Development of an Electronic Portal Imaging Device Dosimetry Method

Abstract

Support arm backscatter and off-axis effects of an electronic portal imaging device (EPID) are challenging for radiotherapy quality assurance. Aiming at the issue, we proposed a simple yet effective method with correction matrices to rectify backscatter and off-axis responses for EPID images. First, we measured the square fields with ionization chamber array (ICA) and EPID simultaneously. Second, we calculated the dose-to-pixel value ratio and used it as the correction matrix of the corresponding field. Third, the correction value of the large field was replaced with that of the same point in the small field to generate a correction matrix suitable for different EPID images. Finally, we rectified the EPID image with the correction matrix, and then the processed EPID images were converted into the absolute dose. The calculated dose was compared with the measured dose via ICA. The gamma pass rates of 3%/3 mm and 2%/2 mm (5% threshold) were 99.6% ± 0.94% and 95.48% ± 1.03%, and the average gamma values were 0.28 ± 0.04 and 0.42 ± 0.05, respectively. Experimental results verified our method accurately corrected EPID images and converted pixel values into absolute dose values such that EPID was an efficient radiotherapy dosimetry tool.

A Novel Approach for Position Verification and Dose Calculation through Local MVCT Reconstruction

“…Our team conducted earlier research on pre-treatment dose verification based on EPID [ 25 ] and in vivo dose verification methods [ 25 , 26 ], discovering that EPID transmission images contain patient anatomical information, which can be utilized for reconstructing the three-dimensional structure of patients. Furthermore, the radiation source used for EPID image acquisition is the same as that used during patient treatment, which addresses the limitations of CBCT for positioning verification to some extent.…”

Using eclipse scripting to fully automate in‐vivo image analysis to improve treatment quality and safety

“…Electronic portal imaging devices (EPIDs), primarily used for pretreatment checks in intensity‐modulated radiation therapy (IMRT) and volumetric‐modulated arc therapy (VMAT), are gaining use for in‐vivo dosimetry. 1 , 2 Studies analyzing the effectiveness of EPIDs in detecting clinically reported incidents have found that when used for pretreatment quality assurance (QA), EPIDs detect a low number of clinically reported incidents (6%). 3 However, they are much more effective when used in‐vivo QA.…”