A simple quality assurance test tool for the visual verification of light and radiation field congruent using electronic portal images device and computed radiography

Abstract

BackgroundThe radiation field on most megavoltage radiation therapy units are shown by a light field projected through the collimator by a light source mounted inside the collimator. The light field is traditionally used for patient alignment. Hence it is imperative that the light field is congruent with the radiation field.MethodA simple quality assurance tool has been designed for rapid and simple test of the light field and radiation field using electronic portal images device (EPID) or computed radiography (CR). We tested this QA tool using Varian PortalVision and Elekta iViewGT EPID systems and Kodak CR system.ResultsBoth the single and double exposure techniques were evaluated, with double exposure technique providing a better visualization of the light-radiation field markers. The light and radiation congruency could be detected within 1 mm. This will satisfy the American Association of Physicists in Medicine task group report number 142 recommendation of 2 mm tolerance.ConclusionThe QA tool can be used with either an EPID or CR to provide a simple and rapid method to verify light and radiation field congruence.

Rapid acceptance testing of modern linac using on-board MV and kV imaging systems

“…Traditionally films were used to verify that light and radiation fields agreed with each other. EPID has been shown as a useful QA tool to perform this test . In the EPID‐based approach, images of different MLC square field sizes through the custom designed phantom are acquired and automatically analyzed to quantify the field size.…”

“…EPID has been shown as a useful QA tool to perform this test. 11,12 In the EPID-based approach, images of different MLC square field sizes through the custom designed phantom are acquired and automatically analyzed to quantify the field size. This test relies on the visual verification of light field position against the embedded steel-spheres on the phantom.…”

Automating quality assurance of digital linear accelerators using a radioluminescent phosphor coated phantom and optical imaging

“…A radiation field is then delivered and the film is examined to compare the field edges and center of both the light and radiation fields. Alternatively, an image of the phantom is captured on an on-board electronic portal imaging devices (EPID) and analyzed with dedicated software (Polak et al 2013; Njeh et al 2012). The time required to complete the setup and testing for a single field using these methods ranges from 14–40 minutes (Polak et al 2013).…”

Daily QA of linear accelerators using only EPID and OBI

“…It has been used to check x-ray field size, flatness and symmetry, light/radiation coincidence, isocentricity check using star shots, beam output, dynamic wedge factor, and MLC performance. [5][6][7][8][9] With sub-millimeter spatial resolution and high contrast resolution, EPID is an ideal tool for LINAC QA. 9 As both MV and kV detector panels are onboard, the setup time for QA procedures can be greatly reduced.…”