Using 2D Ion-chamber Array For MLC Leaf Position Accuracy Of VMAT

IMRT(Intensity Modulated Radiation Therapy)has been the most mainstream of radiation therapy technology, the MLC(multileaf collimator) as the important equipment to adjust the beam intensity has been widely applied in clinical. The position accuracy of multileaf collimator will directly affect the implementation of precise radiotherapy dose. Therefore, the multileaf collimator position accuracy testing and ensure the leaf in place is important for the quality assurance and quality control in radiotherapy. The goal of this research project is to evaluate traditional methods using in leaf position QA. Furthermore, a new method for testing the MLC position accuracy of the Volumetric Modulated Arc Therapy was developed.The methods for testing the multileaf collimator leaf positioning accuracy on intensity including the radiographic film, ion-chamber, 2D array, EPID etc, conjuncted with a leaf edge function to compare the difference among these traditional techniques. The methods for the static MLC could check out the leaf position error effectively. For the dynamic MLC, the MLC was moving at the time of the beam irradiation. VMAT combined with the dynamic intensity modulated and the arc treatment, while the the radiation exposure, the gantry rotate and the MLC movement. The traditional techniques cannot test the MLC position error of VMAT. In this study, the position error of the d-MLC with the gantry rotation will be tested by using 2D ion-chamber array, set up a complete set of VMAT MLC quality assurance for the daily test. The result shows that 0.2mm position error can be detected rapidly, with the gantry rotation, 1mm position error can be detected by 2D ion-chamber.These results show that the method for the MLC quality assurance and quality control by using 2D ion-chamber array is simple and effective, and it can be used for the routine detection of MLC.