radiation protection in diagnostic radiology - RPOP

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Radiation Protection in Paediatric Radiology
Radiation Protection of Children
in Screen Film Radiography
L03
IAEA
International Atomic Energy Agency
Educational objectives
At the end of the programme, the participants
should:
• Become familiar with specific radiation
protection issues in paediatric radiography
• Identify the features of radiographic imaging
equipment used in paediatric radiology
• List important operational considerations in
paediatric radiography
• Discuss important considerations in paediatric
radiography using mobile X-ray units
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Answer True or False
1. Added filtration will reduce the dose to the
patient.
2. Short exposure time is a disadvantage.
3. Proper collimation reduce dose.
4. Shielding of radiosensitive organs is
recommended in paediatric radiography.
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Contents
• Justification in radiography
• Practical optimisation in paediatric
radiography
• Equipment related
• Radiographic technique related
• Important consideration for mobile
radiography
• Image quality and patient dose
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Introduction
• Children have higher radiation sensitivity than
adults due to a longer life expectancy
• For children under age of 10, the probability for
fatal cancer is 2-3 times higher than for whole
population
• The higher radio-sensitivity of the patients should
be taken into account
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Introduction
• Radiologists and radiographers should be
specifically trained for paediatrics
• A paediatric radiological procedure should be
individually planned and projections should be
limited to what is absolutely necessary for a
diagnosis
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General recommendations
Key areas in radiation protection in paediatric
radiology:
• Justification
• Optimisation
• Evaluation of patient dose and image quality
“Do you really need a glossy picture to
make that diagnosis”
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Justification in radiography
• Justification is required for all radiographic studies
• Ask referring practitioner, patient, and/or family
•
•
•
•
about previous procedures
Use referral guidelines where appropriate and
available
Use alternative approaches, such as ultrasound,
MRI where appropriate
Consent, implied or explicit, is required for
justification
Include justification in clinical audit
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Justification in radiography
• Referral guidelines for radiological examinations:
• EUROPEAN COMMISSION, Referral Guidelines for Imaging,
Luxembourg, Radiation Protection 118, Office for Official
Publications of the European Communities, Luxembourg (2001)
and Update (2008)
• THE ROYAL COLLEGE OF RADIOLOGISTS, Making the Best use
of Clinical Radiology Services (MBUR), 6th edition, RCR, London
(2007)
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Examples of radiography examinations not
routinely indicated
• Skull radiograph in a child with epilepsy
• Skull radiograph in a child with headaches
• Sinus radiograph in a child, under 5 years,
suspected of having sinusitis
• Cervical spine radiograph in a child with torticollis
without trauma
• Radiographs of the opposite side for comparison in
limb injury
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Optimisation in radiography
• Justified studies must be optimised
• Various actions taken contribute to systematic
dose savings (from a factor of two to ten, with the
result that their combined effect can dramatically
reduce dose)
• Sustain good practice through a quality assurance
and constancy checking program
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Optimisation in radiography
Selection of equipment:
• Influence on patient dose and image quality
• But, good radiographic technique is the main
factor in improving quality without increasing
dose
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Practical optimisation measures in
radiography (I)
• Have a standard type and number of projections
for specific indications
• Views in addition to standard should only be
performed on a case-by-case basis
• Use manual technique selection pending
equipment developments on small patients or body
parts
• Where practical use a long (or the recommended)
Focus-to-Film Distance
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Practical optimisation measures in
radiography (II)
• Carefully collimate the X-ray beam to area of interest,
excluding other regions, especially gonads, breast, thyroid
and eyes
• Use appropriate gonad, thyroid, and breast shielding
• Fast film-screen combinations are acceptable for the
majority of indications
• Antiscatter grid is often unnecessary in children – do not
use grid for abdominal examination in patients under age of
3, for skull radiography for patients under age of 1 and any
fluoroscopy examination unless high detail is required
(Cook, V. Imaging, (13) 2001:229–238)
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Practical optimisation measures in
radiography (III)
• Use PA projections, where practical, for chest and
•
•
•
•
spine radiographs
Make sure the correct filtration is used to reduce
entry dose
Use as high a kVp as is consistent with
examination requirements
Consider additional filtration at higher kVp
Balance the use of a small focal spot size and
short exposure times
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Practical optimisation measures in
radiography (IV)
• Use of quality assessment, quality assurance and
audit programs for all aspects of the department’s
work, including film processing and justification
• Introduce and use a system that allows patient
dose be assessed regularly
• Monitor reject rate and the causes (overexposure,
underexposure, positioning, motion, and
collimation problems)
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Equipment, practice, dose
and image quality
1. Generators
For paediatric
examinations, the
generator should be:
•
•
•
•
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a high frequency
multi-pulse (converter)
of sufficient power
nearly rectangular
waveform with minimal
voltage ripple
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Equipment, practice, dose
and image quality
2. Exposure time
• When children are uncooperative they
may need immobilization
• They have faster heart and respiratory
rates
• Short exposure times improve quality
without increasing dose
• Only possible with powerful generators
and accurate exposure time switches
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Equipment, practice, dose
and image quality
3. Focal Spot
• Small focal spot
• Improves image quality
• May in some machines increase exposure
time and motion artefacts
• Choice depends on exposure
parameters: time, kVp and FFD (Focusto-Film Distance)
• Recommendation: focal spot should be
0.6 -1.3mm
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Equipment, practice, dose
and image quality
4. Additional filtration
• Additional filtration may lead to
dose reduction
• 0.1 mm of Cu in addition to 2.5
mm of Al*
• reduce ESAK by 20%
• barely noticeable reduction in
image quality
• Some modern systems can
automatically insert either 0.1mm
or 0.2 mm Cu depending on the
examination
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*Cook, V., Imaging, (13) 2001:229–238
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Dose reduction with added filtration
Added filtration
0 mm Al
3 mm Al
Examination
Mean ESD (Gy)
Reduction
Abdomen AP
10 months
(62 kVp)
200
30 %
Chest AP
10 months
(55 kVp)
64
40 %
Pelvis AP
4 months
(50 kVp)
94
51 %
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From: Mooney and
Thomas : Dose reduction
in a paediatric X-ray
department following
optimization of
radiographic technique,
BJR (77) 1998:852-860
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Equipment, practice, dose
and image quality
5. Exposure factors
Increased kVp (reduced mAs):
• Greater penetration and less
absorption
• Reduced patient dose for a
constant film density
Neonatal chest:
• Minimum 60kVp: less contrast but
better assessment of lung
parenchyma
• Lower kVp if looking for bone detail
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Equipment, practice, dose and
image quality
6. Antiscatter grid
• Often unnecessary in children
because smaller irradiated volume
(and mass) results in less
scattered radiation.
• Limited improvement in image
quality but increased dose of
~50% with the use of antiscatter
grids
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Antiscatter grids
• Antiscatter grid should be
removable in paediatric
equipment
• Remove antiscatter grid for:
• abdominal imaging in young
children especially <3 years old
• skull imaging <1 year old
• in most fluoroscopic imaging
Cook, V., Imaging, (13) 2001:229–238
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Antiscatter grids
If used for children,
Antiscatter grids should have*:
• Grid ratio (r) > 8:1
• Line numbers: >100 cm-1
• Low attenuation intersperse
material, such as carbon fibre
Alternative: air gap technique
(reduces the effect of scatter
without dose increase, but the
image is magnified)
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*Cook, V., Imaging, (13) 2001:229–238
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Equipment, practice, dose
and image quality
7. Automatic Exposure Control (AEC)
• Generally not appropriate for small children
• Sensors (size and geometry) are normally designed
for adult patients
• AEC use may be associated with the use of the grid
(where the grid is not removable), which is frequently
unnecessary
• AEC should have specific technical requirements for
paediatrics
• If not appropriate or available, carefully applied
exposure charts are preferred
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Automatic Exposure Control
• Specially designed paediatric AEC:
• Small mobile detector for use behind a lead-free
cassette
• Position can be selected with respect to the
most important region of interest
• This must be done extremely carefully, as even
minor patient movement may be disastrous
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Equipment, practice, dose
and image quality
8. Focus-to-film distance (FFD)
• Longer focus-to-film distances
• Smaller skin dose
• Combined with a small object-to-film distance,
results in less magnification (less geometric
distortion) and improved quality
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Equipment, practice, dose
and image quality
9. Image receptors
• Fast screen-film combinations
have advantages (reduction of
dose) and limitations (reduced
resolution)
• Low-absorbing materials in
cassettes, tables, etc., are
specially important in paediatric
radiology (carbon fibre)
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Film-screen systems
• Fast screen-film system:
• shorter exposure times (requires a
good generator)
• reduction in radiation dose and
prevention of artefacts
• Recommendations:
• 200 speed: bone
• 400 speed: general
• >700 speed – constipation transit
abdominal radiographs, follow-up films,
e.g. scoliosis and hips, swallowed
foreign body,…
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Equipment, practice, dose
and image quality
10. Collimation
• The most important factor for improving
image quality whilst also reducing dose
• The most common radiographic fault
• Good collimation/coning is essential to
achieve better contrast and avoid
exposing unnecessarily other body parts
(dose reduction)
• Body parts outside the region of interest
should not be in the X-ray field
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Collimation
• Require a basic knowledge of paediatric pathology
• Lung fields extremely large in congestive heart failure
& emphysematous pulmonary diseases
• Diaphragm, high in intestinal meteorism, chronic
obstruction or digestive diseases
• Beam-limiting devices automatically adjusting the
field size to the full size of the cassette are
inappropriate for children
• Minimal deviation from the radiation and light beam
may have large effects in relation to the usually
small field of interest - check light beam diaphragm
regularly
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Collimation
• Alignment agreement among the collimators,
radiation beam and the light beam must be
regularly assessed
• Beyond the neonatal period, the tolerance for
maximal field size should be less than 2 cm
greater than the minimal
• In the neonatal period, the tolerance level should
be reduced to 1.0 cm at each edge
• In paediatric patients, evidence of the field limits
should be apparent by clear rims of unexposed film
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Cook, J.V., Imaging, 13 (2001), 229–238
Neonatal anteroposterior supine chest and
abdomen radiograph of newborn: all four cone
Lateral skull radiograph (horizontal beam and
round cone)
marks visible, with no extraneous body parts
included and lead masking of the gonads.
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Equipment, practice, dose
and image quality
11. Shielding
• Standard equipment of lead-rubber shielding of the
body in the immediate proximity of the diagnostic
field
• Special shielding has to be added for certain
examinations to protect against external scattered
and extra-focal radiation
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Shielding
• For exposures of 60 - 80 kV,
maximum gonadal dose reduction
of about 30 to 40% can be obtained
by shielding with 0.25 mm lead
equivalent rubber immediately at
the field edge
• However, this is only true when the
protection is placed correctly at the
field edge
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Shielding
• The gonads in "hot examinations", when they lie
within or close to (nearer than 5 cm) the primary
beam, should be protected whenever this is
possible without impairing necessary diagnostic
information
• It is best to make one's own lead contact shields
for girls and lead capsules for boys
• Must be available in varied sizes
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Shielding
• With appropriate shielding the absorbed dose in
the testes can be reduced by up to 95%
• In girls, shadow masks within the diaphragm of the
collimator are as efficient as direct shields.
• When shielding of the female gonads is effective,
the reduction of the absorbed dose in the ovaries
can be about 50%
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Shielding
• The eyes should be shielded for X-ray
examinations involving high absorbed doses in the
eyes, e.g., for conventional tomography of the
petrous bone, when patient cooperation permits
• The absorbed dose in the eyes can be reduced by
50% - 70%
• In any radiography of the skull the use of PAprojection rather than the AP-projection can reduce
the absorbed dose in the eyes by 95%
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Equipment, practice, dose
and image quality
12. Patient Positioning and Immobilization
• Patient positioning must be exact, whether or not the
patient co-operates.
• In infants, toddlers and younger children immobilization
devices, properly applied, must ensure that:
the patient does not move
the beam can be centred correctly
the film is obtained in the proper projection
accurate collimation limits the field size exclusively to the
required area
 shielding of the remainder of the body is possible.




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Patient Positioning and Immobilization
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Patient Positioning and Immobilization
• Immobilization devices must be
easy to use
• Their usefulness should be
explained to the accompanying
parent(s)
• Radiological staff members should
only hold a patient under
exceptional circumstances
• Even in quite young children the
time allocation for an examination
must include the time to explain the
procedure not only to the parents
but also to the child
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Mobile radiography
• Mobile radiography is valuable on occasions when
it is impossible for the patient to come to the
radiology department
• It can result in
• poorer quality images
• unnecessary staff and patient exposures
• Where practicable, X-ray examinations should be
carried out with fixed units in an imaging
department
• Mobile units should only be used with those who
cannot safely be moved to such a unit
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Mobile radiography
• High output converter generators are
recommended
• Capacitor discharge systems should
be avoided (they have significant
pre- and post-peak soft radiation)
• Appropriate collimation is
essential to avoid exposing
organs outside the diagnostic
area of interest
• Other principles outlined above,
should be followed with mobile
radiography
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Mobile radiography
• Scattered radiation must be
managed to reduce dose to the
patient, parents/guardians and to
hospital personnel
• The advice of the medical
physicist/radiation protection officer
should be obtained on how best to
do this.
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Mobile radiography
Recommendations for Intensive Care Unit
(Duetting et. al. Pediat. Radiol. 29: 158-62 (1999)):
• No additional protection for neighbouring premature
infants is necessary
• The radiographer should wear a lead apron
• Parents and personnel need not interrupt their
activities or leave the room during an X-ray
examination
• When using a horizontal beam, the beam, must be
directed away from other persons – use lead shield
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Criteria related to images
• Incorrect positioning is the most frequent cause of
inadequate image quality in paediatric radiographs
• Image criteria for the assessment of adequate
positioning (symmetry and absence of tilting etc)
are much more important in paediatric imaging
than in adults
• A lower level of image quality than in adults may
be acceptable for certain clinical indications
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Criteria related to images
Guideline resources:
• European Guidelines on
Quality Criteria for Diagnostic
Radiographic Images in
Paediatrics
• American College of
Radiology
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Quality Criteria List
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Chest-PA/AP projection
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Chest radiography-PA/AP projection
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Typical dose levels in paediatric radiography
ESAK (µGy)
Age
Examination
0
1
5
10
15
Abdomen AP
110
340
590
860
2010
Chest PA/AP
60
80
110
70
110
Pelvis AP
170
350
510
650
1300
Skull AP
/
600
1250
/
/
Skull LAT
/
340
580
/
/
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NATIONAL RADIOLOGICAL PROTECTION BOARD, Doses to Patient from Medical
X Ray Examinations in the UK: 2000 review, NRPB-W14, Chilton (2002).
Radiation Protection in Paediatric Radiology
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ICRP-ISR “smart” message for paediatrics
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http://rpop.iaea.org/RPoP/RPoP/Content/index.htm
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Summary
• Particular attention should be given to technical
specifications of X-ray equipment
• Good radiographic technique is the main factor
in improving quality without increasing dose for
protocols used in X-ray paediatric radiology
• Justification of practice
• Application of practical optimisation measures in
radiography
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Answer True or False
1. Added filtration will reduce the dose to the
patient.
2. Short exposure time is a disadvantage.
3. Proper collimation reduce dose.
4. Shielding of radiosensitive organs is
recommended in paediatric radiography.
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Answer True or False
1. True - Filtration absorbs low energy photons that
are absorbed in patient’s skin and superficial
organs and thus giving contributing to dose but
not to image formation.
2. False - It prevents motion artefacts and
unnecessary repetitions.
3. True - Collimation reduces exposed volume, and
reduces scatter radiation that affects both image
quality and dose.
4. True - It is especially important for radiosensitive
organs as breast, gonads and eyes.
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References
• European Guidelines on Quality Criteria for Diagnostic Radiographic
•
•
•
•
Images in Paediatrics, July 1996. EUR 16261. Available at:
http://www.cordis.lu/fp5-euratom/src/lib_docs.htm
Huda W, Assessment of the problem: paediatric doses in screen-film
and digital radiography, Pediatr Radiol 34(Suppl 3) 2004:S173-S182
Duetting,Foerste,Knoch,Darge and Troeger, Radiation exposure during
chest X-ray examinations in a premature intensive care unit: phantom
studies, Pediatr Radiol (29) 1999:158-162
Mooney and Thomas : Dose reduction in a paediatric X-ray department
following optimization of radiographic technique, BJR (77) 1998:852860
Cook, V., Radiation protection and quality assurance in paediatric
radiology, Imaging, (13) 2001:229–238.
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