Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.13/935753
- Title
- Improvement of EPID-based techniques for dosimetry and investigation of linac mechanical performance in advanced radiotherapy
- Author/Creator
-
Rowshan Farzad, Pejman
- Institution
- University of Newcastle. Faculty of Science & Information Technology, School of Mathematical and Physical Sciences
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Advances in radiotherapy have increased the complexity of treatment delivery techniques. The complexity of plans, with dynamic variation of field shape, gantry speed and dose rate require highly accurate techniques for quality assurance of the treatment machines and dosimetric verification of the treatment plans. There has been a growing interest on the application of electronic portal imaging devices (EPIDs) for dosimetry applications and quality assurance testing of linear accelerators (linacs). The ultimate aim of this thesis is to develop methods to ensure more accurate treatment deliveries using EPID-based techniques. The project is divided into two parts. The first part is based on improvement of the accuracy of EPID dosimetry with Varian systems by either accounting for, or reduction of, the effect of backscattered radiation from the treatment room walls and the EPID support arm. The effect of backscatter from the treatment room walls was quantified for the first time using a number of measurement setups and comparisons with measurements in the presence of an independent portable wall. The Varian support arm backscatter was accounted for or reduced by three methods: (a) application of an experimentally derived backscatter kernel into an existing EPID dose prediction model, (b) insertion of lead sheets to reduce the non-uniform backscatter, and (c) insertion of a thicker piece of lead over the arm area and considering it as an arm component which could effectively reduce the backscatter effect. Application of the backscatter kernel measured with this lead shielded arm into the model was the most effective method to improve the accuracy of EPID dosimetry predictions. In the second part of the project, EPID-based measurement methods were used and new algorithms were developed for faster, easier, more robust, more accurate quantitative techniques for characterization of the linac components than existing methods. The results could be used for improvement of EPID dosimetry measurements and/or be included in the linac quality assurance program. The study includes: determination of the mechanical isocentre position with a level of accuracy suitable for stereotactic treatments; determination of the sag in EPID, gantry, jaws and MLC systems during arc deliveries; determination of gantry angle during rotation; and finally, a comprehensive investigation of MLC leaf positioning and dynamic performance in static and arc delivery modes. The proposed methods have been tested and are applicable for routine quality assurance of the linear accelerators used for advanced treatment techniques with all linacs, independent of their make and model.
- Relation
- University of Newcastle Research Higher Degree Thesis
- Date
- 2012
- Keyword(s)
-
EPID;
QA;
support arm;
bunker walls;
cine imaging;
thesis by publication;
linac;
dosimetry;
backscatter;
MLC;
sag;
gantry;
isocentre;
angle
- Resource Type
- thesis
- Rights
- Copyright 2012 Pejman Rowshan Farzad
- Identifier
- http://hdl.handle.net/1959.13/935753
- Language
- eng
-
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