Optimization of Material and Thickness of Accelerator Target for Megavoltage Electronic Portal Imaging Device

Megavoltage electronic portal imaging device(EPID)suffers from poor quality images comparing to those produced with kilovoltage X-rays. The main factors impacting image quality include the target size and material. The target thickness and material on a 6 MV medical linear accelerator were optimized to maximize the image quality by using Geant4 Monte-Carlo simulation. A simple model of the whole imaging chain was developed for investigation of the effect of the target parameters on the quality of the image. The results show that the low-atomic number (Z) and thin targets make a improve contrast in EPID image. The 6 MV EPID electron mode with a 3 mm copper or 10 mm aluminum target is more suitable without flattening filtration.