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Effect of dose reduction on image registration and image quality for cone-beam CT in radiotherapy

Effekt einer Dosisreduktion auf Bildregistrierung und Bildqualität für eine Kegelstrahl-CT in der Strahlentherapie

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Abstract

Introduction

The additional radiation exposure applied to patients undergoing cone-beam computed tomography (CBCT) for image registration in radiation therapy is of great concern. Since a decrease in CBCT dose is linked to a degradation of image quality, the consequences of dose reduction on the registration process have to be investigated.

Material and methods

This paper examines image quality and registration of low-contrast structures on an Elekta XVI for the two treatment areas prostate and chest while gradually decreasing the mAs per frame and the number of projections per CBCT to achieve dose reduction.

Results

Ideal results for image quality were obtained for 1.6 mAs/frame and 377 projections in prostate scans and 0.63 mAs/frame and 440 projections in chest images. Lower as well as higher total mAs lead to a decrease in image quality. In spite of poor image quality, registration can be successfully performed even for lowest possible settings.

Conclusion

The results for registration allow an extensive dose reduction in both treatment areas. Very low mAs, however, do not qualify for clinical use because subjective judgment of the registration process is impossible. Compared to default presets the use of settings for acceptable image quality already permit a decrease in exposure of about 40 % (29.0 to 16.7 mGy) in prostate scans and 60 % (18.3 to 7.7 mGy) in chest scans.

Zusammenfassung

Einleitung

Die zusätzliche Strahlenbelastung von Patienten bei der Lagerungskontrolle mit einer Kegelstrahl-Computertomographie (CBCT) in der Strahlentherapie ist nicht zu vernachlässigen. Die Reduzierung der Dosis durch das CBCT ist mit einer Verschlechterung der Bildqualität verbunden. Aus diesem Grund ist die Untersuchung der Effekte einer Dosisreduktion von großer Bedeutung.

Material und Methoden

Diese Arbeit untersucht die Bildqualität und Bildregistrierung in Bereichen niedrigen Kontrasts mit einem Kegelstrahl CT der Firma Elekta. Betrachtet werden die Behandlungsregionen Prostata und Thorax. Die Dosisreduktion wird durch stufenweise Verringerung der mAs pro Frame und der Anzahl der Projektionen pro Kegelstrahl-CT erreicht.

Ergebnisse

Die optimale Bildqualität wurde bei Aufnahmen im Bereich der Prostata mit 1,6 mAs/Frame und 377 Projektionen und im Bereich des Thorax bei 0,63 mAs/Frame und 440 Projektionen erzielt. Sowohl niedrigere als auch höhere mAs führen zu einer Verschlechterung der Bildqualität. Auch bei schlechter Bildqualität mit den niedrigsten erlaubten Einstellungen ist jedoch eine erfolgreiche Bildregistrierung möglich.

Zusammenfassung

Die Ergebnisse der Bildregistrierung erlauben eine deutliche Dosisreduktion in beiden untersuchten Behandlungsbereichen. Allerdings ist die Wahl sehr geringer mAs für die klinische Routine nicht geeignet, da eine subjektive Beurteilung und Kontrolle der Bildregistrierung wegen der geringen Bildqualität nicht mehr möglich ist. Im Vergleich zu den Standardeinstellung des Herstellers sind bei ausreichender Bildqualität immer noch Reduzierungen der Strahlenbelastungen um 40 % (29,0 auf 16,7 mGy) für den Bereich der Prostata und um 60 % (18,3 auf 7,7 mGy) für den Bereich des Thorax möglich.

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Conflict of interest

B. Loutfi-Krauss, J. Köhn, N. Koch, K. Freundl, T. Koch, E. Kara, C. Scherf, C. Rödel, U. Ramm, and J. Licher state that there are no conflicts of interest. The accompanying manuscript does not include studies on humans or animals.

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Authors and Affiliations

  1. Klinik für Strahlentherapie und Onkologie, Universitätsklinikum Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt am Main, Germany

    B. Loutfi-Krauss, J. Köhn, N. Blümer, E. Kara, C. Scherf Dr. rer. nat., C. Rödel Prof. Dr. med., U. Ramm PD Dr. phil. nat. &  J. Licher

  2. Klinik und Praxis für Radioonkologie und Strahlentherapie, Sozialstiftung Bamberg—MVZ am Bruderwald, Buger Straße 80, Bamberg, 96049, Germany

    K. Freundl & T. Koch Dr. rer. nat.

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  1. B. Loutfi-Krauss
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  2. J. Köhn
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  3. N. Blümer
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  4. K. Freundl
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  5. T. Koch Dr. rer. nat.
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  6. E. Kara
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  7. C. Scherf Dr. rer. nat.
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  8. C. Rödel Prof. Dr. med.
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Correspondence to J. Licher.

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Loutfi-Krauss, B., Köhn, J., Blümer, N. et al. Effect of dose reduction on image registration and image quality for cone-beam CT in radiotherapy. Strahlenther Onkol 191, 192–200 (2015). https://doi.org/10.1007/s00066-014-0750-x

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  • DOI: https://doi.org/10.1007/s00066-014-0750-x

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