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Quasi-IMAT Technique and Secondary Cancer Risk in Prostate Cancer

Quasi-IMAT-Technik und Sekundärmalignomrisiko bei Prostatakarzinom

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Background and Purpose:

Estimates of secondary cancer risk after radiotherapy are relevant for treatment-planning comparison. Recently, the authors investigated the potential of a step-and-shoot intensity-modulated arc therapy (quasi-IMAT [qIMAT]) to improve the intensity-modulated radiotherapy (IMRT) plan quality. Here, the effect of the primary dose distribution, photon scatter and neutron dose, and the risk of secondary malignancies after qIMAT technique were analyzed and compared to IMRT.

Methods:

qIMAT plans with 36 beam directions and IMRT plans with six beam directions were created for 15-MV photons. Both plans were calculated for each of five prostate cancer patients. The obtained differential dose-volume histograms, photon scatter and neutron dose were used to determine the organ-equivalent dose (OED), which is proportional to the secondary cancer risk. Because of the uncertainty of the applicability of biological models to the OED concept both the linear-exponential and the plateau model for the dose-response relationship were applied.

Results:

Both models gave similar results. The OED in scanned CT volume was lower for the qIMAT technique, but higher in the volume not scanned, compared to IMRT. Using a maximum of 36 segments, the increase of risk resulting from qIMAT was < 1% compared to IMRT for both models. By setting the number of segments to 72, an increase of 8% in secondary cancer risk resulted from qIMAT using the linear-exponential model, compared to IMRT (plateau model: 7%). The primary dose is responsible for 88% of the total OED in IMRT and for 86% in qIMAT.

Conclusion:

Although qIMAT uses a large number of fields and therefore the volume of normal tissue that receives low-dose radiation is larger than for IMRT, the total OED (by considering primary and secondary contributions of radiation) does not increase the risk of developing a secondary cancer compared to a conventional IMRT plan.

Hintergrund und Ziel:

Die Abschätzung des strahleninduzierten Sekundärmalignomrisikos ist relevant, um Planvergleiche durchzuführen. Kürzlich haben die Autoren das Potential einer „step-and-shoot“-IMAT-Technik (quasi-IMAT [qIMAT]) zur Erhöhung der Planqualität einer intensitätsmodulierten Strahlentherapie (IMRT) untersucht. Hier wird das Sekundärmalignomrisiko nach dem Konzept der Organäquivalentdosis (OED) bei der Anwendung der qIMAT-Technik auf die Prostatabestrahlung analysiert.

Methodik:

qIMAT-Pläne mit 36 Feldern und IMRT-Pläne mit sechs Feldern wurden mit einer 15-MV-Photonenenergie erzeugt. Beide Techniken wurden auf fünf Patienten mit Prostatakarzinom angewendet. Mittels der erhaltenen Dosis-Volumen-Histogramme sowie publizierter Photonenstreu- und Neutronendosen wurde die Organäquivalentdosis (OED) berechnet, die proportional zum Sekundärmalignomrisiko ist. Wegen der Unsicherheit der Anwendbarkeit biologischer Modelle im OED-Konzept werden sowohl das linear-exponentielle als auch das Plateaumodell der Dosis-Wirkungs-Beziehung zugrunde gelegt.

Ergebnisse:

Beide angewendeten Modelle ergaben ähnliche Werte. Die OED innerhalb des CT-Volumens war bei qIMAT niedriger als bei IMRT, die OED außerhalb war dagegen höher. Bei Anwendung von 36 Segmenten lag die OED für qIMAT im Vergleich zur IMRT < 1% (für beide Modelle). Bei einer Erhöhung der Segmentanzahl auf 72 lag die Differenz bei Anwendung des linear-exponentiellen Modells bei 8% (7% beim Plateaumodell). Die primäre Dosis verursacht 88% der gesamten OED bei IMRT und 86% bei qIMAT.

Schlussfolgerung:

Obwohl qIMAT eine höhere Felderzahl verwendet als IMRT und dadurch mehr gesundes Gewebe mit niedriger Dosis bestrahlt wird, steigt die gesamte OED nicht an. Das Sekundärmalignomrisiko bei beiden Techniken ist in etwa gleich.

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Authors and Affiliations

  1. Department of Radiotherapy, University of Regensburg, Regensburg, Germany

    Ludwig Bogner

  2. Department of Radiotherapy, University of Regensburg, Franz-Josef-Strauß-Allee 11, 93053, Regensburg, Germany

    Judith Alvarez Moret

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  1. Judith Alvarez Moret
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  2. Oliver Koelbl
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  3. Ludwig Bogner
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Correspondence to Judith Alvarez Moret.

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Alvarez Moret, J., Koelbl, O. & Bogner, L. Quasi-IMAT Technique and Secondary Cancer Risk in Prostate Cancer. Strahlenther Onkol 185, 248–253 (2009). https://doi.org/10.1007/s00066-009-1931-x

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  • DOI: https://doi.org/10.1007/s00066-009-1931-x

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