Simple Proposal for Dosimetry with an Elekta iViewGTTM Electronic Portal Imaging Device (EPID) Using Commercial Software Modules

Liebich, J.; Licher, Jörg; Scherf, Christian; Kara, E.; Koch, N.; Rödel, Claus; Ramm, U.

doi:10.1007/s00066-011-2176-z

Cited by 11 publications

(12 citation statements)

References 27 publications

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“…No significant impact on the dose calculation were observed from these effects. However, the impact of ghosting, dose rate variations, and memory effect were studied in previous studies in detail 14,18 …”

Section: Discussionmentioning

confidence: 99%

The fast calibration model for dosimetry with an electronic portal imaging device

Schade

Engenhart‐Cabillic

Zink

et al. 2022

J Applied Clin Med Phys

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The aim of this study was to develop an algorithm that corrects the image of an electronic portal imaging device (EPID) of a linear accelerator so that it can be used for dosimetric purposes, such as in vivo dosimetry or quality assurance for photon radiotherapy. For that purpose, the impact of the field size, phantom thickness, and the varying spectral photon distribution within the irradiation field on the EPID image was investigated. Methods: The EPID measurements were verified using reference measurements with ionization chambers. Therefore, absolute dose measurements with an ionization chamber and relative dose measurements with a detector array were performed. An EPID calibration and correction algorithm was developed to convert the EPID image to a dose distribution. The algorithm was validated by irradiating inhomogeneous phantoms using square fields as well as irregular IMRT fields. Results: It was possible to correct the influence of the field size, phantom thickness on the EPID signal as well as the homogenization of the image profile by several correction factors within 0.6%. A gamma index analysis (3%, 3 mm) of IMRT fields showed a pass rate of above 99%, when comparing to the planning system. Conclusion:The developed algorithm enables an online dose measurement with the EPID during the radiation treatment. The algorithm is characterized by a robust, non-iterative, and thus real-time capable procedure with little measuring effort and does not depend on system-specific parameters. The EPID image is corrected by multiplying three independent correction factors. Therefore, it can easily be extent by further correction factors for other influencing variables, so it can be transferred to other linear accelerators and EPID configurations.

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Section: Discussionmentioning

confidence: 99%

The fast calibration model for dosimetry with an electronic portal imaging device

Schade

Engenhart‐Cabillic

Zink

et al. 2022

J Applied Clin Med Phys

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“…One method of quantifying the EPID signal frequently described in the reviewed literature is by multiplying the number of frames by the averaged frame signals. Although the generally reported EPID characteristic in the reviewed literature is the linear EPID dose response [16], some researchers have reported EPID under-response to small radiation doses [3] [23]. Reported inaccurate EPID dosimetry characteristics may be explained by unclear definitions of the radiation beam properties in terms of EPID parameters.…”

Section: Epid Signal Profilementioning

confidence: 99%

Dosimetric Performance of A-Si Electronic Portal Imaging Devices

Alshanqity¹,

Nisbet²

2016

IJMPCERO

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The majority of EPID dosimetry literature discusses response linearity and the so-called image lag and ghosting effects despite the lack of a common definition of these quantities. However, the results of these studies are generally not consistent, and it is often difficult to compare the results from different studies. We present here a detailed study of the acquisition and readout characteristics of a-Si EPID and its dosimetric performance. EPID response was assessed over the range of 1 -500 MU using different dose rates and integration times. In addition, a computer model was designed to simulate the EPID image formation with different dose, dose rate, and integration time combinations. All aspects of image processing and readout simulation were carried out using custom written MatLab codes. Two distinct signal profiles were observed depending on the delivered dose, dose rate and integration time combination. Total integrated signal (ST) is linear with the delivered dose. For dosimetry, image lag and ghosting effects mainly result in the residual signal (S R ) that appears as delayed signal after the end of irradiation. At its maximum, S R is less than 2.5% of S T . The readout technique is such that it is impossible to measure S R accurately. S R is definable only when readout equilibrium occurs. Signal profiles provide a through and reliable description of the EPID response incorporating the dose, dose rate, integration time, and the residual signal. The definition of EPID signals based on this method shall provide an accurate universal EPID dosimetry framework.

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“…Kilovoltage cone-beam computed tomography (CBCT), a tool for image-guided radiation therapy (IGRT), has been developed to acquire on-line volumetric and anatomical images [3,11,15,27]. Currently, CBCT images are compared with original treatment plans for the most accurate positioning setup [5,6,9,10,14,17,18,25,28].…”

Section: Phase-specific Cone Beam Computed Tomography Reduces Reconstmentioning

confidence: 99%

Phase-specific cone beam computed tomography reduces reconstructed volume loss of moving phantom

Chao

Chen²,

et al. 2011

Strahlenther Onkol

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Simple Proposal for Dosimetry with an Elekta iViewGTTM Electronic Portal Imaging Device (EPID) Using Commercial Software Modules

Abstract: The gamma evaluation indicates good correlation between predicted and acquired EPID images. The EPID-based pretreatment IMRT verification method will help to improve the quality assurance procedure.

Cited by 11 publications

References 27 publications

The fast calibration model for dosimetry with an electronic portal imaging device

The fast calibration model for dosimetry with an electronic portal imaging device

Dosimetric Performance of A-Si Electronic Portal Imaging Devices

Phase-specific cone beam computed tomography reduces reconstructed volume loss of moving phantom

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