Verification of quality parameters for portal images in radiotherapy
Background. The purpose of the study was to verify different values of quality parameters of portal images in radiotherapy.
Materials and methods. We investigated image qualities of different field verification systems. Four EPIDs (Siemens OptiVue500aSi®, Siemens BeamView Plus®, Elekta iView® and Varian PortalVision™) were investigated with the PTW EPID QC PHANTOM® and compared with two portal film systems (Kodak X-OMAT® cassette with Kodak X-OMAT V® film and Kodak EC-L Lightweight® cassette with Kodak Portal Localisation ReadyPack® film).
Results. A comparison of the f50 and f25 values of the modulation transfer functions (MTFs) belonging to each of the systems revealed that the amorphous silicon EPIDs provided a slightly better high contrast resolution than the Kodak Portal Localisation ReadyPack® film with the EC-L Lightweight® cassette. The Kodak X-OMAT V® film gave a poor low contrast resolution: from the existing 27 holes only 9 were detectable.
Conclusions. On the base of physical characteristics, measured in this work, the authors suggest the use of amorphous-silicon EPIDs producing the best image quality. Parameters of the EPIDs with scanning liquid ionisation chamber (SLIC) were very stable. The disadvantage of older versions of EPIDs like SLIC and VEPID is a poor DICOM implementation, and the modulation transfer function (MTF) values (f50 and f25) are less than that of aSi detectors.
Boyer AL, Antomuk L, Fenster A, Van Herk M, Meertens H, Munro P, et al. A review of electronic portal imaging devices (EPIDs). Med Phys 1992; 19: 1-16.
Langmack K A, Phil D. Portal imaging. Brit J Radiol 2001; 74: 789-804.
Whittington R, Bloch P, Hutchinson D, Björrngard BE. Verification of prostate treatment setup using computed radiography for portal imaging. J Appl Clin Med Physi 2002; 3: 88-96.
Johnson LS, Milliken BD, Hodley SW, Pelizzari CA, Haraf DJ, Chen GTY. Initial clinical experience with a video-based patient positioning system. Int J Radiat Oncol Biol Phys 1999; 45: 205-13
Pesznyák Cs, Lövey K, Weisz Cs, Polgár I, Mayer Á. Elektronikus mezőellenőrzés lineáris gyorsítón. Magyar Onkológia 2001; 45: 335-41.
Kasabašić M, Faj D, Belaj N, Faj Z, Tomaš I. Implementing of the offline setup correction protocol in pelvic radiotherapy: safety margins and number of images. Radiol Oncol 2007; 41: 48-55.
Cremers F, Frenzel Th, Kausch C, Albers D, Schonborn T, Schmidt R. Performance of electronic portal imaging devices EPIDs used in radiotherapy: Image quality and dose measurements. Med Phys 2004; 31: 985-96.
Petrovic B, Grzadziel A, Rutonjski K, Slosarek K: Linear array measurements of enhanced dynamic wedge and treatment planning system (TPS) calculation for 15 MV photon beam and comparison with electronic portal imaging device (EPID) measurements. Radiol Oncol 2010; 44: 199-206.
Bailey DW, Kumaraswamy L, Podgorsak MB. A fully electronic intensity-modulated radiation therapy quality assurance (IMRT QA) process implemented in a network comprised of independent treatment planning, record and verify, and delivery systems. Radiol Oncol 2010; 44: 124-30.
Geyer P, Blank H, Alheit H. Portal verification using the KODAK ACR 2000 RT storage phosphor plate system and EC® films. Strahlenther Onkol 2006; 182: 172-8.
Pesznyák Cs, Fekete G, Mózes Á, Kiss B, Király R, Polgár I, et al. Quality control of portal imaging with PTW EPID QC phantom®. Strahlenther Onkol 2009; 185: 56-60.
Van Herk M, Meertens H. A matrix ionisation chamber imaging device for on-line patient set up verification during radiotherapy. Radiother Oncol 1988; 11: 369-78.
Essers M, Hoogervorst BR, van Herk M, Lanson H, Mijnheer BJ. Dosimetric characteristics of a liquid-filled electronic portal imaging device. Int J Radiat Oncol Biol Phys 1995; 33: 1265-72.
El-Mohri Y, Jee KW, Antonuk LE, Maolinbay M, Zhao Q. Determination of the detective quantum efficiency of a prototype, megavoltage indirect detection, active matrix flat-panel imager. Med Phys 2001; 28: 2538-49.
Munro P, Bouius DC. X-ray quantum limited portal imaging using amorphous silicon flat-panel arrays. Med Phys 1998; 25: 689-702.
Winkler P, Hefner A, Georg D. Dose-response characteristics of amorphous silicon EPID. Med Phys 2005; 32: 3095-105.
Pesznyák Cs, Zaránd P, Mayer Á. Digitalization and networking of analog simulators and portal images. Strahlenther Onkol 2007; 183: 117-20.
Pesznyák Cs, Zaránd P, Baráti Zs, Párkányi T. Mevasim szimulátor hálózatban-DICOM RT. In: Pintye É, editor. Proc. X. Hungarian medical physics conference & workshop. Debrecen: Cívis Copy Ltd.; 2004. p. 103-8.
Clements R, Luchka K, Pouliot J, Sage J, Shalev S. Initial comparison of three Am-Si EPIDs using the QC-3V Phantom. The 7th international workshop on electronic Portal Imaging - EPI2K2. Vancouver, BC, June, 27-29; 2002.
Herman MG, James MB, David AJ, McGee KP, Munro P, Shalev S, at al. Clinical use of electronic portal imaging: report of AAPM Radiation Therapy Committee Task Group 58. Med Phys 2001; 28: 712-37.
Wong J. Current status of electronic portal imaging. AAPM 41st annual meeting. Nashville, Tennessee; 1999.
NEMA (National Electrical Manufacturers Association). Digital imaging and communications in medicine (DICOM). Part 3: Information object definitions. Rosslyn: NEMA; 2003. p. 855.
McGarry CK, Grattan MWD, Cosgrove VP. Optimisation of image quality and dose for Varian aS500 electronic portal imaging devices (EPIDs). Phys Med Biol 2007; 52: 6865-77.