Development of Amendments to the U.S. RadiationSafety Standard for Diagnostic XRay Computed Tomograp

1
Development of Amendments to theU.S.
Radiation-Safety Standard forDiagnostic
X-RayComputed Tomography (CT) EquipmentS.H.
Stern, R.M. Gagne, H.H. Knox, M.P. Divine, R.J.
Doyle, C.A. Finder, R.G. Kaczmarek, R.V.
Kaczmarek, H.L. Rourk,T.B. Shope, Jr., D.C.
Spelic, O.H. Suleiman, and S.A. TuckerU.S. Food
and Drug Administration
Presented May 22, 2002 to the Technical
Electronic Product Radiation Safety Standards
Advisory Committee Gaithersburg, Maryland
Based on poster AC 1, FDA Science Forum,
February 20-21, 2002, Washington, DC
2
Advances and Concerns Interplay of
Technology and Clinical Practice in CT
3
CT Applications1 diagnostic identification or
exclusion disease, abnormality, trauma cancer
staging remission, progression,
metastasis treatment planning medical, surgical,
radiotherapeutic real-time visualization during
intervention biopsy, drainage, device placement
4
Predominant CT Technology2

• fan-shaped x-ray beam detectors rotate
• single 360o rotation in 0.5-1.0 sec (fast)
• detectors register x rays transmitted while
  rotating
• radiological techniques set manually
• thin single slice spans 1-10 mm along patient
  length and yields one cross-sectional image per
  rotation
• multi-slice 2-4 adjacent cross-sectional images
  per rotation constructed simultaneously
• axial CT table moves incrementally following
  each single rotation
• spiral (also called helical) CT table moves at
  constant rate during continuous rotations
• exam volume total table movement spans 10-50
  slices

detectors
detectors
detectors
z
Fast, multi-slice, spiral scanning3-5
enables large-volume scanning and
three-dimensional rendering,6 angiography,7-10 sin
gle breath-hold imaging and visualization of
small lung nodules11,12 ? large throughput of
patients,13 frequent utilization14
5
Public Health Concerns ? Responses15 CT dose to
the population many exams, large dose per exam ?
dose survey14 and handbook16 CT exams of
children, small adults inappropriate equipment
settings and scanning techniques17-26 more
radiation than needed? ? public health
notification27 Asymptomatic self-referrals for CT
screening whole-body,28 lungs,29-32 heart
(calcium scoring)33 radiation risk with
uncertain preventive efficacy? ? web page34 CT
fluoroscopy, interventional procedures radiation-i
nduced skin injury?35-38 ? reviewer, manufacturer
guidance
6

• Federal Radiation Protection
• Current Standards for CT Equipment Performance39
• Regulations 20 years old
• Rules apply to manufacturers, not to facilities
  that use CT equipment
• Basic mandate Manufacturers must provide dose
  documentation
• Predates special or new modalities such as
• electron-beam, multi-slice, spiral, fluoroscopic,
  cone-beam CT
• No regulatory ceiling on patient dose
• Few major requirements particular to CT equipment

7
Current FDA Standard for CT Dose
Documentation Computed Tomography Dose Index
(CTDI)40
Single-Slice Dose Profile
Fan-beam in x,y plane
Detectors
CTDI ? 0.82 rad
Thin-slice z-axis collimation
16- or 32-cm diameter acrylic phantom
Source
7T
CTDI ? (1/ nT) ? D(z)dz
7T

• index of system radiation output and absorption
  in acrylic, reference material
• proportional to integral of dose profile of
  primary and scattered radiation
• dose at point x,y in central plane of 14
  contiguous axial scans, reference procedure
• not defined for spiral (helical) scanning
• non-regulatory variants41-43 CTDI100 , CTDIw ,
  CTDIvol ? confusion

8
Amendments Being Considered Technical Features
to Reduce Radiation Dose Initial
Focus Dose-Index Standardization, Display,
Recording Automatic Exposure Control X-Ray-Field
Size Limitation
9

• Patient Examination Dose-Indices Standardization,
  Display, Recording for QA
• User option to have the CT system display and/or
  record
• values of standardized dose indices for each
  patients exam
• Requires formal definition of CT terminology
• e.g. tomographic section thickness (T), pitch
• Facilities could audit doses versus reference
  dose values 44-49
• compare exam doses to norms from which facilities
  could
• investigate anomalies and optimize CT settings,
  protocols50
• Dose-index displays available now on some newer
  CT models51
• Potential impact reduce patient CT dose on
  average 15 52-55

10

• Promising Indices of Patient Dose
• Volume Computed Tomography Dose Index
  (CTDIvol)43
• monitored to optimize exposure settings, e.g.,
  mAs50
• CTDIvol CTDIw / (?z/nT) axial scanning
• CTDIvol CTDIw / pitch spiral scanning
• weighted CTDI CTDIw (1/3)CTDI100,c
  (2/3)CTDI100,p
• Dose-Length Product (DLP)56
• to control irradiation volume and to follow-up
  dose anomalies50
• DLP CTDIvol Length of irradiated volume

?sensitive to particular exam protocols ?valid
for spiral as well as axial CT ?DLP is
practicable indicator of risk ?comports with
European guidelines57
11

• Automatic Exposure Control
• (AEC) via Anatomically Adapted
• X-Ray-Output Modulation58,59
• CT system would automatically adjust x-ray
  emissions to
• amounts needed to image particular patient
  anatomy
• Pediatric, thinner adult patients lower doses
  than thicker patients
• Feasible several different technologies already
  available on newer models60
• E.g. emissions vary as x-ray tube rotates around
  (x,y) table moves patient along (z)

x
y
cross section, torso
thicker arrows more radiation needed to
penetrate cross section thinner arrows less
radiation need to penetrate cross section

• Potential impact reduce patient CT dose 30
  61,62

12
Concern Inefficient Use of Radiation Over-beamin
g in Multi-slice CT4,63,64
Single-slice CT 1 image, 5-mm section
Multi-slice CT 4 images, 1.25-mm sections
z-collimation 15 mm
z-collimation 5 mm
patient-incident exposure profiles umbra
regions penumbra regions
single detector
four detectors

• Multi-slice CT imaging requires that radiation
  incident on patient be
• consistently distributed across each
  area subtended by each
• z-collimation of the source radiation is
  broadened to achieve umbra-region incidence
• multi-slice models broaden the umbra even more to
  compensate for x-ray source excursions
• Multi-slice much radiation not used by
  is incident on the patient65

detector
detectors
13

• X-Ray-Field Size Limitation
• to Reduce Inefficient Use of Radiation in
  Multi-slice CT
• CT system would automatically limit x-ray-field
  sizes to
• no larger than needed to construct multi-slice
  images
• Feasible several approaches patented, one
  implemented on newer models64
• E.g., tracking of itinerant x-ray source with
• continuously updated, real-time collimation
  adjustment
• maintains the narrowest needed umbra region
  incident on 64

detectors
x-ray source
wanders
collimator cams
readjust
four detectors

• Potential impact reduce patient multi-slice CT
  dose 30 64,66

14
Projected Benefits Dose Savings and Prevention
of Radiation-Induced Cancer
15

• Current Annual CT Dose in U.S.
• Preliminary Estimates 2000-01 NEXT Survey14
• Total number of CT exams 58 million (standard
  error 9 million)
• 79 of all CT exams are comprised of scanning in
  6 regions
• brain, abdomen-pelvis, chest, abdomen,
  chest-abdomen-pelvis, pelvis
• 29 of all CT units in U.S. can do multi-slice
  spiral scanning
• Effective dose average for 6 exam regions 6.2
  millisievert (mSv) (0.62 rem 620 mrem)
• Collective dose 360,000 person-sievert

16

• Projected Benefits
• if all CT equipment were to include proposed
  technical features
• Collective-dose savings annually
• display/recording 54,000 person-Sv
• AEC 108,000 person-Sv
• x-ray-field size limitation 31,000 person-Sv
• total 193,000 person-Sv

• Number of radiation-induced cancer mortalities
  avoided 8,700 annually
• projected 20 years after exposure (10-y latency67
  10-y survival)
• Highly uncertain The projection of 8,700
  people for whom premature death may be avoided is
  based on a nominal cancer mortality risk estimate
  for the general population of 0.0045 per 100 mSv,
  the consensus risk value recommended by a Federal
  interagency committee science panel report,68
  from which we adopt the following statement This
  projection applies a linear extrapolation from
  the nominal risk estimate for lifetime total
  cancer mortality at 100 mSv. Other methods of
  extrapolation to the CT dose region (1-20 mSv)
  could yield higher or lower numerical estimates
  of cancer deaths. Studies of human populations
  exposed at low doses are inadequate to
  demonstrate the actual level of risk. There is
  scientific uncertainty about cancer risk in the
  low-dose region below the range of epidemiologic
  observation, and the possibility of no risk
  cannot be excluded. In other words, it is
  possible that there is no cancer mortality
  associated with the levels of CT radiation and
  therefore that the projected dose savings would
  not result in any avoidance of cancer death.

• Pecuniary savings of societal willingness to pay
  to avoid mortality risk69-71
• 5 million per premature mortality avoided

17

• Amendments? Initial Steps
• Framework of analysis
• Concept paper
• CDRH decisions

18
Framework of Analysis
Issues

• Technical feasibility, costs
• Impact on clinical efficacy, practice,
  utilization, costs, benefits
• Individual, collective dose reduction, benefits
• Harmonization with international consensus
  standards
• CDRH test-method development, compliance resource
  requirements, costs
• Overall assessment regulatory amendment? other
  initiatives?

Technical Areas

• Define, standardize CT terms
• Display, record pt. dose index
• Automatic exposure control
• X-ray-field size in multi-slice CT

5. Electron-beam CT 6. CT fluoroscopy 7. Cone-beam
CT
19

• Conclusion
• FDA working group has identified several areas
  for possible development of
• mandatory CT equipment-performance requirements
• Initial focus on technically feasible features
  that would reduce patient dose
• Dose-Index Standardization, Display, Recording
• Automatic Exposure Control
• X-Ray-Field Size Limitation
• Projected collective dose savings estimated
  193,000 person-Sv yearly
• Framework of issues for analysis has been
  established
• Need input from industry, professional and
  stakeholder groups, CRCPD, States, and TEPRSSC
• Timeline
• December 2002 regulatory concept paper with
  completed analysis of issues
• 2003 update for TEPRSSC

20
References and Notes72 1. Joseph K.T. Lee, Stuart
S. Sagel, Robert J. Stanley, and Jay P. Heiken,
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W. Goldman and J. Brian Fowlkes, editors, Medical
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Association of Physicists in Medicine, (published
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McNitt-Gray et al., Radiation dose in Spiral CT
The relative effects of collimation and pitch,
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2223-2230, November 1999. 5. Nico Hidajat et al.,
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2001. 6. Christoph G. Diederichs, David P.
Keating, Gerhard Glatting, and Joerg W. Oestmann,
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Effects of Collimation Width, Pitch, Viewing
Plane, and Windowing in Maximum Intensity
Projection, J. Computer Assisted Tomography Vol.
20, No. 6, pp. 965-974, 1996, and references
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Fishman, Three-Dimensional CT Angiography of
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21
8. Birgitta K. Velthuis et al., Subarachnoid
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208, No. 2, pp. 423-430, August 1998. 9. Martine
Remy-Jardin et al., Acute Central Thromboembolic
Disease Posttherapeutic Follow-up with Spiral CT
Angiography, Radiology Vol. 203, No. 1, pp.
173-180, April 1997. 10. Peter A. Loud et al.,
Combined CT Venography and Pulmonary
Angiography A New Diagnostic Technique for
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2001. 13. Brian R. Herts et al., Comparison of
Examination Times Between CT Scanners Are the
Newer Scanners Faster? American Journal of
Roentgenology Vol. 170, No. 1, pp. 13-18, January
1998. 14. Stanley H. Stern, Richard V. Kaczmarek,
David C. Spelic and Orhan H. Suleiman,
Nationwide Evaluation of X-Ray Trends (NEXT)
2000-2001 Survey of Patient Radiation Exposure
from Computed Tomographic (CT) Examinations in
the United States, poster 262PH, presented at
the 87th Scientific Assembly and Annual Meeting
of the Radiological Society of North America,
November 25-30, 2001, and poster AH 6 (abstract
185), 2002 FDA Science
22
Forum, FDA Building a Multidisciplinary
Foundation, Washington, DC, February 20-21, 2002
http//www.fda.gov/cdrh/ct/ct-next.ppt. 15.
Stanley H. Stern, Radiation Dosimetry in X-Ray
Computed Tomography (CT) Standardization and
Regulation, talk presented at the 28th Meeting
of the Technical Electronic Product Radiation
Safety Standards Committee, Advisory Committee to
the Food and Drug Administration, Rockville,
Maryland, May 17, 2001, (transcript pages 68-110,
http//www.fda.gov/ohrms/dockets/ac/01/transcripts
/3751t1_01.pdf and http//www.fda.gov/ohrms/docket
s/ac/01/transcripts/3751t1_02.pdf). 16. Stanley
H. Stern and Jung Ok Yoon, Development of a
Handbook of Patient Tissue Doses for X-Ray
Computed Tomographic Examinations, poster paper
TU-FXH-72 presented by S.H. Stern at the 2000
World Congress on Medical Physics and Biomedical
Engineering, Chicago, July 25, 2000. 17. Lee F.
Rogers, From the Editors Notebook. Taking Care
of Children Check Out the Parameters Used for
Helical CT, AJR Vol. 176, p. 287, February
2001. 18. David J. Brenner, Carl D. Elliston,
Eric J. Hall, and Walter E. Berdon, Estimated
Risks of Radiation-Induced Fatal Cancer from
Pediatric CT, AJR Vol. 176, pp. 289-296,
February 2001. 19. Anne Paterson, Donald P.
Frush, and Lane F. Donnelly, Helical CT of the
Body Are Settings Adjusted for Pediatric
Patients? AJR Vol. 176, pp. 297-301, February
2001. 20. Lane F. Donnelly et al., Perspective.
Minimizing Radiation Dose for Pediatric Body
Applications of Single-Detector Helical CT
Strategies at a Large Childrens Hospital, AJR
Vol. 176, pp. 303-306, February 2001.
23
21. One Size Does Not Fit All Reducing Risks
from Pediatric CT, ACR Bulletin, Vol. 57, Issue
2, pp. 20-23, February 2001. 22. Eric N. Faerber
et al., ACR Standard for the Performance of
Pediatric and Adult Computed Tomography, American
College of Radiology, 1995 (Res. 1), amended 1995
(Res. 24, 53), revised 1998 (Res. 4), effective
1/1/1999. 23. Lee F. Rogers, "From the Editors
Notebook. Radiation Exposure in CT Why So High?"
AJR Vol. 177, p. 277, Aug 2001. 24. James G.
Ravenel et al., "Radiation Exposure and Image
Quality in Chest CT Examinations," AJR Vol. 177,
pp. 279-284, Aug 2001. 25. Edward L. Nickoloff
and Philip O. Alderson, "Commentary. Radiation
Exposures to Patients from CT Reality, Public
Perceptions, and Policy," AJR Vol.177, pp.
285-287, Aug 2001. 26. John R. Haaga,
"Commentary. Radiation Dose Management Weighing
Risk Versus Benefit," AJR Vol. 177, pp. 289-291,
Aug 2001, and reference 1 cited therein. 27. FDA
Public Health Notification Reducing Radiation
Risk from Computed Tomography for Pediatric and
Small Adult Patients, http//www.fda.gov/cdrh/safe
ty/110201-ct.html, November 2, 2001. 28. The
American College of Radiology Statement on Total
Body CT Screening, http//www.acr.org/departments/
pub_rel/press_releases/total-bodyCT.html,
September 27, 2000. 29. Edward F. Patz, Jr.,
William C. Black, and Philip C. Goodman, CT
Screening for Lung Cancer Not Ready for Routine
Practice, Radiology Vol. 221, No. 3, pp.
587-591, December 2001.
24
30. Olli S. Miettinen and Claudia I. Henschke,
CT Screening for Lung Cancer Coping with
Nihilistic Recommendations, Radiology Vol. 221,
No. 3, pp. 592-596, December 2001. 31. Stephen J.
Swensen et al., Screening for Lung Cancer with
Low-Dose Spiral Computed Tomography, American
Journal of Respiratory and Critical Care Medicine
Vol. 165, No. 4, pp. 508-513, February 15,
2002. 32. Stefan Diederich et al., Screening for
Early Lung Cancer with Low-Dose Spiral CT
Prevalence in 817 Asymptomatic Smokers,
Radiology Vol. 222, No. 3, pp. 773-781, March
2002. 33. Robert A. ORourke et al., American
College of Cardiology/American Heart Association
Expert Consensus Document on Electron-Beam
Computed Tomography for the Diagnosis and
Prognosis of Coronary Artery Disease, Journal of
the American College of Cardiology Vol. 36, pp.
326-340, June 2000. Also see J. Shemesh and M.
Motro, Characteristics of Coronary Calcification
in Patients with Acute vs. Chronic Coronary
Events, Quantified by Multi-Dectector Spiral
Computerized Tomography, paper no. 1130, 87th
Scientific Assembly and Annual Meeting of the
Radiological Society of North America, Chicago,
November 25-30, 2001. 34. CDRH web site,
Whole-Body Scanning Using Computed Tomography
(CT), http//www.fda.gov/cdrh/ct/. 35. Stuart G.
Silverman et al., CT Fluoroscopy-guided
Abdominal Interventions Techniques, Results, and
Radiation Exposure, Radiology Vol. 212, No. 3,
pp. 673-681, September 1999. 36. Richard D.
Nawfel et al., Patient and Personnel Exposure
during CT Fluoroscopy-guided Interventional
Proceducres, Radiology Vol. 216, No. 1, pp.
180-184, July 2000.
25
37. Erik K. Paulson et al., CT
Fluoroscopy-guided Interventional Procedures
Techniques and Radiation Dose to Radiologists,
Radiology Vol. 220, No. 1, pp. 161-167, July
2001. 38. W.M. Teeuwisse et al., Patient and
Staff Dose during CT-guided Biopsy, Drainage and
Coagulation, The British Journal of Radiology
Vol. 74, pp. 720-726, August 2001. 39. 21 CFR
1020.33, Computed tomography (CT) equipment. 40.
Thomas B. Shope, Robert M. Gagne, and Gordon C.
Johnson, "A method for describing the doses
delivered by transmission x-ray computed
tomography," Medical Physics Vol. 8, No. 4, pp.
488-495, July/August 1981. 41. A. Suzuki and M.N.
Suzuki, Use of a Pencil-shaped Ionization
Chamber for Measurement of Exposure Resulting
from a Computed Tomography Scan, Medical Physics
Vol. 5, No. 6, pp. 536-539, 1978. 42. W. Leitz,
B. Axelsson, and G. Szendrö, Computed Tomography
Dose Assessment?a Practical Approach, Radiation
Protection Dosimetry Vol. 57, Nos. 1-4, pp.
377-380, 1995. 43. International Electrotechnical
Commission subcommittee 62B document 451, draft
Amendment 1 to Standard 60601-2-44-Ed. 2,
Medical Electrical Equipment?Part 2-44
Particular Requirements for the Safety of X-ray
Equipment for Computed Tomography, April 3, 2002.
26
44. Patient dose norms are called reference
values, and they correspond to the 75th
percentile of the distribution of measured values
for particular radiological procedures. They
were introduced in the United KingdomNRPB/RCR,
"Patient Dose Reduction in Diagnostic Radiology,"
Doc. NRPB Vol. 1, No. 3, pp. 1-46, 1990, and refs
45, 46and are being adopted throughout western
Europe (refs 47, 48). They are being proposed
in the U.S. by a task group of the American
Association of Physicists in Medicine (ref.
49). Reference values are benchmarks to which
a facilitys practice may be compared in a
radiation-protection quality assurance program
When reference levels are exceeded in any
particular examination, the facility may
investigate to see if its possible to reduce
exposure without adversely affecting image
quality. As part of a quality assurance program,
dose displays would fulfill an essential need in
the first place for evaluation of patient
dose. 45. Dosimetry Working Party of the
Institute of Physical Sciences in Medicine,
National Protocol for Patient Dose Measurements
in Diagnostic Radiology, National Radiological
Protection Board, Chilton, UK, 1992. 46. National
Radiological Protection Board (UK), "Medical
Exposure Guidance on the 1990 Recommendations of
the ICRP," Doc. NRPB Vol. 4, No. 2, pp. 43-74,
1993. 47. International Commission on
Radiological Protection, Radiological Protection
and Safety in Medicine, ICRP Publication 73,
Annals of the ICRP Vol. 26, No. 2, 1996. 48.
European Council, Council Directive
97/43/Euratom of 30 June 1997 on Health
Protection of Individuals Against the Dangers of
Ionizing Radiation in Relation to Medical
Exposure, and Repealing Directive
84/466/Euratom, Official Journal of the European
Communities, No. L 180, pp. 22-27, July 9, 1997.
27
49. Joel E. Gray et al., Report of the Task Group
on Reference Values for Diagnostic X-Ray
Examinations, American Association of Physicists
in Medicine, (unpublished draft, November 1,
2000). 50. K.A. Jessen et al., Quality Criteria
Development within the Fourth Framework Research
Programme Computed Tomography, Radiation
Protection Dosimetry Vol. 90, Nos. 1-2, pp.
79-83, 2000, and reference 23 cited therein A.
Jurik et al., Clinical Use of Image Quality
Criteria in Computed Tomography A Pilot Study,
Radiation Protection Dosimetry Vol. 90, Nos. 1-2,
pp. 47-52, 2000. Also see P.C. Shrimpton and B.F.
Wall, Reference Doses for Paediatric Computed
Tomography, Radiation Protection Dosimetry Vol.
90, Nos. 1-2, pp. 249-252, 2000, and S.J. Golding
and P.C. Shrimpton, Radiation Dose in CT Are We
Meeting the Challenge? The British Journal of
Radiology, Vol 75, pp. 1-4, 2002. 51. For
example, see http//www.gemedicalsystems.com/rad/c
t/images/prod/comp2f.jpg. 52. The percentage dose
reduction projected to follow implementation of a
display/record feature is assumed. The percentage
corresponds approximately to one-half the
difference between 1995 UK survey levels (ref.
55) and 1985 values (ref. 54) for modalities
other than CT. See R.H. Corbett, "A European
Radiologist's View of Diagnostic Reference
Levels," in European Radiation Protection,
Education and Training (ERPET), ERPET Course for
Medical Physicists on Establishment of Reference
Levels in Diagnostic Radiology, Passau, Germany,
13-15 September 1999, Proceedings, edited by H.
Gfirtner et al., EC Directorate General Science,
Research and Development, Doc. RTD/0034/20,
(BfS-ISH, Oberschleissheim/Neuherberg, July
2000), pp. 83-91, and ref. 53. Reference
levels based on the 1985 data were introduced
into the UK in 1990 (refs. 44-46). It is
28
assumed that one-half of the UK dose reduction
from 1985-1995 is due to to technology
improvements alone (e.g., faster film-screen
combinations and the use of digital spot films),
whereas the other half of dose savings stems from
the quality-assurance use of reference levels and
patient dose evaluation. The estimated dose
reduction projected for a display/recording
feature in CT thus presumes (1) facility
implementation of a quality assurance program
making use of patient doses and reference levels
and (2) consequent dose reductions from improved
techniques. 53. A.T. Rogers et al., "The Use of a
Dose-Area Product Network to Facilitate the
Establishment of Dose Reference Levels," in
European Radiation Protection, Education and
Training (ERPET), ERPET Course for Medical
Physicists on Establishment of Reference Levels
in Diagnostic Radiology, Passau, Germany, 13-15
September 1999, Proceedings, edited by H.
Gfirtner et al., EC Directorate General Science,
Research and Development, Doc. RTD/0034/20,
(BfS-ISH, Oberschleissheim/Neuherberg, July
2000), pp. 255-260. 54. P.C. Shrimpton et al., A
National Survey of Doses to Patients Undergoing a
Selection of Routine X-ray Examinations in
English Hospitals, NRPB-R200, National
Radiological Protection Board, Chilton, UK,
September 1986. 55. D. Hart et al., Doses to
Patients from Medical X-ray Examinations in the
UK1995 Review, NRPB-R289, National Radiological
Protection Board, Chilton, UK, July 1996. 56.
K.A. Jessen, P.C. Shrimpton, J. Geleijns, W.
Panzer, and G. Tosi, Dosimetry for Optimisation
of Patient Protection in Computed Tomography,
Applied Radiation and Isotopes Vol. 50, No. 1,
pp. 165-172, January 1999. 57. European
Commission, European Guidelines on Quality
Criteria for Computed Tomography,
(http//www.drs.dk/guidelines/ct/quality/index.htm
), EUR 16262, May 1999.
29
58. Michael Gies, Willi A. Kalendar, Heiko Wolf,
and Christoph Suess, Dose reduction in CT by
anatomically adapted tube current modulation. I.
Simulation studies, Medical Physics Vol. 26, No.
11, pp. 2235-2247, November 1999. 59. Willi A.
Kalendar, Heiko Wolf, and Christoph Suess, Dose
reduction in CT by anatomically adapted tube
current modulation. II. Phantom measurements,
Medical Physics Vol. 26, No. 11, pp. 2248-2253,
November 1999. 60. Sue Edyvean, Recent
Developments in CT Technology Part I, United
Kingdom Radiological Congress, Wembley Exhibition
Centre, http//www.impactscan.org/slides/ukrc2001/
recent1/index.htm, May 24, 2001. 61. The
percentage dose reduction projected to follow
implementation of an automatic exposure control
feature corresponds approximately to the
mid-range of values cited in references 58, 59,
and 62. 62. H. Greess, H. Wolf, U. Baum, M. Lell,
M. Pirkl, W. Kalendar, and W.A. Bautz, Dose
reduction in computed tomography by
attenuation-based on-line modulation of tube
current evaluation of six anatomical regions,
European Radiology Vol. 10, No. 2, pp. 391-394,
2000. 63. H.D. Nagel, Chapter 4 Factors
Influencing Patient Dose in CT, in Radiation
Exposure in Computed Tomography, 2nd edition (in
English) revised and translated by H.D. Nagel and
P.C. Shrimpton, edited by H.D. Nagel, European
Coordination Committee of the Radiological and
Electromedical Industries, Frankfort, (Offizin
Paul Hartung Druck GmbH Co. KG, Hamburg,
Germany, October 2000).
30
64. Thomas L. Toth et al., A dose reduction
x-ray beam positioning system for high-speed
multislice CT scanners, Medical Physics Vol. 27,
No. 12, pp. 2659-2668, December 2000, and
references 4-12 cited therein. 65. D.P. Frush et
al., Radiation Dose from Helical CT in Children
Comparison of Multi-slice and Single-slice
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31
71. D. Mudarri, Costs and Benefits of Smoking
Restrictions An Assessment of the Smoke-Free
Environment Act of 1993, Environmental Protection
Agency, 1994. 72. A number of the ideas presented
as well as notes and references cited in this
poster were first developed in the poster of
S.H. Stern, S.A. Tucker, R.M. Gagne, and T.B.
Shope, Jr., Estimated Benefits of Proposed
Amendments to the FDA Radiation-Safety Standard
for Diagnostic X-Ray Equipment, at the 2001 FDA
Science Forum Science Across the Boundaries,
Washington, DC, February 15-16, 2001,
http//www.fda.gov/cdrh/radhlth/021501_xray.html.