A quality control test for electronic portal imaging devices

Abstract

A quality control (QC) test suitable for routine daily use has been developed for video based electronic portal imaging devices. It provides an objective and quantitative test for acceptable image quality on the basis of the high contrast spatial resolution and the contrast-to-noise ratio (CNR). The test uses a phantom consisting of five sets of high-contrast rectangular bar patterns with spatial frequencies of 0.1, 0.2, 0.25, 0.4, and 0.75 lp/mm. Data obtained during a one month calibration period were used to determine a critical frequency fc for the relative square wave modulation transfer function and a critical contrast-to-noise ratio (CNRc). Subsequent measurements indicating significant deviations from these critical values result in warning messages to the operator indicating potential problems in system performance. Measurements over a period of two years show that the QC test provides a sensitive indication of imaging performance.

Clinical assessment and characterization of a dual‐tube kilovoltage X‐ray localization system in the radiotherapy treatment room

“…( 13 – 15 ) The RMTF is the ratio of the MTF at a specific frequency to the MTF at the lowest frequency of a line‐pair template. In the present study, the 0.6 lp/mm line pair, the lowest frequency in the template, was used as the normalization—that is, $f_1=0.6$ lp/mm.…”

Guide to clinical use of electronic portal imaging

“…Shalev and colleagues have introduced a phantom and software tool that quantifies EPID resolution 45 . The tool provides quantitative resolution information obtained through a reproducible protocol.…”

“…The values they report may be used as baseline values for acceptance testing and ongoing QA of any EPID. The user is encouraged to require the vendor to demonstrate that the EPID meets or exceeds spatial and contrast specifications 45 . Regardless of which phantom is used and whether quantitative software is used, the initial images obtained during acceptance represent base line data for continuing quality assurance of the EPID.…”

“…Most QA for the EPID involves image contrast and spatial resolution. Methodology and phantoms for these procedures have been discussed and include developing baseline images and performance data for routine comparison 45 , 99 . The image and performance data recorded during acceptance and commissioning are the reference standards for continuing QA tests.…”

Quality Assurance for Kilo- and Megavoltage In-Room Imaging and Localization for Off- and Online Setup Error Correction

“…The dramatic improvement in image quality provided by AMFPI systems has limited the usefulness of these early phantoms, and currently source size and contrast limits imposed by Compton scattering heavily influence the degree to which anatomy can be resolved for purposes of patient positioning. Other phantoms were developed around the concept of contrast-to-noise ratio (CNR), as well as high-contrast spatial resolution [8]. These phantoms may be more applicable to modern megavoltage imaging.…”