Joseph A Moore and Jeffrey V Siebers 2005 Phys. Med. Biol. 50 2341 doi:10.1088/0031-9155/50/10/011
Joseph A Moore and Jeffrey V Siebers
Show affiliationsElectronic portal imaging devices (EPIDs), currently used for determining proper patient placement during irradiation in a radiotherapy treatment, can also be used as dosimeters. However, the Varian aS500 portal imager exhibits dosimetric artefacts caused by non-uniform backscatter from mechanical support structures located behind the imager. Monte Carlo simulations predict that adding 5 mm of Pb behind the imaging cassette will reduce the non-uniform backscatter to <1% for 6 MV and to <1.5% for 18 MV photon beams. This study experimentally tested this hypothesis by comparing images using an unmodified test imager and an imager modified by adding 3 and 5 mm of Pb behind the imaging cassette. Using the modified imager containing 5 mm of Pb, the non-uniform backscatter was reduced to <0.5% for 6 MV and <0.6% for 18 MV beams. Addition of the 5 mm of Pb increased the detector contrast by 3.5% ± 0.5% at 6 MV and 5.0% ± 0.7% at 18 MV, and increased the resolution by 0.9% ± 0.2% at 6 MV and 0.5% ± 0.12% at 18 MV.
87.53.Bn Dosimetry/exposure assessment
Issue 10 (21 May 2005)
Received 30 November 2004, in final form 8 March 2005
Published 5 May 2005
Joseph A Moore and Jeffrey V Siebers 2005 Phys. Med. Biol. 50 2341
I Jensen and A J Guttmann 1995 J. Phys. A: Math. Gen. 28 4813
F Darabi 2003 Class. Quantum Grav. 20 3385
J M Stewart 2001 Class. Quantum Grav. 18 4983
David Garfinkle 1999 Class. Quantum Grav. 16 4101
Hao Peng-Fei et al 2006 Chinese Phys. Lett. 23 2815
Yang Chen and Nigel Lawrence 2002 J. Phys. A: Math. Gen. 35 4651
Stephen C Anco 2002 Class. Quantum Grav. 19 6445
Stefan Hollands and Robert M Wald 2004 Class. Quantum Grav. 21 5139
A Lahmam-Bennani et al 2001 J. Phys. B: At. Mol. Opt. Phys. 34 3073