziel:

Es wurden verschiedene Kontrollsystemlimitationen bezüglich ihrer Auswirkungen auf die gemessene Dosisverteilung in Niedrigdosisbereichen von vereinfachten intensitätsmodulierten Feldern mittels eines elektronischen Portal-Imaging-Systems untersucht, um darüber die optimalen Einstellungen des Planungssystems herauszufinden.

Material und Methodik:

Die Autoren kreierten ein Feld mit „optimaler Fluenz“ 1,0 (volle Dosis) und ein Feld mit Intensität 0,0 (keine Dosis) im zentralen Feldanteil. Die Auswirkungen verschiedener Dosisraten (DR) und maximaler Leafgeschwindigkeiten (LS) auf die errechnete und gemessene Dosis und Linienprofile der Felder wurden analysiert.

Ergebnisse:

Bei dem Feld mit Intensität 1,0 fand sich eine gute Übereinstimmung zwischen der errechneten und der gemessenen Dosis für alle Limitationen. Bei dem Feld mit Intensität 0,0 war die gemessene Dosis 20–60% niedriger als die errechnete Dosis der "aktuellen Fluenz". Die Ergebnisse waren abhängig von der gewählten DR und LS.

Schlussfolgerung:

Die Überschätzung der Dosis im Niedrigdosisbereich durch das Bestrahlungsplanungssytem kann momentan nicht durch den Benutzer behoben werden. Unter Berücksichtigung der in dem Feld mit Intensität 1,0 gemessenen Dosis und anderer technischer Limitationen (wie „beam hold interrupts“, Zacken in den Quer- und Längsprofilen) werden eine LS von 2,5 cm/s und eine DR von 500 MU/min befürwortet, um die applizierte Dosis in Niedrigdosisbereichen bei gleichzeitig optimaler technischer Applizierbarkeit zu reduzieren.

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Authors and Affiliations

  1. Department of Radiotherapy and Radiooncology, University Hospital Göttingen, Göttingen, Germany

    Hilke Vorwerk MSc, MD, Daniela Wagner, Hans Christiansen, Hendrik A. Wolff & Clemens F. Hess

  2. Department of Physics and Astronomy, University of Glasgow, Glasgow, Scotland, UK

    Björn Seitz

  3. Department of Radiotherapy and Radiooncology, University Hospital Göttingen, Robert-Koch-Straße 40, 37099, Göttingen, Germany

    Hilke Vorwerk MSc, MD

Authors
  1. Hilke Vorwerk MSc, MD
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  2. Daniela Wagner
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  3. Björn Seitz
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  4. Hans Christiansen
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  5. Hendrik A. Wolff
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  6. Clemens F. Hess
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Correspondence to Hilke Vorwerk MSc, MD.

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Vorwerk, H., Wagner, D., Seitz, B. et al. Overestimation of Low-Dose Radiation in Intensity-Modulated Radiotherapy with Sliding-Window Technique. Strahlenther Onkol 185, 821–829 (2009). https://doi.org/10.1007/s00066-009-2028-2

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  • DOI: https://doi.org/10.1007/s00066-009-2028-2

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