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,

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

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

Technology in 1974 DEC PDP-11/40 ICL 2966 computer DynaTAC cell phone 8th ECMP, Athens, 11-13 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Long history of monitoring patient dose in UK UK reviews of doses from x-ray examinations 1950’s Lord Adrian Committee 1971 - National Radiological Protection Board 2005 - Health Protection Agency 2013 - Public Health England Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

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

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

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

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

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

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

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

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

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

 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 - 0.04 liver - 0.04 colon - 0.12 lungs - 0.12 gonads - 0.08 stomach - 0.12 oesophagus - 0.04 skin - 0.01 E =  wT DT T where the product wT DT is summed over all tissues, T breast - 0.12 Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

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

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 (0.6 - 1.4). Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

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

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

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

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

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

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

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

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

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

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

Local implementation of DRLs – a dynamic process 8th ECMP, Athens, 11-13 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

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

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

UK national reference doses radiography: 1985-2010 8th ECMP, Athens, 11-13 Sept 2014 UK national reference doses radiography: 1985-2010 Radiograph Entrance Surface Dose (mGy) 1985 1995 2000 2005 2010 Skull AP/PA 5 4 3 2 1.8 Skull LAT 3 2 1.6 1.3 1.1 Chest PA 0.3 0.2 0.2 0.15 0.15 Chest LAT 1.5 0.7 1 0.6 0.5 Thoracic spine AP 7 5 3.5 4 3.5 Thoracic spine LAT 20 16 10 7 7 Lumbar spine AP 10 7 6 5 5.7 Lumbar spine LAT 30 20 14 11 10 Abdomen AP 10 7 6 4 4.4 Pelvis AP 10 5 4 4 3.9 2010 / 1985 = 0.41 (HPA-CRCE-034, 2012) Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

UK national reference doses fluoroscopy: 1985-2010 Examination Dose-Area Product (Gy cm2) 1985 1995 2000 2005 2010 IVU (urinary system) 40 23 16 14 14 Ba meal (stomach) 25 17 13 14 12 Ba enema (colon) 60 35 31 24 21 2010 / 1985 = 0.39 (HPA-CRCE-034, 2012) Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

UK national reference doses CT: 1989-2011 (MD) 970 610 910 745 1000 Trend 2 2003-2011: NDRLs for DLP on the increase …. (PHE-CRCE-013, 2014) 2003 (MD) 930 580 470 560 940 Trend 1 1989-2003: NDRLs for DLP fell by 10 - 40% (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

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 1997-2007) 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

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 91 19 CT 7.4 68 Angiography 0.6 5 Interventional 1.0 8 (HPA-CRCE-034, 2012) Shrimpton: Dosimetry in support of patient protection in diagnostic radiology – a valedictory view from the UK

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

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

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,