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Converting from CT- to MRI-only-based target definition in radiotherapy of localized prostate cancer

A comparison between two modalities

Umstellung von CT-gestützter in ausschließlich MR-gestützte Strahlentherapieplanung beim lokalisierten Prostatakarzinom

Vergleich zwischen zwei Modalitäten

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Abstract

Purpose

To investigate the conversion of prostate cancer radiotherapy (RT) target definition from CT-based planning into an MRI-only-based planning procedure.

Materials and methods

Using the CT- and MRI-only-based RT planning protocols, 30 prostate cancer patients were imaged in the RT fixation position. Two physicians delineated the prostate in both CT and T2-weighted MRI images. The CT and MRI images were coregistered based on gold seeds and anatomic borders of the prostate. The uncertainty of the coregistration, as well as differences in target volumes and uncertainty of contour delineation were investigated. Conversion of margins and dose constraints from CT- to MRI-only-based treatment planning was assessed.

Results

On average, the uncertainty of image coregistration was 0.4 ± 0.5 mm (one standard deviation, SD), 0.9 ± 0.8 mm and 0.9 ± 0.9 mm in the lateral, anterior–posterior and base–apex direction, respectively. The average ratio of the prostate volume between CT and MRI was 1.20 ± 0.15 (one SD). Compared to the CT-based contours, the MRI-based contours were on average 2–7 mm smaller in the apex, 0–1 mm smaller in the rectal direction and 1–4 mm smaller elsewhere.

Conclusion

When converting from a CT-based planning procedure to an MRI-based one, the overall planning target volumes (PTV) are prominently reduced only in the apex. The prostate margins and dose constraints can be retained by this conversion.

Zusammenfassung

Ziel

Ziel unserer Studie war es, die Umstellung der Strahlentherapieplanung des Prostatakarzinoms von CT-gestützter in ausschließlich MR-gestützte Zieldefinition zu untersuchen.

Material und Methoden

Bei 30 Patienten mit Prostatakarzinom wurden eine CT und eine MRT unter Planungsbedingungen durchgeführt. Zwei Untersucher konturierten die Prostata in CT- und T2-gewichteten MR-Bildern. Mit Hilfe der Position von Goldstiften und der anatomischen Grenzen der Prostata wurden die CT- und MR-Bilder koregistriert. Es wurden die Genauigkeit der Koregistrierung sowie die Unterschiede der Zielvolumina und der Konturierung gemessen. Die Konvertierung der Prostatakonturen und die Dosisbeschränkung von CT- zu ausschließlich MR-gestützter Therapieplanung wurden bewertet.

Ergebnisse

Die Abweichung der Koregistrierung der Bilder betrug im Durchschnitt 0,4 ± 0,5 mm (Standardabweichung: 1 SD) in lateraler, 0,9 ± 0,8 mm in a.-p.- und 0,9 ± 0,9 mm in der Basis-Apex-Richtung. Das durchschnittliche Verhältnis des Prostatavolumens zwischen CT und MRT war 1,20 ± 0,15 (1 SD). Die MR-basierte Konturierung war verglichen mit der CT-basierten Konturierung im Bereich des Apex der Prostata im Durchschnitt um 2–7 mm , in rektaler Richtung um 0–1 mm und in der übrigen Prostata um 1–4 mm kleiner.

Schlussfolgerung

Unsere Ergebnisse zeigen, dass durch Umstellung von CT- in MR-gestützte Strahlentherapieplanung das Planungszielvolumen nur in der Prostataspitze deutlich reduziert wird. Die Umwandlung von CT-gestützter oder CT- und MR-gestützter in ausschließlich MR-gestützte Strahlenplanung erlaubt die Beibehaltung der Prostatakonturen und der Dosisbeschränkung.

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Authors and Affiliations

  1. Comprehensive Cancer Center, University of Helsinki and Helsinki University Hospital, POB 180, 00029, Helsinki, Finland

    Tiina Seppälä Ph.D., Harri Visapää M.D., Juhani Collan M.D., Mika Kapanen Ph.D., Mauri Kouri M.D., Mikko Tenhunen Ph.D. & Kauko Saarilahti M.D.

  2. HUS Medical Imaging Center, Radiology, University of Helsinki and Helsinki University Hospital, POB 180, 00029, Helsinki, Finland

    Annette Beule M.D.

Authors
  1. Tiina Seppälä Ph.D.
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  2. Harri Visapää M.D.
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  3. Juhani Collan M.D.
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  4. Mika Kapanen Ph.D.
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  5. Annette Beule M.D.
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  6. Mauri Kouri M.D.
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  7. Mikko Tenhunen Ph.D.
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  8. Kauko Saarilahti M.D.
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Corresponding author

Correspondence to Tiina Seppälä Ph.D..

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Conflict of interest

This study was financially supported by grant from the Helsinki University Central Hospital Research Funds, Helsinki, Finland. The authors alone are responsible for the content and writing of the paper.

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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Seppälä, T., Visapää, H., Collan, J. et al. Converting from CT- to MRI-only-based target definition in radiotherapy of localized prostate cancer. Strahlenther Onkol 191, 862–868 (2015). https://doi.org/10.1007/s00066-015-0868-5

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  • DOI: https://doi.org/10.1007/s00066-015-0868-5

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