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. 2011 Mar;45(1):68-74.
doi: 10.2478/v10019-010-0052-6. Epub 2010 Dec 31.

Verification of quality parameters for portal images in radiotherapy

Csilla Pesznyák  1 , István Polgár, Csaba Weisz, Réka Király, Pál Zaránd
Affiliations

Verification of quality parameters for portal images in radiotherapy

Csilla Pesznyák et al. Radiol Oncol. 2011 Mar.

Abstract

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.

Keywords: electronic portal imaging device; portal film; quality control.

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Conflict of interest statement

Disclosure: No potential conflicts of interest were disclosed.

Figures

FIGURE 1.
FIGURE 1.
Structure of the PTW EPID QC PHANTOM®, 1. Signal linearity and signal noise ratio, 2. Isotropy of signal linearity, 3. Geometric isotropy (distortion), 4. Low-contrast resolution, 5. High-contrast resolution (MTF).
FIGURE 2.
FIGURE 2.
Controlling the low contrast resolution with (A) Las Vegas test tool and (B) PTW EPID QC PHANTOM®.
FIGURE 3.
FIGURE 3.
The image analysis with the epidSoft®2.0 program.
FIGURE 4.
FIGURE 4.
SNR as a function of absorption for Siemens BeamView Plus® in the case of different file format: DICOM, bmp and inverse bmp.
FIGURE 5.
FIGURE 5.
The graphic representation of the Varian PortalVision™ equipment’s stability test: A. linearity of copper step wedge, B. local dependence of linearity, C. MTF f(25) vertical and horizontal component, D. signal-to-noise ratio average value.
FIGURE 6.
FIGURE 6.
Comparison of results for low contrast resolution with PTW EPID QC PHANTOM® for Kodak X-OMAT® cassette with Kodak X-OMAT V® film and the Kodak EC-L Lightweight® cassette with Kodak Portal Localisation ReadyPack® film.
See this image and copyright information in PMC

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