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Developments in electronic portal imaging systems

North Western Medical Physics, Radiotherapy Department, Rosemere Cancer Centre, Royal Preston Hospital, Preston, UK

View larger version (89K): [in a new window]   Figure 1. The Kodak CR System for radiotherapy verification.(Images from Kodak website www.kodak.com/go/oncology).

View larger version (76K): [in a new window]   Figure 2. Simple comparison of images acquired of an anthropomorphic type phantom using(a) an amorphous silicon (a-Si) imaging system (Elekta iViewGT) and (b) a CR system (Kodak 2000RT). Both images acquired using 6 MV X-rays. The a-Si image was acquired with 100 MU and the CR with 20 MU. (CR image courtesy of Steve Weston, Cookridge Hospital, Leeds, UK).

View larger version (75K): [in a new window]   Figure 3. Two commercial camera-based electronic portal imaging devices (EPIDs). (a) The Elekta iView system attached to the gantry of an SL Linac. (b) The Infimed (Cablon) Theraview system in its retracted position. Also shown in (a) is a typical portal film cassette (Kodak EC-L system) in its portal film holder.

View larger version (60K): [in a new window]   Figure 4. Active matrix flat panel imagers(AMFPIs) from two of the major radiotherapy equipment manufacturers; (a) Elekta and (b) Siemens. Electronic portal imaging devices (EPIDs) of this type are highly practical devices, being fully motorized and retractable to the gantry of the linear accelerator when not required for use. The AMFPI from Varian uses similar gantry mounting technology.

View larger version (53K): [in a new window]   Figure 5. Images comparing, qualitatively, the image quality obtainable with a camera based first generation EPID(iView) and a new AMFPI system (iViewGT). The subject is the neck region of an anthropomorphic type ("Rando") phantom. All images have been acquired with 6 MV X-rays. (a) iView, 2 MU, (b) iViewGT 2 MU, (c) iViewGT 100 MU. From Kirby et al 2002 [41].

View larger version (44K): [in a new window]   Figure 6. Images comparing, qualitatively, the image quality obtainable with(a) an ionization chamber matrix electronic portal imaging device (EPID) (PortalVision) and (b) a new active matrix flat panel imager (AMFPI) system (as500). Both images show bony detail for lateral pelvic treatment fields after image enhancement. (Images courtesy of Margaret Bidmead, Royal Marsden Hospital, London, UK).

View larger version (37K): [in a new window]   Figure 7. Images showing the visibility of bony detail(a) before and (b) after image processing and enhancement. Image acquired with the Varian as500 AMFPI. (Images courtesy of Margaret Bidmead, Royal Marsden Hospital, London, UK).

View larger version (90K): [in a new window]   Figure 8. Examples of some typical artefacts that have been observed with commercial active matrix flat panel imager(AMFPI) electronic portal imaging devices (EPIDs). (a) Component of the offset correction image present in clinical images at low exposures (linear, streaking artefact which has been ringed). (b,c) Examples of line artefacts arising from pulsing of the linac. (d) Example of loss of signal in rows of pixels in a complete segment caused by radiation damage to the associated electronics (ringed area).

View larger version (64K): [in a new window]   Figure 9. Images acquired with an active matrix flat panel imager(AMFPI) for a lateral pelvic treatment (6 MV X-rays). (a) An image acquired with a reticule present to indicate central axis position, orientation and verify scaling. A 4 MU exposure was used. (b) An image acquired with the full treatment exposure (approximately 80 MU). Distinct differences can be seen in image quality between the two, with (a) having a poorer signal to noise ratio (primarily due to the increased presence of both structured and random noise components).