Radiation Dose from Adult and Pediatric Multidetector Computed Tomography (Medical Radiology Diagnostic Imaging)

275 Pages·2007·7.02 MB·English

by  A.L. Baert

I
Contents
MEDICAL RADIOLOGY
Diagnostic Imaging
Editors:
A. L. Baert, Leuven
M. Knauth, Göttingen
K. Sartor, Heidelberg
III
Contents
D. Tack · P. A. Gevenois (Eds.)
Radiation Dose from
Adult and Pediatric
Multidetector
Computed Tomography
With Contributions by
H. T. Abada · T. Batch · P. Bellinck · A. Blum · N. Buls · K. H. Chadwick · E. Coche
B. Cohen · J. de Mey · G. Ferquel · P. A. Gevenois · S. Golding · M. K. Kalra · C. Keyzer
H. P. Leenhouts · T. Ludig · T. Mulkens · H.-D. Nagel · A. Noël · R. Patel · J.-F. Paul
B. Sauer · R. Salgado · G. Stamm · J. Stoker · D. Tack · T. L. Toth · H. W. Venema
P. Vock · R. E. Van Gelder · D. Winninger · R. Wolf
Foreword by
A. L. Baert
With 148 Figures in 273 Separate Illustrations, 58 in Color and 47 Tables
123
IV
Contents
Denis Tack,
MD, PhD
Clinic of Cardiac Imaging
Department of Radiology
Hôpital Erasme
Université libre de Bruxelles
Route de Lennik 808
1070 Brussels
Belgium
Pierre Alain Gevenois,
MD, PhD
Professor of Radiology
Clinic of Chest Imaging
Department of Radiology
Hôpital Erasme
Université libre de Bruxelles
Route de Lennik 808
1070 Brussels
Belgium
Medical Radiology · Diagnostic Imaging and Radiation Oncology
Series Editors: A. L. Baert · L. W. Brady · H.-P. Heilmann · M. Knauth · M. Molls · K. Sartor
Continuation of Handbuch der medizinischen Radiologie
Encyclopedia of Medical Radiology
Library of Congress Control Number: 2006925265
ISBN 10 3-540-28888-0 Springer Berlin Heidelberg New York
ISBN 13 978-3-540-28888-6 Springer Berlin Heidelberg New York
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V
Contents
Foreword
A major portion of the total irradiation dose applied for medical purposes now
derives from the use of computed tomography. Indeed, over the past two decades a
steady increase in the use of this high-performance, non-invasive diagnostic modality
has been observed in the developed world. This trend in medical practice is a source of
major concern to public health authorities and clinicians.
This highly topical and serious problem is addressed and comprehensively covered
in this new volume of our Medical Radiology series.
The fi rst part provides the theoretical basis for our understanding of radiation issues
and the risks involved in the clinical applications of multidetector CT. The second part
deals with the various anatomic body areas and offers detailed guidelines on how to
conduct multidetector CT studies of specifi c organs under optimal circumstances of
dose reduction. A separate chapter is devoted to CT studies in children, an age group
for which radiologists should make maximal efforts in dose reduction due to the greater
risk of long-term harmful effects.
All contributors are internationally renowned experts. They have provided us with
a well balanced and highly informative text which will undoubtedly be very helpful
for all radiologists in training, certifi ed radiologists, as well as for all referring general
practitioners and specialists.
I am very much indebted to the editors, D. Tack and P.A. Gevenois, for this interest-
ing and outstanding volume.
Leuven Albert L. Baert
VII
Contents
Introduction
The use of computed tomography (CT) has seen enormous growth over the past decade.
In the US, approximately 63 million examinations were performed in 2005 (Niagara
Health Quality Coalition 2004) compared to 35 million in 2000. The increased number
of clinical applications (e.g., in emergency and trauma, paediatric, cardiac, and vas-
cular disorders) made possible by the fast scanning capabilities of multidetector CT
(MDCT) will drive even greater growth.
CT is already the main cause of radiation dose to the US population (Wiest et al.
2002; Mettler et al. 2000), and this will surely increase as the number of examinations
per patient increases. This is a serious concern with which the radiology community is
now confronted. The signifi cant uncertainty associated with radiation risk estimates,
long delays between exposure and cancer manifestation, and the fact that carcinogen-
esis is proved by statistical inference rather than by direct observation tend to reduce
the perceived urgency to reduce radiation dose delivered by CT. However, the radiology
community needs to be made aware that the small but acceptable risk–benefi t decisions
made at the individual patient level are amplifi ed by the huge number of CT procedures
performed each year. In a recent report on the biological effects of ionizing radiation
(Beir 2005), the overall probability of death due to a solid tumor induced by a single
10-mGy CT examination is estimated to be approximately 0.00041. This apparently
very low risk – multiplied by the 63 million CT examinations performed each year
– suggests in fact that 25,420 fatal cancers are induced by CT every year.
This calculation, however, has a number of major fl aws. The most important fl aw is
the fact that the risk factors were derived for generally healthy individuals in the popu-
lation of Japanese A-bomb survivors, whereas patients who undergo CT are usually
older and have a lower life expectancy than those in the general population. Moreover,
the health benefi t of CT-derived diagnostic information is immediate, whereas the risk
of induced cancer is decades away. Nevertheless, this mathematical calculation was
meant to underscore the importance of restraint in the use of MDCT.
Given these fi gures, what are radiologists supposed to do? Should they refuse to per-
form CT examinations on the patients referred to them? Conservative estimates of the
benefi t-to-risk ratios for CT are 100:1 and even higher. This discussion does suggest,
however, that CT should not be performed for dubious or trivial clinical indications.
Appropriateness criteria need to be vigilantly applied for all patients referred for a CT
examination. Appropriate medical training in radiation risk management would be
helpful in reducing the number of inappropriate requests for CT examinations. Aca-
demic radiologists should push for this training and organize dedicated lectures in
medical schools. In training hospitals, CT examinations requested by young residents
should be approved by senior physicians.
VIII
Introduction
MDCT has the potential to revolutionize cross-sectional imaging. However,
substantial improvements are necessary for maximal diagnostic utility. Radi-
ologists need to revise the CT protocols, change viewing strategies, and develop
new visualization skills to use these scanners to their full potential. The excel-
lent temporal resolution of most modern MDCT will be used for rapid imaging
of the heart and elsewhere, generating a new appreciation of the functional
capabilities of dynamic CT.
As radiation doses delivered to patients will increase further still with these
modern MDCT scanners, the radiology community needs to develop and
adhere to updated appropriateness criteria for routine MDCT examinations.
There is also a need for evidence-based benefi t–risk analyses. Such analyses
should include patient age and parameters related to his or her health status.
The increase in clinical applications and in image quality that permit MDCT
scanners will induce strong modifi cations in disease assessment and diagnos-
tic medicine. To remain masters of this technology, radiologists need to know
when to use or not to use this technique, to be conversant and knowledgeable
about radiation risk issues, to be aware of the CT parameters that infl uence
the radiation dose delivered to the patient, and to optimize MDCT acquisition
and reconstruction parameters suited for the clinical indication, as well as for
individual risk factors depending on the underlying disease, gender, and age.
Radiologists will then be able to develop radically new acquisition and inter-
pretation practices that will improve the diagnostic accuracy of MDCT exami-
nations at a substantially lower radiation risk.
References
Niagara Health Quality Coalition (2004) CT scanner services in Western New York. Finger Lakes
Health Systems Agency, Rochester, NY
Wiest PW, Locken JA, Heintz PH et al. (2002) CT scanning: a major source of radiation exposure.
Semin Ultrasound CT MR 23:402–410
Mettler FA Jr, Wiest PW, Locken JA et al. (2000) CT scanning: patterns of use and dose. J Radiol
Prot 20:353–359
BEIR VII phase 2 (2005) Health risks from exposure to low levels of ionizing radiation. National
Academies Press, Washington, DC
IX
Contents
Contents
1 Clincical Expansion of CT and Radiation Dose
Rajesh Patel and Stephen Golding. . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Part I: Radiation Risks in Multidetector CT
. . . . . . . . . . . . . . . . . . . . 9
2 Risks from Ionising Radiation
Kenneth H. Chadwick and Hendrik P. Leenhouts . . . . . . . . . . . . . . . . . 11
3 The Cancer Risk from Low-Level Radiation
Bernard L. Cohen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4 CT Parameters that Infl uence the Radiation Dose
Hans-Dieter Nagel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5 Collective Radiation Dose from MDCT: Critial Review of Surveys Studies
Georg Stamm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6 Methods and Strategies for Radiation Dose Optimization – and Reduction –
in MDCT with Special Focus on the Image Quality
Denis Tack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
7 Automatic Exposure Control in Multidetector-Row Computed Tomography
Mannudeep K. Kalra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
8 Patient Centering in MDCT: Dose Effects
Mannudeep K. Kalra and Thomas L. Toth . . . . . . . . . . . . . . . . . . . . . . 129
Part II: Clinical Approaches of Dose Optimization, and Reduction
. . 133
9 Dose Optimization and Reduction in CT of the Head and Neck, Including Brain
Tom Mulkens, Rodrigo Salgado, and Patrick Bellinck . . . . . . . . . . . . . . 135
10 Dose Reduction and Optimization in Computed Tomography of the Chest
Pierre Alain Gevenois and Denis Tack . . . . . . . . . . . . . . . . . . . . . . . . 153
11 Dose Optimization and Reduction in MDCT of the Abdomen
Caroline Keyzer, Pierre A. Gevenois, and Denis Tack. . . . . . . . . . . . . . . 161
12 Optimization of Radiation Dose in Cardiac and Vascular Multirow-Detector CT
Jean-François Paul and Hicham T. Abada. . . . . . . . . . . . . . . . . . . . . . . 171
X
Contents
13 Dose Optimization and Reduction in CT of the Musculoskeletal System
Including the Spine
Alain Blum, Alain Noël, Daniel Winninger, Toufi k Batch,
Thomas Ludig, Gilles Ferquel, and Benoît Sauer . . . . . . . . . . . . . . . . . .185
14 Dose Reduction in CT Fluoroscopy
Nico Buls and J. de Mey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
15 Dose Optimization and Reduction in CT of Children
Peter Vock and Rainer Wolf. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
16 Radiation Risk Management in Low Dose MDCT Screening Programs
Emmanuel Coche, Jaap Stoker, Henk W. Venema, and
Rogier E. Van Gelder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
16.1 Lung Cancer Screening Including Pulmonary Nodule Management
Emmanuel Coche . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
16.2 Dose Reduction in Screening Programs: Colon Cancer Screening
Jaap Stoker, Henk W. Venema, and Rogier E. van Gelder . . . . . . . . . . 255
Subject Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
List of Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
1
Clinical Expansion of CT and Radiation Dose
1
Clinical Expansion of CT and Radiation Dose
Rajesh Patel and Stephen Golding
CONTENTS
tists and physicians and in this chapter we provide
an introduction to the main themes which are of
1.1 Introduction 1
concern.
1.2 Clinical Expansion 2 Since its inception in 1973 (Hounsfi eld 1973)
1.3 The Dose Problem 3 the development of computed tomography (CT)
has been dramatic and the technique continues to
1.4 Approaches to the Problem 5
1.4.1 The ALARA Principle 5 mature. Twenty-fi ve years ago a typical study con-
1.4.2 The Role of the Referrer: Justifi cation 5 sisted of 10-mm sections, a 20-s exposure time and
1.4.3 The Role of the Operator: Optimization 6 a 60-s image reconstruction time. Technical devel-
1.4.4 The Role of Guidelines in MDCT 6
opments including the development of slip rings,
1.4.5 The Role of Evidence: Vigilance 6
increased X-ray tube heat capacity, advances in
References 7 detector technology and improvement in computers
now permit rapid sub-second exposures for acquir-
ing sub-millimetre sections and almost instanta-
neous image reconstruction. These improvements
1.1 have brought benefi ts in clinical examination,
Introduction extending the applications of CT into new areas
and facilitating diffi cult or demanding examina-
The principles of protecting the subject undergoing tions in all applications. The major development
investigation by radiation are clear and well known: in technology has been multidetector CT (MDCT),
it is the responsibility of all radiological services which has dramatically increased the performance
to ensure the information required for the clinical capability of CT. Successive generations of systems
management of the patient is obtained with the low- capable of acquiring 4, 8 or 16 sections simultane-
est practicable exposure to radiation. Within this ously have been introduced (Berland and Smith
clear objective, however, medical investigation oper- 1998; Hu et al. 2000; Kalender 2000). Even greater
ates in a constantly changing scenario infl uenced confi gurations are now becoming available, with the
by increasing knowledge of disease processes and latest cone beam systems capable of simultaneously
advancing technological development. This syn- acquiring 256 sections (Mori et al. 2006).
drome ensures that as time passes differing objec- The incorporation of slip ring technology into
tives and concerns come to the fore. Over the past the design of scanners in the late 1980s removed
few years the emergence of multidetector computed the need for rigid mechanical linkage between the
tomography (MDCT) has posed new challenges in power cables and the X-ray tube. The ability to rotate
radiological protection, to the extent that some now the tube continuously in one direction allowed the
claim that this represents today’s greatest single development of helical CT and re-established CT
challenge in clinical radiation protection. This book as a front-line imaging modality. Helical CT allows
expounds the challenges posed by MDCT to scien- a volume of tissue rather than individual slices to
be scanned as the table supporting the patient also
moves continuously while the tube is rotating; the
R. Patel, MD
data are reformatted automatically to display the
S. Golding, MD
images as axial slices. Furthermore, whereas con-
Radiology Research Group, Nuffi eld Department of Surgery,
University of Oxford, MRI Centre, John Radcliffe Hospital, ventional and spiral scanners use a single row of
Oxford, OX3 9DU, UK detectors, MDCT scanners currently have up to