Far reaching developments and technical advances took place within the field of radiotherapy in the last years. Radiotherapy within the chest and abdomen area is especially important in the field of radiotherapy. Within this regions, organ and tumor positions are significantly affected by patient respiration. The tumor motion, caused due to respiration is compensated by extending the treated area. This extension covers all possible positions of the tumor and therefore also includes healthy tissue.
Several clinical studies provide evidence of a survival advantage for higher dose levels. To spare a maximum of healthy tissue physicians use ’gated radiotherapy’. Common recent approaches for gated radiotherapy are based on the observation of a surrogate. This either can be an implanted fiducial marker or an external signal, which is trying to capture the patients’ respiration.
Within this thesis principles and methods of ’gated radiotherapy’ are described. Additionally an overview of recent patents and products related to radiotherapy are presented and advantages and disadvantages of both common approaches are discussed. This discussion leads to a new developed method, which is introduced. The method joins advantages of both known methods but disregards their disadvantages. The developed algorithm is using image guided methods and methods of medical image processing. A mapping between a 4D-CT planning volume and a most recent acquired fluoroscopic sequence of the same patient is calculated before treatment. Using this mapping and an external breathing signal the physician can define gating intervals and treat the patient in certain breathing phases.
The developed algorithm is included in an existing prototype developed by Siemens Corporate Research (SCR) in Princeton, NJ, USA. Using this prototype, the application of the method is shown. Furthermore another prototype to acquire respiration synchronized fluoroscopic sequences is developed. Both applications are introduced within this thesis.
Table of Contents
1 Introduction
2 Related Work and Patents
3 Managing Respiratory Motion in Radiation Therapy
3.1 Introduction
3.2 Treatment Planning
3.3 Motion-encompassing methods
3.3.1 Slow CT scanning
3.3.2 Inhalation and exhalation breath-hold CT
3.3.3 Four-dimensional CT/respiration-correlated CT
3.4 Respiratory Gating Methods and Procedures
3.4.1 Internal Gating
3.4.2 External Gating
3.5 Clinical Procedure
4 Image Sequence Synchronization
4.1 Introduction
4.2 Proposed Method
4.3 Similarity Matrix
4.4 Preprocessing
4.4.1 Gain Removal
4.4.2 Wild Card
4.4.3 Transition matrix
4.5 Model-based Dynamic Programming
5 Clinical Prototype
5.1 Introduction
5.2 Clinical Systems
5.2.1 SOMATOM Sensation Open
5.2.2 ONCOR Linear Accelerator
5.2.3 Respiratory Gating System
5.3 Clinical Applications
5.3.1 AcquireIt
5.3.2 RTReg4D
6 Results
6.1 Introduction
6.2 Level I: Synthetic Data
6.3 Level II: Phantom Data
7 Discussion and Future Work
7.1 Introduction
7.2 Wild Card Detection Improvement
7.3 Model Improvement
7.4 Cone Beam Acquisition Integration
7.5 On-the-fly Expansion
7.6 Registration Improvement
7.7 Parallelization
8 Summary
Objectives and Core Themes
The primary goal of this thesis is to develop an image-guided method for gated radiotherapy that achieves an accurate correlation between patient respiration and tumor movement without the need for invasive procedures or excessive radiation exposure. By synchronizing a 4D-CT planning volume with real-time fluoroscopic sequences using a novel synchronization algorithm, the study aims to enable precise gating intervals and reduce the irradiation of healthy tissue.
- Comparison and evaluation of existing internal and external gating technologies.
- Development of an image sequence synchronization algorithm based on dynamic programming and Markov chains.
- Integration of the proposed algorithm into a medical prototype to demonstrate clinical applicability.
- Implementation of preprocessing techniques, including gain removal and statistical wild card detection, to improve data robustness.
- Validation of the method using synthetic and phantom datasets under varying noise and deformation conditions.
Excerpt from the Book
3.3 Motion-encompassing methods
As it is important to estimate the mean position and range of motion during CT imaging, because respiration induces tumor motion during treatment several techniques are existing to account this problem. The introduced techniques are dealt in the order of the increasing workload.
3.3.1 Slow CT scanning
The first method is called slow CT scanning and provides an opportunity to acquire multiple respiration phases per slice [Lag01] [Kos01] [Kos03]. Therefore, the CT scanner is operated very slowly, and/or multiple CT scans are averaged. As most CT scanners are able to acquire a slow CT scan this application can be implemented at almost every location, which is a big advantage of this method. Images which are acquired by using this method are showing the full extent of respiratory motion that occurred during the acquisition. Therefore, the couch has to stay at the same position for the whole acquisition time. The loss of resolution due to motion blurring is one disadvantage of slow CT scanning. Another disadvantage is the increased dose for slow CT compared to conventional CT scanning.
Chapter Summaries
1 Introduction: This chapter introduces the challenges of respiratory-induced tumor motion in radiation therapy and outlines the need for a non-invasive, image-guided solution.
2 Related Work and Patents: This chapter provides a literature review of existing gated radiotherapy techniques and discusses relevant current patents in the field.
3 Managing Respiratory Motion in Radiation Therapy: This chapter explains the clinical and technical aspects of respiratory management, including different motion-encompassing and gating strategies.
4 Image Sequence Synchronization: This chapter details the proposed algorithm for synchronizing 4D planning volumes with fluoroscopic sequences using preprocessing and dynamic programming.
5 Clinical Prototype: This chapter describes the implementation of the algorithm within existing Siemens medical prototypes and the workflow for data acquisition and validation.
6 Results: This chapter presents the evaluation of the algorithm using both synthetic datasets and phantom studies, focusing on accuracy and runtime efficiency.
7 Discussion and Future Work: This chapter analyzes the performance limitations of the proposed method and offers insights into potential improvements and future research directions.
8 Summary: This chapter concludes the thesis by synthesizing the main contributions, the developed approach, and the potential impact on clinical radiotherapy practice.
Keywords
Radiotherapy, Respiratory motion, Gated radiotherapy, 4D-CT, Image sequence synchronization, Dynamic programming, Markov chains, Tumor tracking, Fluoroscopy, Medical imaging, Image-guided treatment, Clinical prototype, Motion-encompassing, Dose escalation, Surrogate signal
Frequently Asked Questions
What is the core focus of this research?
The research focuses on optimizing gated radiotherapy for lung cancer by creating a more accurate correlation between tumor position and patient breathing using image-guided methods, avoiding the need for invasive markers.
What are the primary challenges this work addresses?
It addresses the trade-off between radiation treatment accuracy and patient burden, specifically reducing the exposure of healthy tissue to high radiation doses caused by moving tumor targets.
What is the central research question?
The study asks how image-guided synchronization can be achieved efficiently to define precise gating windows based on real-time imaging rather than relying on potentially inaccurate external surrogates.
Which methodology is employed?
The author employs an algorithm that synchronizes 4D-CT planning volumes with fluoroscopic sequences through a similarity matrix, processed via dynamic programming and modeled using Markov chains.
What does the main body of the work cover?
The main body covers the clinical background of radiation therapy, the technical details of the synchronization algorithm (including preprocessing like gain removal and wild card detection), and the implementation in medical prototypes.
What are the key keywords defining this work?
The key keywords include Radiotherapy, Gated radiotherapy, Respiratory motion, 4D-CT, Dynamic Programming, and Image-guided treatment.
What is the role of the "wild card" in the algorithm?
The "wild card" acts as an additional state within the breathing cycle that allows the algorithm to detect and handle missing correlations, such as noisy images or periods where the patient's breathing pattern deviates from the reference.
How is the accuracy of the algorithm verified?
Verification is conducted through two levels of testing: synthetic datasets based on patient 4D-CT data and actual breathing phantom datasets, evaluating performance under various noise and deformation conditions.
- Quote paper
- cand. Dr.-Ing. Dipl.-Inf. cand-kfm. Christian Schaller (Author), 2007, 4D Image Verification, Munich, GRIN Verlag, https://www.grin.com/document/73280
