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School of Medical Radiation Sciences

Trends in CT Abdominal Doses in Malaysian Practices

Mohd. Hanafi Ali

MHSc

This research thesis is presented as part of the requirements for the award of the

degree of Doctor of Health Science of the Faculty of Health Sciences of the

University of Sydney

March 2005

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Declaration of Authorship I hereby certify that the work embodied in this thesis is the result of original research

and has not been submitted for a higher degree to any other University or institution.

Mohd Hanafi Ali

School of Medical Radiation Sciences

Faculty of Health Sciences

The University of Sydney

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ACKNOWLEDGEMENTS I wish to express my gratitude to my chief supervisor Dr Donald McLean for his

guidance and patience. I also thank both co-supervisors Dr Sarah Lewis and Prof Ng

Kwan-Hong with their advice and professionalism. Appreciation also goes to Dr

Robert Heard who made statistical studies more interesting and Dr Alastair Davison

whose kindness made this study a reality.

I really enjoyed the knowledge that was shared by experienced lecturers in the Health

Sciences Doctorate Team namely, Dr Rod Rothwell, (Theory in Health Profession);

Dr Ian Hughes who introduced me to doctoral foundation studies; Dr Kate

O’Loughlin, (Research Development and inquiry); Dr Karen Pepper, (SPSS); and Dr

Zakia Hossain (statistics). Thank to you Wendy Manuel who kept communication

within HScD community alive.

I also like to acknowledge Mr Wang Hwee Beng, Deputy Director of Radiation

Protection Division, Engineering Department, Ministry of Health Malaysia for his

understanding and appreciation of this study. To all Directors of Hospitals, Head of

Radiology Departments, Managers and Senior Radiographers, and CT Radiographers,

I sincerely appreciate your contribution. I also like to extend my gratitude to the

administration staff of University Technology MARA in Malaysia and Medical

Radiation Science School at The University of Sydney.

Finally, and most important, I dedicate this thesis to my lovely wife Faridah Jaffar,

my inspiring children Taufiq, Farid, Hanif, Hidayah and Haidah. I wish to thank them

for their love, patience and sharing the time during the study and forever with me.

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TABLE OF CONTENTS

DECLARATION ................................................................................................................ ii

ACKNOWLEDGEMENTS............................................................................................... iii

TABLE OF CONTENTS................................................................................................... iv

LIST OF FIGURES AND TABLES.................................................................................. ix

LIST OF ABREVIATIONS, SYMBOLS AND UNITS ................................................. xiv

ABSTRACT.......................................................................................................................xx

CHAPTER 1: INTRODUCTION....................................................................................... 1

1.1 Rationale for this study ....................................................................................... 1

1.2 Study objectives .................................................................................................. 3

1.3 Hypothesis of the study....................................................................................... 4

1.4 Introduction to thesis method.............................................................................. 5

1.5 Synopsis of this thesis......................................................................................... 7

CHAPTER 2: REVIEW OF DOSIMETRY IN COMPUTED TOMOGRAPHY...............9

2.1 Introduction................................................................................................................9

2.2 Principles of Computed Tomography........................................................................9

2.3 Historical Development of CT Systems ..................................................................10

2.3.1 The first and second generation scanners .........................................................10

2.3.2 Third and fourth generation scanners ...............................................................12

2.3.3 Spiral CT scanners ............................................................................................12

2.3.4 Electron beam scanners.....................................................................................13

2.4 Principles of CT Abdominal Procedures .................................................................14

2.4.1 Abdominal regions and organs .........................................................................14

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2.4.2 Contrast media in CT examination ...................................................................16

2.4.3 CT abdominal examination protocols...............................................................19

2.5 X-ray and matters.....................................................................................................20

2.5.1 X-ray characteristics and spectrum...................................................................20

2.5.2 Filtration............................................................................................................21

2.5.3 Attenuation and Half Value Layer....................................................................22

2.6 General Definition of Exposure and Dose ...............................................................23

2.6.1 Kerma................................................................................................................24

2.6.2 Absorbed Dose..................................................................................................25

2.6.3 Equivalent Dose ................................................................................................26

2.6.4 Effective Dose...................................................................................................27

2.6.5 The f- factor ......................................................................................................28

2.7 Radiation Dose Specific to CT ................................................................................30

2.7.1 Requirement for different dose descriptors.......................................................31

2.7.2 Measurement instruments .................................................................................32

2.7.3 CTDI measurement in air..................................................................................34

2.7.4 CTDI measurement using standard phantoms ..................................................35

2.7.5 Specific Dose unit for CT .................................................................................36

2.7.6 Principle of Monte Carlo Dose Calculations ....................................................38

2.7.7 Effective dose using Monte Carlo Calculations................................................39

2.7.8 Alternative Effective Dose Measurement methods ..........................................42

2.8 Factors that affect CT dose ......................................................................................43

2.8.1 X-ray Beam Energy ..........................................................................................43

2.8.2 Photon Fluence..................................................................................................45

2.8.3 Pitch Factor .......................................................................................................45

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2.8.4 X-ray Beam Collimation...................................................................................45

2.8.5 Object Diameter ................................................................................................46

2.8.6 Special Technical Features ...............................................................................46

2.8.7 Indirect factors ..................................................................................................47

2.9 Radiation Protection and Dose Optimization ..........................................................47

2.9.1 Typical CT Dose ...............................................................................................47

2.10 Methods to reduce patient dose..............................................................................50

2.10.1 Diagnostic Reference Levels ..........................................................................51

2.10.2 Determination of DRL ....................................................................................52

2.10.3 The need of DRLs implementation.................................................................54

2.11 Summary ................................................................................................................55

CHAPTER 3: MATERIALS AND METHODS .............................................................. 57

3.1 Introduction............................................................................................................. 57

3.2 Sample Selection..................................................................................................... 59

3.3 Survey tools ............................................................................................................ 60

3.4 Criteria for data collection ...................................................................................... 61

3.4.1 Scanners criteria .............................................................................................. 62

3.4.2 Patient and examination criteria ..................................................................... 62

3.5 Data compilation..................................................................................................... 63

3.6 Calculation of series, length, and RAL................................................................... 64

3.7 Dose calculation...................................................................................................... 68

3.8 Statistical analysis................................................................................................... 70

3.8.1 Selection of criteria for analysis datasets ........................................................ 71

3.8.2 Analysis of data sample distribution................................................................ 72

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3.8.3 Descriptive analysis of general parameters .................................................... 72

3.8.4 Descriptive analysis of dose parameters ......................................................... 73

3.8.5 Inferential analysis of dose parameters related to hypotheses ........................ 73

CHAPTER 4: RESULTS.................................................................................................. 76

4.1 Introduction............................................................................................................. 76

4.2 Analysis of distribution........................................................................................... 77

4.2.1 Scanners distribution ....................................................................................... 77

4.2.2 Other scanner related information .................................................................. 80

4.2.3 Hospital size..................................................................................................... 83

4.2.4 Patient distribution .......................................................................................... 84

4.3 Descriptive analysis of general parameters............................................................. 86

4.3.1 Analysis of data set .......................................................................................... 87

4.3.2 Examination performed ................................................................................... 87

4.3.3 Exposure parameters for different abdominal regions.................................... 93

4.3.4 Exposure parameters for all abdominal regions ............................................. 93

4.4 Descriptive analysis of dose parameters ................................................................. 97

4.4.1 Dose parameters for different abdominal regions........................................... 97

4.4.2 Dose parameters for all abdominal regions .................................................. 100

4.4.3 Comparison of dose parameters for spiral and non-spiral CT scanners ...... 101

4.4.4 Ratio of CTDIW over mAs and Ratio of Effective dose over DLP.................. 102

4.5 Example of scanning approach for pancreatitis patient ........................................ 105

4.6 Inferential analysis of parameters related to hypotheses ...................................... 107

4.6.1 Hypothesis 1: ................................................................................................. 107

4.6.2 Hypothesis 2: ................................................................................................. 108

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4.6.3 Hypothesis 3: ................................................................................................. 108

4.6.4 Hypothesis 4: ................................................................................................. 109

4.6.5 Hypothesis 5: ................................................................................................. 110

4.6.6 Hypothesis 6: ................................................................................................. 110

CHAPTER 5: DISCUSSION...........................................................................................111

5.1 Introduction............................................................................................................111

5.2 Comparison of effective dose to other studies.......................................................111

5.3 Comparison of CTDIW and DLP to other studies ..................................................117

5.4 Possibility of radiation dose optimisation..............................................................121

5.5 Weaknesses and limitations ...................................................................................123

CHAPTER 6: CONCLUSION ........................................................................................126

REFERENCES ................................................................................................................130

APPENDIX A - J .............................................................................................................147

APPENDIX A..............................................................................................................148

APPENDIX B ..............................................................................................................168

APPENDIX C ..............................................................................................................176

APPENDIX D..............................................................................................................189

APPENDIX E ..............................................................................................................229

APPENDIX F...............................................................................................................246

APPENDIX G..............................................................................................................251

APPENDIX H..............................................................................................................262

APPENDIX I ...............................................................................................................264

APPENDIX J ...............................................................................................................267

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LIST OF FIGURES AND TABLES

Figure 2.1: Development of computed tomography generation. .................................11

Figure 2.2: Electron Beam CT.....................................................................................14

Figure 2.3: Drawing of normal male (left) compared to mid-coronal cut of MRI

image..........................................................................................................15

Figure 2.4 The f-factor for air, water and different constituents of the body. .............29

Figure 2.5: Configuration of CT system. .....................................................................31

Figure 2.6: Arrangement of the ionisation chamber for CTDI measurement in air. ...33

Figure 2.7: A body (large) and head (small) phantom for measurement of CT Dose

Index. .........................................................................................................35

Figure 3.1: Survey flow chart ………………………………………………………..58

Figure 4.1: Distribution of the 35 scanners in the sample from all over Malaysia......77

Figure 4.2: Hospital size where the scanners operated. ...............................................83

Figure 4.3: Distribution of 443 patients scanned by 35 scanners ................................85

Figure 4.4: Distribution of patient weight in kilogram based on gender. ....................86

Figure 4.5: Percentage of phase series of the examination..........................................88

Figure 4.6: The frequency of Relative Abdominal Length (RAL) per examination ...92

Figure 5.1: Effective dose from 35 scanners in the current study. ............................115

Figure 5.2: The Weighted CTDI (CTDIW) per series for 35 scanners in the current

study.........................................................................................................124

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Figure 5.3: Dose Length Product per examination (DLPexam) for 35 scanners in the

current study.............................................................................................125

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Tables

Table 2.1: List of examination of abdomen and pelvis................................................16

Table 2.2: Several protocols for abdominal region based on indication of the

examination................................................................................................18

Table 2.3: Radiation weighting factors........................................................................27

Table 2.4: Tissue weighting factor...............................................................................28

Table 2.5: Normalised values of effective dose per dose length product (DLP) over

various body regions. .................................................................................42

Table 2.6: Typical effective doses from diagnostic medical exposures in the 1990s.

....................................................................................................................49

Table 2.7: Contribution to the UK collective dose and frequency from the 15 medical

and dental x-ray examinations making the biggest contributions to

collective dose............................................................................................50

Table 2.8: The world annual number of medical X-ray examination and its annual

collective dose............................................................................................54

Table: 3.1: Documents included in a package sent to the centres ...............................60

Table 3.2: Phase terms were used in each series of the examination. .........................65

Table 3.3:Reference anatomical levels (in cm) derived from ADAM and EVA.........66

Table 3.4: Basic information required for dose calculation in the CT-EXPO program

....................................................................................................................69

Table 3.5: Methods in selection of data for analysis of datasets .................................71

Table 4.1: Distribution scanners at hospitals and medical centres ..............................78

Table 4.2: Distribution of scanners based on manufacturers type ...............................79

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Table 4.3: Distribution of scanners manufacturer and age ..........................................80

Table 4.4: General scanner quality assurance history and other information..............82

Table 4.5: Patients’ physical measurements (mean ± standard deviation) ..................84

Table 4.6: Total number of examination series according to abdominal region. ........87

Table 4.7: Comparison of number of patient examinations for the different phase

series and regions involved........................................................................89

Table 4.8: Frequency of the examination indication sorted to the highest first...........90

Table 4.9: Organs, organ system or regions of diagnostic interest, for abdominal CT

examination................................................................................................90

Table 4.10: Frequency of acquisition series for various abdominal regions. ..............91

Table 4.11: Frequency of phase series conducted to all abdominal regions per patient

....................................................................................................................91

Table 4.12: Summary of descriptive average mean parameters for upper abdomen,

pelvis, and full abdomen regions. ..............................................................95

Table 4.13: Summary of descriptive average mean parameters for all abdominal

regions........................................................................................................96

Table 4.14: Average means dose for different abdominal regions. .............................99

Table 4.15: Average means dose for all abdominal regions......................................101

Table 4.16: Comparison mean dose values between spiral and conventional scanners.

Doses from conventional scanners always higher than spiral scanners as

noted in the last row.................................................................................101

Table 4.17: The ratio value of CTDIw/mAs and E/DLP for 35 scanners calculated

from each series of the examination. .......................................................103

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Table 4.18: Comparison of ratio doses values for different scanners model. Standard

deviation was calculated for the same scanner models that more than one

unit. ..........................................................................................................104

Table 4.19: The used of different approaches in examining patient with infection and

inflammation pancreas. ............................................................................106

Table 4.20: Summarised of ANOVA test result of dose descriptors variation amongst

CT scanners in Malaysia..........................................................................108

Table 4.21: Summarised of Pearson Correlation test result of dose descriptors and

main exposure parameters for 771 examination series ............................109

Table 5.1: Scanner density and typical dose between countries................................112

Table 5.2: Comparison of CT Abdominal radiation doses mean between countries.119

Table 5.3: Comparison of exposure parameters mean between countries.................120

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LIST OF ABBREVIATIONS, SYMBOLS AND UNITS

Abbreviations

ACR American College of Radiology

ALARA As Low As Reasonably Achievable

CEU the Council of the European Union

CM contrast media

CT Computed Tomography

CT-DOSE A tool for Dose evaluation in Computed tomography from NRPB

CT-EXPO A tool for Dose evaluation in Computed tomography from Germany

CVCT Cardiovascular Computed Tomography

DFOV Displayed field of view

DNA Deoxyribonucleic Acid

Exam Examination

FDG Federal Democratic of Germany

GSF Gesellschaft fur Strahlen und Umweltforschung (National Research

Centre for Environment and Health, Germany)

IAEA International Atomic Energy Agency

ICRP International Commission on Radiological Protection

ImPACT Imaging and Performance Assessment of CT Scanners

ISD Interscan Delay

IVU Intravenous urography

LAT Lateral

MC Monte Carlo

MCNP4B Monte Carlo N-Particles version 4B

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MIRD V Medical International Radiation Dose V

MMA Malaysian Medical Association

MOH Ministry of Health

MSCT Multi-slice Computed Tomography

NRPB National Radiation Protection Boards in the United Kingdom

PA Postero-anterior

PET Positron Emission Tomography

PMMA Polymethyl-methacrylate

RAL Relative Abdominal Length

SFOV Scanned field of view

Ser Series

SSCT Single Slice Computed Tomography

TLD Thermoluminescent dosemeter

UFCT Ultra Fast Computed Tomography

UK The United Kingdom

UNSCEAR United Nations Scientific Committee on the Effects of Atomic Radiation

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Symbols HE Effective dose equivalent

ε Energy imparted in tissue

z Axis along patient length

ρ Density

µ linear attenuation coefficient

C Constant

CTDI Computed Tomography Dose Index

CTDI100 Computed Tomography Dose Index measured using 100 mm

ionisation chamber

CTDI100,c Computed Tomography Dose Index measured using at the centre of the

phantom using 100 mm ionisation chamber

CTDI100,p Computed Tomography Dose Index measured using at the periphery of

the phantom using 100 mm ionisation chamber

CTDIvol CTDI volume (synonym to CTDIw, eff )

CTDIw Weighted Computed Tomography Dose Index

CTDIw,eff Effective weighted CTDI (synonym to CTDIvol )

DLP Dose Length Product

DRL Diagnostic Reference Level

DT Absorbed dose in tissue

dz Effective width of overbeaming range in mm

E Effective Dose

E Energy (italic)

e The base of the natural logarithm

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EDLP Normalised values of effective dose per dose length product (or

conversion coefficient factor)

E.DLP-1 Conversion Coefficient (mSv.mGy-1.cm-1)

ET Effective dose for tissue

F Fluoride

f(z) Exposure to absorbed dose conversion factor

href slice thickness to which the statement of normalised CTDI applies

HT The equivalent dose in tissue

HVL Half Value Layer

I Intensity (italic)

K Kerma

kOB The overbeaming correction factor

L Length in centimetre

Li Lithium

M Mass

Mg Magnesium

N Number of slices (or the number of slices which can be acquired

simultaneously)

nCTDIw Normalised Weighted CTDI (mGy.mAs-1)

p pitch

Q Charge of the ion

T Tissue or organ

Tc Technetium

Th Thelium

Uref Tube potential (or kVp)

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WT Tissue weighted factor

X Exposure

x the thickness of the material

Xe Xenon

Z Atomic number

zU Upper anatomical level for the anthropomorphic mathematical

phantoms ADAM and EVE

zL Lower anatomical level for the anthropomorphic mathematical

phantoms ADAM and EVE

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Units C Coulomb

cm centimetre

g gram

Gy Gray

J Joule

J.kg-1 Joule per kilogram

keV kilo electron volt

kg kilogram

kVp peak Kilovoltage

mAs milliampere-second

mAseff milliampere-second effective (milliampere second divided by pitch)

MeV Mega electron volt

mGy milli-Gray (10-3 Gy)

mGy.cm milli-Gray-centimetre

mGy.mAs-1 milli-Gray per milliampere-second

mSv.mGy-1.cm-1 milli-Sivert per milli-Gray per centimetre

ml millilitre

mm millimetre

mSv milli-sievert

Rad Radiation absorbed dose

Sec second

Sv Sievert

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ABSTRACT

Introduction: An investigation of clinical Abdominal Computed Tomography (CT)

dose, and associated clinical diagnostic protocols, has been undertaken. This research

was carried out to study the pattern of CT dose from routine abdominal examinations

in Malaysian practices. From this study it is hoped to establish a Dose Reference

Level (DRL) to assist in optimising radiation dose for CT abdominal examination in

Malaysia.

Method: Questionnaires studying both the CT imaging system and exposure

parameter details were sent for completion to 95 centres nationwide. Centres were

requested to give details on scan parameters including the patient abdominal

circumference, used for 15 abdominal cases. From these data dose descriptors such as

Weighted Computed Tomography Dose Index (CTDIw), Volume Computed

Tomography Dose Index (CTDIvol), Dose Length Product (DLP) and Effective Dose

(E) were calculated using a computer program based on the Monte Carlo method (CT-

EXPO) per series and for the full examination.

Result: The survey successfully sampled 34.6% of the 101 CT scanners in Malaysia.

The data consists of 443 CT abdominal examinations comprising 771 individual

series. The mean patient weight was (61±8 kg), with BMI of (23±3) being identical to

the national average. The third quartile values of CTDIw, CTDIvol, and DLPexam were

23 mGy, 20 mGy and 824 mGy.cm respectively, while the mean examination

effective dose (Eexam) was 13 mSv.

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Discussion: This study showed that dose parameters were lower or equal to those of

the European Commission (EC) standards, however for the mean effective dose was

higher in Malaysia than reported for the UK in NRPB-4. Average CT exposure

parameters were found to be lower than those reported from the EC. However the

total exam scan lengths used in Malaysia were greater than those of the EU due to the

additional number of series or phases used. A small number of centres had

unacceptably high patient doses and are considered as outliers.

The volume CTDI pattern for CT abdominal procedures was found to be not related to

patient weight but rather to be related to scanner centre characteristics. This finding

suggests further study is needed on why patient weight is not being used as a guide for

the scan exposure factors and points to the need for continuing education on CT

applications and dose optimisation. Further, the abdominal circumference is an

available alternative parameter useful for determining appropriate tube potential and

tube current for examinations.

Conclusion: There was a wide variation of CT doses in CT abdominal examinations

in Malaysia and DRL values for CT abdominal examination of this study can be

suggested for dose optimisation in future.