Evaluation of Dosimetic Characteristics of Electronic Portal Imaging Device (EPID) for Flattening Filter Free (FFF) Beams

Abstract

Objective: To evaluatethe dosimetric characteristics of electronics portal imaging device (EPID) for 6 and 10 megavoltage(MV) of flattening filter-free (FFF) beams.Material and Method: The EPID characteristicsfor FFF beams have been evaluated as follows; saturation with sourcedetector-distance (SDD), saturation with dose rate, dose linearity response with monitor unit (MU), and the scatterd radiation with field size.Results: The saturation of signal was not occurred at 150 cm and 180 cm SDD for 6 and 10 MV of FFF beams, respectively. When the signals were measured with optimal SSD according to vendor suggestion (150 cm and 180 cm), the standard deviation for all dose rate were ±1.35 and ±1.64 CU for 6 and 10 MV of FFF beams,respectively. The dose linearity response showed that EPID has a good linearity response between signals and MU forthe both of 6 and 10 MV of FFF beams. The results of scatterd radiation with field size were found that FFF beams have different respose from flattening filter (FF) beams with the highest differences of 5.50% and 6.78% for 6 and 10 MV of FFF beams, respectively.Conclusion: EPID has a good characteristic for FFF beams, and an extended SSD can be used to reduce the satured signal effects in FFF beams.