Effect of Photon-Beam Energy on VMAT and IMRT Treatment Plan Quality and Dosimetric Accuracy for Advanced Prostate Cancer

Der Einfluss der Photonenenergie auf VMAT- und IMRT-Planqualität und dosimetrische Genauigkeit für fortgeschrittenen Prostatatumor



The goal of the research was to evaluate treatment plan quality and dosimetric accuracy of volumetric modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) plans using 6, 10, and 15 MV photon beams for prostate cancer including lymph nodes.


In this retrospective study, VMAT and IMRT plans were generated with the Pinnacle© treatment planning system (TPS) (V9.0) for 10 prostate cancer cases. Each plan consisted of two target volumes: PTVB included the prostate bed, PTVPC+LN contained PTVB and lymph nodes. For plan evaluation statistics, the homogeneity index, conformity index, mean doses, and near-max doses to organs at risk (OAR) were analyzed. Treatment time and number of monitor units were assessed to compare delivery efficiency. Dosimetric plan verification was performed with a 2D ionization chamber array placed in a full scatter phantom.


No differences were found for target and OAR parameters in low and high energy photon beam plans for both VMAT and IMRT. A slightly higher low dose volume was detected for 6 MV VMAT plans (normal tissue: Dmean = 16.47 Gy) compared to 10 and 15 MV VMAT plans (Dmean = 15.90 Gy and 15.74 Gy, respectively), similar to the findings in IMRT. In VMAT, > 96% of detector points passed the 3%/ 3 mm γ criterion; marginally better accuracy was found in IMRT (> 97%).


For static and rotational IMRT, 15 MV photons did not show advantages over 6 and 10 MV high energy photon beams in large volume pelvic plans. For the investigated TPS and linac combination, 10 MV photon beams can be used as the general purpose energy for intensity modulation.



Vergleich von Planqualität und dosimetrischer Genauigkeit von volumetrisch modulierter Rotationstherapie (VMAT) und intensitätsmodulierter Strahlentherapie (IMRT) mit 6, 10 und 15 MV Photonenenergie für Patienten mit fortgeschrittenem Prostatatumor einschließlich Lymphabfluss.

Patienten und Methoden:

In dieser retrospektiven Planungsstudie wurden VMAT- und IMRT-Pläne mit dem Pinnacle©-Planungssystem (V9.0) für 10 Patienten mit Prostatatumoren (PC) generiert. Jeder Plan enthielt 2 Zielvolumina: PTVB umschloss die Prostata, PTVPC+LN beinhaltete PTVB und den Lymphabfluss. Für die Beurteilung der Planqualität wurden Homogenitätsindex, Konformitätsindex, mittlere Dosis und Nahe-Maximum-Dosis für Risikoorgane (OAR) berechnet. Als Parameter für die Bestrahlungseffizienz wurden Bestrahlungszeit und Anzahl der Monitoreinheiten (MU) herangezogen. Die Planverifikation wurde mit einer 2D Ionisationskammer-Matrix in einem Festkörperphantom durchgeführt.


Es wurden keine Unterschiede zwischen niedrigen und hohen Energien für Zielvolumen- und Risikoorgan-Parametern in VMAT- und IMRT-Plänen gefunden (Tabellen 2 und 3, Abbildung 2). In 6-MV-VMAT-Plänen wurde ein geringfügig höheres Niedrigdosisvolumen (Normalgewebe: Dmean = 16,47 Gy) als in 10- und 15-MV-Plänen (je Dmean = 15,90 Gy und 15,74 Gy) gefunden; ähnliche Ergebnisse wurden für IMRT-Pläne ermittelt. VMAT-Pläne erreichten einen Gamma-Index < 1 (3 mm Abstand und 3% Dosis) für > 96% der Detektorpunkte; IMRT-Pläne erreichten > 97% der Detektorpunkte (Abbildung 3).


Unsere Studie zeigt für große Beckenvolumina bei 15-MV-VMAT- und -IMRT-Plänen keinen Vorteil gegenüber Plänen mit 6 und 10 MV. Für die verwendete Kombination von TPS und Linac wurde festgestellt, dass 10-MV-Photonen als ‚Universal’-Energie für Intensitätsmodulation verwendet werden können.

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Correspondence to Assoc. Prof. Dr. Dietmar Georg.

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Pasler, M., Georg, D., Wirtz, H. et al. Effect of Photon-Beam Energy on VMAT and IMRT Treatment Plan Quality and Dosimetric Accuracy for Advanced Prostate Cancer. Strahlenther Onkol 187, 792–798 (2011). https://doi.org/10.1007/s00066-011-1150-0

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Key Words

  • VMAT
  • IMRT
  • Advanced prostate cancer


  • VMAT
  • IMRT
  • Fortgeschrittener Prostatatumor