Searching standard parameters for volumetric modulated arc therapy (VMAT) of prostate cancer

Background Since December 2009 a new VMAT planning system tool is available in Oncentra® MasterPlan v3.3 (Nucletron B.V.). The purpose of this study was to work out standard parameters for the optimization of prostate cancer. Methods For ten patients with localized prostate cancer plans for simultaneous integrated boost were optimized, varying systematically the number of arcs, collimator angle, the maximum delivery time, and the gantry spacing. Homogeneity in clinical target volume, minimum dose in planning target volume, median dose in the organs at risk, maximum dose in the posterior part of the rectum, and number of monitor units were evaluated using student’s test for statistical analysis. Measurements were performed with a 2D-array, taking the delivery time, and compared to the calculation by the gamma method. Results Plans with collimator 45° were superior to plans with collimator 0°. Single arc resulted in higher minimum dose in the planning target volume, but also higher dose values to the organs at risk, requiring less monitor units per fraction dose than dual arc. Single arc needs a higher value (per arc) for the maximum delivery time parameter than dual arc, but as only one arc is needed, the measured delivery time was shorter and stayed below 2.5 min versus 3 to 5 min. Balancing plan quality, dosimetric results and calculation time, a gantry spacing of 4° led to optimal results. Conclusion A set of parameters has been found which can be used as standard for volumetric modulated arc therapy planning of prostate cancer

Präzise Modellierung von Risikoorganen und Zielvolumina für die Protonentherapie intraocularer Tumoren

In der vorliegenden Arbeit wurde ein Verfahren zur pr. azisen Modellierung von Ri- sikostrukturen und Zielvolumina f. ur die Protonentherapie intraocularer Tumore ent- wickelt. Ziel ist, durch die genaue Kenntnis der Patientengeometrie die Gefahr von . Uberdosierungen im Normalgewebe und damit die Wahrscheinlichkeit von unerw. unsch- ten Nebenwirkungen zu minimieren. Es wurde ein dreidimensionales geometrisches Au- genmodell entwickelt, das im Rahmen einer multimodalen modellbasierten Segmentie- rung auf Grundlage von 3D-Bilddaten pr. azise an die Geometrie des Auges angepa¡t werden kann. Da sich in den 3D-Daten jedoch das Zielvolumen nicht eindeutig abgren- zen l. a¡t, werden hierzu Fotogra en des Augenhintergrundes herangezogen. Dazu wurde eine Methode entwickelt, die die Informationen aus Modell, 3D-Daten und Fundusfoto- gra e geometrisch korreliert in einem zweidimensionalen Diagramm des Augenhinter- grundes vereinigt und eine eineindeutige Zuordnung zwischen dem zweidimensionalen Fundusdiagramm und den 3D-Daten erm. oglicht. Die dreidimensionale Tumorober . ache wird aus der vom Benutzer direkt in das Fundusdiagramm eingezeichneten Tumorba- sis und der aus Ultraschallmessungen gewonnenen Tumorh. ohe automatisch berechnet. Dieses Verfahren erm. oglicht die Erstellung eines dreidimensionalen Patientenmodells, das sowohl die einzelnen Strukturen des Auges als auch dasTumorvolumen pr. azise be- schreibt. Zur Anwendung in der Protonentherapie von Augentumoren wurde hieraus ein Softwaremodul erstellt und in das Bestrahlungsplanungssystem OCTOPUS integriert

The influence of radiotherapy techniques on the plan quality and on the risk of secondary tumors in patients with pituitary adenoma

Background This planning study compares different radiotherapy techniques for patients with pituitary adenoma, including flatness filter free mode (FFF), concerning plan quality and secondary malignancies for potentially young patients. The flatness filter has been described as main source of photon scatter. Material and methods Eleven patients with pituitary adenoma were included. An Elekta Synergy (TM) linac was used in the treatment planning system Oncentra (R) and for the measurements. 3D plans, IMRT, and VMAT plans and non-coplanar varieties were considered. The plan quality was evaluated regarding homogeneity, conformity, delivery time and dose to the organs at risk. The secondary malignancy risk was calculated from dose volume data and from measured dose to the periphery using different models for carcinoma and sarcoma risk. Results The homogeneity and conformity were nearly unchanged with and without flattening filter, neither was the delivery time found substantively different. VMAT plans were more homogenous, conformal and faster in delivery than IMRT plans. The secondary cancer risk was reduced with FFF both in the treated region and in the periphery. VMAT plans resulted in a higher secondary brain cancer risk than IMRT plans, but the risk for secondary peripheral cancer was reduced. Secondary sarcoma risk plays a minor role. No advantage was found for non-coplanar techniques. The FFF delivery times were not shortened due to additional monitor units needed and technical limitations. The risk for secondary brain cancer seems to depend on the irradiated volume. Secondary sarcoma risk is much smaller than carcinoma risk in accordance to the results of the atomic bomb survivors. The reduction of the peripheral dose and resulting secondary malignancy risk for FFF is statistically significant. However, it is negligible in comparison to the risk in the treated region. Conclusion Treatments with FFF can reduce secondary malignancy risk while retaining similar quality as with flattening filter and should be preferred. VMAT plans show the best plan quality combined with lowest peripheral secondary malignancy risk, but highest level of second brain cancer risk. Taking this into account VMAT FFF seems the most advantageous technique for the treatment of pituitary adenomas with the given equipment

Linac Twins in Radiotherapy

In a radiotherapy department having more than one linear accelerator, it is rather common to match the dose output of all machines. In particular, the recently developed flattening filter free mode requires new investigations regarding the feasibility of matching and the consequences for quality assurance and workload. This refers also to the beam model of the radiotherapy treatment planning system. Our results show that matching is possible not only for flat beams but also for flattening filter free mode. Therefore, the machines can substitute each other in the case of breakdown or service without new treatment planning even in the case of complex intensity-modulated radiotherapy or volumetric-modulated arc therapy. The quality assurance is reduced to only one data set for both the linear accelerators and the radiotherapy treatment planning system

Einfluss des Dosisberechnungsalgorithmus' und des Planungssystems auf die Qualität von Verifikationsplänen mit fluenzmodulierter Technik beim Prostatakarzinom

Einführung Die Qualität berechneter Dosisverteilungen von Verifikationsplänen hängt vom Algorithmus ab. In dieser Arbeit soll der Einfluss zweier Algorithmen - Monte Carlo-Algorithmus und Collapsed Cone - auf diese Qualität untersucht werden. Material und Methoden Für diese Untersuchung wurden IMRT- und VMAT- Pläne mit und ohne Ausgleichskörper für zehn Patienten mit lokalisiertem Prostatakarzinom erstellt. Im primären Plannungssystem (Oncentra, Fa. Elekta) wurden die Pläne optimiert und auf ein Phantom übertragen, das ein 2D-Array (MatrixxEvolution, Fa. IBA) enthielt. In diesem Phantom wurden die Verifikationspläne mit einem Collapsed Cone-Algorithmus berechnet. Anschließend wurden diese Pläne auf ein sekundäres Planungssystem übertragen (Monaco, Fa. Elekta) und dort unverändert mit einem Monte Carlo-Algorithmus nachgerechnet. Die berechneten Dosisverteilungen wurden mit den Messungen in diesem Phantom per Gamma-Index verglichen. Die Prozentsätze der positiv ausgewerteten Messpunkte wurden statistisch mit dem Wilcoxon-Test für verbundene Stichproben ausgewertet Ergebnisse Die Unterschiede zwischen beiden Algorithmen waren sehr klein. Ohne Ausgleichskörper gab es keinen signifikanten Unterschied, mit Ausgleichskörper war der Collapsed Cone-Algorithmus geringfügig besser bei IMRT, während bei VMAT ein ähnlich kleiner Vorteil beim Monte Carlo-Algorithmus lag. Ein IMRT-Plan konnte nicht nachgerechnet werden, da ein Feld nur aus einem Segment bestand, was vom sekundären System als unerlaubte Mischtechnik abgelehnt wurde. Diskussion und Schlussfolgerung Beide Planungssysteme stammen vom selben Hersteller; deshalb kann ein äquivalentes Qualitätsniveau angenommen werden. Das weitgehend homogene Phantom stellt nur eine kleine Herausforderung für beide Algorithmen dar. Mit kleinen Einschränkungen kann das sekundäre System für Nachrechnungen und damit als Verifikationssystem des primären Systems angewendet werden

Treatment Planning for Pituitary Adenomas - A Comparison of Flatness Filter Free and Flat Beam Plans

Introduction Radiotherapy of pituitary adenomas is often applied as postoperative therapy of tumors that cannot be removed completely. Fluence modulating techniques like IMRT or VMAT support the use of the flatness filter free (FFF) mode in modern linear accelerators. In this mode a considerably higher dose rate is achieved by omitting the flatness filter. This planning study compares different plans for patients with pituitary adenoma. The plans were optimized using both modes: flattened beam (FB) and FFF. The aim of this study is to evaluate the plan quality. Material and Methods Data sets of 11 patients with pituitary adenoma were used for this retrospective planning study. The objectives for the PTV were set to a minimum dose of 49.4Gy and a maximum dose of 51.4Gy in 28 fractions, aiming for a fraction dose of 1.8Gy. Further objectives were set for the following regions of interest (ROI): brain, brainstem, chiasm, and both lenses, bulbs, lacrimal glands, and parotids. The planning was performed with the treatment planning system (TPS) Oncentra External Beam v4.5 (Elekta AB, Sweden) using the collapsed cone algorithm. In both modes (FB and FFF) IMRT plans with nine equispaced coplanar fields were generated; in a second variant a tenth non-coplanar field was added. Similarly two VMAT plans were optimized: one single arc rotation (182°-178°), and the second with an added half rotation in the sagittal patient plane (0°-180°). The applied linac Synergy Agility (Elekta AB, Sweden) offers a dose rate of 550MU/min (FB) and 1700MU/min (FFF). The leaves have a width of 5mm projected to the isocenter. The following parameters were evaluated: the average dose DAv to the PTV, homogeneity index HI, and the conformity index CI. For all plans the observance of the objectives for the organs at risk given in table 1 was investigated. Results For both modes FB and FFF the dose volume statistics are very close. With some minor exceptions the objectives for the ROIs are met. Only the maximum dose to the chiasm is slightly exceeded in most cases, as it is part of the PTV. Regarding the PTV (HI and CI) pronounced differences are found in the comparison of IMRT and VMAT. The distinction between coplanar and non-coplanar techniques is less important. Discussion The difference in the plan quality of FB and FFF plans is of no clinical importance. A decision for the preferred treatment technique will therefore be taken based on measurements of the delivery time and peripheral dose which will follow. All non-coplanar techniques will require more linac time due to couch rotations without showing advantages in plan quality

Volumetric-modulated arc therapy and intensity-modulated radiation therapy treatment planning for prostate cancer with flattened beam and flattening filter free linear accelerators

This study on patients with localized prostate cancer was set up to investigate valuable differences using flattened beam (FB) and flattening filter free (FFF) mode in the application of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT). For ten patients, four different plans were calculated with Oncentra planning system of Elekta, using Synergy machines: IMRT and VMAT, with and without flattening filter. Homogeneity and conformity indexes, dose to the organs at risk, and measurements of peripheral dose and dosimetric plan verification including record of the delivery times were analyzed and statistically evaluated. The indexes for homogeneity and conformity (CTV and PTV) are either advantageous or not significantly different for FFF compared to FB with one minor exception. Regarding the doses to the organs at risk and the measured peripheral dose, equivalent or lower doses were delivered for FFF than with FB. Furthermore, the delivery times were significantly shorter for FFF. VMAT compared to IMRT reveals benefits or at least equivalent values. VMAT-FFF combines the most advantageous plan quality parameters with the shortest delivery times and reduced peripheral dose and is therefore recommended for the given equipment and cancer localization