A-Si FLAT PANEL

Flat Panel Illustration In 2000, a large array A-Si flat panel EPID detector was installed (AL-7) on one of the PRIMUS accelerator at UCSF to allow for a comparison of performance. During the development period of MVCBCT, the introduction in 2004 of a new flat panel (AG-9) better optimized for high energy photons showed a several fold increase in sensitivity, allowing the routine acquisition of portal images with only 1M.U. When not specified, the characteristics and performance presented below are for device AL-7. Physical Property The principle of operation of an a-Si-detector is shown schematically in Figure 1. The flat-panel imager consists of a two-dimensional array of imaging pixels, which are configured as photodiodes. They convert the photons emitted from the phosphor to charge and store that charge on the pixel capacitance. The signal is read out by activation of scanning control lines for each row of the device, connected to thin film fieldeffect transistors (TFT) located on each detector pixel. The physical properties of the imager are summarized in Table 1.