Performance Optimization of the Varian aS500 EPID System

Abstract

The general aim of this study was to optimize the acquisition parameters of a commercially available Electronic Portal Imaging Device (EPID) for clinical use in radiation therapy. Special attention was paid to selection of the parameter corresponding to the number of rows acquired between accelerator pulses, NRP, for various beam energies and dose rates.
The image acquisition system (IAS2) has been studied and portal image acquisition was found to be strongly dependent on the accelerator pulse frequency. This frequency is set for each ?energy ? dose rate? combination of the linear accelerator. For all combinations, the image acquisition parameters were systematically changed to determine the influence on the performances of the Varian aS500 EPID system.
The results showed that NRP had a major influence on detector saturation and the dose per image. Image quality was relatively insensitive to these parameters.