This document discusses key concepts in radiation dosimetry for medical imaging, including: 1) It defines common radiation protection terms like absorbed dose, equivalent dose, effective dose and explains their appropriate and limited uses for evaluating patient risk from medical imaging. 2) It notes that effective dose should not be used to assess risk to individuals from medical exposures and that organ doses are more relevant. 3) It discusses how uncertainty increases at each step moving from measurement of organ doses to estimation of effective dose and risk, limiting the usefulness of effective dose for medical applications. 4) For medical imaging, more detailed knowledge of organ doses, dose distributions and patient factors is needed than just effective dose alone to properly assess radiation

1. 1
Adjunct Assistant Professor (Radiology)
The George Washington University School of Medicine and Health Sciences
Cari Borrás, D.Sc., FACR, FAAPM, FIOMP
Washington DC, USA
Chair, AAPM International Educational Activities Committee
Improving Patient Radiation
Protection or Evaluating Risks in
Medical Imaging?
What matters most?

2. Lecture Outline
▲ Radiation Protection Dosimetry Terms
▲ Radiology Dosimetry Terms
• Machine related
• Patient related
▲ Diagnostic Reference Levels
▲ Patient Organ Doses
• Measurements
• Look up Tables
• Monte Carlo Simulations
• Dicom Standards: RDSR & P-RDSR
2

3. 3
Radiation Protection Dosimetric
Quantities and Units (ICRP / ICRU)
▲ Incorporate Exposures
• External and Internal
▲ Are Different For:
• Low doses of (low-LET) radiation < 0.5 Gy
o Stochastic (probabilistic) effects, LNT is applicable
• Cancer induction
• Hereditary diseases
• High doses of radiation
o Tissue reactions (deterministic effects), threshold exists

4. 4
RP Dosimetric Quantities and Units
Absorbed Dose, D
Where d ε is the mean energy imparted by
ionizing radiation in a volume element and
d m is the mass of the matter in that volume
The SI unit is J kg-1 and the special name is
gray (Gy)
D = d ε / d m

5. 5
RP Dosimetric Quantities and Units
Tissue Reactions
RBE : Relative Biological Effectiveness
differs for
• different biological endpoints and
• different tissues or organs
Dose to Tissue = Absorbed Dose * RBE
The SI unit is J kg-1 and the special name is gray (Gy)

6. 6
RP Dosimetric Quantities and Units
Stochastic Effects
ICRP 26 (1977) ICRP 60 (1991) ICRP 103 (2007)
* Equivalent Dose Equivalent Dose#
Effective Dose
Equivalent
Effective Dose Effective Dose
* No specific term
# Radiation Weighted Dose proposed but not accepted
The SI unit is J kg-1 and the special name is sievert (Sv)
Evolution of Terminology

7. 7
RP Dosimetric Quantities and Units
Stochastic Effects (Sv)
Equivalent Dose, HT, in a tissue T:
HT = ΣR wR D T,R
wR is the radiation weighting factor, which accounts for
the detriment caused by different types of radiation
relative to photon irradiation
D T,R is the absorbed dose averaged over the tissue
T due to radiation R
wR values are derived from in vivo and in vitro RBE studies
They are independent of dose and dose rate in the low dose region

8. 8
Radiation Weighting Factors in
1991 (ICRP 60) and in 2007 (ICRP 103)
Radiation type and energy range 1991 2007
Photons 1 1
Electrons and muons 1 1
Protons (1991, 2007), pions (2007) 5 2
Alpha particles, fission fragments, heavy ions 20 20
Neutrons, energy < 10 keV 5
Continuous
Function
10 keV to 100 keV 10
> 100 keV to 2 MeV 20
> 2 MeV to 20 MeV 10
> 20 MeV 5

9. 9

10. 10
RP Dosimetric Quantities and Units
Stochastic Effects (Sv)
E = ΣT wT H T = ΣT ΣR wT wR D R,T
Effective Dose, E
ΣT wT = 1
wT represents the relative contribution of that
tissue or organ to the total detriment resulting
from uniform irradiation of the body
A uniform dose distribution in the whole body gives
an effective dose numerically equal to the radiation-
weighted dose in each organ and tissue of the body

11. 11
Tissue Weighting Factors in 1977 and 1991
Tissue ICRP 26 ICRP 60
Bone surface 0.03 0.01
Bladder 0.05
Breast 0.15 0.05
Colon 0.12
Gonads 0.25 0.20
Liver 0.05
Lungs 0.12 0.12
Esophagus 0.05
Red bone marrow 0.12 0.12
Skin 0.01
Stomach 0.12
Thyroid 0.03 0.05
Remainder 0.30 0.05
TOTAL 1.0 1.0

12. 12
Tissue Weighting Factors
ICRP 103 (2007)
* Remainder Tissues: Adrenals, Extrathoracic region, Gall bladder, Heart,
Kidneys, Lymphatic nodes, Muscle, Oral mucosa, Pancreas, Prostate, Small
intestine, Spleen, Thymus and Uterus/cervix
Tissue wT ∑ wT
Bone-marrow (red), Colon, Lung, Stomach, Breast,
Remainder Tissues*
0.12 0.72
Gonads 0.08 0.08
Bladder, Oesophagus, Liver, Thyroid 0.04 0.16
Bone surface, Brain, Salivary glands, Skin 0.01 0.04
Total 1.00

13. 13
RP Dosimetric Quantities and Units
▲ Incorporate Exposures
• External
• Internal
In this presentation we will not discuss the
magnitudes for exposures from radionuclides:
Committed Equivalent Dose
Committed Effective Dose

14. 14
RP Dosimetric Quantities and Units
Stochastic Effects
Collective Effective Dose, S
(due to Individual Effective Doses E1 and E2)
• d N / d E : number of individuals who experience
an effective dose between E and E + d E
• ΔT specifies the time period within which the
effective doses are summed

15. 15
Limitations of
Equivalent and Effective Doses
▲ Are not directly measurable
▲ Point quantities needed for area monitoring (in
a non-isotropic radiation field, effective dose
depends on the body’s orientation in that field)
▲ Instruments for radiation monitoring need to
be calibrated in terms of a measurable
quantity for which calibration standards exist
Operational protection quantities are needed!

16. 16
RP Operational Quantities - ICRU
Dose Equivalent, H
H = Q * D (Sv)
Where: D = Absorbed Dose
Q = Quality Factor, function of L∞ (LET)
Where: DL is the distribution
of D in L for the charged
particles contributing to D
At a point in tissue:

17. 17
H*(10) and HP (10) – photons > 12 keV and neutrons
HP (0.07) – α and β particles and doses to extremities
Ω in RP usually not specified. Instead,
Maximum H’(0.07, Ω) is obtained
by rotating meter seeking maximum reading
Hp (3) – lens of the eyes

18. 18
Conversion Coefficients
for External Exposure
(ICRU 57, 1998)
For Photons, Neutrons, Electrons

19. 19
System of Quantities for Radiological Protection
Absorbed dose, D
Equivalent dose, HT, in an
organ or tissue T
Effective dose, E
Committed doses,
HT (τ) and E(τ)
Collective effective dose, S
For external exposure
Dose quantities for
area monitoring and
individual monitoring
For internal exposure
Activity quantities in
combination with
biokinetic models and
computations
Operational
Quantities
Dose Quantities
defined in the body

20. 20
2003
2013

21. Are the radiation protection (RP)
dosimetry terms applicable to
patient exposures in diagnostic
medical imaging and
interventional radiology
procedures?
21

22. 22
RP Dosimetric Quantities and Units
▲ Retrospective dose assessments
▲ Epidemiological studies without careful
consideration of the uncertainties and
limitations of the models and values used
▲ Estimation of specific individual human
exposures and risk
E is calculated averaging
gender, age and individual sensitivity
Caveats
Effective Dose should not be used for

23. 23
RP Dosimetric Quantities and Units
Caveats
Dose to Individuals
Absorbed doses to organs or tissues should be
used with the most appropriate biokinetic
parameters, biological effectiveness of the
ionizing radiation and risk factor data, taking
into consideration the associated uncertainties.
Medical exposures fall in this category!

24. NCRP 160
(2009)
UNSCEAR 2008
(2010)

25. Effective Doses from Radiation Sources
in the US (UNSCEAR 2008 & NCRP 160)
25

26. 26
Trends in average effective doses resulting from selected
diagnostic medical examinations (UNSCEAR 2008)
Examination
Average effective dose per examination (mSv)
Health care level I
1970–1979 1980–1990 1991–1996 1997–2007
Chest
radiography 0.25 0.14 0.14 0.07
Abdomen X-ray 1.9 1.1 0.53 0.82
Mammography 1.8 1 0.51 0.26
CT scan 1.3 4.4 8.8 7.4
Angiography 9.2 6.8 12 9.3

27. 0
5
10
15
20
25
30
35
40
45
50
OrganDose(mGy)
Bone Marrow Breast Ovaries Heart Skin Thyroid
Sestamibi Rest/Stress
Dx Coronary Angiogram
CT Coronary Angio
CT Coronary Calcium
Chest X-ray
Cynthia McCollough, Ph.D.
Exam
Bone
Marrow Breast Ovaries Heart Skin Thyroid
Sestamibi Rest/Stress 9.40 6.40 15.40 13.10 6.0 8.50
Dx Coronary Angiogram 6.10 3.18 0.09 23.70 450.0 2.16
CT Coronary Angio 0.08 7.60 0.08 47.30 5.3 1.10
CT Coronary Calcium 0.02 2.40 0.02 14.74 1.6 0.30
Chest X-ray 0.05 0.15 0.00 0.23 0.5 0.06
Organ Dose (mGy)

28. Effective Dose vs Organ Doses
in Medical Exposures
Effective Dose is an adequate parameter to
intercompare doses from different radiological
techniques in order to optimize protection
However, to assess risks it is necessary to
determine organ doses
28

29. 29

30. 30
Increasing levels of uncertainty at each step of the
dose and risk estimation process using effective dose
Durand et al. 2012

31. 31
BEIR VII, 2005

32. 32

33. 33

34. 34
F Mettler 2012

35. 35
Conclusion
For an assessment of the risk due to
induction of stochastic and deterministic
effects by medical x-ray imaging detailed
knowledge is required of organ doses,
absorbed-dose distribution, and the age
and gender of the group of patients
concerned, rather than effective dose.
ICRU 74

36. 36J Harrison 2013

37. 37J Harrison 2013

38. Dosimetric and Geometric Quantities for
Determination of Patient Dose (ICRU 74, 2005)
38
PKA represents the
integral of air kerma
across the entire x-ray
beam emitted from the
x-ray tube.
Its units are Gy cm2
Tolerance ± 35 % for
> 2.5 Gy cm2
The accuracy of the
display can be checked
directly or indirectly

39. 39
ICRU
74
DLP
CTDI ICRU 87 2012

40. Ka,r (mGy)
“Interventional reference point”, “Cumulative reference point air
kerma”, “Cumulative dose”, “Patient entrance reference point”
40IEC 60601-2-43, 2000 & NCRP 168, 2010
The accuracy of the Ka,r display is
checked with an ion chamber
Tolerance ± 35 % for ≻ 100
mGy
Ka,r (mGy)
Ka,r approximates Ka,e for
adult patients undergoing
cardiac interventions, but
overestimates it for patients in
cerebrovascular interventions.

41. 41
Protection Dosimetry
▲ Kai, Kae, PKA
▲ Maximum (Peak) Organ Dose
• Skin
• Eye Lens
▲ Stochastic Effects
▲ Deterministic Effects
Patient Follow-up may be needed in Interventional Radiology
These terms are the ones mostly used in Diagnostic Reference Levels

42. 42
Radiation
Measurements
In air
In/On Phantom
On Patient
Radiation
Instrumentation
Ion Chamber
Film: Silver Halide
and Radiochromic
Diodes
TLD, OSL

43. 4343
Determination of Ka,e
Ka,e
Ka,i
HJ Khoury, 2009 43
DIRECT INDIRECT
TLDs on patient skin X Ray tube output
Imaging parameters

44. 444444
Radiography

45. 45
PKA
Ka,i
HJ Khoury, 2009
Determination of PKA
DIRECT INDIRECT
X Ray tube output
Imaging parameters
Rad area
Removable
KAP meter
on collimator
exit
KAP (DAP)
Display on
control

46. 46
2013

47. 47
DirectIndirect
JA Seibert 2007

48. 48
High pixel electronic noise can be reduced by
incorporating a solid state avalanche layer of
a-Se over the TFT array, which amplifies the
signal (HARP)
Summary of Digital Detectors
for Radiography / Fluoroscopy
JR Scheuermann, 2018JA Seibert, 2018

49. CR and DR systems assess the recorded signal through
histogram analysis
 Tests with defined beam conditions are used to verify
that correct indicators are being reported
 Recommended exposure indicator ranges are used by
technologists to check each radiographic exposure
JA Seibert 2018
Exposure Indicators

50. Region to assess signal indicator
Systems vary in the
region used to assess the
signal for an image.
Full Image
Regular regions
Corresponding
histograms JA Seibert 2018

51. Region to assess signal indicator
IEC 62494-1
 Gray histogram for the entire image
 Black histogram for the anatomic region
(relevant region)
JA Seibert 2018

52. Computation of an exposure indicator
Median value of the signal values determined in the histogram
of the relevant image region
Manufacturers have proprietary methods
 Algorithms, values, and calibration methods are widely
different, leading to confusion amongst users
 Inappropriate image segmentation can produce inaccuracies
and incorrect feedback values
JA Seibert 2018

53. Manufacturer Symbol 5 Gy 10 Gy 20 Gy
Canon REX 50 100 200
IDC (ST = 200) F# -1 0 1
Philips (CR-Fuji) EI 200 100 50
Philips (DR) EI 200 400 800
Fuji S 400 200 100
Carestream EI 1700 2000 2300
Siemens EI 500 1000 2000
Approximate EI Values vs. Receptor Exposure
….. The need for a standard is clearly evident
Estimated receptor exposure
JA Seibert 2018
IEC 62494-1

54. Calibration of Radiography EI value
Fuji – CR & DR
 Follow manufacturer documentation
 Measure incident AK
 Compare to indicated value / 100
JA Seibert 2018

55. Deviation Index (DI)
Exposure Indices
𝐷𝐼 = 10 × 𝑙𝑜𝑔10
𝐸𝐼
𝐸𝐼 𝑇(𝑏. 𝑣)
 EIT is a target index value that is to be determined for each body
part b, view , procedure type, and clinical site
 When EI equals EIT, DI = 0
DI = +3.0 for 2x target exposure
DI = -3.0 for ½x target exposure
± 1 is one step on a standard generator mAs
control or AEC compensation (ISO R5 scale)
JA Seibert 2018

56. Target Exposure Index - EIT
 EIT depends on detector type, examination type,
diagnostic question and other parameters
 Establishing EIT values requires feedback from
technologists and radiologists working with MP
 EIT values are (must be) provided as a data base in the
digital imaging system
 Be aware that systems have default values that might
be inappropriate – Must review all values & protocols!
JA Seibert 2018

57. Target exposure index, EIT
 Examples:
 CR adult PA chest, desired S#: EIT = 700
 CR pediatric chest EIT = 500
 Noting the efficiency of CR is ~½ that of DR, the EIT for DR devices
are adjusted accordingly
 DR adult chest EIT = 350
 DR pediatric chest EIT = 250
 Extremities: higher EIT
 Large patients: higher EIT ??
JA Seibert 2018

58. Acquisition technique differences with CR and DR
 A function of detector detective quantum efficiency
JA Seibert 2018

59. Caveats
 The EI does not describe patient dose
 EI is derived from detector signal (dose at the detector)
 Best indicator for patient dose is PKA (mGy-cm2)
 The EI is not a dose measurement tool
 Dose calibration only valid at one radiation quality
 Same EI obtained on different digital systems might not
have similar image quality
 Influence of detector DQE, scattered radiation, beam quality
JA Seibert 2018

60. Why is incident detector exposure index
(EI) important?
• Is proportional to the image SNR (for given DQE)
Signal to Noise Ratio “image quality”
• Is indirectly related to patient exposure
• Is not linked with image appearance as with screen-
film receptors
• Assists the technologist in identifying appropriate
“equivalent speed” and therefore SNR
JA Seibert 2010 60

61. 61
JA Seibert 2018

62. Fluoroscopy
Image Intensifier
or
Flat Panel Detector

63. 63
https://slideplayer.com/slide/1379353/8/images/23/Irrespective+of+the+image+receptor+system%2C+i.+e.jpg
Air Kerma Rate Measurements

64. The KAP meter
should be calibrated
for all the fluoro and
cine techniques used
clinically
64

65. 65

66. 66

67. Fluoroscopic Equipment Performance Evaluation (ACR 2016)
67

68. ▲ Kerma Rate vs Phantom Thickness
• Variables
o Tube Potential (kV)
o Tube Current (mA)
o Pulse Width (ms)
o Cu filter (new angio systems)
▲ Maximum Patient Surface Kerma Rate
68
Automatic Brightness Control
Check: Fluoro and Cine

69. 69
Flat Panel – Filtration Options

70. 70
Variation of air kerma rate, tube potential, tube current and
Cu filtration vs water-equivalent phantom - FLUOROSCOPY
N. Lunelli, 2012
Flat Panel

71. 71
IAEA NAHU No. 24
DOSIMETRY IN
DIAGNOSTIC
RADIOLOGY FOR
PAEDIATRIC
PATIENTS
2013

72. Fluoroscopic Equipment Performance Evaluation (ACR 2016) - cont
72

73. IAEA
73
73
In-Room Monitor Displays
(Siemens System)
73PKA Ka,r

74. 74
J Boone 2013
CT Dosimetry

75. 75
CT Dosimetry
Measurements can be done with the ion chamber in air at the
isocenter or in a CT (FDA) phantom using appropriate corrections

76. BSS
MSAD
I
D z dz
N I
N I




1
2
2
( )
U .S. C D R H
MSAD
I
D z dzN I
I
I




1
2
2
, ( ) CTDI
N T
D z dz
T
T




1
7
7
( )
EC
CTDI
T
D z dz
 
 

1
( ) DLP CTDI T NW
i
 
CTDI CTDI CTDIW cm c cm p 






1
3
2
310 10, ,
CT Dosimetry Before Helical CT

77. 77
AAPM TG 246, 2019

78. 78
Volume CTDIW (CTDIvol)
CTDIvol = CTDIW • N • T / I
where:
I = the table increment per axial scan, or the table increment
per rotation of the x-ray tube in a helical scan. In helical CT,
the term pitch (P) is defined as the ratio of the table
increment per tube rotation to the nominal (total) width of the
radiation beam. Hence,
Pitch = I / (N • T) and CTDIvol = CTDIW /pitch
CTDIvol is the parameter that best estimates the average dose
at a point with the scan volume for a particular scan protocol.
Dose Length Product (DLP)
DLP = CTDIvol (mGy) • scan length (cm)
CT Dosimetry After Helical CT

79. 79
Axial scan
Helical scan

80. Current dose reporting methods
▲ Computed Tomography Dose Index, CTDIvol (mGy)
• Provides dose comparison for scan protocols or scanners
• Useful for obtaining “benchmark” data
• Not good for estimating patient dose
▲ Dose Length Product (DLP): CTDIvol × scan length
• Volume dose delivered to the patient (mGy-cm)
• In limited scan range, DLP is less useful, e.g., density-time
studies such as brain perfusion
▲ Effective Dose: a crude measure of whole body dose
• Conversion factors are generated from Monte Carlo transport
methods in standardized phantoms
• Not intended for individual patient dose metrics
• Estimated from DLP
Adapted from JA Seibert 2011

81. 81
J Boone 2013

82. 82
J Boone 2013

83. Dose estimate conversion factors for body size
JA Seibert 2011
2011

84. Family of physical phantoms
Cynthia McCollough, Mayo Clinic
standard phantoms
Tom Toth & Keith Strauss
Monte Carlo phantoms (1 – 50 cm)
John M. Boone, UC Davis
Anthropomorphic Monte Carlo phantoms
Mike McNitt-Gray, UCLA
AAPM Task Group 204 – Size-Specific CT Dose
JA Seibert 2011

85. effective diameter
Relativedose
CTDIvol
JA Seibert 2011

86. lateral dimension
AP dimension
Effective
diameter
same
area
Determine effective diameter
JA Seibert 2011

87. patient size (effective diameter)
dose
CTDIvol
32 cm PMMA
normalization point
Normalize scanner output to CTDIvol
JA Seibert 2011

88. conversionfactor
CTDIvol
32 cm
after normalization
1.0
patient size
Normalized output
JA Seibert 2011

89. ConversionFactor
JA Seibert 2011

90. 90J Boone 2013

92. 92
J Boone 2011

93. 93
J Boone 2013

94. 94
ICRU Method
J Boone 2011

95. 95
beam profileJ Boone 2011

96. 96J Boone 2011

97. 97
J Boone 2013

98. CT Dose by Convolution AAPM TG 246, 2019

99. 99AAPM TG 246, 2019

100. 100
Protection Dosimetry
▲ Kai, Kae, PKA
▲ Maximum (Peak) Organ Dose
• Skin
• Eye Lens
▲ Stochastic Effects
▲ Deterministic Effects
Patient Follow-up may be needed in Interventional Radiology
These terms are used for Diagnostic Refence Levels

101. 101
To Optimize Radiation Protection
The best way is to establish
Diagnostic Reference Levels (DRLs)
… derived from
the data from wide
scale quality
surveys … for the
most frequent
examinations in
diagnostic
radiology...
UK 2000
75% Percentile

102. J. L. Heron 2013

103. D Hart et al. 2012

104. 104
www.eu-alara.net/index.php/surveys-mainmenu-53/36-ean-surveys/156-drls.html www.hc-
sc.gc.ca/ewh-semt/pubs/radiation/safety-code_35-securite/index-eng.php
NCRP 172
C J Martin et al. Approaches to aspects of optimisation of protection in diagnostic radiology
in six continents. IOP PUBLISHING, J. Radiol. Prot. Accepted June 2013

105. 105
Achievable dose
A dose which serves as a
goal for optimization
efforts. This dose is
achievable by standard
techniques and
technologies in
widespread use, while
maintaining clinical image
quality adequate for the
diagnostic purpose. The
achievable dose is typically
set at the median value of
the dose distribution.
2012

106. NCRP recommended DRLs and
achievable doses (mGy) -
Radiography
106

107. NCRP recommended DRLs and achievable
doses - Fluoro
107
mGy

108. NCRP recommended DRLs and achievable
doses (mGy) - CT
108

109. 109
Cody & McCullough 2011

110. 110
McNitt-Gray, 2014

111. DRL Requirements – BSS
A review is conducted to determine whether the
optimization of protection and safety for patients
is adequate, or whether corrective action is
required if, for a given radiological procedure:
i. typical doses or activities exceed the relevant
diagnostic reference level; or
ii. typical doses or activities fall substantially
below the relevant diagnostic reference level
and the exposures do not provide useful
diagnostic information or do not yield the
expected medical benefit to the patient. 111

112. Patient Organ Doses
▲ Medical Imaging
• Radiography
• Mammography
• Fluoroscopy
• CT
▲ Interventional Radiology
112

113. Organ Dose Determination
▲ Direct Radiation Measurements
▲ Table Look Up
▲ Monte Carlo Simulations using Patient and Radiation
Transport Modeling
• Mathematical phantoms
• Special features of the active bone marrow
• Voxel phantoms
• Anthropometric phantoms
▲ Calculations from Imaging System Dose Metrics
• and/or „Dose Report‟
▲ DICOM Standards
113

114. Threshold doses for approximately 1% morbidity incidence
114
ICRP 118 , 2012

115. 115
Trends in average effective doses resulting from selected
diagnostic medical examinations (UNSCEAR 2008)
Examination
Average effective dose per examination (mSv)
Health care level I
1970–1979 1980–1990 1991–1996 1997–2007
Chest
radiography 0.25 0.14 0.14 0.07
Abdomen X-ray 1.9 1.1 0.53 0.82
Mammography 1.8 1 0.51 0.26
CT scan 1.3 4.4 8.8 7.4
Angiography 9.2 6.8 12 9.3

116. Effective Dose vs Organ Doses
in Medical Exposures (ICRU, ICRP)
Effective Dose is an adequate parameter to
intercompare doses from different radiological
techniques in order to optimize protection
However, to assess risks
it is necessary to determine organ doses
116

117. 117
The Essentials of Medical Imaging 3d Ed, 2012

118. Organ Doses
from Ka,i
(“Exposure”)
-
Radiography
118
http://www.fda.gov/cdrh/ohip/organdose.html

119. 119DRMelo 2016
Organ Doses from Diagnostic Radiography
DR Melo 2016

120. 120
www.grupodoin.com

121. 121
Patient Dose - Mammography
 Kerma in Air
 Reproducibility and Linearity
 Average Glandular Dose
 Half Value Layer
 Thickness of Compressed Breast
 Estimation of Breast Tissue Composition
(Dg)av = (DgN)av * Ka,i

122. 122L Rothenberg 2009

123. Organ Doses from Ka,i (“Exposure”) -
Fluoroscopy
123
http://www.fda.gov/cdrh/ohip/organdose.html

124. 124
Thermoluminiscent dosimeters being placed on patient
undergoing fluoroscopic examination
to measure dose
NRPB

125. 125
Skin Dose Measurements - TLD
SILVA et al., 2009
TLDs placed directly
on a patient’s back
Matrix of TLDs placed on a sheet
under a patient undergoing a
cardiac interventional procedure

126. 126
Placement of Radiosensitive Indicators
Skin Dose Assessment - Neuroembolization
Suzuki AJNR 29 Jun-Jul 2008

127. 127
Matrix of Photoluminiscent Dosimeters
Moritake et al, 2008Cerebral embolization

128. A and B, Nonoptimal lateral projection without and with subtraction where the left eye is irradiated.
R.M. Sánchez et al. AJNR Am J Neuroradiol 2016;37:402-407
©2016 by American Society of Neuroradiology

129. Position of the OSL dosimeters on patient eyes.
R.M. Sánchez et al. AJNR Am J Neuroradiol 2016;37:402-407
©2016 by American Society of Neuroradiology

130. Adult patient doses received during interventional cerebral
procedures performed in Recife
Dosimeters
: TLD-100

131. 131
In Interventional Exams, Maximum Skin Dose and PKA can be
Determined with Film: Silver Halide and Radiochromic
Film Position (Cardio)

132. Radiochromic Films (Neuro)
132

133. 133
Curvas de Calibração
com scanner e densitômetros
Silva et al., 2009

134. 134
Skin Dose (DT) Calculations
Ka,e = Ka,r ftable (SRD/SSD)2 BSF
DT = Ka,e ( ) ≃ Ka,e 1.06
Ka,e: Entrance surface Air Kerma
Ka,r: Air Kerma at Reference Point
ftable: Table and pad attenuation
factor
SRD: Source-reference distance
SSD: Source-entrance surface
µen,a / ρ: Air
mean energy
absorption
coefficient
µen,T / ρ: Skin
mean energy
absorption
coefficient
µen,T
ρ
µen,a
ρ

135. 135
Coronary Angioplasty Results
Loc Dose (Gy)
A 0.43
B 2.27
C 3.92
D 0.57
E 3.56
F 3.97
G 2.28
H 1.39
I 0.41
J 0.9
L 1.39
M 1.22
N 0.28
SILVA et al., 2009

136. 136
Maximum Skin Dose - Results
Neuroradiology Interventions
N. Lunelli, 2012
Reaction in the patient –
MSD=8030 mGy

137. Patient Exposure Form
JA Seibert 2018

138. Patient Exposure Assessment
JA Seibert 2018

139. CT Dose Reporting…… HOW?
▲ Scanner dose measurement indicators: CTDIvol & DLP
▲ How to get the CT provided data?
• Dose summary page and Optical Character Recognition
• Open-source or commercial “dose gathering” products
Image
DOSE
Summary
page
Adapted from JA Seibert 2011

140. http://www.impactscan.org/ctdosimetry.htm
CT
Dosimetry
140

142. Radimetrics eXposure: Dose calculation engine
• Receives CT study
• Extracts patient dose
metric information
• Pushes dose metrics
to radiology report
• Maintains database
• Provides dashboards
142
JA Seibert 2013

143. Summary
▲ Neither CTDIvol nor DLP should be used to
estimate effective dose or potential cancer risk
for any individual patient
▲ Estimation of organ dose and use of age- and
gender-specific risk coefficients are necessary to
determine individual risk
▲ Investigations using Monte Carlo photon
transport within CT scan data, identification /
segmentation of organs, and tabulating organ
doses are a start to individual, customized dose
measurements
JA Seibert 2011

144. Radiation Dose to Pediatric Patients
of Different Body Stature from CT
Exams Using Deformable Realistic
Phantoms
HPS, 59th Annual Meeting, Baltimore, MD, 2014
Stabin, M. et al. Vanderbilt University Nashville, TN, USA
• Using the Geant4 Monte Carlo toolkit, created a
radiation transport code to simulate patients
undergoing exams on a CT scanner similar to that
at Vanderbilt University Children's Hospital.
• Used measured values of dose in a physical
phantom to calibrate the simulated output from the
Geant CT source.

145. Adults
15-yr-olds
10-yr-olds
5-yr-olds
1-yr-olds
12-yr-olds
7 and 8-yr-olds
Stabin et al., 2014

146. Segmented organs in 9-year-old female patient
Stabin et al., 2014

147. Organ Name Dose (mGy)
Body 10.7
Esophagus 11.2
Liver 13.1
Gall bladder 11.7
Stomach 12.5
Spleen 10.9
Heart 13.6
Pancreas 12.1
Bladder 11.9
Small intestine 12.2
Uterus 10.8
Skin 10.1
Thyroid 9.0
Lungs 12.7
Kidneys 13.5
Adrenals 12.8
Ovaries 10.1
Skeleton 22.6
Effective Dose (ICRP 103) (mSv) 13.0
Dose values for a selection of organs for a 9 year-old female patient.
Stabin et al., 2014

148. 9
10
11
12
13
14
15
16
17
0 2 4 6 8 10 12 14 16
Dose(mGyormSv)
Age (yr)
50th Percentiles, Age
esophagus (7) lungs (12)
liver (13) gall bladder (14)
kidneys (15) adrenals (16)
stomach (17) spleen (18)
ED
10
10,5
11
11,5
12
12,5
13
13,5
0 10 20 30 40 50 60 70 80 90 100
Dose(mGyormSv)
Percentile
10-yr-olds, Percentiles
esophagus (7) lungs (12)
liver (13) gall bladder (14)
kidneys (15) adrenals (16)
stomach (17) spleen (18)
ED
Stabin et al., 2014

149. Conclusions
• As with internal dosimetry, using deformable
NURBS phantoms greatly facilitates the
development of phantom-based dosimetry.
• We have used a Geant4-based CT dosimetry
program to calculate doses to a wide range of
patient and phantom models.
• These data can be used to produce patient-
individualized organ and effective doses that
are far better than CT scanner reported doses.
Stabin et al., 2014

150. So, what should be used for
patient risk?
▲ Using Monte Carlo photon transport on organ-segmented CT scan data of
patients
▲ Estimation of specific individual’s organ doses
▲ Accumulating organ dose for each instance
▲ Applying age- and sex-specific risk coefficients
. . . . . .
▲ This is a large undertaking, and will take time for implementation
JA Seibert 2011

151. organ dosesCT scan & patient
parameters
Monte Carlo modeling should be
the basis for patient CT dosimetry
Monte
Carlo
JA Seibert 2011

152. 152
AAPM TG 246, 2019

153. 153
AAPM TG 246, 2019

154. DICOM Standards
154
▲ DICOM Header
▲ DICOM Services
• e.g. modality performance procedure step
(MPPS)
▲ Radiation Dose Structured Report (RDSR)
▲ Patient-RDSR (P-RDSR)

155. 155SILVA et al., 2009

156. 156
Standard dose
report
E. Vañó, 2018
DICOM RDSR

157. DICOM RDSR from Philips (rooms 3-4 San Carlos Hospital)
157
Radiation Dose Structured Report 67: pages, 30 runs of fluoro + 10 runs of cine; all
technical, dose and geometry details included (part 3 Fluoro example)
Irradiation Event X-Ray Data
Acquisition Plane : Single Plane
DateTime Started : 2013-08-12, 12:51:07.958
Irradiation Event Type : Fluoroscopy
Reference Point Definition : 15cm below BeamIsocenter
Irradiation Event UID :
1.3.46.670589.28.3711502481496.20130812125107317.
1
Dose Area Product = 1.8E-06 Gy.m2
Dose (RP) = 0.00017185537709Gy
Positioner Primary Angle = 1.6 °
Positioner Secondary Angle = -0.1°
X-Ray Filters
X-Ray Filter Type : Strip filter
X-Ray Filter Material : Copper or Copper compound
X-Ray Filter Thickness Minimum = 0.9 mm
X-Ray Filter Thickness Maximum = 0.9 mm
X-Ray Filters
X-Ray Filter Type : Strip filter
X-Ray Filter Material : Aluminum or Aluminum
compound
X-Ray Filter Thickness Minimum = 1 mm
X-Ray Filter Thickness Maximum = 1 mm
Fluoro Mode : Pulsed
Pulse Rate = 7.5 pulse/s
Number of Pulses = 11no units
X-Ray Tube Current = 120 mA
Distance Source to Isocenter = 765 mm
KVP = 97.97 kV
Pulse Width = 9.2 ms
Irradiation Duration = 1.466 s
Patient Table Relationship : headfirst
Patient Orientation : recumbent
Patient Orientation Modifier : supine
Target Region : Chest
Number of Frames = 11no units
SubImages per Frame = 1 no units
Wedges and Shutters
Bottom Shutter = 82.5mm
Left Shutter = 82.5mm
Right Shutter = 82.5mm
Top Shutter = 82.5mm
Beam Position
Longitudinal Beam Position = 1562mm
Beam Angle = 0 °
Table Height Position = 920 mm
E. Vañó, 2018

158. DICOM RDSR from Philips (rooms 3-4 San Carlos Hospital)
158
Radiation Dose Structured Report 67: pages, 30 runs of fluoro + 10 runs of cine; all technical,
dose and geometry details included (part 4 cine example)
Irradiation Event X-Ray Data (series 1 manual
note)
Acquisition Plane : Single Plane
DateTime Started : 2013-08-12, 12:52:31.098
Irradiation Event Type : Stationary Acquisition
Reference Point Definition : 15cm below
BeamIsocenter
Acquired Image : Image X-Ray Angiographic
Image Storage (SOP Instance UID: )
Irradiation Event UID :
1.3.46.670589.28.3711502481496.201308121252
30407.1
Dose Area Product = 0.0004013 Gy.m2
Dose (RP) = 0.06913345231013Gy
Positioner Primary Angle = 11.8°
Positioner Secondary Angle = -0.1°
X-Ray Filters
X-Ray Filter Type : No Filter
X-Ray Tube Current = 865.6 mA
Distance Source to Isocenter = 765 mm
KVP = 82.57 kV
Pulse Width = 7.3 ms
Distance Source to Detector = 1068mm
Irradiation Duration = 5.2 s
Patient Table Relationship : headfirst
Patient Orientation : recumbent
Patient Orientation Modifier : supine
Target Region : Chest
Number of Frames = 78no units
SubImages per Frame = 1 no units
Wedges and Shutters
Bottom Shutter = 67.5mm
Left Shutter = 67mm
Right Shutter = 67mm
Top Shutter = 67.5mm
Beam Position
Longitudinal Beam Position = 1562mm
Beam Angle = 0 °
Table Height Position = 920 mm
E. Vañó, 2018

159. Study level – summary of a procedure II
Sample of the graphical representation of
DICOM RDSR data of a neuro-
interventional study carried out in a bi-
plane cath-lab, that allows to see the
different fluoroscopy and acquisition
modes used during the procedure.
J.M. Fernandez-Soto et al., 2016

160. Sample of a radiochromic film image
placed at the patient back in an
interventional cardiology procedure
(right) and two types of dose maps
obtained from the DICOM RDSR for the
same procedure. This also allows the
estimation of the maximum dose at the
skin entrance.
Skin Dose Maps
(JM Fernandez-Soto et al., 2016)

161. RDSR - Radiography

162. 162

163. Supplement 191 Patient Dose SR
• Current Radiation Dose SR contains only information about the x-ray system or information
the x-ray system can determine, e.g.:
• radiation output, geometry, x-ray source, detector system, etc.
• Estimation of patient/organ dose requires knowledge of:
• Radiation beam characteristics that interact with patient
• Models of the patient/organs
• Models of radiation interaction within the patient
• Methods to do patient dose estimations are being developed and improved continuously
• storage of these estimations in a different object would allow more versatile utilization of
the data
163D. Pelc, 2016

164. 164
RDSR
IOD
- X-Ray exposure techniques
- Table, Gantry Angle, Beam
Geometry, collimation, …
- Dose measures: CTDI, DAP, ...
X-Ray
Equipment
Modality
IOD
Patient Dose Determination: Data Flow Requirements
Organ Dose
Reporter
System
Modality Frame of Reference
(FOR)
Signifies part of Supplement 191 Patient RDSR
D. Pelc, 2016

165. 165Signifies part of Supplement 191 Patient RDSR
RDSR
IOD
- X-Ray exposure techniques
- Table, Gantry Angle, Beam
Geometry, collimation, …
- Dose measures: CTDI, DAP, ...
X-Ray
Equipment
Modality
IOD
Organ Dose
Reporter
System
Patient Model
Registration
IOD
Equipment Information
- Table dimension
- Attenuating material, …
Modality Frame of Reference
(FOR)
Patient Model
FOR
Patient Dose Determination: Data Flow Requirements
D. Pelc, 2016

166. 166Signifies part of Supplement 191 Patient RDSR
RDSR
IOD
- X-Ray exposure techniques
- Table, Gantry Angle, Beam
Geometry, collimation, …
- Dose measure: CTDI, DAP, ...
Registration
IOD
X-Ray
Equipment
Modality
IOD
Patient Model
Organ Dose
Reporter
System
Patient
Dose SR
Calculated data for
documentation and reference
to images and RDSR’s
Patient Dose Determination: Data Flow Requirements
Equipment Information
- Table dimension
- Attenuating material, …
Patient Dose 2D view/map
(e.g. iso-dose map)
Patient Dose Surface
3D map/view
Modality Frame of Reference
(FOR)
Patient Model
FOR
D. Pelc, 2016

167. Final Considerations: What Matters Most?
▲ Patient organ doses will be useful for refining dose response
curves and carry out epidemiological studies
▲ Will determining patient doses allow us to estimate patient risk?
▲ Risk is population-based, it cannot be applied to a single
individual! Risk is a probability!!
▲ Do we need individualized dosimetry for radiation protection?
▲ If the goal is to protect the patient, can we just use diagnostic
reference levels, which are usually machine parameters,
something much simpler to determine than organ doses?
▲ Can we report such parameters in the patient chart? Some
countries / states require it….

168. Agency
Regulatory Requirement
(ID: Individual Dose)
FDA &
NEMA
Kai limit for fluoroscopy. Dg limit for
mammography.
All new CT scanners to comply with the NEMA
XR-25 Dose Check Standard
State of
California
ID: CTDIvol and DLP included in each patient
record and transferred to PACS. Effective dose
limits for repeated exams unless approved by a
physician. All CT facilities accredited.
State of Texas
Kai limits for some radiography exams. Maintain
records for output of fluoroscopically-guided
interventions to include cumulative Ka,r or PKA.
ID for CT: Dose recording and reporting plus
skin dose determination. Recommends
establishing a “CT reference level” and patient
follow up when value is exceeded.
.

169. Agency Accreditation Requirements
The Joint
Commission
CT: CTDIvol and DLP or SSDE specific for
each exam, summarized by series or anatomic
area and retrievable. Review and analyze
values if they exceed expected dose index
ranges. Compare with external benchmarks.
Fluoro: Establish radiation exposure and skin
dose threshold levels. If exceeded, review
procedure and evaluate patient (>15 Gy =
Sentinel event). Ka,r or PKA documented in a
retrievable format.
Both: Evaluation of equipment performance
and imaging protocols.
American
College of
Radiology
Dg limit, CTDIvol limit for adult and pediatric
head and abdomen CT scans. DRLs
recommended.

170. Example from a California Patient CT Chart
This patient received a total of 1 exposure event(s) during this CT
examination. The CTDIvol and DLP radiation dose values for each exposure
are: Exposure: 1; Series: 2; Anatomy: Neck; Phantom: 32 cm; CTDIvol: 19;
DLP: 498 The dose indicators for CT are the volume Computed
Tomography (CT) Dose Index (CTDIvol) and the Dose Length Product
(DLP), and are measured in units of mGy and mGy-cm, respectively. These
indicators are not patient dose, but values generated from the CT scanner
acquisition factors. The report includes radiation exposure data for
exposures received during this examination. If multiple reports are
produced from this examination, the exposure data is duplicated in each
report. The exposure data reported is indicative, but not determinative, of
the radiation dose received by this patient.

171. 171Bushberg 2014