The use of extended dose range film for dosimetric calibration of a scanning liquid-filled ionization chamber electronic portal imaging device

A scanning liquid filled ionization chamber electronic portal imaging device (SLIC-EPID) and Extended Dose Range (EDR2) films were used to evaluate transmitted dose profiles for homogeneous and inhomogeneous phantoms. The pixel values acquired from the electronic portal images (EPIs) were converted to dose using calibrated ionization chamber measurements. Since SLIC-EPID is developed to have a uniform response for all liquid ionization chambers, the off-axis dose values were reconstructed using a correction factor matrix (CFM), defined as the ratio of relative EDR2 film and corresponding EPID dose values measured in air. The transmitted dose distributions in the EPID detector layer were also modelled using Pinnacle3 treatment planning system (TPS). The agreement between transmitted dose distributions measured using a SLIC-EPID, EDR2 films and those calculated using TPS was assessed using the gamma function algorithm. For both homogenous and inhomogeneous phantoms, more than 90 % agreement was achieved using gamma criteria of 2%/3mm and 3%/2.5mm, respectively. The results indicate that the calibration procedure, proposed in the current study, should be performed if SLIC-EPID is to be used as a reliable two-dimensional transmitted dosimeter for clinical purposes.