Background and Purpose:
Intensity-modulated radiation therapy (IMRT) has shown its superiority to three-dimensional conformal radiotherapy in the treatment of prostate cancer. Different optimization algorithms are available: algorithms which first optimize the fluence followed by a sequencing (IM), and algorithms which involve the machine parameters directly in the optimization process (DSS). The aim of this treatment-planning study is to compare both of them regarding dose distribution and treatment time.
Patients and Methods:
Ten consecutive patients with localized prostate cancer were enrolled for the planning study. The planning target volume and the rectum volume, urinary bladder and femoral heads as organs at risk were delineated. Average doses, the target dose homogeneity H, D5, D95, monitor units per fraction, and the number of segments were evaluated.
Results:
While there is only a small difference in the mean doses at rectum and bladder, there is a significant advantage for the target dose homogeneity in the DSS-optimized plans compared to the IM-optimized ones. Differences in the monitor units (nearly 10% less for DSS) and the number of segments are also statistically significant and reduce the treatment time.
Conclusion:
Particularly with regard to the tumor control probability, the better homogeneity of the DSS-optimized plans is more profitable. The shorter treatment time is an improvement regarding intrafractional organ motion. The DSS optimizer results in a higher target dose homogeneity and, simultaneously, in a lower number of monitor units. Therefore, it should be preferred for IMRT of prostate cancer.
Hintergrund und Ziel:
Die intensitätsmodulierte Strahlentherapie (IMRT) hat ihre Überlegenheit gegenüber der dreidimensionalen konformalen Strahlentherapie in der Behandlung des Prostatakarzinoms gezeigt. Verschiedene Optimierungsalgorithmen stehen zur Verfügung: Algorithmen, die erst die Fluenz optimieren und anschließend eine Segmentierung durchführen (IM), und Algorithmen, die die Maschinenparameter direkt in den Optimierungsprozess integrieren (DSS). Ziel dieser Planungsstudie ist es, beide hinsichtlich Dosisverteilung und Bestrahlungszeit zu vergleichen.
Patienten und Methodik:
In die Planungsstudie wurden zehn aufeinanderfolgende Patienten mit lokalisiertem Prostatakarzinom eingeschlossen. Das Planungszielvolumen und als Risikostrukturen das Rektumvolumen, Harnblase und beide Femurköpfe wurden markiert. Die durchschnittliche Dosis in den Risikoorganen, die Homogenität im Zielvolumen, D5, D95, die Monitoreinheiten pro Fraktion und die mittlere Segmentzahl wurden ermittelt.
Ergebnisse:
Während nur ein kleiner Unterschied in der mittleren Dosis in Rektum und Blase besteht, findet sich ein signifikanter Vorteil bezüglich der Homogenität im Zielvolumen für die mit „direct step and shoot“ optimierten Pläne gegenüber denjenigen mit Fluenzoptimierung. Die Unterschiede bei den Monitoreinheiten (fast 10% weniger für den DSS-optimierten Plan) und der Segmentzahl sind ebenfalls statistisch signifikant.
Schlussfolgerung:
Insbesondere im Hinblick auf die Tumorkontrollwahrscheinlichkeit ist die größere Homogenität der DSS-optimierten Pläne vorteilhafter. Die kürzere Behandlungszeit stellt eine Verbesserung in Bezug auf intrafraktionelle Organbewegung dar. Der DSS-Optimierer führt zu einer besseren Homogenität im Zielvolumen bei einer reduzierten Anzahl von Monitoreinheiten. Deshalb sollte er für die IMRT des Prostatakarzinoms bevorzugt werden.
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Treutwein, M., Hipp, M., Kölbl, O. et al. IMRT of prostate cancer. Strahlenther Onkol 185, 379–383 (2009). https://doi.org/10.1007/s00066-009-1950-7
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DOI: https://doi.org/10.1007/s00066-009-1950-7
Key Words:
- Direct step and shoot
- Direct machine parameter optimization
- Intensity-modulated radiation therapy
- IMRT
- Prostate cancer