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E-raamat: Physics of CT Dosimetry: CTDI and Beyond [Taylor & Francis e-raamat]

  • Formaat: 210 pages, 23 Tables, black and white; 40 Line drawings, black and white; 2 Halftones, black and white; 42 Illustrations, black and white
  • Sari: Series in Medical Physics and Biomedical Engineering
  • Ilmumisaeg: 04-Apr-2019
  • Kirjastus: CRC Press
  • ISBN-13: 9780429023330
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  • Taylor & Francis e-raamat
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Physics of CT Dosimetry: CTDI and BeyondSuurem pilt
  • Formaat: 210 pages, 23 Tables, black and white; 40 Line drawings, black and white; 2 Halftones, black and white; 42 Illustrations, black and white
  • Sari: Series in Medical Physics and Biomedical Engineering
  • Ilmumisaeg: 04-Apr-2019
  • Kirjastus: CRC Press
  • ISBN-13: 9780429023330
Teised raamatud teemal:
Taylor & Francis e-raamatudRohkem infot Taylor & Francis e-raamatute kohta
Raamatu kodulehekülg: https://www.taylorfrancis.com/books/9780429023330

This book explores the physics of CT dosimetry and provides practical guidance on best practice for medical researchers and practitioners. A rigorous description of the basic physics of CT dosimetry is presented and illustrates flaws of the current methodology.

It also contains helpful (and rigorous) shortcuts to reduce the measurement workload for medical physicists. The mathematical rigor is accompanied by easily-understood physical explanations and numerous illustrative figures.

Features:

  • Authored by a recognised expert in the field and award-winning teacher
  • Includes derivations for tube current modulation and variable pitch as well as stationary table techniques
  • Explores abnormalities present in dose-tracking software based on CTDI and presents methods to correct them
Preface xv
Acknowledgments xvii
Author xix
About the Series xxi
Chapter 1 Introduction and History 1(10)
1.1 Introduction
1(1)
1.2 A Historical View Of CT Dosimetry
1(5)
1.2.1 The Early Universe
1(1)
1.2.2 The Birth of CTDI - 1981
2(1)
1.2.3 Enter the Regulators - 1989
3(1)
1.2.4 The Standard Dosimetry Phantoms
3(1)
1.2.5 Enter CTDI100 - 1995
4(1)
1.2.6 The Advent of Multi-Detector CT (MDCT) - 1998
5(1)
1.2.7 Enter CTDIvoi (A Misnomer) but an Improvement since It Eliminates nT (N x T)
5(1)
1.2.8 Dose Length Product
6(1)
1.2.9 Helical Scanning - Scanning with Continuous Table Motion - 1990
6(1)
1.3 Slipping The Surly Bonds Of CTDI
6(1)
1.3.1 An Alternative to the Pencil Chamber - 2003
6(1)
1.3.2 AAPM TG-111 - 2010
7(1)
1.3.3 Limitations of the CTDI-Paradigm and the Pencil Chamber Acquisition
7(1)
1.4 The IEC Attempts To Circumvent The Limitations Of CTDI
7(2)
1.4.1 For Shift-Variant Techniques
8(1)
1.4.2 For the Stationary Phantom/Table
8(1)
1.4.3 Wide Beam Widths
8(1)
1.4.4 Use of the Scanner-Reported CTDI
8(1)
1.4.5 Size-Specific Dose Estimates (SSDE)
8(1)
References
9(2)
Chapter 2 Derivation of Dose Equations for Shift-Invariant Techniques and the Physical Interpretation of the CTDI-Paradigm 11(16)
2.1 Introduction
11(1)
2.2 Derivation Of The Dose Equations And The CTDI- Paradigm On The Phantom Central Axis For A Shift- Invariant Helical Technique In Which No Parameters Vary With Z (Constant Tube Current, Pitch, Aperture, Etc.)
12(3)
2.3 Limitations Of THE CTDI-Paradigm: The Requirement For Shift-Invariance
15(2)
2.4 Extension Of The Derivations To Axial Scans And To Helical Scans On The Peripheral Axes
17(5)
2.4.1 Derivation of the Dose Equations for Axial Scans
18(1)
2.4.2 Derivation of the Helical Dose Distribution on the Peripheral Axes
19(2)
2.4.3 Longitudinal Average vs. Angular Average for Helical Scans
21(1)
2.5 Total Energy E Absorbed In The Phantom (And DLP)
22(3)
2.5.1 CTDI-Aperture
23(1)
2.5.2 The Physical Meaning of CTDIfree-in-air
24(1)
2.5.3 Three-Dimensional Calculation of the Total Energy Deposited in the Phantom
24(1)
Glossary
25(1)
References
26(1)
Chapter 3 Experimental Validation of a Versatile System of CT Dosimetry Using a Conventional Small Ion Chamber 27(26)
3.1 Introduction
27(1)
3.2 Summary Of CT Dose Theory In A Cylindrical Phantom
28(1)
3.3 Accumulated Dose (Or CTDI) Measurements
29(3)
3.3.1 Pencil Chamber Acquisition Method
29(1)
3.3.2 Small Ion Chamber Acquisition Method
30(1)
3.3.3 The Measured Quantity - A Phantom Dose Surrogate
31(1)
3.4 Materials And Methods
32(1)
3.5 Measurements Validating The Precision And Accuracy Of The Dosimetry System Itself
33(2)
3.5.1 Test of the "Stem Effect" for NE 2571 Farmer Chamber
33(1)
3.5.2 Effect of Phantom Cavity on Farmer Chamber Reading
33(1)
3.5.3 Cross Comparison of Ion Chambers
33(2)
3.5.4 Validation of the Manufacturer-Supplied Pencil Chamber Active Length l
35(1)
3.6 Body Phantom Measurements And Results
35(4)
3.6.1 Effect of Phantom Length on CTD/100
35(1)
3.6.2 Experimental Plan for Demonstration of the Small Ion Chamber Acquisition Method
36(1)
3.6.3 Selection of Scan Parameters for the Small Ion Chamber Acquisition
37(1)
3.6.4 Results of Measurements Made in the 400 mm Long Body Phantom
37(2)
3.7 Analysis Of Body Phantom Data
39(2)
3.7.1 Underestimation of Equilibrium Dose in the 400 mm Phantom Due to Truncation of Integration Length to 100 mm
39(1)
3.7.2 Underestimation of Equilibrium Dose by CTDI100 - Total Shortfall
40(1)
3.7.3 Farmer vs. Pencil Chamber Comparison
40(1)
3.8 CTDI-Aperture
41(2)
3.8.1 A Useful Constant Deriving from Conservation of Energy and a Robust Measurement Shortcut
41(2)
3.9 Validation Of Peripheral Axis Data
43(2)
3.9.1 Correcting a Misconception
43(1)
3.9.2 Testing the Sensitivity of the Peripheral Axis Data to Averaging Errors
43(1)
3.9.3 Visualization of the Actual Measurement Field on the Peripheral Axis
44(1)
3.9.4 An Alternate Method to Circumvent the Possibility of Peripheral Axis Averaging Errors
45(1)
3.10 A Suggested New CT Dose Measurement Protocol
45(2)
3.11 The Central Axis Dose Gains In Relative Importance
47(1)
3.12 Summary Of Results
47(1)
3.13 Conclusion
48(1)
Appendix A: Illustration Of CTDI-Aperture Constancy
49(1)
Glossary
49(1)
References
50(3)
Chapter 4 An Improved Analytical Primary Beam Model for CT Dose Simulation 53(34)
4.1 Introduction
53(1)
4.2 Primary Beam Model
54(7)
4.2.1 The Simple Geometric Model
54(1)
4.2.2 Detailed Primary Beam Model on the Axis of Rotation
55(2)
4.2.3 Outline of Primary Beam Model Derivation
57(2)
4.2.4 Convolution Approximation for the Tilted Anode
59(1)
4.2.5 Integral Theorem
60(1)
4.2.6 Model Application to the "Z-Flying Focal Spot"
60(1)
4.3 Experimental Validation Of The Primary Beam Model On The Axis Of Rotation
61(2)
4.3.1 Materials and Methods
61(1)
4.3.2 Primary Beam Profiles: Measurement vs. Theory
61(2)
4.3.3 Tilted vs. Flat Anode Challenge
63(1)
4.4 Sensitivity Profile
63(1)
4.5 Scatter Model
64(2)
4.5.1 Defining CTDI-Aperture
66(1)
4.6 Extension Of The Primary Beam Model To The Peripheral Phantom Axes
66(4)
4.6.1 Primary Beam Model for the Peripheral Axes
68(2)
4.6.2 Determination of the Angular Dependence of the Primary Beam Dose Rate A(9)
70(1)
4.7 Model Predictions For Cumulative Dose Distributions
70(6)
4.7.1 Transforming the Helical Dose Equation on a Peripheral Axis into an Axial Format
70(2)
4.7.2 Basic Equations Describing the Accumulated Dose
72(1)
4.7.3 Smoothing Conditions for the Quasi-Periodic Cumulative Dose
73(1)
4.7.4 Simulation of the Accumulated Dose on the Peripheral Axes
74(1)
4.7.5 Experimental vs. Simulated Accumulated Dose Distributions
75(1)
4.8 Cumulative Dose (Or CTDI) Measurements Using A Small Ion Chamber
76(1)
4.9 Summary And Conclusions
77(1)
Acknowledgments
78(1)
Appendix A: Details Of Primary Beam Model On The Axis Of Rotation
78(4)
A.1 The "Inverse Square" Correction Term
79(1)
A.2 Heel Effect Term
79(1)
A.3 Uniformity of Phantom Attenuation Across the Slice
80(1)
A.4 Approximation of the Constraint Equation
81(1)
A.5 Solving the Tilted Anode Problem for fp (z)
82(1)
Appendix B: Peripheral Phantom Axes
82(3)
B.1 Heel Effect - Peripheral Axis
83(1)
B.2 Constraint Equation for a Peripheral Axis
83(2)
Glossary Of Model Parameters And Their Magnitudes
85(1)
References
86(1)
Chapter 5 Cone beam CT Dosimetry: A Unified and Self-Consistent Approach Including All Scan Modalities - With or Without Phantom Motion 87(30)
5.1 Introduction
87(1)
5.2 Theory
88(7)
5.2.1 Conventional CT Scanning Using Table/Phantom Translation: Accumulated Dose Equations for Helical or Axial Scan Trajectories Utilizing Table/Phantom Translation Along z
88(2)
5.2.2 Helical Scanning
90(1)
5.2.2.1 Transition from Helical to Stationary Table/Phantom
90(1)
5.2.2.2 The Following Important Points Are Clear From the Foregoing:
90(1)
5.2.2.3 In Summary
91(1)
5.2.3 The Case of the Stationary Phantom
91(3)
5.2.3.1 Relating the Dose and the Dose Distribution in SCBCT to That of Conventional CT
91(2)
5.2.3.2 Measurement of the Central Ray Dose f(0) for a Wide Cone Beam and a Stationary Phantom in SCBCT
93(1)
5.2.4 The Equilibrium Dose Constant Aeq
94(1)
5.3 Numerical Analysis Of Experimental SCBCT Dose Data
95(3)
5.3.1 The Inapplicability of the CTDI-Paradigm and the Pencil Chamber to Stationary Phantom Dosimetry
96(1)
5.3.2 The Approach to Scatter Equilibrium for SCBCT
97(1)
5.3.3 The Approach to Equilibrium Function H(λ)
97(1)
5.4 Modeling The Cone Beam
98(11)
5.4.1 General Considerations
98(1)
5.4.2 The Heel Effect
98(1)
5.4.3 A Simple Beam Model Predicting the Observed Dose Data
98(8)
5.4.3.1 The Integral Theorem
99(1)
5.4.3.2 Relation Between Aeq and the Total Energy Deposited in the Phantom (Integral Dose)
100(1)
5.4.3.3 Calculation of the Relevant Stationary Phantom Peak Dose f(0) Using this Model
100(1)
5.4.3.4 The Scatter LSFs Exhibit Surprising Simplicity - the Monte Carlo Model
101(1)
5.4.3.5 Derivation of the Equation for the Peak Dose f(0) Using the Scatter LSF
102(1)
5.4.3.6 The Approach-to-Equilibrium Function H(a)
103(1)
5.4.3.7 The Commonality of the Approach to Equilibrium Function H(a)for Both Stationary Phantom Scanning (e.g., SCBCT) and Conventional Helical or Axial CT Scanning
104(1)
5.4.3.8 Comparison of the Theoretical Equation for H(a) with Experiment
104(2)
5.4.4 Extension to Peripheral Axes
106(3)
5.4.4.1 Derivation of the Expression for f(z) and f(0) on the Peripheral Axis using the LSF
106(3)
5.5 Generating The Complete Data Set For Conventional And Stationary Phantom CT From A Single Measurement Of The Peak Dose F(0) Resulting From A Single Axial Rotation - An Example
109(2)
5.5.1 Crossover to Conventional CT dose
111(1)
5.6 Summary And Conclusions
111(2)
Acknowledgment
113(1)
Appendix A: Derivation Of The LSF Formulation For The Peripheral Axis
113(2)
Glossary
115(1)
References
116(1)
Chapter 6 Analytical Equations for CT Dose Profiles Derived Using a Scatter Kernel of Monte Carlo Parentage Having Broad Applicability to CT Dosimetry Problems 117(24)
6.1 Introduction
117(3)
6.1.1 Summary of Pertinent Results from the Previous
Chapter
117(1)
6.1.2 Deriving an Analytical Function Describing the Complete Dose Profile
117(1)
6.1.3 The Utility of the Analytical Dose Profile Function f(z)
118(2)
6.2 Materials And Methods
120(1)
6.3 Theory
120(2)
6.3.1 The Primary Beam Component of the Axial Dose Profile fp(z)
120(1)
6.3.2 Derivation of the Scatter Component of the Axial Profile from the Scatter LSF
121(1)
6.3.3 Calculation of the Complete Axial Dose Profile on the Phantom Central Axis
121(1)
6.4 Comparison Of Theory With Experimental Data
122(5)
6.4.1 Primary Beam Function as Measured Free-In-Air
122(1)
6.4.2 Dose Profiles f(z) Measured on the Central Axis of the 32 cm PMMA Body Phantom Including Scatter
123(2)
6.4.3 The Heel Effect and Wide Cone Beams
125(1)
6.4.4 Stationary Phantom CT
126(1)
6.4.5 Helical CT with Wide Cone Beams and with Table Translation - CTDIL Can Again Apply
127(1)
6.5 Deriving Analytical Equations For CTDIL And Related Quantities For Conventional CT Using The Dose Profile Functions Previously Derived (L > a)
127(5)
6.5.1 Providing New Insight into the Physics of CT Dosimetry
128(2)
6.5.1.1 The CTDI Equation - Looking Behind its Integral Facade
129(1)
6.5.2 The Effect of the Weak Coupling Between Scan Length L and Beam Width a for Conventional CT Using Table Translation
130(1)
6.5.3 Application to Problems Beyond the Reach of the CTDI Method
130(2)
6.5.3.1 Understanding and Exploiting the Symmetries Implied by the Convolution
130(1)
6.5.3.2 The Case of a Near-Stationary Phantom for which L < a
130(1)
6.5.3.3 Evaluation of the Accumulated Dose DL(z) for an Arbitrary Value of znot = to 0
131(1)
6.6 Theoretical Dose Distributions On The Peripheral Axes For Single And Multiple Rotations
132(3)
6.6.1 An Analytical CT Dose Simulator - SIMDOSE
132(1)
6.6.2 Comparison of Theory with the Peripheral Axis Dose Profiles of Mori
132(3)
6.7 Application To Shift-Variant Scan Protocols
135(1)
6.8 Summary And Conclusions
136(1)
Acknowledgments
137(1)
Appendix A: Heel Effect Function
137(1)
Appendix B: Scatter Function Using The Full Double-Exponential LSF [ EQ. (6.7A)]
138(1)
Glossary
138(1)
References
138(3)
Chapter 7 Dose Equations for Tube Current Modulation in CT Scanning and the Interpretation of the Associated CTD/voi 141(28)
7.1 Introduction
141(1)
7.2 Methods
142(1)
7.2.1 Review of the Physical Meaning of the Traditional CTDIvol Based on Constant Tube Current (Constant mA)
142(1)
7.2.2 A Brief Review of the Relation of CTDIvol to Patient Dose
143(1)
7.3 Derivation Of The Theoretical Equations For Automatic Tube Current Modulation (TCM)
143(6)
7.3.1 Shift-Invariant Helical Technique Using Constant mA
143(2)
7.3.2 Deriving the Dose Equations for a Shift-Variant TCM Technique
145(4)
7.4 Total Energy Absorbed For Automatic Tube Current Modulation (TCM)
149(1)
7.5 The Trouble With The Reported Values Of CTDIvol
150(2)
7.5.1 Defining CTDITCMvol for a Shift-Variant, Auto TCM Protocol
150(1)
7.5.2 Tube Current Modulation (TCM) Versus Constant Current Summary
151(1)
7.5.2.1 A Pencil Chamber Measurement Has No Utility Whatsoever for Auto TCM nor for Shift-Variant Techniques in General
152(1)
7.6 A General Method For Handling Shift-Variant Protocols
152(8)
7.6.1 Simulation for a Shift-Invariant Constant mA
153(1)
7.6.2 Simulation of Shift-Variant Protocols (such as z-axis TCM) for which the Formulae of the CTDI-Paradigm Eqs (7.1-7.3) are Not Valid
154(5)
7.6.3 Calculation of Average Doses for the Profiles in Figure 7.6 - the Search for Some Commonality of CTDITCMvol and CTDIvol for Constant mA
159(1)
7.7 Derivation Of Some New Analytical Equations Treating Energy And Accumulated Dose
160(3)
7.7.1 Restricting the Derivation to the Cen
160(1)
7.7.2 Foiled by CTDI100
161(1)
7.7.3 The IEC Version of a "local CTDIvol(z)" and Global CTDITCMvol for Tube Current Modulation (TCM)
162(1)
7.8 Summary And Conclusions
163(1)
7.8.1 The Total Energy Absorbed E (Integral Dose) and DLP are Robust between Auto TCM and Constant mA Protocols (but Only for the Same Scan Length L= vto)
163(1)
7.8.2 The Scanner-Reported Value of "CTDIvol" Is Not Robust in the Dose Domain
164(1)
Appendix A
164(1)
Glossary
165(1)
References
166(3)
Chapter 8 Dose Equations for Shift-Variant CT Acquisition Modes Using Variable Pitch, Tube Current, and Aperture, and the Meaning of their Associated CTDIvol 169(22)
8.1 Introduction
169(1)
8.2 Materials And Methods
170(1)
8.3 Derivations
170(8)
8.3.1 Accumulated Dose for a Shift-Invariant Scan (Constant Tube Current and Pitch)
171(2)
8.3.2 Accumulated Dose Equation for Tube Current Modulation TCM [ Variable i(z), Constant Pitch]
173(1)
8.3.3 Accumulated Dose Equation for Variable Pitch (Pitch Modulation or PM) at Constant Current
174(3)
8.3.3.1 Table Kinematics for Variable Pitch
175(1)
8.3.3.2 Using a Helical Shuttle as a Specific Example for Illustration of Table Kinematics
176(1)
8.3.3.3 Summary for TCM and PM
177(1)
8.3.4 Accumulated Dose for Concurrent Tube Current and Pitch Modulation (Concurrent TCM and PM)
177(1)
8.4 Summary Of Equations For Various Scan Protocols
178(1)
8.5 Total Energy E Absorbed In The Phantom (And DLP)
178(1)
8.6 Variable Z-Collimator Aperture
179(1)
8.7 Dose Simulations
180(5)
8.7.1 Shift-Invariant Manual Technique - Constant Tube Current and Pitch
181(1)
8.7.2 Variable Tube Current or Variable Pitch
181(1)
8.7.3 Helical Shuttle (Variable Pitch, Constant Tube Current)
181(2)
8.7.3.1 Short Helical Shuttle
181(1)
8.7.3.2 Helical Shuttle vs. Cone Beam
182(1)
8.7.4 Summary of Accumulated Dose Distributions for All Simulated CT Protocols in a Single Figure
183(2)
8.8 Summary And Conclusions
185(1)
8.8.1 The Trouble with Scanner-Reported Values of CTDIvol for Shift- Variant Scan Techniques
185(1)
Appendix A
186(1)
Glossary
187(1)
References
188(3)
Chapter 9 Stationary Table CT Dosimetry and Anomalous Scanner- Reported Values of CTDIvol 191(14)
9.1 Introduction
191(1)
9.2 The Stationary Phantom Problem - And Its Solution
191(4)
9.2.1 Analysis Using a Simulation
191(2)
9.2.2 The Scanner-Reported CTDIvol
193(1)
9.2.3 Clinical Examples of Anomalous Values of CTDIvol
194(1)
9.2.4 Total Energy Absorbed E and DLP
195(1)
9.3 Appropriate Stationary Phantom Dose Equations - The Fix Is Easy
195(2)
9.4 Relation Of Scanner-Reported Dose Indices To Actual Patient Dose
197(2)
9.4.1 Size-Specific Dose Estimates (SSDE)
198(1)
9.4.2 Anomalous Values of SSDE
199(1)
9.5 CTDI100 For Wide Beams (IEC Version) - Cracking The "Ctdi Enigma" Code
199(3)
9.6 Summary And Conclusions
202(1)
References
203(2)
Chapter 10 Future Directions of CT Dosimetry and A Book Summary 205(4)
10.1 Beyond CTDI
205(2)
10.1.1 Estimation of Organ Doses
205(1)
10.1.1.1 Tube Current Modulation (TCM) and SSDE
205(1)
10.1.2 Understanding Risks from CT Exams
206(1)
10.1.2.1 The Gambler's Fallacy
207(1)
10.1.2.2 Death by Coefficient
207(1)
10.2 Book Summary
207(1)
References
208(1)
Index 209
Robert L. Dixon, Ph.D, FACR, FAAPM is Professor Emeritus in the Department of Radiology, Wake Forest University School of Medicine, USA and holds a Ph.D. in Nuclear Physics.

He has taught physics and medical physics for decades, and is a recipient of the Radiology Departments Teaching Excellence Award. He is also a past president of the American Association of Physicists in Medicine (AAPM) as well as past Chairman of the AAPM Science Council and CT Committee; and is a past Vice President of RSNA. He has published many papers on CT dosimetry in the journal Medical Physics and is a five-time winner of the SEAAPM Best Publication Award.

Prof. Dixon is a member of the IEC MT30 CT committee; is a designated US CT Expert (ANSI); and has been an invited keynote speaker at multiple International Conferences. He has also been a member of the Governing Board and the Executive Committee of the American Institute of Physics (AIP), and has received the Distinguished Service Award and the Lifetime Achievement Award of the American Board of Radiology (ABR).

He was also an airshow performer (1991-2006) flying former military aircraft including an ex- Soviet Air Force jet.
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