The physics of conformal radiotherapy : advances in technology

384 Pages·1997·20.835 MB·English

by  Steve Webb

Medical Science Series
THE PHYSICS OF
CONFORMAL
RADIOTHERAPY
Advances in
Technology
Steve Webb
Professor of Radiological Physics,
Joint Department of Physics,
Institute of Cancer Research and
Royal Marsden NHS Trust, Sutton, Surrey, UK
Institute of Physics Publishing
Bristol and Philadelphia
Copyright © 1997 IOP Publishing Ltd
@ IOP Publishing Ltd 1997
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ISBN 0 7503 0396 4 (hbk)
ISBN 0 7503 0397 2 (pbk)
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Series Editors:
R F Mould, Croydon, UK
C G Orton, Karamanos Cancer Institute, Detroit, USA
J A E Spaan, University of Amsterdam, The Netherlands
J G Webster, University of Wisconsin-Madison, USA
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Copyright © 1997 IOP Publishing Ltd
CONTENTS
...
PREFACE xi11
ACKNOWLEDGEMENTS xix
1 DEVELOPMENTS AND CONTROVERSIES IN
THREE-DIMENSIONAL TREATMENT PLANNING 1
1.1 The rationale for developing conformal therapy 1
1.2 Methods for and controversies in determining the contours
of target volumes, organs-at-risk and their beam’s-eye-view
projections 4
1.2.1 The interaction with the human observer 6
1.2.2 The influence of organ movement 7
1.2.3 Setup errors 10
1.2.4 The use of multiple-modality imaging 11
1.2.5 Beam apertures 13
1.3 Treatment planning and a tutorial on treatment-plan
optimisation by simulated annealing 14
1.3.1 What is treatment-plan optimisation? 14
1.3.2 Classes of inverse-treatment-planning techniques 16
1.3.3 Simulated annealing; general concepts and properties 18
1.3.4 The power of simulated annealing; cost functions 25
1.3.5 Classical and fast simulated annealing 29
1.3.6 Practicalities of implementing simulated annealing
for inverse treatment planning 30
1.3.7 Implementations at the Institute of Cancer Research
(ICR) and Royal Marsden MIS Trust (RMNHST) 32
1.3.8 Conclusion 36
1.4 Progress in 3D treatment-plan optimisation by simulated
annealing at Memorial Sloan Kettering Hospital (MSK),
New York 37
1.5 Optimisation at Delft University of Technology 40
1.6 Projection and backprojection issues in analytic inverse
treatment planning for optimising IMBs 41
1.7 Dose calculation for inverse planning of IMBs 45
vii
Copyright © 1997 IOP Publishing Ltd
...
vi11 Contents
1.8 Deterministic iterative optimisation of IMBs: Holmes’
solution 47
1.9 Deterministic iterative optimisation of IMBs: Bortfeld’s
solution 50
1.10 Optimisation using IMBs, a biological cost function and
iterative techniques 55
1.1 1 Optimisation of 2D planning of IMBs by minimum norm,
maximum entropy and genetic methods 60
1.12 Iterative optimisation of IMBs at the University of
Wisconsin; the power of cost functions and an electrostatic
analogy 62
1.13 Optimisation of dynamic therapy 64
1.14 Optimisation of beam orientations 65
1.15 Sherouse’s method for combining wedged fields by analysis
of gradients 70
1.16 Controversies in determining the ‘best plan’ 75
1.17 Summary 76
References 77
2 METHODS TO CREATE INTENSITY-MODULATED BEAMS
(IMBS) 96
2.1 Class 1: 2D Compensators 97
2.2 Class 2: Dynamic-leaf collimation 99
2.2.1 The solution of Convery and Rosenbloom 101
2.2.2 The solution of Svensson et a1 103
2.2.3 The solution of Stein et a1 106
2.2.4 The solution of Spirou and Chui 110
2.2.5 The solution of Yu and Wong 115
2.2.6 Iterative optimisation of scanning-leaf configurations 124
2.2.7 The solution of Spirou and Chui including upstream
fluence modulation 125
2.2.8 Experimental delivery of IMBs with dynamic-leaf
movement 127
2.3 Class 3: Leaf-sweep and close-in; the Bortfeld and Boyer
method of multiple-segmented (static) IMBs 130
2.4 Class 4: tomotherapy; The Carol collimator and the Mackie
machine 138
2.4.1 The NOMOS 2D intensity-modulating collimator 152
2.4.2 A diagnostic analogue 155
2.5 Class 5: Creation of IMBs by the moving-bar technique 156
2.6 D intensity modulation using conventional collimators 162
2.7 Scanning-beam therapy 162
2.8 Verification of IMB delivery 165
Copyright © 1997 IOP Publishing Ltd
Contents ix
2.9 Summary 166
References 167
3 THE MULTILEAF COLLIMATOR (MLC) IN CLINICAL
PRACTICE 176
3.1 Characterising the physical properties of an MLC 177
3.2 Can an MLC replace shaped cast blocks? 186
3.2.1 Setting leaves with respect to the beam’s-eye-view
of the PTV 192
3.2.2 Does the use of the MLC save time? 195
3.3 The MLC in clinical use 197
3.3.1 The MLC creating multiple fields for conformal
therapy 197
3.3.2 Coplanar versus non-coplanar irradiation 198
3.3.3 The MLC in conformal stereotactic radiotherapy 198
3.3.4 Sparing dose to normal brain tissue with shaped
fields 20 1
3.3.5 Theoretical studies of normal-tissue sparing in
stereotactic radiotherapy using various field-shaping
collimators 202
3.4 Computer control of MLC leaves and interface to imaging 207
3.5 Verifying MLC leaf position 208
3.6 Two new MLCs 209
3.6.1 The GEMS MLC 209
3.6.2 A prototype multi-rod MLC 21 1
3.7 Summary 2 14
References 214
4 MEGAVOLTAGE PORTAL IMAGING, TRANSIT DOSIMETRY
AND TISSUE COMPENSATORS 22 1
4.1 The use of portal images to assess and correct patient setup
error 221
4.1.1 The use of radio-opaque markers for patient
(re)positioning 223
4.2 Transit dosimetry 224
4.2.1 The digital reconstructed radiograph (DRR) 225
4.2.2 Registration of the DRR with the portal image;
creation of treatment-time 3D CT data 227
4.2.3 Portal fluence: primary exit fluence from measured
data 228
4.2.4 Backprojection to obtain a 3D map of the primary
fluence in the patient 238
4.2.5 Determination of terma 239
4.2.6 Determination of the 3D dose distribution 239
Copyright © 1997 IOP Publishing Ltd
Contents
X
4.2.7 Verification of verification, MRI of dose-sensitive
gels 24 1
4.3 Use of portal imaging for compensator construction 245
4.4 Summary 249
References 249
5 CONVERTING 3D DOSE TO BIOLOGICAL OUTCOMES:
TUMOUR CONTROL PROBABILITY (TCP) AND
NORMAL-TISSUE-COMPLICATION PROBABILITY (NTCP) 258
5.1 Tumour control probability: general considerations 25 8
5.2 Models for TCP with inter- and intra-tumour heterogeneity 259
5.3 Mechanistic prediction of TCP 263
5.4 DVH reduction techniques and formulae for computation of
NTCP 266
5.4.1 Equivalence of the Lyman expression and the
Logistic formula for NTCP 272
5.5 A model for NTCP based on parallel tissue architecture 273
5.5.1 Homogeneous irradiation 273
5.5.2 Inhomogeneous irradiation 277
5.6 Ranking 3D treatment plans using proxy attributes 279
5.7 Error estimation in determining DVH, TCP and NTCP 280
5.8 Controversies concerning reporting volumes 283
5.9 Summary 284
References 285
6 PROGRESS IN PROTON RADIOTHERAPY 288
6.1 New facilities 288
6.2 The Clatterbridge facility in the UK 294
6.3 The clinical proton facility at Loma Linda, USA 297
6.4 The clinical proton facility at Orsay, Paris, France 299
6.5 The clinical proton facility at PSI, Switzerland 300
6.6 The clinical proton facility at Faure, South Africa 30 2
6.7 The clinical proton facility at Indiana University, USA 30 5
6.8 The clinical proton facility at UCSF Davis, USA 306
6.9 The clinical proton facility at TRIUMF, Canada 306
6.10 The proposed UK high-energy proton facility 307
6.1 1 Fixed- versus variable-modulation treatment modes 308
6.1 1.1 Physical description 308
6.1 1.2 Clinical comparison 30 9
6.1 1.3 Treatment planning for spot scanning 3 10
6.1 1.4 Proton tomotherapy and distal-edge tracking 311
6.12 Photons or protons? 31 1
6.13 Proton radiography 313
Copyright © 1997 IOP Publishing Ltd
Contents xi
6.14 Summary 3 14
References 315
7 IMAGE FORMATION, UTILISATION AND DISPLAY, THE
ROLE OF 3D AND THE CT-SIMULATOR 322
7.1 Tomography ‘drives’ conformal radiotherapy 322
7.2 Cross section imaging on a radiotherapy simulator 323
7.3 Multimodality imaging and image compression 33 1
7.4 D display of anatomy and radiation quantities 333
7.4.1 ‘Tumour’s-eye-view’ 34 1
7.5 The CT-simulator 342
7.6 Information coordination 345
7.7 Computational advances that assist radiation therapy 346
7.8 Summary 347
References 348
EPILOGUE 353
APPENDICES 355
A DECISION TREES IN CONFORMAL TREATMENT
PLANNING 355
B METHODS OF COMPUTING DOSE TO A POINT AND
FEATURES OF EACH METHOD 359
C QUALITY ASSURANCE OF CONFORMAL THERAPY 362
D A NOTE ON THE WORK OF GEORGE BIRKHOFF 365
References 3 67
INDEX 36 9
Copyright © 1997 IOP Publishing Ltd