Monte Cario Simulation of a Micro-multileaf Collimator

摘要

The performance of a dynamic micro-multileaf collimator manufactured by 3D-Line, for stereotactic radiosurgery has been studied. Monte Cario simulations based on PENELOPE code and measurements with three different detectors (PTW Semiflex 31010 chamber, PTW PinPoint 31016 chamber and PTW Diode 60008) have been carried out. The geometry of the micro-multileaf collimator was tested by calculating the transmission through it and it was needed to reduce the separation between the leafs indicated by the manufacturer to reproduce the experimental results. An approximate simulation in which only Compton interactions of photons are considered was analyzed, providing a good agreement with the full simulations. With the Monte Cario model fixed, output factors for various field sizes were calculated and compared to the experimental ones, obtaining a good agreement. Percentage depth doses and transverse profiles at two depths measured with the Diode for small fields were well reproduced by the simulation, while the measurements performed with the PinPoint chamber showed differences in the Percentage depth doses, at large depths, and in the transverse profiles, at the penumbra. Monte Cario simulations and Semiflex and Diode measurements, performed for a 7 cm × 7 cm field, were in nice agreement, while those obtained with the PinPoint chamber showed differences that increased with the depth in water. At the phantom entrance, all measurements showed non-negligible differences what made Monte Cario a good option to estimate the absorbed dose in this region.