Radiation Protection in Paediatric Radiology
Understanding Radiation Units
L02
Educational Objectives
At the end of the programme, the participants
should become familiar with the following:
• Why is it important to measure radiation dose in
children?
• How radiation dose can and should be
expressed?
• Understand the radiation quantities and units
used in diagnostic radiology.
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Answer True or False
1. The same amount of radiation falling on the
person at level of breast, head or gonads will
have the same biological effects.
2. Effective dose can be easily measured.
3. Diagnostic reference levels are not
applicable to paediatric radiology.
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Contents
• Dose descriptors outside the patient’s body.
• Dose descriptors for effects that have threshold
(deterministic effects)
• Dose descriptors to estimate stochastic risks
• Diagnostic reference levels
• Dose descriptors and units for staff dose
assessment
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Introduction
• Several quantities and units are used in the field of
diagnostic radiology to measure and describe
radiation dose
• Some can be measured directly while others can
only be mathematically estimated
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Two types of radiation effects
Stochastic effects
• Where the severity of the result is the same but the
probability of occurrence increases with radiation dose,
e.g., development of cancer
• There is no threshold for stochastic effects
• Examples: cancer, hereditary effects
Deterministic effects
• Where the severity depends upon the radiation dose,
e.g., skin burns
• The higher the dose, the greater the effect
• There is a threshold for deterministic effects
• Examples: skin burns, cataract
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Hot Coffee – Energy contained in a sip
Excess Temperature = 60º - 37 = 23º
1 sip = 3ml
3x 23 = 69 calories
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Radiation Dose
Lethal Dose= 4Gy
LD 50/60 = 4 Gy
For man of 70 kg
Energy absorbed = 4 x 70 = 280 J
= 280/418= 67 calories
= 1 sip
Energy content of a sip of coffee if derived in the form of Xrays can be lethal
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Dose of Radiation
• Radiation energy
absorbed by a body
per unit mass.
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Dose Quantities and Radiation units
- Dose quantities external to the patient’s body.
- Dose quantities to estimate risks of skin injuries
and effects that have threshold.
- Dose quantities to estimate stochastic risks.
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Why so many quantities?
Radiation dose is a complex topic
• 1000 Watt heater giving off heat (IR radiation) - unit
is of power which is related with emission intensity
• Heat perceived by the person will vary with so
many factors: distance, clothing, room temperature
• As can be seen with the example of heat, the
energy transformation is a highly complicated issue
• This is the case with X-rays - radiation can’t be
perceived
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Basic Radiation Quantities
• Used to quantify a beam
of X or γ-rays
• There are:
• Quantities to express
total amount of
radiation.
• Quantities to express
radiation at a specific
point
Total radiation
•Total photons
•Integral dose
Radiation Protection in Paediatric Radiology
Radiation at a
specific point
•Photon fluence
•Absorbed dose
•Kerma
•Dose equivalent
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Exposure: X
• Exposure is a dosimetric quantity for measuring
ionizing electromagnetic radiation (X-rays & Ɣrays), based on the ability of the radiation to
produce ionization in air.
Units:
coulomb/kg (C/kg)
or
roentgen (R)
1 R = 0.000258 C/kg
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KERMA
KERMA (Kinetic Energy Released in a Material):
• Is the sum of the initial kinetic energies of all charged
ionizing particles liberated by uncharged ionizing
particles in a material of unit mass
• For medical imaging use, KERMA is usually expressed in
air
SI unit = joule per kilogram (J/kg)
or gray (Gy)
1 J/kg = 1 Gy
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Absorbed dose: D
Absorbed dose, D, is the mean energy
imparted by ionizing radiation to matter
per unit mass.
SI unit = joule per kg (J/kg) or gray (Gy).
Harold Gray
In diagnostic radiology, KERMA and D
are equal.
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Mean absorbed dose in a tissue or organ
The mean absorbed dose in a tissue or organ DT
is the energy deposited in the organ divided by
the mass of that organ.
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Now things get a little more complicated !
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Radiation Dose Quantities
• Primary physical quantities are not used directly for
dose limitation
• The International Council on Radiation Protection
(ICRP) has defined values for dose limits in
occupational exposure
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Radiation Dose Quantities
Equivalent Dose:
• Accounts for the type of radiation
• Different radiation types have different level of
biologic damage per unit absorbed dose
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Radiation Weighting Factors, wR
Radiation type
Radiation weighting factor, wR
Photons
1
Electrons and muons
1
Protons and charged pions
2
Alpha particle, fission
fragments, heavy ions
Neutrons
20
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A continuous curve
as a function of
neutron energy
L02. Understanding
radiation units
(Source:
ICRP 103)
Equivalent Dose : HT,R
The absorbed dose in an organ or tissue multiplied
by the relevant radiation weighting factor :
H T , R  wR  DT , R
where DT,R is the average absorbed dose in the
organ or tissue T, and wR is the radiation weighting
factor for radiation R.
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Radiation Quantities and Units
Equivalent dose (Unit = sievert, Sv )
• Compares the biological effects for
different types of radiation, X-rays,
Ɣ-rays, electrons, neutrons,
protons, α-particles etc.
• For X-rays, Ɣ-rays, electrons :
Rolph Sievert
absorbed dose and equivalent
dose have the same value Gy = Sv.
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Detriment
• Radiation exposure to different organs and tissues
in the body results in different probabilities of harm
and different levels of severity.
• The combination of probability and severity of
harm is called “detriment”.
• Effective dose reflects the combined detriment
from stochastic effects due to the equivalent doses
in all the organs and tissues of the body.
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Effective Dose: ET
• Effective dose takes into account the organ specific
radio-sensitivity to develop cancer and hereditary
effects from radiation
• Unit = sievert, Sv
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Effective Dose: ET
A summation of the tissue equivalent doses, each
multiplied by the appropriate tissue weighting
factor:
E   wT H T
T
where HT is the equivalent dose in tissue T and
wT is the tissue weighting factor for tissue T.
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Tissue Weighting Factors, wT
• The organs have different weighting factors, wT.
• These factors are published in ICRP 103 (2007)
and have been changed over the years due to
increased knowledge.
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Tissue Weighting Factors
• The weighting factors sum up to 1.0.
• They are relative and compares one organ with the
other.
• They are the same for children and adults!
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Tissue Weighting Factors
• Data is primarily taken
from knowledge derived
from studying the
Japanese population
exposed to atomic bombs
in Hiroshima and Nagasaki
• On going research has
changed the weighting
factors from 1990 (ICRP
60) to 2007 (ICRP 103).
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Tissue Weighting Factors
Multipliers of the equivalent dose to an organ or tissue to account for the
different sensitivities to the induction of stochastic effects of radiation.
Tissue
Bone-marrow (red), Colon, Lung, Stomach, Breast,
Remainder Tissues**(nominal weighting factor
applied to the average dose to 14 tissues)
Gonads
Bladder, Esophagus, Liver, Thyroid
Bone surface, Brain, Salivary glands, Skin
weighting
factor
wT*
∑ wT
0.12
0.72
0.08
0.04
0.08
0.16
0.01
0.04
*ICRP 103
**Remainder Tissues (14 in total): Adrenals, Extrathoracic (ET) region, Gall bladder,Heart, Kidneys,
Lymphatic nodes, Muscle, Oral mucosa, Pancreas, Prostate, Small intestine, Spleen, Thymus,
Uterus/cervix..
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Effective Dose (E)
Dose to lungs times their
weighting factor; DL x wL
+
Dose (mean absorbed dose) to
gastrointestinal tract times their
weighting factor; DGI x wGI
+
....(summation over organ after
organ)
=
Effective dose
E   wT H T
T
where T stands for tissue
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Effective Dose (E)
We can compare different paediatric imaging
procedures through their different effective doses, E.
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Radiation Quantities and Units used in Diagnostic
Radiology
•
•
•
•
•
•
Incident air kerma
Entrance surface air kerma
Air kerma-area product
Air kerma-length product
Dosimetric quantities for CT
Dosimetric quantities for interventional radiology
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Incident Air Kerma
Measured Free in Air on the central beam axis at
the focal spot to surface distance.
Only primary beam is considered, that is, no
scatter contribution.
Unit: joule/kg or gray (Gy)
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Entrance Surface Air Kerma (ESAK)
• ESAK measured on the surface of the patient or
phantom where X-ray beam enters the patient or
phantom.
• Includes a contribution from photons scattered
back from deeper tissues, which is not included in
free in air measurements.
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Entrance Surface Air Kerma (ESAK)
• If measurements are made at other distances than
the true focus - to - skin distance, doses must be
corrected by the inverse square law and
backscatter factor incorporated into the
calculation.
References:
• Dosimetry in Diagnostic Radiology: An International code of
practice, TRS 457, IAEA, 2007
• Phys. Med. Biol. 43 (1998) 2237-2250.
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Dose Measurement
Kerma in X-ray field can be
measured using calibrated:
• Ionization chamber
• Semiconductor dosimeter
• Thermoluminescent dosimeter
(TLD)
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Kerma-Area Product: KAP
• The kerma - area product (KAP) is
defined as the kerma in air in a
plane perpendicular to the incident
beam axis, integrated over the
area of interest.
• This is the dose related quantity
measured and displayed on all
modern X-ray equipment
excluding CT.
KAP meter
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Kerma-Area Product: KAP
• The KAP (Gy·cm2) is
constant with distance since
the cross section of the beam
is a quadratic function which
cancels the inverse quadratic
dependence on dose .
• KAP remains constant along
the beam axis as long as it is
not measured close to the
patient/phantom surface
which introduces backscatter.
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Kerma-Area Product: KAP
KAP = K x Area
the SI unit of KAP is the
Gy·cm2
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d1=1
Area = 1
Dose = 1
Area = 4
Dose = 1/4
d2=2
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Kerma-Area Product: KAP
KAP is independent of
distance from the X-ray
source, as:


Air Kerma decreases with the
inverse square law.
d1=1
Area = 1
Dose = 1
Area = 4
Dose = 1/4
d2=2
Area increase with the square
distance
KAP is usually measured at the
level of the tube diaphragms
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KAP (kerma-area product)
This is a picture of a KAP meter which measures the kerma area product
Unit: Gy·cm2
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Example of a dose display during
fluoroscopy or cine runs with dose
rate as shown
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Kerma-Area Product
In paediatric radiology KAP may be used for:
• Diagnostic reference levels (DRLs)
• By use of conversion factors, it can be
converted to skin dose and/or effective dose
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Dosimetric Quantities for CT
• Computed Tomography Dose
Index (CTDI)
- determined using scan
protocol parameters.
-useful for comparison of
different scanners.
• Dose-Length Product (DLP)
- measure of dose to patient
- used to estimate effective
dose
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CT and Risk
KERMA
(in phantom)
CTDI
(dose in phantom per slice)
Length of scan and pitch
DLP
Effective dose
Risk
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Measurement of Dosimetric Quantities in CT
• Pencil ionisation chamber with
active length of 100 mm.
•
• Measurements free-in-air or in
standard dosimetry phantom.
• Alternatives: TLD, solid state
detectors.
• CTDIVOLshould be displayed on the
console, reflecting the conditions
of operation selected (IEC, 2003)
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Dose Indicators in Interventional Radiology
•
•
For quality assurance purposes
To estimate the probability of occurrence of
stochastic effects use:
Kerma-air product rate (KAP, PKA)
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Dose Indicators in Interventional Radiology
•
For quantifying the threshold and severity
of deterministic effects use:
• Maximum skin dose (MSD)
• Cumulative dose (CD) to Interventional
Reference Point (IRP)
•
In a complex procedure skin dose is highly
variable
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Interventional Procedures: Skin Dose
• In some procedures,
patient skin doses
approach those used in
radiotherapy fractions
• Maximum skin dose
(MSD) or peak skin dose
is the maximum dose
received by a portion of
the exposed skin.
Radiodermatitis in the right arm. 7
year-old patient. Photograph taken
4 months after radiofrequency
ablation. Surce: ICRP 85
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Cumulative Dose to
Interventional Reference Point*
•
•
•
•
IRP is located 15 cm from the isocentre towards
the focal spot
The air kerma accumulated at a specific point in
space relative to the fluoroscopic gantry (IRP)
during a procedure
Cumulative dose does not include tissue
backscatter and is measured in Gy.
Cumulative dose is sometimes referred to as
cumulative air kerma
*IRP
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Cumulative dose to
Interventional Reference Point
Cumulative dose to IRP is measured with a
flat ion chamber or calculated by the system
and displayed in the angiography room
15 cm
15 cm
IRP
IRP
Isocenter
Isocenter
(IEC-60601-2-43)
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MSD vs. Cumulative dose
• In some procedures, cumulative dose to IRP is
well correlated with MSD
• Cumulative dose to IRP can be a good
indicator of doses higher than the thresholds
for skin injures
• A “trigger value” for cumulative dose can be
adopted to alert interventionalists the threshold
for skin erythema could be reached.
• A follow-up protocol can be adopted.
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Other related dose parameters
Fluoroscopy time:
• Has a weak correlation with KAP
• But, in a quality assurance programme it can
be adopted as a starting unit for
• comparison between operators,
centres, procedures
• for the evaluation of protocol
optimization, and
• to evaluate operator skill
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Other related dose parameters
Number of acquired images and number of
series:
• Patient dose is a function of total acquired
images
• But dose/image can have big variations
• There is an evidence of large variation in
protocols adopted in different centres
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Diagnostic reference levels (DRLs)
• ICRP, IAEA, EC: introduced the concept of
diagnostic reference levels (DRLs) for patients
• DRLs are a form of investigation level, apply to an
easily measured quantity at the surface of a simple
standard phantom or a representative patient.
• An optimisation tool, not dose limits
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Diagnostic Reference Levels (DRLs)
• DRLs calls for local investigation (often very
simple) if constantly exceeded
• DRLs: Management of patient doses must be
consistent with the required clinical imaging
information
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Quantities for Establishment of DRLs
• Incident air kerma and entrance-surface air
kerma
• Incident air kerma rate and entrance-surface
air kerma rate
• Air kerma–area product
• CT Dose index, CT Dose–length product
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Quantities and Units for Staff Dose
Assessment
• Personal dosimetry services typically provide
monthly estimates of Hp(10) (mSv), the dose
equivalent in soft tissue at 10 mm depth. This is in
most of the cases used to estimate the effective
dose.
• Sometimes, Hp(0.07) (mSv) is also reported: the
dose equivalent in soft tissue at 0.07 mm depth)
• Personal dosememters (film, thermoluminescent...)
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Personal Dosimetry Methods
• Single dosimeter worn
• above the apron at neck level
Radiation
Lens dose, optional
protection
measures
(recommended) or under the
apron at waist level
Finger dose, optional
Second dosemeter
Image
intensifier
• Two dosimeters worn
Patient
at the neck, optional
Personal dose
dosemeter behind the lead apron
(recommended in
intrevational procedures)
Dose limits
of occupational exposure
• one above the apron at neck
level
• another under the lead apron
at waist level
outside and above the apron
(ICRP 60)
Effective dose
20 mSv in a year
averaged over a period of 5 years
X-ray
tube
Anual equivalent dose in the
lens of the eye 150 mSv
skin
500 mSv
hands and feet 500 mSv
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Dose Measurement
Dose due to scatter
radiation at a point
occupied by the
operator can be
measured with a
portable ionization
chamber
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Summary
• Dosimetric quantities are useful to know the
•
•
•
•
potential hazard from radiation and to determine
radiation protection measures to be taken
Physical quantities - Directly measurable
Protection quantities - Defined for dose limitation
purposes, but not directly measurable.
Application specific quantities - Measurable in
medical imaging.
Diagnostic Refernce Levels
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Answer True or False
1. The same amount of radiation falling on the
person at level of breast, head or gonads will
have same biological effects.
2. Effective dose can be easily measured.
3. Diagnostic reference levels are not
applicable to paediatric radiology.
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Answer True or False
1. False -Different organs have different
radio-sensitivity and tissue weighting
factors as given by ICRP.
2. False -It can be only calculated using
different methods.
3. False - DRLs apply for paediatric
radiology, but these are age-specific.
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References
• INTERNATIONAL COMMISSION ON RADIATION UNITS AND
•
•
•
•
MEASUREMENTS, Patient Dosimetry for X Rays Used in Medical
Imaging, ICRU, Rep. 74, ICRU, Bethesda, MD (2006).
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION,
Radiological Protection in Medicine, Publication 105, Elsevier, Oxford
(2008)
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION,
Recommendations of the ICRP, Publication 103, Elsevier, Oxford
(2008)
EUROPEAN COMMISSION, Guidance on Diagnostic Reference Levels
(DRLs) for Medical Exposure, Radiation Protection 109, Office for
Official Publications of the European Communities, Luxembourg (1999)
INTERNATIONAL ATOMIC ENERGY AGENCY, Dosimetry in
Diagnostic Radiology: an International Code of Practice, Technical
Report Series No 457, IAEA, Vienna (2007)
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Additional information
Quantities for radiation measurement
• Physical quantities - Directly measurable
• Protection quantities - Defined for dose
limitation purposes, but not directly
measurable
• Application specific quantities - Measurable
in medical imaging
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Radiation quantities and units
• Fundamental dosimetric quantities
• Protection quantities
• Equivalent dose
• Effective dose
• Application specific dosimetric quantities used in DR
• Incident air kerma
• Entrance surface air kerma
• Air kerma area product
• Air kerma length product
• Dosimetric quantities in CT and mammography
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Physical Quantities
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Physical quantities
• Fluence
• Exposure
• Kerma
• Absorbed dose
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Fluence : f
The fluence, f , is the quotient of dN by
da, where dN is the number of particles
incident on a sphere of cross section da,
thus
f = dN/da
The unit of fluence is m-2
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Exposure: X
dQ
X
dm
where dQ is the absolute value of the total charge of ions
produced in air when all the electrons liberated in air of mass
dm are completely stopped in air.
The SI unit of exposure is the coulomb per kilogram (C/kg)
The special unit of exposure is the röntgen (R).
1R = 2.58 x 10-4 C kg-1
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KERMA
The KERMA (Kinetic Energy Released in a MAterial)
dEtrans
K
dm
where dEtrans is the sum of the initial kinetic
energies of all charged ionizing particles liberated
by uncharged ionizing particles in a material of
mass dm
The SI unit of kerma is the joule per kilogram (J/kg),
termed gray (Gy).
.
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Exposure and KERMA
Exposure, X, in units of C kg-1, is related to air kerma
as follows:
K a 1  g e
X
W
where W is the average energy spent by an electron
to produce an ion pair, g is the fraction of secondary
charged particles that is lost to bremsstrahlung
radiation production and e is the electronic charge
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Absorbed Dose: D
The fundamental dosimetric quantity absorbed dose,
D, is defined as:
d
D
dm
where d  is the mean energy imparted by ionizing
radiation to matter in a volume element and dm is the
mass of matter in the volume element.
The SI unit of absorbed dose is the joule
per kilogram (J/kg), termed the gray (Gy)
In diagnostic radiology, KERMA and D are equal
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Exposure and Absorbed Dose or KERMA
• Exposure can be linked to air dose or kerma
by suitable conversion coefficients.
• For example, 100 kV X-rays that produce an
exposure of 1 R at a point will also give an
air kerma of about 8.7 mGy and a tissue
kerma of about 9.5 mGy at that point.
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Application Specific Quantities
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Imaging
modality
Radiography
Measurement
subject
Measured radiation
quantity
Remark
Phantom
Patient
Incident air kerma
ESAK, KAP
Fluoroscopy/
Interventional
procedures
Phantom
Patient
ESAK
KAP/Peak skin dose
CT
Phantom
Patient
CT air kerma index
Measured in PMMA head
CT air kerma- length and body phantom
product
Mammography
Phantom
Patient
Incident air kerma,
ESAK
Incident air kerma
Dental
radiography
Patient
Incident air kerma
Air kerma-length
product
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Calculated from X-ray
tube output
Calculation of mean
glandular dose
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Application Specific Quantities
X-ray tube
focal spot
position
Focal-spot to
image
receptor
distance
(FFD)
Incident air kerma (no
backscatter)
Focal-spot to
patient skin
distance (FSD)
Entrance surface air
kerma (including
backscatter)
Image receptor
Patient
thickness
Schematic diagram showing some dosimetric and geometric quantities
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Entrance Surface Air Kerma (ESAK)
 FDD
ESAK  Y (kVp, FDD )  mAs  
 FFD  t
p

2

  BSF


where Y(kVp, FFD) is tube output for actual kVp used
during examination, mAs is actual tube current-time product
used during examination and FFD is focus-to-film distance.
BSF is the backscatter factor that depends on kVp and total
filtration of X-rays
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Backscatter Factors (Water)
HVL
Field size (cm x cm)
mmAl
10 x 10
15 x 15
20 x 20
25 x 25
30 x 30
2.0
1.26
1.28
1.29
1.30
1.30
2.5
1.28
1.31
1.32
1.33
1.34
3.0
1.30
1.33
1.35
1.36
1.37
4.0
1.32
1.37
1.39
1.40
1.41
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Kerma-Area Product: KAP
• If the KAP is calculated by the system, you must
know if the user added filtration you use is included
or not !
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Kerma-Area Product: KAP
• It is always necessary to calibrate and to check the
transmission chamber for the X-ray installation in
use
• In some European countries, it is compulsory that
new equipment is equipped with an integrated
ionization transmission chamber or with automatic
calculation methods
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Dosimetric Quantities for CT
• Computed Tomography
Dose Index (CTDI)
• CT air kerma index
• Dose-Length Product
(DLP)
• Air kerma-length product
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ICRU 74 / IAEA TRS 457
• CT air kerma index
• Free-in-air (Ck)
• In phantom (Ck,PMMA)
• Air kerma length
product (PKA)
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Dosimetric Quantities for CT
Principal dosimetric quantity in CT is CT air kerma index:
Ca ,100
1

NT
50
 K ( z )dz
50
where K(z) is air kerma along a line parallel to the axis of
rotation of the scanner over a length of 100 mm.
N = Number of detectors in multi-slice CT
T = Individual detector dimension along z-dimension
The product NT defines the nominal scan beam
width/collimation for a given protocol.
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Dosimetric Quantities for CT
Weighted CT air kerma index, CW, combines
values of CPMMA,100 measured at the centre and
periphery of a standard CT dosimetry phantoms
1
Cw  C PMMA,100,c  2C PMMA,100, p 
3
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Dosimetric Quantities for CT
Pitch (IEC, 2003):
I
p
NT
T= Single detector dimension
along z-axis in mm.
N=Number of detectors used in a
given scan protocol (N>1 for
MDCT), N x T is total detector
acquisition width or collimation
I=table travel per rotation
Radiographic, 2002, 22:949-62
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Dosimetric Quantities for CT
• Volume CTDI describes the average dose over the
total volume scanned in sequential or helical
sequence, taking into account gaps and overlaps
of dose profiles (IEC, 2003):
CVOL
NT
 CW
l
• Average dose over x, y and z direction
• Protocol-specific information
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Dosimetric Quantities for CT
• Kerma-length product (PKL):
PKL  CVOL  L
where L is scan length is limited by outer margins
of the exposed scan range (irrespective to pitch)
• PKL for different sequences are additive if refer to
the same type of phantom (head/body)
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Maximum Skin Dose (MSD)
• Measurement/evaluation of MSD
• Point or area detectors
• Cumulative dose at IRP (interventional radiology
point)
• Calculation from technical data
• Off line methods
• Area detectors: TLD array, slow films, radiochromic
films
• From KAP and Cumulative dose measurement
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Method for MSD Evaluation:
Radiochromic Large Area Detector
Example: Radiochromic films type Gafchromic XR R 14”x17”
• useful dose range: 0.1-15 Gy
• minimal photon energy dependence (60 - 120 keV)
• acquisition with a flatbed scanner:b/w image, 12-16 bit/pixel
or, measure of OD measurement with a reflection densitometer
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Benefits of Radiochromic Films
• The radiochromic film:
• displays the maximum dose and its location
• shows how the total dose is distributed
• provides a quantitative record for patient files
• provides physician with guidance to enable safe
planning of future fluoroscopically guided procedures
• improves fluoroscopic technique and patient safety
• possible rapid semi-quantitative evaluation
Example of an exposed
radiochromic film in a cardiac
interventional procedure
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Rapid Semi-Quantitative Evaluation: Example
• For each batch number (lot #) of gafchromic film a Comparison
Tablet is provided
• In the reported example we easily can recognise that the darkness
area of the film, corresponding to the skin area that has received the
maximum local dose, has an Optical Density that correspond at
about 4 Gy
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DRLs for Complex Procedures
Reference levels (indicative of the state of the practice): to help
operators to conduct optimized procedures with reference to patient
exposure
For complex procedures
reference levels should
include:
• more parameters
• and, must take into
account the complexity
of the procedures.
(European Dimond
Consortium
recommendations)
3rd level
“Patient risk”
2nd level
“Clinical protocol”
Level 2 + DAP
+ Peak Skin Dose (MSD)
Level 1
+ No. images + fluoroscopy time
1st level
“Equipment
performance”
Radiation Protection in Paediatric Radiology
Dose rate and dose/image
(BSS, CDRH, AAPM)
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