- Title
- Time-resolved quality assurance and delivery verification for external beam radiation therapy using an electronic portal imaging device
- Creator
- Zwan, Benjamin J.
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2020
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Advances in science and technology have led to the development of increasingly complex delivery techniques for external beam radiation therapy (EBRT). Modern techniques such as intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), rely on synchronization of multiple dynamic control systems and require a high degree of mechanical and dosimetric accuracy. Real-time adaptive delivery techniques, such as multileaf collimator (MLC) tracking, have even greater complexity as each treatment is modified in real time to account for measured tumor motion. Due to the technical and dynamic nature of these delivery types, dose verification and quality assurance (QA) techniques are challenging, time consuming and cannot detect all types of delivery errors. Time-resolved imaging using an electronic portal imaging device (EPID) can be used to acquire high spatial and temporal resolution images of the radiation beam. This imaging modality has the potential to address many of the challenges and shortcomings in modern EBRT delivery verification and QA. Despite this, there are a limited number of techniques in the literature which utilise this imaging modality and even fewer in routine clinical use. The overall aim of this work is to generate, test and implement a series of novel techniques for QA and verification of modern radiotherapy deliveries which rely solely on time-resolved EPID imaging. The first specific aim of this work was to develop and test a system for automated QA of the dynamic MLC using time-resolved EPID imaging. This method improves on current QA techniques by directly measuring the trajectory of each MLC leaf as a function of time during the delivery. The measured trajectories can then be used to reconstruct the dose in the patient to determine the dosimetric effect of measured MLC errors. The methodology was shown to be sensitive to a range of MLC errors, was independent of the delivery control system and could be fully automated. This MLC QA technique was then implemented in a clinical radiotherapy department and used to detect and characterize a dosimetrically significant MLC positional error. The second aim of this work was to create a comprehensive suite of tests for commissioning and ongoing QA of VMAT delivery systems relying solely on time-resolved EPID imaging. The techniques developed here were designed to systematically verify all aspects of VMAT deliveries including MLC positional accuracy, dose delivery accuracy, dose rate constancy, beam profile constancy, gantry speed constancy and synchronization between the MLC, dose rate and gantry angle. In the next phase of this work, a system was developed for real-time verification of MLC tracking radiotherapy based on EPID imaging during treatment. Time-resolved EPID imaging was utilized for clinical deliveries where MLC tracking was implemented for the treatment of lung cancer patients. This dataset was used to develop and test the methodology which aims to independently verify the delivery in real-time. It is intended that this system can be used for future MLC tracking clinical trials to detect delivery errors and improve the accuracy of treatment for MLC tracking radiotherapy. The last aim of this work was to use time-resolved EPID imaging to improve the accuracy of pre-treatment patient specific QA for IMRT and VMAT. A method was developed to correct for the energy response of the EPID to radiation that has transmitted through the MLC. This technique was incorporated into an existing EPID dose-to-water conversion model and was shown to improve the accuracy of the model for dose verification. In summary, time-resolved EPID imaging has been used to improve QA and verification for modern EBRT and been shown to address several challenges in the following specific areas: (1) QA of dynamic MLC systems, (2) QA of VMAT delivery systems, (3) delivery verification for MLC tracking radiotherapy and (4) patient-specific QA for IMRT and VMAT. It is the intention of this work to encourage and enable more widespread utilisation of time-resolved EPID imaging in clinical radiotherapy departments to improve the safety and quality of modern radiotherapy treatment.
- Subject
- radiotherapy; medical physics; EPID; QA; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1431126
- Identifier
- uon:38923
- Rights
- Copyright 2020 Benjamin J. Zwan
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 4 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 172 KB | Adobe Acrobat PDF | View Details Download |