1. 8th ECMP, Athens, 11-13 Sept 2014 8th ECMP, Athens, 12 September 2014,
Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK
Dr Paul C Shrimpton
Formerly Leader of Medical Dosimetry Group
Centre for Radiation, Chemical & Environmental Hazards
Public Health England, Chilton, UK
8th ECMP, Athens, 12 September 2014,

2. 1974 Valedictory view over the last 40 years
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

3. But neither in medical physics!
Yes, really, 40 years!
Dinosaurs …
… and Lycra
But neither in medical physics!
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

4. Technology in 1974 DEC PDP-11/40 ICL 2966 computer DynaTAC cell phone
8th ECMP, Athens, Sept 2014
Technology in 1974
ICL 2966 computer
DynaTAC cell phone
DEC PDP-11/40
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

5. 1974 – an era before ICRP’s concept of effective dose
1974 ?Genetic effects?
1977 ICRP 26 (HE)
1990 ICRP 60 (E)
2007 ICRP 103 (E)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

6. Medical Dosimetry Group, NRPB -1979
Barry Wall
Humphrey
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

7. Birth of computed tomography
1972 sales brochure
1971: First clinical image
(Atkinson‐Morley Hospital
London
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

8. Growth in number of UK CT scanners
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

9. Patient exposure trends from x-rays in UK over last 50 years
Number of x-ray exams has more than doubled over last 50 years
But mean population dose has remained much the same ….
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

10. Trends in contributions to UK annual per caput dose by type of x-ray procedure
Growth from CT offset by reductions for conventional x-rays:
(HPA-CRCE-034, 2012)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

11. Trends in contributions to USA annual per caput dose by type of x-ray procedure
Pattern in USA quite different (relative to UK trend):
(National Council on Radiation Protection and Measurements, 2009)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

12. How has dosimetry supported this UK pattern?
Patient protection
Dosimetry
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

13. Importance of patient protection
Diagnostic
radiology is an
invaluable imaging
tool …
…. with significant potential
benefit for the healthcare of
patients:
Diagnosis
Clinical management
… BUT ….
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

14. Patient protection is a balance
…. Imperative to balance benefits against risks
Risks
Radiation
Benefits
Diagnosis
Clinical management
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

15. Potential radiation risks from x-ray examinations
High doses (… but not impossible during x-ray procedures …) Tissue reactions (deterministic effects) Dose thresholds
©Eric Bailey
©FDA
Lower doses
Stochastic effects
Cancer
Hereditary effects
Epidemiological studies
Dose
Excess cancer
Assume LNT in absence of compelling evidence
Presentation title - edit in Header and Footer
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

16. Eliminate unnecessary exposures :
Radiation protection for medical exposures
Avoid tissue reactions
Minimise stochastic effects
Eliminate unnecessary exposures :
Problem Action
Insufficient clinical benefit - Justify
More radiation than necessary - Optimise patient protection
for clinical purpose (ensure doses ALARA/ ALARP)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

17. Principles of radiation protection for medical exposures
International Commission on Radiological Protection
(ICRP Publication 103 (2007)) :
Justification
Do more good than harm (net benefit)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

18. Principles of radiation protection for medical exposures
International Commission on Radiological Protection
(ICRP Publication 103 (2007)) :
Justification
Do more good than harm (net benefit)
Optimisation
Maximise benefit (Doses ALARA/ ALARP)
Image Quality
Patient Dose
Clinical Purpose
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

19. Principles of radiation protection for medical exposures
International Commission on Radiological Protection
(ICRP Publication 103 (2007)) :
Justification
Do more good than harm (net benefit)
Optimisation
Maximise benefit (Doses ALARA/ ALARP)
But NO DOSE LIMITS
No limit on benefit!
Dosimetry is an essential component of patient protection
Safety
Dosimetry
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

20. Long history of monitoring patient dose in UK
UK reviews of doses from x-ray examinations
1950’s Lord Adrian Committee
National Radiological Protection Board
Health Protection Agency
Public Health England
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

21. National Patient Dose Database (excl CT)
Systematic UK national patient dose surveys
1st X-ray survey
Review
Review
Review
Review
National Patient Dose Database (excl CT)
1995
1990
2000
2005
2010
1985
1st CT survey
2nd CT survey
3rd CT survey
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

22. Why do we measure dose? Dose
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

23. Dosimetry needs to be fit for purpose
Dosimetry in support of patient protection
Quantities
Organ doses
Effective dose
ESD, DAP
CTDIVol, DLP
SSDE
Purpose
Justification (risk)
Optimisation of protection
Monitor/ compare practice
Know typical doses
Monitor population exposure
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

24. Reasons for wanting to know dose in diagnostic radiology
Assess risk (Justification)
Need organ doses ( … effective dose, E?)
Difficult to measure directly
Sophisticated dosimetry
Only estimate for reference patients
Not useful routinely for individual patients
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

25. Conventional X-ray exam
Normalised organ doses to reference patients
Use Monte Carlo simulation techniques
to model radiation transport through
mathematical or voxel reference patients
Relate organ and effective doses to
measurable dose quantities (ESD, DAP,
CTDIvol or DLP)
Conventional X-ray exam
Family of
mathematical
phantoms
CT examination
Baby 1y 5y 10y 15y Adult
Voxel
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

26. Assessment of radiation risks
Organ dose
Additional risk of cancer incidence
Use organ and age and sex specific risk coefficient
Key Sources:
ICRP Publication 103 (2007)
BEIR VII (US National Academy of Sciences/
National Research Council) (2006)
UNSCEAR (2006)
Challenges in data analysis:
Allowing for high dose rates
(DDREF, Dose and Dose Rate Enhancement Factor)
Transferring observed risk to different populations
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

27. ICRP 103 radiation risk model – cancer incidence
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

28. Differences between ICRP & BEIR VII radiation risk models
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

29. Assessment of typical radiation risks
Organ dose
Not patient specific (yet ….?)
Typical for an examination and reference patient of
an appropriate standard size
Uncertainties and precision
Additional risk of cancer incidence
Not patient specific
Typical for an exposure at given age/ sex (x 2-3 uncertainty)
Derived from observations on a population
Variation in individual sensitivity (x 10?)
Uncertainties and precision
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

30.  ICRP effective dose (E) and tissue weighting factors (2007) wT DT
Commonplace to summarise partial body exposures from
diagnostic radiological examinations in terms of effective
dose, E:
thyroid
liver
colon
lungs
gonads
stomach
oesophagus
skin
E = 
wT DT T
where the product
wT DT is summed
over all tissues, T
breast
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

31. Key limitations on use of effective dose, E
Developed by the International Commission on Radiological Protection (ICRP) as part of its system for controlling sources of exposure (ie, compliance with dose limits or constraints for workers and public) (ICRP 103, 2007)
Transforms particular exposure into an equivalent uniform whole body exposure that allows comparison and summation of doses, whether whole or partial body, or from external and internal sources
E defined for a population of all ages and both sexes, on the basis of mean doses to a reference man and a reference woman (ICRP 110, 2009)
It should not be calculated for individuals, or patients ….
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

32. Evolution of ICRP tissue weighting factors ( wT )
Organ
ICRP 1977
ICRP 1990
ICRP 2007
Gonads
0.25
0.20
0.08
Bone marrow (red)
0.12
Lung
Breast
0.15
0.05
Thyroid
0.03
0.04
Bone surfaces
0.01
Remainder
0.30
Colon -
Stomach
Bladder
Liver
Oesophagus
Skin
Salivary glands
Brain
ICRP 1977 (Report 26)
ICRP 1990 (Report 60)
ICRP 2007 (Report103)
Some influence on
values of effective
dose for medical
exposures:
Ratio E2007/ E1990 varies
by a few 10’s % for
common examinations
( ).
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

33. Influence on E of differing anthropomorphic models
Deviations in E for use of:
Adult MIRD (mathematical
phantom)
HPA18+
Estimates for AM & AF for common examinations differ
by a few 10’s of % relative to MIRD values (0.7 – 1.4)
ICRP 103
Use Voxel Adult Male (AM) and Adult
Female (AF) (ICRP Report 110) for
average organ doses
AF AM
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

34. E defined for purposes of RP (ICRP Publication 103, 2007)
Risk Factors for Radiation Protection, 10-2 Sv-1
Public
Workers
Cancer
(detriment weighted)
Heritable effects
Total detriment
5.5
0.2
5.7
4.1
0.1
4.2
Not to be used for assessment of risks to individuals
or patients!
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

35. Risks from x-ray examinations – HPA analysis
ICRP 103 risk models to calculate age- and sex-
specific lifetime risks of cancer for Western population;
Typical organ and effective doses calculated for range of
x-ray examinations from periodic HPA surveys in UK;
Typical risks for each type of exam calculated using organ
doses and age- and sex-specific risk factors;
Risk per unit effective dose calculated as a function of
age, sex and type of exam.
‘Radiation risks from medical x-ray examinations as a function of the age and sex of the patient’
BF Wall, R Haylock, JTM Jansen, MC Hillier, D Hart and PC Shrimpton
Report HPA-CRCE-028 (2011)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

36. Cancer induction risk (% / Sv) for x-ray examinations (HPA-CRCE-028, 2011)
Region
Age group (years)
0-9
10-19
20-29
30-39
40-49
50-59
60-69
70-79
80-89
90-99
Male
Head 18 13
9.1
6.8
5.2
3.6
2.2
1.2
0.5
0.1
Neck
6.2
4.1
2.8
2.0
1.3
0.8
0.4
0.2
0.0
Chest
8.3
7.0
5.8
5.1
4.6
4.0
3.0
1.9
Abdo & Pelv 12
9.7
7.5
6.0
4.7
3.4
1.1
Whole body 10
8.0
4.2
3.3
0.6
0.04
Female 15 11
7.6
5.5
1.7
0.9
0.3 20
7.2
2.6
1.6
1.0 14
8.8
7.1
5.4
6.6
4.4
3.2
8.5
3.1
1.8
0.7
0.02
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

37. X-rays – How safe are they?
Broad risk of cancer from typical x-ray procedures
X-rays – How safe are they?
(NRPB, 2001)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

38. More reasons for wanting to know dose in diagnostic radiology
Assess risk (Justification)
Need organ doses ( … effective dose, E?)
Difficult to measure directly
Sophisticated dosimetry
Only estimate for reference patients
Not useful routinely for individual patients
(2) Monitor & compare performance overtime/ between centres (Optimisation)
Simple practical measurements
ESD, DAP, CTDIVol and DLP to characterise exposure (Not E!)
Dose indicators … not patient doses!
Allow comparison of performance
Can also provide basis for typical organ dose/ risk assessment
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

39. Monitoring performance in diagnostic radiology
Key principle in patient protection
Keep doses As Low As Reasonably Achievable/ Practicable
for clinical purpose (ALARA/ ALARP)
But what happens in practice?
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

40. Adult CT head (acute stroke)
Optimisation of medical exposures – practical reality
Significant variations in typical dose suggest lack of uniform application of
ALARA: 5 10 15 20 25 30 35
500
1000
1500
2000
2500
Dose-length product (mGy cm)
Frequency
2003 UK (2003)
118 Standard Protocols:
Adult CT head (acute stroke)
3rd Quartile = 790 mGy cm
Diagnostic reference levels help promote improvements in practice to
eliminate unnecessary exposures.
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

41. Purpose of diagnostic reference levels (DRLs)
The specification of examination-specific DRLs facilitates
comparison of practice and so promotes improvement towards
ALARA.
In practice, DRL concept operates at 2 different levels:
National DRLs (NDRLs)
Set from large-scale surveys as a tool to help identify unusually
high typical doses;
Local DRLs (LDRLs)
Set by each x-ray department as characterising their typical dose
levels to facilitate comparison.
(Institute of Physics and Engineering in Medicine, 2004)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

42. National reference doses (diagnostic reference levels)
Tool to identify those hospitals using unusually high doses
Based on 3rd quartile values of mean hospital doses
(ESD, DAP, CTDIVol & DLP) seen in national surveys
and so already met by 75% of hospitals
Relate to typical practice (not individual patients)
A trigger to the first step in optimisation of patient doses
- investigate and correct higher doses,
unless clinically justified
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

43. Local implementation of DRLs – a dynamic process
8th ECMP, Athens, Sept 2014
Local implementation of DRLs – a dynamic process
For each x-ray unit, establish (optimised) imaging
protocols for each examination and patient group;
Measure typical doses as means for patient samples
(following IPEM Report 91 (2005));
Compare with National DRLs (NDRLs), etc?...
Compare with/ set as (revised) Local DRLs (LDRLs);
Periodic review (eg: 3 yearly or on change).
Too high
(Institute of Physics and Engineering in Medicine, 2004; IPEM, 2005)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

44. UK national DRLs
DRLs
Reference doses for conventional x-ray examinations
first suggested for UK in 1989
Concept of DRLs now widely implemented, but UK still
has most comprehensive and well-established set of
national DRLs from NRPB/ HPA/ PHE periodic national dose surveys:
Conventional x-rays: 1985, 1995, 2000, 2005, 2010*
CT: 1989, 2003, 2011*
UK national DRLs for over 50 types of radiographic, fluoroscopic and CT
examination on adults and children
(* Reports HPA-CRCE-034, 2012 & PHE-CRCE-013, 2014)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

45. DRLs – the UK experience
DRLs useful within a nationally coherent approach to managing patient dose
Agreed protocol for dose measurements
Central NRPB/ HPA/ PHE database (presently voluntary submission)
Periodic analysis for updated NDRLs
Commitment to patient protection (& ALARA)
Regulations
Healthcare professionals
NDRLs for conventional x-ray exams on adults have fallen by over a factor
of two in UK since 1985:
Reduction of unnecessary dose facilitated by NDRLs.
(HPA-CRCE-034, 2012)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

46. UK national reference doses radiography: 1985-2010
8th ECMP, Athens, Sept 2014
UK national reference doses radiography:
Radiograph Entrance Surface Dose (mGy)
Skull AP/PA
Skull LAT
Chest PA
Chest LAT
Thoracic spine AP
Thoracic spine LAT
Lumbar spine AP
Lumbar spine LAT
Abdomen AP
Pelvis AP
2010 / 1985 = 0.41
(HPA-CRCE-034, 2012)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

47. UK national reference doses fluoroscopy: 1985-2010
Examination Dose-Area Product (Gy cm2)
IVU (urinary system)
Ba meal (stomach)
Ba enema (colon)
2010 / 1985 = 0.39
(HPA-CRCE-034, 2012)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

48. UK national reference doses CT: 1989-2011
(MD)
970
610
910
745
1000
Trend : NDRLs for DLP on the increase ….
(PHE-CRCE-013, 2014)
2003
(MD)
930
580
470
560
940
Trend : NDRLs for DLP fell by %
(SS)
760
430
460
510
Examination (Indication)
Head (Stroke)
Chest (Lung cancer)
Abdo (Liver mets)
Abdo & Pelv (Abscess)
Chest, Abdo & Pelv (Cancer)
1989
(SS)
1050
650
900 -
Dose-Length Product (mGy cm)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

49. Variations in national x-ray exposure
Europe UK
HCL1 - Data from United Nations Scientific Committee on the Effects of Atomic Radiation 2008 Report (for period
) for Health Care Level 1 countries of the world with >1 physician per 1000 population.
All other studies for 2008 unless indicated.
Norway & USA – Data exclude dental x-rays.
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

50. Radiation protection for medical exposures
© Royal Mail and Du Cane Medical Imaging Ltd
CT is a natural focus for special efforts in patient protection
Collective dose
Key importance is not simply the size …
… But how much is unnecessary
Annual UK use of medical and dental x-rays (2008)
Category % Frequency % Collective Dose
Conventional Radiology CT
Angiography
Interventional
(HPA-CRCE-034, 2012)
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

51. Patient dosimetry - a valedictory UK view
Knowledge of doses is essential for effective patient protection
and the elimination of unnecessary exposures
Match dosimetry to specific purpose:
Complex risk assessment organ doses, effective dose
(with care ….)
Routine monitoring ESD, DAP, CTDIVol (SSDE), DLP
Application of examination/ indication specific National & Local
DRLs over the last 25 years has proved an effective tool for
promoting optimisation in UK
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

52. Thank you for your kind attention!
Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

53. 8th ECMP, Athens, 11-13 Sept 2014 8th ECMP, Athens, 12 September 2014,
Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK
Dr Paul C Shrimpton
Formerly Leader of Medical Dosimetry Group
Centre for Radiation, Chemical & Environmental Hazards
Public Health England, Chilton, UK
8th ECMP, Athens, 12 September 2014,