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Dosimetric integration of daily mega-voltage cone-beam CT for image-guided intensity-modulated radiotherapy

Dosisintegration von täglichen Megavolt-Cone-Beam-CTs (MV-CBCT) für die bildgestützte intensitätsmodulierte Strahlentherapie

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Abstract

Purpose

The goal of this work was to compare different methods of incorporating the additional dose of mega-voltage cone-beam CT (MV-CBCT) for image-guided intensity modulated radiotherapy (IMRT) of different tumor entities.

Material and methods

The absolute dose delivered by the MV-CBCT was calculated and considered by creating a scaled IMRT plan (scIMRT) by renormalizing the clinically approved plan (orgIMRT) so that the sum with the MV-CBCT dose yields the same prescribed dose. In the other case, a newly optimized plan (optIMRT) was generated by including the dose distribution of the MV-CBCT as pre-irradiation. Both plans were compared with the orgIMRT plan and a plan where the last fraction was skipped.

Results

No significant changes were observed regarding the 95% conformity index of the target volume. The mean dose of the organs at risk (OAR) increased by approx. 7% for the scIMRT plan and 5% for the optIMRT plan. A significant increase of the mean dose to the outline contour was observed, ranging from 3.1 ± 1.3% (optIMRT) to 13.0 ± 6.1% (scIMRT) for both methods over all entities. If the dose of daily MV-CBCT would have been ignored, the additional dose accumulated to nearly a whole treatment fraction with a general increase of approx. 10% to the OARs and approx. 4% to the target volume.

Conclusion

Both methods of incorporating the additional MV-CBCT dose into the treatment plan are suitable for clinical practice. The dose distribution of the target volume could be achieved as conformal as with the orgIMRT plan, while only a moderate increase of mean dose to OAR was observed.

Zusammenfassung

Zielsetzung

Vergleich verschiedener Methoden zur Integration der zusätzlichen Dosis von täglichen Megavolt-Cone-Beam-CTs (MV-CBCT) für die bildgestützte intensitätsmodulierte Strahlentherapie (IMRT) verschiedener Tumorentitäten.

Material und Methoden

Der absolute zusätzliche Dosisbeitrag durch das MV-CBCT wurde jeweils berechnet. In einem Fall wurde durch Re-Normalisierung ein skalierter IMRT-Plan (scIMRT) erzeugt, bei dem die Summe aus IMRT-Plan und MV-CBCT die verschriebene Dosis des klinisch akzeptierten IMRT-Plans (orgIMRT) ergab. Im anderen Fall wurde ein neu optimierter IMRT-Plan (optIMRT) erstellt, der die zusätzliche Dosis des MV-CBCT als Vorbelastung berücksichtigt. Beide Pläne wurden mit dem orgIMRT-Plan und einem Plan, bei dem die letzte Fraktion weggelassen wurde, verglichen.

Ergebnisse

Es zeigten sich keine signifikanten Veränderungen des 95%-Konformität-Index des Zielvolumens. Die mittlere Dosisbelastung der Risikoorgane (OAR) erhöhte sich beim scIMRT-Plan um etwa 7% und beim optIMRT-Plan um etwa 5%. Es zeigte sich ein signifikanter Anstieg der mittleren Dosis der Außenkontur des Patienten im Bereich von 3,1 ± 1,3% (optIMRT) bis 13,0 ± 6,1% (scIMRT) bei beiden Methoden über alle Lokalisationen. Der zusätzliche Dosisbeitrag eines täglichen MV-CBCT lag in der Größenordnung einer Fraktion und führte insgesamt zu einer Zunahme der Belastung der Risikoorgane um etwa 10% und der Dosis im Zielvolumen um etwa 4%.

Schlussfolgerungen

Beide Methoden zur Integration der zusätzlichen Dosis eines MV-CBCT in den Bestrahlungsplan eigenen sich für die klinische Routine. Die Dosisverteilung des Zielvolumens war im Vergleich zur IMRT ähnlich konformal, bei moderatem Anstieg der mittleren Dosisbelastung der Risikoorgane.

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Conflict of Interest

The corresponding author states that there are no conflicts of interest.

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Authors and Affiliations

  1. Department of Radiooncology, University of Heidelberg, INF 400, 69120, Heidelberg, Germany

    A. Zabel-du Bois & S. Milker-Zabel

  2. Department of Radiotherapy, German Cancer Research Center, Heidelberg, Germany

    A. Zabel-du Bois

  3. Department of Medical Physics, German Cancer Research Center, Heidelberg, Germany

    S. Nill, S. Ulrich, U. Oelfke, B. Rhein, P. Haering & A. Schwahofer

Authors
  1. A. Zabel-du Bois
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  2. S. Nill
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  3. S. Ulrich
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  4. U. Oelfke
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  5. B. Rhein
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  8. A. Schwahofer
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Correspondence to A. Zabel-du Bois.

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Zabel-du Bois, A., Nill, S., Ulrich, S. et al. Dosimetric integration of daily mega-voltage cone-beam CT for image-guided intensity-modulated radiotherapy. Strahlenther Onkol 188, 120–126 (2012). https://doi.org/10.1007/s00066-011-0021-z

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  • DOI: https://doi.org/10.1007/s00066-011-0021-z

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