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Dosimetric properties and commissioning of cone-beam CT image beam line with a carbon target

Dosimetrische Eigenschaften und Kommissionierung der „Image-beam-line“-Cone-Beam-CT mit einem Kohlenstofftarget

Abstract

Background and purpose

Accurate patient positioning before radiotherapy is often verified using advanced imaging techniques such as cone-beam computed tomography (CBCT). Even for dedicated imaging beam lines, the applied dose is not necessarily negligible with respect to the treatment dose and should be considered in the treatment plan.

Materials and methods

This study presents measurements of the beam properties of the Siemens kView (Siemens AG, Munich, Germany) image beam line (IBL) and the commissioning in the Philips Pinnacle3 treatment planning system (TPS; Philips, Amsterdam, Netherlands).

Results

The percent depth dose curve reaches its maximum at a depth of 10 mm, with a surface dose of 44 %. The IBL operates in flattening filter-free mode, showing the characteristic dose falloff from the central axis. Stability over several days to months is within less than 2 % dose deviation or 1 mm distance-to-agreement. Modelling of the IBL beam line was performed using the Pinnacle3 automatic modelling routine, with absolute dosimetric verification and film measurements of the fluence distribution.

Conclusion

After commissioning of the IBL beam model, the dose from the imaging IBL CBCT can be calculated. Even if the absolute dose deposited is small, repeated imaging doses may sum up to significant amounts and can shift the position of the dose maximum by several centimetres.

Zusammenfassung

Hintergrund und Ziel

Zur präzisen Lagerungskontrolle der Patienten werden in der Strahlentherapie vor der Bestrahlung fortgeschrittene Bildgebungsmethoden wie Cone-Beam-CT (CBCT) verwendet. Die dabei abgestrahlte Dosis ist nicht unbedingt vernachlässigbar und sollte deshalb im Behandlungsplan eingerechnet werden.

Material und Methode

Es werden Messungen der Strahleigenschaften des Siemens-kView-IBL („image beam line“; Siemens AG, München, Deutschland) und der Kommissionierung im Pinnacle3-Planungssystem von Philips (TPS, „treatment planning system“; Philips, Amsterdam, Niederlande) vorgestellt.

Ergebnisse

Die Tiefendosiskurve erreicht in 10 mm Tiefe ihr Maximum; die prozentuale Oberflächendosis beträgt 44 %. Die IBL hat die charakteristischen konischen Profile ohne Glättungsfilter („flattening filter-free beams“). Die Stabilität über Zeiträume von Tagen bis Monaten beträgt weniger als 2 % der Dosiswerte oder 1 mm Verschiebung bis zur Übereinstimmung. Die Modellierung mit dem automatischen Modellierungsalgorithmus in Pinnacle3 gelingt mit ausreichender Präzision und ist dosimetrisch verifizierbar.

Zusammenfassung

Nach erfolgreicher Kommissionierung des IBL-Beam-Modells kann die Bildgebungsdosis in den Behandlungsplan eingerechnet werden. Der Absolutbetrag der Dosis eines CBCT ist klein. Bei häufiger Bildgebung kann die akkumulierte Dosis signifikant werden und zu einer deutlichen Verschiebung des Dosismaximums führen.

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Acknowledgements

Many thanks to Georg Blass for his assistance with the TLD measurements, to Stephanie Kremp for her help in printing out the Pinnacle3 results and to Achim Elzer for providing technical details on the IBL and flat panel. We thank the associate editor and an anonymous reviewer for helpful comments on this manuscript.

Conflict of interest

On behalf of all authors, the corresponding author states that there are no conflicts of interest.

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Correspondence to Y. Dzierma.

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Dzierma, Y., Nuesken, F., Licht, N. et al. Dosimetric properties and commissioning of cone-beam CT image beam line with a carbon target. Strahlenther Onkol 189, 566–572 (2013). https://doi.org/10.1007/s00066-013-0330-5

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Keywords

  • Intensity-modulated radiation therapy
  • Dose distribution
  • Organs at risk
  • Imaging
  • Radiosurgery

Schlüsselwörter

  • Intensitätsmodulierte Strahlentherapie
  • Dosisverteilung
  • Risikoorgane
  • Bildgebung
  • Radiochirurgie