Transcript European Diagnostic Reference Levels in Paediatric Imaging

European Diagnostic
Reference Levels in Paediatric
Imaging
Stephen Evans, Head of Medical
Physics, Northampton General
Hospital, UK
EFOMP Officer, Chair Projects
“Children are at a much higher risk
compared to adults from developing cancer”
It’s not child’s play
• UNSCEAR (2010) estimates
– 250 million paediatric radiological examinations (including
dental) per annum worldwide
• Children may receive substantial radiation doses
– in early life
– life-threatening disease
• Children may develop
– childhood leukaemia
– breast cancer or
– thyroid cancer
It’s not child’s play
• Children need special attention:
– diseases specific to childhood
– additional risks
• Children need special care:
– provided by parents and carers
– from specially trained personnel
• Justification and optimization principles are even
more important for children
Why so high ?
• Higher sensitivity
to radiation
• Longer life
expectancy
• Paediatric doses
will exceed adult
doses if the same
exposure settings
are used
Paediatric effective dose and risk
Examination
Effective dose (mSv)
Lifetime risk of fatal cancer
Limbs
<0.005
1/few million
Chest (PA)
Spine (AP, PA, Lat) 0.07
1/150,000
Pelvis
?
1/million
0.08
1/120,000
AXR
0.10
1/100,000
CT Head
2
1/5,000
CT Body
10
1/1,000
0.01
Twice the adult risk
i.e. 10% per Sv.
Cook JV, Imaging, 13 (2001), Number 4
Paediatric risk
CHILD
ADULT
Is this sensitive enough?
Risk from single CT exam
Single CT exam
1 in 400
Not
1 in 1000
1 in 1000
Not
1 in 5000
Estimated Risks of Radiation-Induced Fatal Cancer from Pediatric CT
David J. Brenner1, Carl D. Elliston1, Eric J. Hall1 and Walter E. Berdon2,AJR February 2001, Volume 176, Number 2
Read More: http://www.ajronline.org/doi/full/10.2214/ajr.176.2.1760289
What’s the main issue?
• Estimated about
– 85% paediatric dose from CT,
interventional fluoroscopy and cardiac
nuclear medicine
– 15% paediatric dose from radiography and
general fluoroscopy
So what have we done about it?
Well, we have our Directives…
COUNCIL DIRECTIVE 2013/59/EURATOM
of 5 December 2013
laying down basic safety standards for protection against the dangers arising
from exposure to ionising radiation, and repealing Directives 89/618/Euratom,
90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom
(28)
…important technological and scientific developments have
led to a notable increase in the exposure of patients.
…Directive should emphasise the need for justification of
medical exposure, … the use of diagnostic reference
levels and the availability of dose-indicating devices.
COUNCIL DIRECTIVE 2013/59/EURATOM
Art 4
(20) "diagnostic reference levels" means dose levels in medical radiodiagnostic or
interventional radiology practices, or, in the case of radio-pharmaceuticals, levels of
activity, for typical examinations for groups of standard-sized patients or
standard phantoms for broadly defined types of equipment;
Art 22
(iii) where practicable, specific diagnostic reference levels are put in place;
Art 56
2. Member States shall ensure the establishment, regular review and use of
diagnostic reference levels for radiodiagnostic examinations, having regard to the
recommended European diagnostic reference levels where available, and where
appropriate, for interventional radiology procedures, and the availability of guidance
for this purpose.
Art 58
(f) appropriate local reviews are undertaken whenever diagnostic reference levels
are consistently exceeded and that appropriate corrective action is taken without
undue delay.
Art 53
MPE (a) optimisation of the radiation protection of patients and other individuals
subject to medical exposure, including the application and use of diagnostic
reference levels;
And, we have many many scientific
studies and Reports…
DRLs typically range x1.5 to upto x7
What does all this mean?
1996
EUR 16261, 1996
used the 3rd quartile
entrance-surfacedose for a standard
five-year old child as
the reference dose
for all paediatric
patients
EUR 16261, 1996
NEVER EVENT
DRLs
Good Radiographic Practice
JUSTIFICATION
Conclusions of EUR 16261
• Every effort should be made to reduce doses for
children less than 5 years of age to below the values
presented
• Strict adherence to all the radiographic technique
factors recommended can lead to significant dose
reduction
• X-ray generators employed in paediatric
examinations should be capable of selecting the low
mAs values required to ensure that the
recommended kV values can be employed
1999
"Guidance on diagnostic reference
levels DRLs for medical exposure",
European Commission Radiation
Protection 109 (RP 109), 1999)
– exposures requiring the most attention and
are of the most importance for the
establishment of DRLs are the high-dose
medical examinations, especially
computed tomography (CT) and
interventional procedures (IR)
RP 109
“DRLs should be set by Member States
…………….. harmonised levels might be
feasible and are certainly preferable.”
RP-109 - Factors affecting dose
• Equipment factors
– inappropriate exposure protocols
– deterioration of the image chain
• Human factors
– inattention, indifference or too much work
pressure
– individual reluctance to accept generallyaccepted standard procedures
DRLs in practice
• DRLs can be assessed using:
– entrance surface doses, measured with TLD, or
– DAP [Gy.cm2]
• DAP is more practical because
(i) the whole examination is recorded;
(ii) the position of the patient in the beam is less important
(iii) there is no need to disturb the patient
• For CT
– Dose Length Product (DLP)
DAP DRL issues
• Disadvantages using DAP
– absorbed organ dose needs to be measured
• not always a fixed relationship between the DAP
and the absorbed dose
– where small areas are exposed,
• the DAP can be low while the absorbed dose is
high
– when a large area is exposed,
• the DAP can be high but the absorbed dose low
– the field size is often changed during fluoroscopy
procedure
CT DRL issues
• Disadvantages of using DLP
DLP = scan length (cm) x CTDIvol (mGy)
– Depends on height of patient
• Equipment characteristics
– iterative reconstruction -50%
– AEC variable mAs – ?%
• might be set too high
• dose could be more
DLP - Dose
AEC
no AEC
Dose (Size specific)
DLP
no AEC
AEC
“Image Gently”
Alliance for Radiation Safety in
Pediatric Imaging
“One size does not
fit all...so when we
image, let's image
gently!“
IAEA No. 24, 2013
“… standardized methodologies to determine
paediatric dose for all major modalities, such as
general radiography, fluoroscopy and computed
tomography.”
“children can receive doses in excess of those
delivered to Adults”
IAEA No. 24,
2013
5y old
5y old
Weight?
Height?
25 kg
to
15 kg
115 cm
to
100 cm
CENTRE FOR DISEASE CONTROL AND PREVENTION, 2000 CDC
Growth Charts for the United States: Methods and Development, Vital
and Health Statistics, Department of Health and Human Services, Rep.
(PHS) 2002-1696, Hyattsville, MD (2002).
IAEA No. 24 – Patient size
• Options
– Age (v. Poor)
– Patient thickness
• good for projection radiography
• not so good for CT
• how to measure?
– Equivalent Cylindrical Diameter (ECD)
W is weight in gms and H is height
in cm
Equivalent Cylindrical Diameter
H2O
H2O
ECD
ECD
2011
Size-Specific Dose Estimate - SSDE
CTDIvol for 32 or 16 diameter phantom
SSDE =
f32/16
x
x CTDIvol
x depends on projection
Effective Diameter
Circle of same area
A
A
LAT
AP
SSDE
Effective diameter for typical 5 year old = 18.5 cm
Conversion Factor for 5 year old (32 cm phantom) ~ 1.9
This means for a given CTDIvol the dose will be twice as
much for a typical 5 year old compared to an adult.
Q: Can these factors be used to define the required
exposure conditions or do we need equivalent
cylindrical diameter ?
Interventional Fluoroscopy
• Equipment should be appropriately designed. Consider:
– Beam filter
– Beam area
– Minimum tube currents
– Reduced exposure pulse (need fast for heart)
– Removal of the anti-scatter grid
– Decreased magnification
– Appropriate exposure levels - programming
• RIS – PACS, Repeat procedures
– Any repeat exposure within the last 60 days should be
considered additive
Fluoroscopy
• What DRLs do we need?
– Incident air kerma Ki (mGy)
Ki = Y(d)Pit(d/dFSD)2
Y(d)
Pit
dFSD
– output at distance d
-- tube loading (mAs)
– focus to skin distance
– Entrance Surface Air Kerma (ESAK) Ke (mGy)
Ke = Ki.B (Backscatter factor)
– Kerma-area-product (PKA) (mGy.cm2)
• KAP or DAP meter
IAEA No. 24
Possibilities
• Is it possible to have DRLs for fluoroscopy?
– Probably yes
• Skin dose ?
– Would not expect for small patients to be high
– Obese older patients!!
• DAP ?
– Field size varies
– Sometime bigger (field) is better (visualisation)
• Monitor fluoroscopy exposure time + acquisitions
runs (images) per procedure ?
– May be our best indicator for Optimised systems!
– TIME – Timely Intervention of Monitored Event
DRLs
• DRLs
– show what should be possible
– encourage changes in working procedures
• DRLs
– Need to be tailored or take account of
• Equipment performance
• Patient demographics
So what more do we need to do?
•
•
•
•
Identify Equipment factors
Sort out Human factors
Extend the range of DRLs
Base DRLs on individuals
– do we use Equivalent Cylindrical Diameter ? or
– effective diameter ? or
– something else ?
Planar CT Floro
DAP
DLP TIME
o
E
E
?
So what are we going to do?
PiDRL - consortium
•
•
•
•
European Society of Radiology, ESR
European Society of Paediatric Radiology, ESPR
European Federation of Radiographer Societies, EFRS
European Federation of Organisations for Medical Physics,
EFOMP
• Finnish Radiation and Nuclear Safety Authority, STUK with two
sub-contractors:
– Helsinki University Hospital, HUS, and
– Public Research Centre Henri Tudor
PiDRL - objectives
• Agree on a methodology for establishing and
using DRLs for paediatric imaging, and
• Update and extend the European DRLs to
cover more procedures and a wider patient
age / weight range.
PiDRL – Work packages
• WP0 - management and general coordination of the project
• WP1 - methodology for DRLs, and producing European
guidelines
• WP2 updating and extending the existing European DRLs
• WP 3 organize the European workshop
THE END
It’s TIME for a change