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Image quality and dose distributions of three linac-based imaging modalities

Bildqualität und Dosisverteilungen dreier Linac-basierter Bildgebungssysteme

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Abstract

Background and purpose

Linac-based patient imaging is possible with a variety of techniques using different photon energies. The purpose of this work is to compare three imaging systems operating at 6 MV, flattening free filter (FFF) 1 MV, and 121 kV.

Patients and methods

The dose distributions of all pretreatment set-up images (over 1,000) were retrospectively calculated on the planning computed tomography (CT) images for all patients with prostate and head-and-neck cancer treated at our institution in 2013. We analyzed the dose distribution and the dose to organs at risk.

Results

For head-and-neck cancer patients, the imaging dose from 6-MV cone beam CT (CBCT) reached maximum values at around 8 cGy. The 1-MV CBCT dose was about 63–79 % of the 6-MV CBCT dose for all organs at risk. Planar imaging reduced the imaging dose from CBCT to 30–40 % for both megavoltage modalities. The dose from the kilovoltage CBCT was 4–10 % of the 6-MV CBCT dose. For prostate cancer patients, the maximum dose from 6-MV CBCT reached 13–15 cGy, and was reduced to 66–73 % for 1 MV. Planar imaging reduces the MV CBCT dose to 10–20 %. The kV CBCT dose is 15–20 % of the 6-MV CBCT dose, slightly higher than the dose from MV axes. The dose distributions differ markedly in response to the different beam profiles and dose–depth characteristics.

Zusammenfassung

Hintergrund und Ziel

Linac-basierte Bildgebung zur Patientenlagerung ist mit einer Vielzahl von Techniken unterschiedlicher Photonenenergien möglich. Ziel dieser Arbeit ist der Vergleich dreier Bildgebungssysteme mit 6 MV (Megavolt), FFF 1 MV, und 121 kV (Kilovolt).

Patienten und Methoden

Für alle im Jahr 2013 an unserer Klinik behandelten Prostata- und HNO-Patienten wurden retrospektiv die Dosisverteilungen aller Verifikationsaufnahmen (über 1000 insgesamt) auf der Planungs-Computertomographie (CT) berechnet. Wir analysierten die Dosisverteilung und die Dosis an den Risikoorganen.

Ergebnisse

Bei HNO-Patienten erreichte die Dosis von 6 MV „Cone-beam“-CT (CBCT)Maximalwerte um 8 cGy. Mit 1 MV wird die Dosis auf 63–79 % des 6 MV-Werts reduziert. Planare Bildgebung reduzierte die Bildgebungsdosis von CBCT für beide MV-Bildgebungen auf 30–40 %. Die Dosis von kV-CBCT betrug etwa 4–10 % der Dosis von 6 MV CBCT. Für Prostatapatienten erreichte die Bildgebungsdosis von 6 MV CBCT-Werte von 13–15 cGy, was durch Anwendung der 1-MV-Energie auf 66–73 % reduziert wurde. Planare Bildgebung reduzierte diesen Wert auf 10–20 %. Die Dosis von kV-CBCT lag bei 15–20 % der 6-MV-CBCT-Dosis, etwas höher als die Dosis von MV-Achsen. Die Dosisverteilungen unterschieden sich aufgrund der verschiedenen Strahlprofile und Tiefendosiskurven.

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Correspondence to Yvonne Dzierma.

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Conflict of interest

Y. Dzierma, E. Ames, F. Nuesken, J. Palm, N. Licht, and C. Rübe state that there are no conflicts of interest.

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Dzierma, Y., Ames, E., Nuesken, F. et al. Image quality and dose distributions of three linac-based imaging modalities. Strahlenther Onkol 191, 365–374 (2015). https://doi.org/10.1007/s00066-014-0798-7

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  • DOI: https://doi.org/10.1007/s00066-014-0798-7

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