Evaluation of Image Quality for Various Electronic Portal Imaging Devices in Radiation Therapy*

A phantom based evaluation of the clinical imaging performance of electronic portal imaging devices

“…The knowledge of CTF norm and NPS enables the introduction of the SNFR, which is a variable that can be associated with the signal to noise ratio at the detector output, expressed in the spatial frequency domain. SNFR is calculated by using the following formula: Where, CTF norm is the normalized CTF to the lowest spatial frequency f. SNFR may act as a substitution of Detective Quantum Efficiency, DQE [ 1 , 8 ], since it does not require neither the knowledge of the X-ray spectrum properties, nor the air-kerma. In addition, the use of CTF instead of MTF in the nominator makes the calculation of SNFR more straight forward without the absolute need of specialized software.…”

“…Electronic Portal Imaging Devices (EPIDs) were initially created to validate the geometric accuracy of patient positioning during radiotherapy [ 1 , 2 ]. The high-resolution images acquired by EPIDs, combined with the widespread adoption of modern radiotherapy techniques such as Intensity Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) extended their use to also assist the quality assurance (QA) of linear accelerators [ 3 ].…”

“…In previously published investigations methods for EPID quality assurance and image evaluation have been described, which are based on measuring the Signal to Noise Ratio (SNR), the Modulation Transfer Function (MTF), the Noise Power Spectrum (NPS), using specific methods, phantoms and dedicated software [ 1 , 5 , [7] , [8] , [9] ]. Studies, e.g.…”

“…Concerning the iViewGT portal imaging device, mounted on Elekta radiotherapy equipment is considered, the MTF with the edge method, the NNPS, Detective Quantum Efficiency (DQE) and the system response has been calculated for a range of Monitor Units (MUs) and by exploiting a Monte Carlo code for finding the number of X-ray photons needed for DQE calculation [ 1 ]. In addition, SNR, MTF and contrast for radiation incidence corresponding to 1–15 MUs for an Elekta iView EPID, measured with a PTW EPID QC phantom has been reported [ 5 ].…”

Towards the Implementation of a Phantom for the Low Contrast Evaluation of Electronic Portal Imaging Detectors (Epid): A Theoretical Study

“…It is therefore of essence to test the imaging performance of these detection devices. The assessment of the imaging performance of an EPID is performed with dedicated phantoms and methods as part of the quality control procedure [9], [10]. The phantoms may contain areas of low and high atomic number materials of different shapes so that parameters like image contrast, resolution and noise, to be evaluated [11], [12].…”