1. Radiation safety and CT dose
PARM AUTUMN SYMPOSIUM
October 6 & 7, 2011
Radiation safety and CT dose
Margaret “Peggy” Blackwood, MS, DABR
System Director, Radiation Physics
Radiation Safety Officer
West Penn Allegheny Health System

2. Radiation safety…we’ve come a long way

3. Ct…we’ve come a long way
Over 1 hour per head sca
16cm of Z-axis coverage allows an entire CT scan of the head to be performed in a single 0.75 second rotation, perfect for trauma and congenital follow ups in children at 20% lower dose.

4. CT Growth Single largest source of radiation to US population
80 M CT/yr*
1 in 5
7M ped CT/yr*
10% growth/yr
*one phase
Single largest source of radiation to US population
Brenner D, Hall E. N Engl J Med 2007;357:

5. POPUlation DOSES MEDICAL IMAGING ~ DOUBLED BACKGROUND 1980 2006
Radiology, V 253, #2, Nov 2009

6. Benefits…. And risks Stochastic Deterministic Cell mutation Cancer
No threshold; uncertainties below 100 mGy (10 rads)
Linear relationship of risk with dose
Deterministic
Cell death
Skin effects and cataracts
Threshold doses ~1-2 Gy ( rads)

7. Stochastic Risks
Review Article Computed Tomography — An Increasing Source of Radiation Exposure
David J. Brenner, Ph.D., D.Sc., and Eric J. Hall, D.Phil., D.Sc.
N Engl J Med, Volume 357(22): , Nov 29, 2007
CT organ doses in range for which there is direct evidence of a statistically significant increase in risk of cancer

8. DETERMINISTIC EFFECTS
Brain perfusion studies
3-7Gy ( rads)

9. Pediatric CT doses 2001-Society for Pediatric Radiology (SPR)
“ALARA Conference Proceedings. The ALARA Concept in Pediatric CT-Intelligent Dose Reduction”
2002-National Council on Radiation Protection and Measurements (NCRP) Conference on CT Dose

10. Conclusions of early CT conferences
Excess cancer incidence in those exposed to radiation doses comparable to CT dose levels
Small but statistically significant excess of cancer mortality over an individual’s lifetime
Children are more sensitive to radiation than middle-aged adults by factor of 10; girls are more sensitive than boys
Small risk per CT multiplied by large number of CT exams is public health issue, particularly in children

11. Lifetime risk of cancer

12. Conclusions of early CT conferences
CT dose reduction important but must maintain acceptable diagnostic image quality
Appropriateness of study
Adjust CT doses to patient size (not fixed mA)
Automatic dose reduction methods in CT scanners
Standardize CT protocols; periodic review
Dose reporting information CT exams
Develop CT accreditation and QC programs

13. Ct image quality and dose
Contrast-to-noise (CNR)
Noisier image as dose reduced
Loss of low contrast detectability

14. Conclusions of early CT conferences
No consensus regarding single expression of dose
Effective dose
Organ dose
CT dose index (CTDI)
Dose length product
Dissemination of information and education regarding risks and need for CT dose reduction

15. Alliance for Radiation Safety in Pediatric Imaging (“ALLIANCE”)
2008-Founded
SPR, AAPM, ACR, ASRT
60+ organizations; 750,000 medical imaging professionals
Promotes radiation protection for children
Awareness
Education
Advocacy-based social marketing campaign: Image Gently

16. Image gently (pedrad.org/associations/5364/ig)
Tests/Procedures CT
Fluoroscopy
Interventional Radiology
Nuclear Medicine
What can I do?
Parents
Radiologist
Pediatricians
Radiologic technologists
Medical physicists

17. Image gently (pedrad.org/associations/5364/ig)
What can I do? – Radiologists
Comprehensive Background & Guidance Document
Review of pediatric CT dose and strategies to manage radiation dose
“Medical Radiation in Children”-powerpoint
Image-Gently Web-based Practice QI Program
Articles and Resources
How to Develop CT Protocols for Children

18. ED Visits with CT under age 18

19. Image gently (pedrad.org/associations/5364/ig)
What can I do? – Technologists
On-line educational modules
CT Practice Standards
The Increasing Use of CT and its Risks
Patient Dose from CT - Literature Review*
ASRT White Paper: Computed Tomography in the 21st Century: Changing Practice for Medical Imaging and Radiation Therapy Professionals*

20. ASRT White paper: CT in the 21st century
2007-Consensus Conference
Increasing use of CT technology is changing practice faster than educational institutions, vendors, medical providers and regulators expected
Medical imaging professionals need more education in CT technology, including operation, application and dose optimization to ensure patient safety
Challenges: insufficient educational programs, educated RTs in CT, education and training of entry level and experienced CT techs

21. Image wisely (imagewisely.org)
Radiation Safety in Adult Medical Imaging
Sponsored by aaom, acr, rsna, asrt

22. Image wisely (imagewisely.org)
Sections for imaging professionals: physicians, RTs and medical physicists; referring practitioners and patients
Take the “Image Wisely” pledge
Educational sections
ACR Appropriateness Criteria
Download for mobile devices
American Imaging Management Patient Safety: Ask AIMEE (interactive patient exposure calculator)
Sponsored by aaom, acr, rsna, asrt

23. Image wisely (imagewisely.org)
Patient Medical Imaging Record
Sponsored by aaom, acr, rsna, asrt

24. Image wisely (imagewisely.org)
Education, resources and links to websites
CT Equipment: Operation, Performance
CT Protocols
Design methodologies
Protocols from other sites
ACR Appropriateness Criteria
Online communities for CT tech questions and info
Sponsored by aaom, acr, rsna, asrt

25. CT Protocol development & QA
Establish set CT protocols for each indication by scanner, to optimize image quality and dose
Vendor protocols are not optimized
Begin with most frequently performed exams
Include all aspects of exam, e.g. patient positioning, nursing instructions, exam parameters, reconstruction/reformatting instructions, CTDI and DLP reported values
Protocol team(s) should include radiologist(s), CT technologist(s), physicist(s) and administrator(s)

26. CT Protocol development & QA
Establish set CT protocols…
Benchmark with published protocols and doses
Develop consensus among radiologists regarding image quality requirements
Establish ONE standard of care
Fully understand and utilize automatic dose reduction techniques on CT scanner:
Establish criteria for automatic dose reduction parameters, e.g. reference mAs, noise index, etc.

27. CT Protocol development & QA
Develop policy and procedure for use of reviewed and approved CT protocols
radiologists should not request and technologists should not manually modify approved CT protocols
Develop a process to regularly review CT protocols
to ensure they have not been modified and cannot be improved further

29. How to develop CT protocols for children
Abd-baseline
kVp=120
mA=200
Time=0.5s
Abd Pitch=1
Th Pitch=1
PA thickness (cm)
Approximate age
Abdomen
Thorax
mAs RF
Est mAs 9
Newborn
0.43 43
0.42 42 12
1 yr
0.51 52
0.49 49 14
5 yr
0.59 59
0.57 57 16
10 yr
0.66 66
0.64 64 19
15 yr
0.76 76
0.73 73 22
Sm adult
0.90 90
0.82 82 25
Med adult
Baseline
100
0.91 91 31
Lg adult
1.27
127
1.16
116
RF=Reduction factor; Est mAs = Baseline *RF

30. Ct dose metrics

31. Ct dose metrics

32. Ct dose metrics

33. ACR CTDIv Pass/Fail & Reference Doses
CT dose metrics
CTDIv
Accounts for beam width, detector configuration and pitch
ACR CTDIv Pass/Fail & Reference Doses
CT Exam
CTDIv (mGy)
Pass/Fail
Reference Level
Adult Head 80 75
Adult Abdomen 30 25
Ped Head (1 y.o.)
To be determined
Ped Abd
(5 y.o., 40-50#) 20

34. Ct dose metrics CTDIvol is NOT Patient Dose Limitations
Reference standard for radiation output of CT
Limitations
Multi-detector (MDCT) wider beam
Phantom shorter than patient torso
Underestimation of scattered radiation
as much as 40%
Not valid when table does not move, e.g. brain perfusion or wide cone-beam systems

35. Ct dose metrics CTDIvol
Displayed on scanner console PRIOR to scan
Allows operator to confirm proper protocol in use
Included in DICOM “dose report” or “patient dose report”; reinforcing incorrect belief that CTDI is a measure of patient dose
Patient dose is directly dependent of size and shape of the patient

36. Ct dose metrics CTDIvol
Displayed on scanner console PRIOR to scan
Allows operator to confirm proper protocol in use
Included in DICOM “dose report” or “patient dose report”; reinforcing incorrect belief that CTDI is a measure of patient dose
Patient dose is directly dependent of size and shape of the patient

37. Ct dose metrics Size-specific dose estimate
Conversion factor based on patient size to estimate patient dose (mGy)
Organ dose estimation not possible with this method
Effective dose (mSv) cannot be estimated

38. Ct dose metrics Effective diameter Calculated Lateral + AP
Lateral or AP only
Eff dia = (APxLAT)1/2
Look up tables by effective diameter method and CTDI phantom utilized

39. Ct dose metrics
32 cm PMMA phantom
ACR report 2004

40. Ct dose metrics Effective dose (mSv) Absorbed dose to each organ
Tissue-weighting factor-accounts for radiosensitivity of each tissue irradiated
Whole body effective dose equivalent
Effective dose=S(wT*organ equivalent dose)
wT = tissue weighting factor

41. Tissue Weighting Factors
ICRP 26 (1977)
ICRP 60 (1991)
ICRP 103 (2007)
Gonads
0.25
0.20
0.08
Red bone marrow
0.12
Lung
Colon
Stomach
Breast
0.15
0.05
Bladder
0.04
Liver
Esophagus
Thyroid
0.03
Skin
0.01
Bone surface
Brain
Salivary glands
Remainder
0.30

42. Stochastic Risk Estimates
Statistically significant increase in cancer at doses > 10 mSv
Radiation risk: 1/1000 per 10 mSv
Averaged across all ages and genders
Normal background risk of cancer:400/1000
Total increased risk: 401/1000

43. NEJM, Aug 2009, Fazel et al

44. Highmark Radiology Management Program
Highmark Radiology Management Program
Radiation Safety Awareness Program
Highmark/NIA identify “at-risk” patients
Dose Limit Threshold, equal to or greater than 50 mSv, patient’s cumulative radiation exposure based on Highmark claims data
“a level that has been identified as causing a statistically (epidemiologically) significant increased risk of developing radiation-associated cancers

45. Radiation safety Awareness Program
Goals
Raise awareness regarding radiation exposure
Risk v benefit
Alternative studies
How results of study will impact on patient management
Identification of patient’s prior imaging studies
Evaluate necessity of repeat studies
Consider discussing information with patient

46. Radiation safety Awareness Program
Physicians notified when preauthorization requested
Offered NIA peer discussion
Dose Limit Threshold Notification sent with authorization or adverse determination letter
“Important Note: The patient’s level of radiation exposure does not impact the preauthorization or decision-making process for requested imaging studies.”
Does not apply to patients with cancer diagnosis

47. TJC Sentinel Event Alert, Issue 47 (8/23/11)
Radiation Risks of Diagnostic Imaging
Right test
Right dose
Effective processes
Safe technology
Safety culture

48. TJC Sentinel Event Alert, Issue 47 (8/23/11)
Alert focused on diagnostic imaging, NOT therapeutic radiation or fluoroscopy (i.e. CT)
Addressing contributing factors to eliminate avoidable radiation dosing
Activities that can help eliminate avoidable radiation doses
11 recommendations with 21 specific actions

49. TJC Sentinel Event Alert, Issue 47 (8/23/11)
Comprehensive patient safety program, including education about dosing in imaging departments
Training on how to use complex new technology
Knowledge regarding typical doses
Clear protocols that identify the maximum dose for each type of study
7 other recommendations…education, communication, equipment checks,…

50. TJC Sentinel Event Alert, Issue 47 (8/23/11)
Right test
Use of alternative non-ionizing tests
Create and implement processes that enable radiologists to provide guidance to and dialogue with referring physicians regarding the appropriate use of diagnostic imaging using the ACR Appropriateness Criteria

51. TJC Sentinel Event Alert, Issue 47 (8/23/11)
Right dose
Adhere to ALARA
Adhere to Image Gently and Image Wisely guidelines
Provide reference doses, with ranges, to MDs and techs, based on anatomy, study purpose and pt size
Radiologists should ensure that the proper dosing is in place for the patient being treated
Annual or bi-annual protocol review
Track doses from repeat exams; address & resolve
Record dose/exposure in summary report of findings

52. TJC Sentinel Event Alert, Issue 47 (8/23/11)
Effective processes
Policies and procedures delineating staff responsible for approving changes to password protected protocols; for monitoring new developments; control of password by RS “group”
P & P delineating physical RS measures; e.g. lead
Expand RSO role to explicitly include patient safety and involve RSO in Patient Safety Committee

53. TJC Sentinel Event Alert, Issue 47 (8/23/11)
Safe technology
Organization-wide audit survey of rad equip; centralize quality and safety performance under physicist, RSO, RS group
Qualified medical physicist to test all diagnostic equipment annually and review scanning protocols and doses
Ensure QC and PM testing done; delineate responsibilities in writing
Invest in technologies that optimize or reduce dose.

54. TJC Sentinel Event Alert, Issue 47 (8/23/11)
Safety culture
Promote safety culture for safe use of diagnostic radiation
Additional recommendations
Endorse national radiation dose tracking registry
Encourage manufacturers to incorporate dosage safeguards into EMR and national dose registry
Support stricter regulations to eliminate avoidable imaging and monitor the appropriateness of self-referred imaging studies

55. DOSE REDUCTION TECHNOLOGIES
Detector advancements
Axial Helical
Multi-detector CT (MDCT)
Automatic exposure control
Z-axis modulation
Angular and Z-axis modulation
Dual source
Iterative reconstruction methods (e.g. ASIR)

56. Graph shows typical scanner output level (expressed as volume CT dose index [CTDIvol]) for a routine abdominal CT examination from the 1980s, when xenon detectors were used, to 2004, when 64–detector row CT systems were introduced.
Graph shows typical scanner output level (expressed as volume CT dose index [CTDIvol]) for a routine abdominal CT examination from the 1980s, when xenon detectors were used, to 2004, when 64–detector row CT systems were introduced. Data from the 1980s represent different scanner models in use during that period. Solid-state detectors were used on the systems represented here from 1988 onward. Until the mid-1990s, the typical image represented a 10-mm section of anatomy, and scans required several minutes to acquire. Much improved image quality is now obtained by using 3–5-mm section widths and scan times of 10–20 seconds.
Hricak H et al. Radiology 2011;258:
©2011 by Radiological Society of North America

57. Automatic exposure control

58. DOSE REDUCTIONS IN CT ANGIOGRAPHY
Graph shows dose reductions in cardiac CT angiography. Cardiac spiral CT was introduced into clinical practice around 2000 after the introduction of the four-section scanner. Electrocardiographically controlled milliampere (mA) modulation was introduced to clinical practice in about 2002, the step-and-shoot mode for cardiac imaging was introduced in about 2006, and dual-source spiral CT with high pitch was introduced in around For cardiac examinations that do not require images of the heart throughout the entire cardiac cycle, the radiation can be turned down with the use of tube current (milliampere) modulation, or off in the case of nonspiral scans. This is often done for phases of the cardiac cycle where the heart is moving fastest, when motion blurring or artifact would be most severe. (Image from reference 68).
Hricak H et al. Radiology 2011;258:
©2011 by Radiological Society of North America

59. GOALS Medically necessary Least invasive modality
Discussion of options between radiologist and referring MD
Minimize study as appropriate
“Right size” radiation dose
Education for patients and medical personnel
SIGN THE IMAGE GENTLY AND IMAGE WISELY PLEDGES!
Radiation Safety in Adult Medical Imaging

60. PROGESS… CT doses 1/3 lower than a decade ago
Expect 10-fold+ or more reduction in next few years
ACR National Dose Registry-collect data on all CT exams