1. Optimizing Patient Radiation Dose
John Aldrich PhD FCCPM
Department of Radiology
Vancouver Coastal Health
University of British Columbia

2. Outline Changes in Medical Imaging Dose, Effective Dose and Risk
Medical Imaging Utilization
Status of Patient Dose in BC
Skin Doses
Summary

3. Radiology
The use of x-rays in medical imaging has shown rapid growth in the last 10 years
This has been due to
Shorter imaging times
Increased indications for use
This has increased concern over the associated radiation dose to patients

4. Exam Type and Patient Dose at VGH
Over the 11 year period the average dose to patients almost doubled
Aldrich et al. CARJ 2005;56:94-99

5. Benefit and Risk
In all medical interventions there is a balance between benefit and risk
In the vast majority of cases the benefit from diagnostic x-ray studies far outweighs any detriment

6. What do we mean by Dose? Surface Dose (mGy)
The surface dose of interest is normally the dose to skin
Effective Dose (mSv)
Effective dose takes into account the radiation sensitivity of different organs.
External Radiation D E
Surface Dose mGy
From Air Kerma it is straightforward to calculate the surface dose, and the dose to any organ in the body can be estimated from published tables. E
Effective Dose mSv

7. Patient Dose
The risk from radiation is measured by Effective Dose, a quantity which combines the radiation dose to the organs irradiated and their radiation sensitivities.
Common unit is the millisievert - mSv
Background radiation in Canada is 2 mSv per year
Risk of a lethal cancer is 1 in 20,000 per mSv
ICRP (2008) Report 103

8. Procedure mSv Natural Background
Effective Dose
mSv
Months of
Natural Background
Very Low Dose
Bone density scan
0.0002
0.001
Low Dose
Skull series
0.05
0.3
Chest PA
Extremity
0.1
0.6
Thoracic Spine AP
0.5 3
Lumbar Spine AP 1 6
Mammography 2views
Abdomen AP
Intermediate Dose
Pelvis AP
1.6
9.6
Head CT 2 12
Upper GI Series
2.8 30
IVP 24
Lower GI Series 5
Higher doses
Chest CT 7 42
Abdomen CT 9 54
Pelvis CT
Cardiac Angiogram 8 48

9. Patient Doses Procedure Effective Dose mSv ZERO <1 1 - 5 5 - 10 2
No Dose
MRI, US
ZERO
Low Dose
CXR
Extremities
<1
Intermediate Dose
IVP, lumbar spine, abdomen
bone scan, CT head and neck
1 - 5
Higher doses
Chest or Abdomen CT
Nuclear cardiogram
Cardiac angiogram
5 - 10
Natural Background 2

10. Age and Cancer Mortality Risk15 30 10 5 20 25
1996 Re-analysis
Lifetime mortality risk per 100,000 per mSv)
female
ICRP 60 average
male 10 70 60 40 50 30 20
Age at time of exposure

11. Age and Cancer Mortality Risk
Relative Risk
Male
Female
Newborn 3 6 10 2 4 20
1.5
2.5 30 1 40
0.6 50
0.4
0.7 60
0.2
0.5 70
0.1

12. ACR Recommendations 2007 Wider dissemination of Referral Guidelines
Routine monitoring of patient doses and optimization where necessary
Improved education regarding radiation dose from x-ray procedures for all staff involved in or using diagnostic imaging
American College of Radiology
J Am Coll Radiol 2007;4:

13. CAR - Referral Guidelines in Diagnostic Imaging (2005)
A useful study is one in which the result will alter management or add confidence to the clinician’s diagnosis
It is thought that about 15% of studies are not useful
CAR - Referral Guidelines in Diagnostic Imaging (2005)

14. Referral Guidelines
The chief causes of the wasteful use of radiology are:
Repeating investigations which have already been done
Investigation when results are unlikely to affect patient management
Investigating too often
Doing the wrong investigation
Failing to provide appropriate clinical information and questions

15. Patient Dose in BC
In the past we have not continuously monitored patient dose
‘Snapshots’ have been taken of the situation
In BC we estimated doses from CT in 2004
At VGH we estimated CR and DR doses in 2004
In VCHA we estimated CR doses in 2007

16. Optimum Dose
The 'optimum dose' is the minimum dose that provides the required diagnostic accuracy.
However, this is difficult to determine
A simpler first approach is to determine what doses are clearly TOO HIGH
Then a Reference Dose or Reference Level is normally set at the 75th percentile.
The optimal dose would be the minimum dose required to produce an image of required diagnostic quality. This optimal dose will therefore vary from clinic to clinic and is difficult to define. However, it is possible to find out what are the typical doses used for diagnostic exams by measurements at several clinics, and from this to define a Reference Dose, the dose that most clinics can operate within (75th percentile).

17. BC CT Dose Survey 2004
Hospitals around BC were asked to provide data on routine head, chest, abdomen, and pelvis CT
Patient age, weight, slice width, number of slices, kVp, mA, CTDIvol, DLP
Data was collected from 18 hospitals

18. BC Patient Dose – Head CT

19. BC Patient Dose - Chest

20. Summary - BC CT Survey 2004 Study Range mSv Mean Dose Head 2 – 5 2.8
Chest
3 – 27
9.0
Abdomen
4 – 27
10.2
Pelvis
4 – 16
Abdo-Pelvis
7 – 32
16.5
Aldrich et al CARJ 2006;57:281

21. Comparison of Mean Doses (mSv)
CT Study EU
1999 US
2000
Germany
2002 UK
2003 BC
2004
Head
2.0
2.8
2.1
Chest
8.8
9.1
5.7
9.9
9.0
Abdomen
7.8
8.3 -
7.1
10.2
Pelvis
7.9
5.4
7.2
Abdomen-Pelvis
12.1
14.4
9.5
16.5

22. Diagnostic Reference Levels
Dose-length product (DLP) is the ‘dose’ reported
on each CT scanner for each patient
CT Study
EU 1999
US 2000
UK 2003
BC 2004
Head
1050
960
930
1300
Chest
650
640
580
600
Abdomen
780
530
470
920
Pelvis
570
510 -
Abdomen-Pelvis
910
560
1100
*75% DLP values mGy.cm for a 70 kg patient

23. Optimization of Abdomen CT

24. Predicted and Actual mA
Decrease
noise
Increase
noise
Increase
dose
Decrease
dose
Aldrich J et al CARJ :347

25. Computed Radiography(CR)
x-ray image
Cassette - based system using a storage phosphor instead of film-screens
Exposure
Latent Image l1 l2
Readout
Erase

26. CR Relative Light Emission AEC Centre Cell
Optimized Level

27. Summary – VCH CR Survey Radiographic Study Relative Dose AP Abdomen
4 – 14
PA Chest
4 – 22

28. Patient Dose Monitoring
It is now technically possible to estimate patient dose from most x-ray systems
Equipment
Dose Indicator
Status CT
Dose-length product DLP
Available on all CTs
Radiographic/
Fluoroscopic/
Angiographic
Dose-area product DAP
Available on all new units- can be retrofitted CR
Exposure Index (EI) of detector
All CR
Both DLP and DAP values are directly related to patient dose

29. Dose Area Product Meter
Collimator
X-ray field
Dose Area Product meter intercepts all radiation produced
X-ray Tube

30. Diagnostic Reference Levels
Exam
Dose Area Product
Gy cm2
DAP to E Conversion Factor
mSv/Gy cm2
Skull AP 2
0.03
Chest PA
0.11
0.12
Abdomen AP
2.6
0.2
Pelvis AP
2.1
Barium Meal 14
IVP
0.1
Coronary Angiography 29
0.15

31. Practical Measurement
Meter records patient dose for the whole procedure
Record these values rather than fluoroscopy time
Newer units record DAP and Skin Dose
Dual display of skin dose and effective dose during fluoroscopy/angiography

32. Skin Doses
During the 1990s there were many reported injuries to patients following fluoroscopy
High doses to the skin of the patient can cause erythema and even hair loss
This only occurs during long interventional angiographic procedures
The threshold for these effects is about 2000 mGy to the skin

33. Patient Doses - Fluoroscopy
Fluoroscopy Exam
Skin Dose Rate
mGy/min
Elbow 5
Chest PA 10
Abdomen PA 20
Digital spot
3 mGy/frame
This table shows typical skin doses for fluoroscopy of an average patient.

34. Angiography Skin Doses Published Data
Procedure
Diagnostic mGy
Therapeutic mGy
Cerebral Angiography
1200
1310
Carotid Angiography
215
154
Thoracic Angiography
260 -
Hepatic Angiography
360
540
Renal
620
660
Lower Extremity 68
146
Upper Extremity 73
150
Coronary catheterization
410
PTCA
760
PTCA with stenting
1800
These are typical skin doses measured in a teaching hospital.
1. Bor et al BJR 2004;77:315
2. McParland et al BJR 1998;71:175
3. Van de Putte et al BJR 2000;73:504

35. Skin Doses It is essential that operators are correctly trained.
A course for physicians who use fluoroscopy is mandatory in VCHA and is now being implemented on the VCHA/FH/VIHA intranet
Skin dose should be monitored with a DAP meter, so that patients can be counselled if necessary

36. Summary - Referring Physicians
Avoid repeating investigations which have already been done
Choose the appropriate investigation
Provide appropriate clinical information and questions

37. Summary - Education
CAR Referral Guidelines should be made widely available
More information needs to be provided to users of diagnostic imaging on patient dose
Training course for physicians who use fluoroscopy

38. Summary – Purchasers and Managers
Monitor patient doses
CT DLP
Radiographic Rooms (DR, CR) DAP and EI
Fluoroscopy/Angiography DAP
Only purchase new equipment which incorporates patient dose estimation systems
Display dose indicators as overlays on PACS

39. Summary – Radiologists, Technologists
Review patient doses
Use Diagnostic Reference Levels for comparison
Optimize techniques based on this information
Relatively easy to reduce higher doses