Application of Filtration Plate in Megavoltage EPID

EPID with megavoltage X-rays suffers from poor quality compared to kilovolt X-rays, so the accuracy of the patient positioning and position verification is affected. By using Monte Carlo method, a new way was explored to raise the resolution in current EPID system without altering its target. According to Monte Carlo simulation, it was found that the primary cause leading to a low resolution was the Compton scattering rays with low energy. The key technique raising the resolution and definition is to avoid the interference of low energy X-ray. From the simulation results and the experimental results by clinical megavoltage EPID, it can be found that the 2 mm Cu filtration plate is more helpful in improving the image quality.