Heidelberg 2006 – scientific programme

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ST: Strahlen- und Medizinphysik

ST 11: Verbesserung der Bestrahlungsplanung

ST 11.6: Talk

Tuesday, March 14, 2006, 17:40–17:50, D

Assessment of a new Multileaf Collimator Concept using Geant4 Monte Carlo simulations — •Martin Tacke, Hanitra Szymanowski, and Uwe Oelfke — Deutsches Krebsforschungszentrum, Im Neuenheimer Feld 280, D-69120 Heidelberg

The aim of the work was to investigate the dosimetric properties of a new multileaf collimator (MLC) concept with the help of Monte Carlo (MC) simulations prior to prototype production. The MC code Geant4 allows the implementation of new geometrical designs like the leaf packages which were imported with the help of CAD (Computer Aided Design) data. An experimentally validated phase space combined with a virtual Gaussian-shaped source model was employed to simulate a 6 MV therapy beam. First, transmission values for different tungsten alloys were extracted using the MC codes Geant4 and BEAMnrc and experimental measurements. High resolution simulations were performed to detect leakage. The 20%-80% penumbra was determined using 10x10 cm² fields shifted along the center axes. The transmission values, determined as linear absorption coefficients for different sinter, showed a good agreement with experimental measurements. Simulations with varying widths of the radiation source showed its impact on leakage and penumbra: for widths of 2 mm and 4 mm, the interleaf leakage is below 0.3% and 0.75%. The results for penumbra (4.7 ± 0.5mm) and leakage also agreed well with the measurements. As shown by this study, Geant4 is an appropriate tool for the dosimetric investigation of an MLC. The quantification of leakage, penumbra, and tongue-and-groove effect and an evaluation of the impact of different beam parameters was possible.