PhD

University of Sheffield | Faculty of Engineering

Logo of UOS in the 1990s

Volume Rendering of a CT study.

PhD Thesis

VISUALIZATION IN RADIOTHERAPY PLANNING

A THESIS SUBMITTED TO THE UNIVERSITY OF SHEFFIELD FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN THE FACULTY OF ENGINEERING

Klaus de Geus

Department of Computer Science

PhD Thesis | PDF

Abstract

Computer graphics has always been known for its achievements in the field of arts and entertainment. In recent years, science has gradually become one of the areas in which computer graphics has played an important role. Visualization in Scientific Computing is now a recognized discipline, which has given science a new degree of understanding in terms of presentation of abstract data generated from mathematical methods and simulations and concrete data extracted from sources using real measurements. Computer imagery in medicine has allowed physicians to achieve a much higher degree of success in planning surgery and other kinds of treatments. In particular, radiotherapy has developed to a much higher level of reliability and successful treatment by means of computer graphics tools, which are used to aid the planning process.

This thesis presents techniques developed for the application in radiotherapy planning. It can be subdivided into three parts. Firstly, the foundations of three-dimensional representation of computed tomography data as well as investigation on some of its important topics are presented. Then, techniques for the outline of structures of interest are investigated. Geometric stylization of structures attempts to simplify this process and make it more efficient. Finally, the geometric relationship between various parameters in three-dimensional radiotherapy planning is discussed, and methods of three-dimensional display are presented.

Radiation Treatment Planning: The Physician's-Eye-View.

Abstract

Preface

Acknowledgements

1 Visualization in Medicine

1.1 Representation of Volumetric Data

1.2 Three-Dimensional Computer Graphics Applied to Medicine

1.2.1 Geometric Surface Modelling Techniques

1.2.2 Volume Rendering Techniques

2 Practical Considerations on Volume Rendering

2.1 Depth Cueing

2.2 Perspective in Volume Rendering

2.2.1 Incremental Mapping in Orthographic Projection

2.2.2 An Approximation to True Perspective Projection by an Incremental Mapping Method

3 Conventional and State-of-the-Art Radiotherapy Planning Systems

3.1 Definition and Delineation of Structures

3.2 Placement of Radiation Beams

3.3 Dose Distribution

3.4 Evaluation of Treatment Plans

3.4.1 Dose-Volume Histograms

3.4.2 Isodose Distribution Display

3.4.3 Dose Distributions on the Surface of Structures

3.4.4 Superimposition of Dose Distributions Displayed as Isodose Lines or as a Colour-Wash Overlay

3.4.5 Dose Difference Display Between Two Rival Plans

3.4.6. Volumes of Regret

4 Extraction, Delineation and Stylization of Structures of Interest

4.1 Current Techniques for Extracting Structures of Interest

4.2 Investigation of Techniques for the Extraction and Stylization of Structures of Interest

4.2.1 The Use of Bounding Volumes

4.3 Outline of Structures of Interest Using Extensions of Seed Fill Algorithms to Three Dimension

4.3.1 Vertebrae Delineation Using Seed Fill Algorithms

4.3.2 Direct Volume Fill Algorithm

4.3.3 The Need for a Scan Line/Plane Algorithm

4.3.4 Scan Line/Plane Volume Fill Algorith

4.3.5 Performance Considerations

4.3.6 Results

4.4 Stylization of the Spinal Cord

4.4.1 Overview of Spinal Cord Delineation Process

4.4.2 Methods for Spinal Cord Localization on Slices Based on its Relationship with the Vertebrae

4.4.3 A Method Based on Convolution in a Soft-Tissue Field

4.5 Stylization of the Eyeballs

4.5.1 Delineation and Stylization of the Eyeballs Using an Adaptation of the Hough Transform for Three Dimensions

4.5.2 Moving Circles Method

4.5.3 Practical Consideration

4.5.4 Lenses

4.5.5 Definition of a Sphere from a Series of Circles

4.5.6 Volumetric Extraction of the Eyeballs

4.5.7 Results

5 Radiotherapy Planning Geometry and Rendering

5.1 Normal Anatomy and Structures of Interest

5.2 Beam's-Eye-Vie

5.3 External Beams

5.3.1 Edge Representation

5.3.2 Solid Representation

5.4 Dose Distributions

5.4.1 Cloud Representation

5.4.2 Isodose Surfaces

5.4.3 Dose on Surfaces

6 The Quest for a New Clinical Dimension

6.1 An Account of the Research Developed in the Project

6.2 The Past: Two-Dimensional System

6.3 The Present: The Introduction of Three-Dimensional Techniques

6.4 The Future: Three-Dimensional Systems in Clinical Practice

A Bresenham's Algorithm for Line Generation

B Bresenham's Algorithm for Circle Generation

C View Transformation for CT Data

D Calculation of Dose Distributions

D.1 Primary Component of Radiation

D.2 Scatter Component of Radiation

Bibliography

Volume rendering of CT data showing bones

3D reconstruction of a skull, using a raycast algorithm, showing bones. Developed in The C Programming Language, running on Unix on a Sun Workstation, between 1990 and 1992.

Physician's-eye-view of volume rendering of CT data, stylization of critical structures and interaction between X-ray beams and bones

3D reconstruction of a skull, using a raycast algorithm, with stylization of structures of interest (eyeballs and spinal cord), modelling of X-ray treatment beams and the interaction between them and bones. Developed in The C Programming Language, running on Unix on a Sun Workstation, between 1990 and 1992.

Volume rendering of CT data showing bones (completely opaque) and soft-tissue (semitransparent)

3D reconstruction of a skull, using a raycast algorithm, showing bones and soft-tissue. Developed in The C Programming Language, running on Unix on a Sun Workstation, between 1990 and 1992.

Radiation Treatment Planning: Beam's-Eye-View

Volume rendered skull with completely opaque bones (left) and semitransparent bones (right). Stylizations of the spinal cord, the eyebalss and a simulated tumour are shown. The polygon with blue edges is the representation of a radiation beam. The reason it is represented by a polygon rather than a solid is that the divergence degree of the beam is identical to the perspective degree of the image.

Radiation Treatment Planning: Beam's-Eye-View

Volume rendered skull with completely opaque bones and semitransparent vertebrae. Stylizations of the spinal cord, the eyebalss and a simulated tumour are shown. Three radiation beams of a radiotherapy planning can be seen. One of them is represented by the polygon with white edges. The reason it is represented by a polygon rather than a solid, like the other two beams, is that the divergence degree of the beam is identical to the perspective degree of the image. The yellow colour of an eyeball means that it is hit by a radiation beam. This should be avoided because the eyeball is a critical structure, which means that it is highly sensitive to radiation and can be damaged if exposed to high doses.