Table Of ContentINVERSE RADIOSURGERY TREATMENT PLANNING THROUGH
DECONVOLUTION AND CONSTRAINED OPTIMIZATION
by
JOSEPH F. HARMON JR.
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1994
LD
iiiiiiiii
ACKNOWLEDGMENTS
Many individuals have contributed to the completion of
this research. First, I am grateful for the guidance and
helpful comments provided by all of my committee members.
Special thanks are due Dr. Frank Bova for his valuable
insight and support while serving as committee chairman. I
wish to also extend my thanks to Dr. Rodhe Mohan and Michael
Lovelock at Memorial Sloan Kettering Cancer Center for
providing me with the differential pencil beam data so
critical to this endeavor. Finally, and most of all, I wish
to thank my wife. Rose, and my children, Ashley, Sarah, and
Taylor, for their patience and never ending support.
TABLE OF CONTENTS
page
ABSTRACT V
CHAPTERS
1 INTRODUCTION 1
Overview 1
Stereotactic Radiosurgery 2
Inverse Treatment Planning 4
Treatment Implementation 6
2 REVIEW OF LITERATURE 10
Dosimetry Algorithms 10
Overview 10
Matrix Models 10
Separation of Primary and Scattered Components.. 12
Monte Carlo Techniques 13
Energy Deposition Kernels 14
Inverse Radiotherapy Planning Approaches 23
Analytical Methods 24
Iterative Methods 28
3 DOSIMETRY CALCULATIONS 32
Introduction 32
Energy Deposition Kernel 32
TERMA 41
Convolution 42
4 BREMSSTRAHLUNG SPECTRA 48
Introduction 48
Spectrum Model 49
Optimization Algorithm 56
Results 59
5 DOSIMETRY MEASUREMENTS 66
Overview 66
Radiochromic Film 67
TLD Sheets 77
6 INTENSITY MODULATION 83
Overview 83
Optimal Intensity Modulation 83
Deconvolution 83
Backprojection 88
Single Beam Intensity Modulated Dosimetry 93
7 RADIOSURGERY PLANNING 97
Overview 97
Coordinate Transformation 98
Multiple Beam Optimization 102
Annealing Parameters 104
Example Results 107
8 EXTENSION TO GENERAL RADIOTHERAPY 135
Overview 135
Small Field Approximations 136
Large Field Dosimetry verification 137
Example Inverse Radiotherapy Case 149
9 SUMMARY AND CONCLUSIONS 153
APPENDIX 156
REFERENCES 226
BIOGRAPHICAL SKETCH 233
IV
Abstract of Dissertation Presented to the Graduate School of
the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
INVERSE RADIOSURGERY TREATMENT PLANNING THROUGH
DECONVOLUTION AND CONSTRAINED OPTIMIZATION
By
Joseph F. Harmon Jr.
April 1994
Chairman: Frank J. Bova, Ph.D.
Major Department: Nuclear Engineering Sciences
An inverse treatment planning approach is presented for
radiosurgery which permits conformal dose distributions to
small, irregularly shaped targets. Traditionally, such
targets would require somewhat complex, multiple isocenter
plans, arrived at after much trial and error effort. In
contrast, the approach presented here requires only one
isocenter location and arrives at an optimal plan
automatically. The single isocenter is made possible by
allowing complete beam intensity modulation for multiple
beam's eye views (BEVs) of the target. The automation is due
to incorporation of a deconvolution procedure to determine
the intensity modulation of each BEV and a simulated
annealing algorithm to optimize their respective weighting.
Additionally, this method is fully 3-D and accurately models
phantom scatter by incorporating Monte Carlo generated
energy deposition kernels into the dosimetry process. The
extension of this methodology to larger targets for general
radiotherapy cases is also addressed.
VI
CHAPTER 1
INTRODUCTION
Overview
The goal of this research was development of an
automated conformal 3-D treatment planning tool for
radiosurgery sized targets incorporating photon beam
intensity modulation and phantom scatter. Development of
such a tool is considered a necessary step to eventually
permit improved treatment of irregularly shaped radiosurgery
sized target lesions by sparing dose to adjacent normal and
critical structure tissue.
Automation of the planning procedure should reduce
excessive trial and error treatment planning times
associated with such radiosurgery cases. Also, due to the
single isocenter approach of this method, the treatment
delivery times should also be significantly reduced.
Finally, the nature of the approach taken will permit a very
flexible beam arrangement thus allowing a wide variety of
mechanical treatment delivery methods.
This chapter will present a brief introduction to
radiosurgery, inverse treatment planning, and potential
methods of conformal treatment delivery. Subsequent chapters
will present details of the specific approach taken and how
it differs from other inverse treatment planning approaches.
. .
stereotactic Radiosurcrery
Stereotactic radiosurgery was originally introduced in
1951 as a method of carefully focusing several small beams
of ionizing radiation to destroy tumors in the brain
(Leksell 1951) Over the years, the idea has been
.
implemented with a wide range of radiation sources including
200-300 kV x-rays, multiple ^'-'Co sources, higher energy
photons from linear accelerators, and heavy particles such
as protons (Friedman & Bova 1989a) . Of these possibilities,
producing photons with a linac is the least expensive and
thus most widely available option. Recently, this option has
been made even more attractive for radiosurgery due to
development of a system which quickly couples to an existing
linac to improve positional accuracy. This system
incorporates precision machined bearings and a gimbal device
to ensure an isocenter accuracy of 0.2 + 0.1 mm (Friedman &
Bova 1989b)
The attractiveness of radiosurgery is due to the
ability to treat lesions in regions of the brain that are
otherwise inaccessible (Winston & Lutz 1988) . Examples of
the clinical applications include treatment of arteriovenous
malformations (AVMs) acoustic schwannomas, malignant brain
,
neoplasms, and meningiomas (Friedman, Bova & Spiegelmann
1992) The majority of the lesions treated are less than 30
.
mm in size and are subjected to single fraction doses
ranging from 1500 to 3000 cGy (Friedman, Bova & Spiegelmann
1992)
.
In conventional radiation therapy, treatment is broken
into many fractions in an attempt to take advantage of
repair of normal tissues. This is accomplished through the
differential biological sensitivity of healthy and tumor
tissue to radiation (Hendrickson & Withers 1991) . In
stereotactic radiosurgery however, the radiation is usually
delivered in a single fraction due to the difficulty in
accurately localizing the lesion and positioning the patient
over several treatments. In fact, the developments in
radiosurgery have been slowed partly due to the need for
more precise localization of the target (Leksell 1983)
Because of the high, single fraction doses involved, it is
obviously more important than ever to ensure lesion coverage
while sparing healthy tissue. Thus, a highly accurate method
of dose delivery is needed.
Depending on the specific case, target localization is
accomplished with angiography, CT, MRI or a combination of
these techniques. For example, due to the limitations of
angiography, all AVM radiosurgery planning is supplemented
with CT to ensure adequate target identification
(Spiegelmann, Friedman & Bova 1992) . The reference frame for
localization is a precisely built Brown-Roberts-Wells (BRW)
ring, mounted to the patient's head. An additional
localizing frame is then attached to the top of the head
ring. A different localizer is used for each of the possible
diagnostic procedures mentioned earlier. They each, however,
contain reference points which allow one to locate the
