:: Volume 2, Issue 4 (3-2005) ::
Int J Radiat Res 2005, 2(4): 175-183 Back to browse issues page
The physical characteristics of a SLIC-EPID for transmitted dosimetry
M. Mohammadi, E. Bezak
, Mahamma@mail.rah.sa.gov.au
Abstract:   (17133 Views)



for treatment verification in radiation therapy. Several physical characteristics of Scanning

Liquid filled Ionization Chamber EPID (SLIC-EPID) including: extra build-up layer,

reproducibility and uniformity, and noise level were investigated.

Electronic Portal Imaging Devices (EPIDs) have found an outstanding position

Materials and Methods:

equilibrium, 1-30 mm white water materials (RW3) were placed on the EPID cover and the

variation of pixel values were investigated. To assess the short term reproducibility, a series of

10 consecutive Electronic Portal Images (EPIs) were acquired. The variation of pixel values

were then determined in irradiated field using MATLAB software. For long term reproducibility,

the described above experiment was then repeated seven times. To determine the noise level

in EPID images, 10 consecutive flood images were acquired. The measurement was repeated

after two days during a fortnight.

To determine the extra build-up layer to reach the electronic


No significant variation was observed between the maximum thickness of build-up layer

required for the central axis and peripheral points. For reproducibility measurements, no systematic

variation was observed between mean, maximum and minimum acquired pixel values.

Both the long-term and short term reproducibility was found to be less than 1%. The noise level

was generally less than 1% and this can be referred as an acceptable dose level

5 mm of RW3 material was found to increase the pixel values to the maximum possible..


can be used for dosimetry. However, for a particular linac energy and EPID image acquisition

mode, the extra build-up layer thickness must be known for the EPID to be used for dosimetric


The physical characteristics, measured in this work, suggest that the SLIC-EPID. Iran. J. Radiat. Res., 2005 2 (4): 175-183
Keywords: transmitted dosimetry, portal dosimetry, physical characteristics, SLIC-EPID
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Type of Study: Original Research | Subject: Radiation Biology

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