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 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifi - cally the rights of translation, reprinting, reuse of illustrations, recitations, broadcasting, reproduction on microfi lm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag. Violations are liable for prosecution under the German Copyright Law. Springer is part of Springer Science+Business Media http//www.springer.com (cid:164) Springer-Verlag Berlin Heidelberg 2007 Printed in Germany The use of general descriptive names, trademarks, etc. in this publication does not imply, even in the absence of a specifi c statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Product liability: The publishers cannot guarantee the accuracy of any information about dosage and application contained in this book. In every case the user must check such information by consulting the relevant literature. Medical Editor: Dr. Ute Heilmann, Heidelberg Desk Editor: Ursula N. Davis, Heidelberg Production Editor: Kurt Teichmann, Mauer Cover-Design and Typesetting: Verlagsservice Teichmann, Mauer Printed on acid-free paper – 21/3151xq – 5 4 3 2 1 0 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