Dosimetric characteristics and day-to-day performance of an amorphous-silicon type electronic portal imaging device

Abstract

This study investigated the dosimetric characteristics of an amorphous-silicon (aSi) electronic portal imaging device (EPID) and the utility and consistency of its daily output. This investigation utilised the portal dose prediction function of aSi-1000 EPID panel to test the panel for linearity, field size, dose rate and source to detector distance (SDD). To check daily output consistency, to acquire fluence by aSi EPID and reading calibration unit (CU) value every working day. Percentage variance of daily output also was measured using alternative two different types of dosimeter, EBT3 film and a multiple-channels output check device. Total of 165 daily output readings of EPID showed an average variance of 0.36% ± 0.53 from July 2014 to February 2015. The other two results between EBT3 film with BeamChecker Plus were −0.17% ± 2.36 and 0.35% ± 0.14, respectively. From correlation analysis, results of EPID is significantly correlated with BeamChecker Plus's (0.625, p << 0.001). Furthermore, the dosimetric characteristic of EPID indicated that CU values were a linear function of monitor units (MUs). When field size or dose rate varied, the panel's response was within 2%. The inverse square relation was between variable SDD and responding signal of panel. As compared with other dosimeters, the daily output monitor of aSi EPID was found to be reasonably consistent with commercial daily output device and replace with complex film-based procedure.