The application of electronic portal imaging device for quality assurance of medical linear accelerators in radiation therapy

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The application of electronic portal imaging device for quality assurance of medical linear accelerators in radiation therapy

 

Author: Wu, Peng
Title: The application of electronic portal imaging device for quality assurance of medical linear accelerators in radiation therapy
Degree: M.Sc.
Year: 2011
Subject: Imaging systems in medicine.
Radiotherapy -- Instruments.
Linear accelerators.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Health Technology and Informatics
Pages: viii, 66 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2462936
URI: http://theses.lib.polyu.edu.hk/handle/200/6365
Abstract: Purpose: Due to its high image quality and dosimetry properties, the applications of Electronic Portal Imaging Device (EPID) in the quality assurance (QA) of medical linear accelerators (LINAC) have been widely studied. Most of the applications of EPID in LINAC QA used old type of EPIDs and without considering the dosimetry application of the EPIDs. This study aimed to compare the conventional film-based method with the dosimetric EPID method in three QA tests for the medical LINAC. Method: The QA tests conducted were: (1) Congruence test of X-ray and light field. The X-ray fields were determined using 50% isodose curves from dosimetric portal images. The light fields were determined by a specially developed test tool. The congruence errors were collected and compared to the conventional film based method analyzed by the QA software for congruence errors. (2) Beam profile constancy. Inplane and crossplane profiles of EPID based dosimetric portal images were analyzed and compared to measurements by both absolute 2D water scan system and relative 2D daily QA device (3) Beam central axis output constancy. The central axis dose constancy of EPID based portal images was compared to those by absolute weekly QA dose constancy measurements and relative daily QA dose measurements. All the test results were compared for means using unpaired t-test or one way ANOVA with post-hoc analysis using Turkey method. Results: For congruence test of X-ray and light field, EPID showed the same measurement accuracy and measurement errors compared with the conventional film based method. For beam profile constancy, the EPID method showed the same measurement errors in symmetry measurements but not in flatness measurements. For symmetry constancy, EPID showed the consistency and accuracy were same as the measurements made by the standard 2D water scanner. For central axis output constancy, the measurements by EPID did not behave as accurately as those measured by the absolute dosimetry method. Conclusions: EPID with the high image resolution and stable dosimetry response can be a power tool in the QA of LIANC. It can be an alternative approach in congruence test between the X-ray field and light field and constancy test of symmetry of the radiation beam. Compared to the conventional QA methods, EPID method is fast and also accurate.

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