ABSTRACT
Widespread clinical implementation of intensity-modulated radiation therapy (IMRT) using conventional linear accelerator (LINAC) equipment increased rapidly in this century following a decade of development of the equipment and techniques. Scatter of the incident beam will occur in the conversion layer and the phosphor layer and potentially also in layers distal to the detector. Both forward and backward radiation scatter can contribute to dose deposition in the electronic portal imaging devices (EPID). EPIDs exhibit a strong energy-dependent response due to the high atomic number conversion and phosphor layers. Each individual pixel in the photodiode matrix can exhibit a unique offset or background signal and unique gain response to incident radiation. Another dosimetric feature of EPIDs that should be considered for dosimetry is the deviation from linearity that can occur for small monitor unit (MU) deliveries or with particular types of imaging modes.
