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Target volume coverage and dose to organs at risk in prostate cancer patients

Dose calculation on daily cone-beam CT data sets

Zielvolumenerfassung und Risikoorgandosis bei Prostatakarzinompatienten

Dosisberechnung auf täglichen Cone-Beam-CT-Datensätzen

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Abstract

Purpose

On the basis of correct Hounsfield unit to electron density calibration, cone-beam computed tomography (CBCT) data provide the opportunity for retrospective dose recalculation in the patient. Therefore, the consequences of translational positioning corrections and of morphological changes in the patient anatomy can be quantified for prostate cancer patients.

Materials and methods

The organs at risk were newly contoured on the CBCT data sets of 7 patients so as to evaluate the actual applied dose. The daily dose to the planning target volume (PTV) was recalculated with and without the translation data, which result from the real patient repositioning.

Results

A CBCT-based dose recalculation with uncertainties less than 3 % is possible. The deviations between the planning CT and the CBCT without the translational positioning correction vector show an average dose difference of − 8 % inside the PTV. An inverse proportional relation between the mean bladder dose and the actual volume of the bladder could be established. The daily applied dose to the rectum is about 1–54 % higher than predicted by the planning CT.

Conclusion

A dose calculation based on CBCT data is possible. The daily positioning correction of the patient is necessary to avoid an underdosage in the PTV. The new contouring of the organs at risk— the bladder and rectum—allows a better appraisal to be made of the total applied dose to these organs.

Zusammenfassung

Ziel

Basierend auf einer Kalibrierung der Hounsfield-Einheiten zur Elektronendichte bieten Cone-Beam-Computed-Tomography-(CBCT)Datensätze die Möglichkeit, die applizierte Dosis im Patienten retrospektiv zu berechnen. Auf dieser Grundlage können die Konsequenzen einer Lagerungskorrektur und der morphologischen Veränderungen für Prostatakarzinompatienten quantifiziert werden.

Materialien und Methoden

Die Risikoorgane wurden auf den CBCT-Daten von 7 Patienten neu konturiert, um die tatsächlich applizierte Dosis zu evaluieren. Die tägliche Dosis im Planungszielvolumen (PTV) wurde mit und ohne die real erfolgten Translationsdaten neu berechnet.

Ergebnisse

Eine Dosisberechnung auf CBCT-Datensätzen mit Unsicherheiten kleiner 3 % ist möglich. Die Abweichungen zwischen Planungs-CT und CBCT ohne Berücksichtigung der bildgestützten Repositionierung des Patienten zeigen im Mittel eine Dosisdifferenz von − 8 % im PTV. Es konnte ein umgekehrt proportionaler Zusammenhang zwischen der mittleren Dosis in der Blase und dem tatsächlichem Volumen der Blase festgestellt werden. Die täglich applizierte Dosis im Rektum ist zwischen 1 und 54 % höher, als im Planungs-CT berechnet wurde.

Schlussfolgerung

Eine Dosisberechnung auf CBCT-Datensätzen ist möglich. Die tägliche Lagerungskorrektur des Patienten ist nötig, um eine Unterdosierung im Zielvolumen zu vermeiden. Die Neukonturierung der Risikostrukturen ermöglicht eine bessere Abschätzung der tatsächlich applizierten Dosis in Blase und Rektum.

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Acknowledgments

Supported by a research grant of the University Medical Center Giessen and Marburg (UKGM).

Compliance with ethical guidelines

Conflict of interest. P. Hüttenrauch, M. Witt, D. Wolff, S. Bosold, R. Engenhart-Cabillic, J. Sparenberg, H. Vorwerk, and K. Zink state that there are no conflicts of interest. All studies on humans described in the present manuscript were carried out with the approval of the responsible ethics committee and in accordance with national law and the Helsinki Declaration of 1975 (in its current, revised form). Informed consent was obtained from all patients included in studies.

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Authors and Affiliations

  1. Klinik für Strahlentherapie, Universitätsklinikum Gießen-Marburg GmbH, Klinikstr. 33, 35392, Gießen, Germany

    P. Hüttenrauch, M. Witt, D. Wolff, S. Bosold, R. Engenhart-Cabillic, J. Sparenberg & K. Zink

  2. Institut für Medizinische Physik und Strahlenschutz, Technische Hochschule Mittelhessen, Gießen, Germany

    P. Hüttenrauch, M. Witt & K. Zink

  3. Klinik für Strahlentherapie und Radioonkologie, Universitätsklinikum Gießen-Marburg GmbH, Marburg, Germany

    R. Engenhart-Cabillic, H. Vorwerk & K. Zink

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  1. P. Hüttenrauch
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  2. M. Witt
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  3. D. Wolff
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  4. S. Bosold
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  7. H. Vorwerk
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  8. K. Zink
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Correspondence to P. Hüttenrauch.

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Hüttenrauch, P., Witt, M., Wolff, D. et al. Target volume coverage and dose to organs at risk in prostate cancer patients. Strahlenther Onkol 190, 310–316 (2014). https://doi.org/10.1007/s00066-013-0483-2

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  • DOI: https://doi.org/10.1007/s00066-013-0483-2

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