Seminario Web número 20 a cargo de la Dra. Cari Borras SW organizado por la Red Latinoamericana de Protección Radiológica del Paciente - Red LAPRAM

1. 1
Adjunct Assistant Professor (Radiology)
The George Washington University School of Medicine and Health Sciences
Cari Borrás, D.Sc., FACR, FAAPM, FIOMP, FHPS
Washington DC, USA
Consultora, Física Radiológica y Servicios de Salud
Chair, AAPM International Educational Activities Committee
Optimizar la Protección Radiológica del Paciente
o Inferir Riesgos de Radiación
en Procedimientos con Rayos X:
¿Qué es más importante?

2. Índice de Temas
▲ Aspectos Básicos de Radiobiología
▲ Dosimetría en Protección Radiológica
▲ Dosimetría en Radiología
• Indicadores de Dosis (Términos Relacionados con el Equipo)
• Dosis en Órganos de Pacientes
o Mediciones
o Tablas de Consulta
o Simulaciones de Montecarlo
▲ Niveles de Referencia Diagnósticos
▲ Estándares DICOM: RDSR y P-RDSR
2

3. Efectos Biológicos de las Radiaciones Ionizantes
3

4. Threshold dose (TD)
1%
ICRP 41, 60, 103, and 118
TD
ICRP Symposium J. Hendry 2011
Reacciones
Tisulares Nocivas
(Efectos
Deterministas)
Efectos de la radiación
en poblaciones de células
irradiadas. En general,
existe un umbral de dosis
por encima del cual la
gravedad del efecto
aumenta con la dosis; se
miden en gray (Gy).
4

5. Threshold doses for approximately 1% morbidity incidence
5
ICRP 118 , 2012

6. 6
Reacciones Tisulares Nocivas
(Efectos Deterministas)
Efectos de la radiación en poblaciones de células
irradiadas. En general, existe un umbral de dosis por
encima del cual la gravedad del efecto aumenta con la
dosis; se miden en gray (Gy).
Efectos Estocásticos
Efectos de la radiación incidente en una célula que se
muta a causa de la radiación. La probabilidad de
ocurrencia es proporcional a la dosis pero la gravedad es
independiente de la dosis; se miden en sievert (Sv).

7. 7
ICRP Detriment-Adjusted Nominal Risk
Coefficient for Cancer
(10-2 Sv-1 – Percent per Sievert)
Exposed
Population
ICRP 103 (2007)
Cancer
Induction
ICRP 60 (1991)
Cancer Fatality
Whole 5.5 6.0
Adult 4.1 4.8

8. 8
BEIR VII, 2005

9. 9

10. 10

11. 11
F Mettler 2012

12. ICRP
Sv
Gy
Dosimetría
en
Protección
Radiológica

13. ¿Dosis Efectiva para Exposiciones Médicas?
La Dosis Efectiva es un parámetro adecuado para
comparar dosis en grupos de pacientes con el objetivo
de optimizar la protección radiológica
13
Se calcula promediando
el sexo, la edad y la radiosensibilidad individual
y se aplica a cualquier tipo de cáncer

14. 14
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

15. 15M. Mahesh, 2019

16. 16
▲ Evaluaciones de dosis retrospectivas
▲ Estudios epidemiológicos sin una consideración
cuidadosa de las incertidumbres y limitaciones de
los modelos y valores usados
▲ Estimación de exposiciones y riesgos de seres
humanos específicos
Advertencias (ICRU/ICRP)
La Dosis Efectiva no se debe usar para
¡Las exposiciones médicas entran en esta última categoría!

17. 17
Conclusión
Para una evaluación del riesgo debido a la inducción de
efectos estocásticos y deterministas por imágenes médicas
con rayos X, se requiere un conocimiento detallado de las
dosis a órganos, la distribución de dosis absorbida y la
edad y el sexo del grupo de pacientes involucrados, en
lugar de la dosis efectiva.
ICRU 74

18. 18

19. 19
Increasing levels of uncertainty at each step of the
dose and risk estimation process using effective dose
Durand et al. 2012

20. 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)

21. 21
ICRU
74,
2005
DLP
CTDI ICRU 87, 2012
Dosimetría
en
Radiología

22. Dosimetric and Geometric Quantities for
Determination of Patient Dose (ICRU 74, 2005)
22
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

23. Ka,r (mGy)
“Interventional reference point”, “Cumulative reference point air
kerma”, “Cumulative dose”, “Patient entrance reference point”
23IEC 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.

24. IAEA
24
24
In-Room Monitor Displays
(Siemens System)
24PKA Ka,r

25. 25
Resumen - Dosimetría
▲ Kai, Kae, PKA
▲ Dosis Máxima (Pico) a un Órgano
• Piel
• Cristalino
▲ Efectos Estocásticos
▲ Efectos Deterministas
En Radiología Intervencionista puede ser necesario dar
seguimiento clínico al paciente
Estos términos son los mas usados en los Niveles de Referencia Diagnósticos

26. 26
Mediciones
En aire
Sobre / Dentro del
Maniquí
Sobre el Paciente
Instrumentación
Cámara de Ionización
Película: Haluro de
Plata y Radiocrómica
Diodos
TLD, OSL
Dosimetría
Práctica en
Radiología

27. Cámaras de Ionización
27
Mediciones de
radiación incidente,
retrodispersada y
de PKA

28. 28
Determination of Ka,e
Ka,e
Ka,i
HJ Khoury, 2009
DIRECT INDIRECT
TLDs on patient skin X Ray tube output
Imaging parameters

29. 292929
Radiography

30. 30
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

31. 31
2013

32. 32
DirectIndirect
JA Seibert 2007

33. Region to assess
signal indicator
Systems vary in the
region used to assess the
signal for an image.
Full Image
Regular regions
Corresponding
histogramsJA Seibert 2018
Exposure Indicators
CR and DR systems assess the recorded
signal through histogram analysis
33

34. 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 34

35. 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
35

36. 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
36

37. Acquisition technique differences with CR and DR
 A function of detector detective quantum efficiency
JA Seibert 2018 37

38. Organ Doses
from Ka,i
(“Exposure”)
-
Radiography
38
http://www.fda.gov/cdrh/ohip/organdose.html

39. 39DRMelo 2016
Organ Doses from Diagnostic Radiography
DR Melo 2016

40. 40
www.grupodoin.com

41. 41
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

42. 42L Rothenberg 2009

43. Fluoroscopy
Image Intensifier
or
Flat Panel Detector

44. 44
https://slideplayer.com/slide/1379353/8/images/23/Irrespective+of+the+image+receptor+system%2C+i.+e.jpg
Air Kerma Rate Measurements

45. 45

46. ▲ 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
46
Automatic Exposure Control
Check: Fluoro and Cine

47. 47
Flat Panel – Filtration Options

48. 48
Variation of air kerma rate, tube potential, tube current and
Cu filtration vs water-equivalent phantom - FLUOROSCOPY
N. Lunelli, 2012
Flat Panel

49. 49
IAEA NAHU No. 24
DOSIMETRY IN
DIAGNOSTIC
RADIOLOGY FOR
PAEDIATRIC
PATIENTS
2013

50. Organ Doses from Ka,i (“Exposure”) -
Fluoroscopy
50
http://www.fda.gov/cdrh/ohip/organdose.html
1995

51. 51
Thermoluminiscent dosimeters being placed on a patient
undergoing a fluoroscopic examination
to measure dose
NRPB

52. 52
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

53. 53
Matrix of Photoluminiscent Dosimeters
Moritake et al, 2008Cerebral embolization

54. 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
54

55. 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 55

56. 56
In Interventional Exams, Maximum Skin Dose and PKA can be
Determined with Film: Silver Halide and Radiochromic
Film Position (Cardio)

57. Radiochromic Films (Neuro)
57
Curvas de Calibração
com scanner e densitômetros
Silva et al., 2009
N. Lunelli 2012

58. 58
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 distance
BSF: Back scatter factor
µen,a / ρ: Air
mean energy
absorption
coefficient
µen,T / ρ: Skin
mean energy
absorption
coefficient
µen,T
ρ
µen,a
ρ

59. 59
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

60. 60
Maximum Skin Dose - Results
Neuroradiology Interventions
N. Lunelli, 2012
Reaction in the patient –
MSD=8030 mGy

61. Patient Exposure Form
JA Seibert 2018 61

62. Patient Exposure Assessment
JA Seibert 2018 62

63. 63
J Boone 2013
CT Dosimetry
CTDI es la
integral del
perfil de dosis
de un corte de
TC a lo largo
del eje z,
normalizada al
espesor de la
sección
escaneada (T)

64. 64
CT Dosimetry
Measurements can be done with the ion chamber in air at the
isocenter or in a CT (FDA) phantom using appropriate corrections

65. 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
65

66. 66
Volume CTDIW (CTDIvol)
CTDIvol = CTDIW * N * T / I
Where: N = Nr. scans of thickness T
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, pitch (P) is the ratio of the table increment per tube rotation to
the nominal (total) width of the radiation beam (NT)
Hence, Pitch = I / (N • T) and CTDIvol = CTDIW /pitch
Dose Length Product (DLP)
DLP = CTDIvol (mGy) • scan length (cm)
CT Dosimetry After Helical CT

67. 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 67

68. 68
J Boone 2013

69. Dose estimate conversion factors for body size
JA Seibert 2011
2011
69

70. ConversionFactor
JA Seibert 2011 70

71. 71
J Boone 2013

72. 72
AAPM TG 246, 2019

73. 73

74. 74MTF Insert NPS Section
Polyethylene
60 cm L
30 cm ⦵

75. 75
J Boone 2011- 2013
An Integrated CT Image Quality / Dosimetry Phantom

76. 76
Axial scan
Helical scan

77. CT Dose by Convolution AAPM TG 246, 2019

78. 78AAPM TG 246, 2019

79. http://www.impactscan.org/ctdosimetry.htm
CT Organ
Dose
Computation
79
NRPB
Stylized
Computational
Phantom

80. Radimetrics eXposure: Dose calculation engine
• Receives CT study
• Extracts patient dose
metric information
• Pushes dose metrics
to radiology report
• Maintains database
• Provides dashboards
80
JA Seibert 2013

81. 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
81

82. organ dosesCT scan & patient
parameters
Monte Carlo modeling should be
the basis for patient CT dosimetry
Monte
Carlo
JA Seibert 2011
82

83. 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
83

84. 84
AAPM TG 246, 2019

85. 85
Para Optimizar la Protección Radiológica
Lo major es establecer
Niveles de Referencia Diagnósticos (NRD)
UK 2000
75% Percentil
Al fijar esos NRD se tendrá en
cuenta la necesidad de lograr una
calidad adecuada de las
imágenes… Estos NRD se
basarán, en la medida de lo
posible, en estudios a gran escala
o en valores publicados que sean
apropiados para las
circunstancias locales (NBS, 2016)

86. J. L. Heron 2013
86

87. 87
D Hart et al. 2012

88. 88
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

89. NCRP recommended DRLs and
achievable doses (mGy) -
Radiography
89

90. NCRP recommended DRLs and
achievable doses - Fluoro
90
mGy

91. NCRP recommended DRLs and achievable
doses (mGy) - CT
91

92. 92
McNitt-Gray, 2014

93. Niveles de Referencia Diagnósticos (NBS)
93
Se ha de realizar “un examen para determinar si la optimización
de la protección y la seguridad de los pacientes es adecuada, o si se
precisa una medida correctora, con respecto a un procedimiento
radiológico determinado, en caso de que:
• las dosis o actividades típicas superen el nivel de referencia para
diagnóstico pertinente; o
• las dosis o actividades típicas sean considerablemente inferiores al nivel
de referencia para diagnóstico pertinente y las exposiciones no
proporcionen información de diagnóstico útil o no reporten al paciente el
beneficio médico previsto”.

94. 94

95. DICOM Standards
95
▲ DICOM Header
▲ DICOM Services
• e.g. modality performance procedure
step (MPPS)
▲ Radiation Dose Structured Report (RDSR)
▲ Patient-RDSR (P-RDSR)

96. 96SILVA et al., 2009

97. 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

98. 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)

99. RDSR - Radiography

100. 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
100D. Pelc, 2016

101. 101Signifies 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

102. Consideraciones finales: ¿Qué es lo más importante?
▲ ¿Necesitamos dosimetría individualizada?
▲ Las dosis en órganos de pacientes serán útiles para refinar las curvas de
respuesta a la dosis y realizar estudios epidemiológicos
▲ La determinación de la dosis al paciente ¿nos permitirá inferir su riesgo?
▲ El riesgo es una probabilidad
• El coeficiente de riesgo del ICRP se basa en la población, no se puede aplicar a
un individuo
▲ Si el objetivo es proteger radiológicamente al paciente, ¿podemos usar
niveles de referencia diagnósticos, que generalmente son parámetros del
equipo, algo mucho más simple de determinar que las dosis en órganos?
▲ ¿Podemos registrar tales parámetros en la historia clínica del paciente?
Algunos países / estados lo requieren ... 102

103. 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.
103

104. 104Bushberg 2014

105. 105
Cari Borrás, D.Sc., FACR, FAAPM, FIOMP, FHPS
Washington DC, USA
Optimizar la Protección Radiológica del Paciente
o Inferir Riesgos de Radiación
en Procedimientos con Rayos X:
¿Qué es más importante?
Borrasca2008@Gmail.com