1. Part No...., Module No....Lesson No
Module title
IAEA Regional Training Course RADIATION PROTECTION OF PATIENTS FOR RADIOGRAPHERS Accra, Ghana, July 2011
Radiation units, dose quantities and biological effects
Part …: (Add part number and title)
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Learning objectives: Upon completion of this lesson, the students will be able to: …
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IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

2. Greetings from Sydney, Australia!

3. A few questions for you, to help us
Who are using automatic wet film processing?
Who have manual film processing?
Who have CR or DR?

4. Topics Exposure and exposure rate Absorbed dose and KERMA
Mean Absorbed Dose in a tissue
Equivalent dose H
Effective Dose
Related dosimetry quantities (surface and depth dose, backscatter factor…..)
Specific dosimetry quantities (Mammography, CT,…)

5. Exposure: X
Exposure is a dosimetric quantity for ionizing electromagnetic radiation, based on the ability of the radiation to produce ionization in air.
This quantity is only defined for electromagnetic radiation producing interactions in air.

6. Exposure: X Before interacting with the patient
(direct beam) or with the staff (scattered radiation), X Rays interact with air
The quantity “exposure” gives an indication of the capacity of X Rays to produce a certain effect in air
The effect in tissue will be, in general, proportional to this effect in air

7. Exposure: X The SI unit of exposure is Coulomb per kilogram [C kg-1]
The former special unit of exposure was Roentgen [R]
1 R = 2.58 x 10-4 C kg-1
1 C kg-1 = 3876 R

8. Exposure rate: X/t
Exposure rate (and later, dose rate) is the exposure produced per unit of time.
The SI unit of exposure rate is the [C/kg] per second or (in old units) [R/s].
In radiation protection it is common to indicate these rate values “per hour” (e.g. R/h).

9. Patient dosimetry quantities

10. Absorbed dose, D
The absorbed dose D, is the energy absorbed per unit mass. This quantity is defined for all ionizing radiation (not only for electromagnetic radiation, as in the case of the “exposure”), and for any material.
The SI unit of D is the Gray [Gy].
1 Gy = J/kg.
The former unit was the “rad”. 1 Gy = 100 rad.

11. Absorbed dose, D and KERMA
The KERMA (kinetic energy released in a material)
The SI unit of kerma is the joule per kilogram (J/kg), termed Gray (Gy).
In diagnostic radiology, Kerma and D are equal.

12. Relation between absorbed dose and exposure
It is possible to calculate the absorbed dose in a material if the exposure is known
D [Gy]. = f . X [C kg-1]
f = conversion coefficient depending on medium
The absorbed energy in a quantity of air exposed to 1 [C kg-1] of X Rays is [Gy]
f(air) = 0.869

13. 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 (0.87 rad) and a tissue kerma of about 9.5 mGy (0.95 rad) at that point.

14. Equivalent dose: H
The equivalent dose H is the absorbed dose multiplied by a dimensionless radiation weighting factor, wR which expresses the biological effectiveness of a given type of radiation
To avoid confusion with the absorbed dose, the SI unit of equivalent dose is called the sievert (Sv). The old unit was the “rem”
1 Sv = 100 rem

15. Radiation weighting factor, wR
For most radiation used in medicine (X Rays, , e-) wR is = 1, so the absorbed dose and the equivalent dose are numerically equal

16. Detriment
Radiation exposure of the different organs and tissues in the body results in different probabilities of harm and different severity
The combination of probability and severity of harm is called “detriment”.

17. Tissue weighting factor
To reflect the combined detriment from stochastic effects due to the equivalent doses in all the organs and tissues of the body, the equivalent dose in each organ and tissue is multiplied by a tissue weighting factor, wT, and the results are summed over the whole body to give the effective dose E

18. Tissue weighting factors, wT (ICRP103)
Organ/Tissue WT
Bone marrow
0.12
Lung
Brain
0.01
Oesophagus
Bone surface
Skin
Breast
Stomach
Colon
Thyroid
0.04
Gonads
0.08
Remainder
Liver

19. Effective dose, E E = T wT.HT E: effective dose
wT: weighting factor for organ or tissue T
HT: equivalent dose in organ or tissue T

20. Entrance surface dose (ESD)
Absorbed dose is a property of the absorbing medium as well as the radiation field, and the exact composition of the medium should be clearly stated.
Usually ESD refers to soft tissue (muscle) or water

21. Entrance surface dose (ESD)
On the other hand, the ESD measured on the surface of the patient or phantom includes a contribution from photons scattered back from deeper tissues, which is not present for free air measurements
For this reason, correction factor (backscatter factor) must be introduced
If measurements are made at other distances than the true focus-to-skin distance, doses must be corrected by the inverse square law

22. Dose area product (I)
The dose-area product (DAP) quantity is defined as the dose in air in a plane, integrated over the area of interest
The DAP (cGy·cm2) is constant with distance since the area of the beam increases with the square of the distance, and cancels the inverse square law effect

23. Inverse square law

24. DAP-meter (Diamentor ®)

25. Specific dosimetry quantities for mammography and CT

26. Mammography
The Average Glandular Dose (AGD) is the dosimetry quantity generally recommended for risk assessment in mammography
The use of AGD is recommended by the ICRP, the British Institute of Physical Sciences in Medicine, the NCRP, the BSS and the Netherlands Commission on Radiation Dosimetry (NCS)

27. The average glandular dose AGD
The AGD cannot be measured directly but it is derived from measurements with the standard phantom for the actual technique set-up of the mammographic equipment
The Entrance Surface Air Kerma (ESAK) free-in-air (i.e. without backscatter) has become the most frequent used quantity for patient dosimetry in mammography
For other purposes (compliance with reference dose level) one may refer to ESD which includes backscatter

28. The ESAK (mammography)
ESAK is usually determined by a radiation dosimeter with a dynamic range covering at least 0.5 to 100 mGy (better than  10% accuracy)
Tables are then used to convert the ESAK to AGD, knowing the x-ray beam properties (see later)

29. Dosimetric quantities for CT
CTDI (Computed Tomography Dose Index)
DLP (Dose-Length Product)
MSAD (Multiple Scan Average Dose)

30. Computed Tomography Dose Index (CTDI)
Dose profile
Nominal slice width

31. Computed tomography dose index (CTDI)
The CTDI is the integral along a line parallel to the axis of rotation (z) of the dose profile (D(z)) for a single slice, divided by the nominal slice thickness T
In practice, a convenient assessment of CTDI can be made using a pencil ionization chamber with an active length of 100 mm so as to provide a measurement of CTDI100 expressed in terms of absorbed dose to air (mGy).
D(z)dz T 1 = + -
CTDI ò

32. Computed tomography dose index (CTDI)
Various definitions of CTDI are used, but the most relevant is CTDIW
From this we can obtain an even more relevant figure, the CT dose-length product (DLP)

33. CTDIW
On the assumption that dose in a particular phantom decreases linearly with radial position from the surface to the centre, then the average dose to the slice is approximated by the weighted CTDI, measured as mGy(mAs)-1
Without going into details, CTDIW is measured in a perspex phantom, with doses being measured with a 100mm long ion chamber near the surface, and at the centre

34. Dose-length product
A very useful dose indicator for a complete CT examination
Now routinely displayed or available at the CT console
Can be recorded for future use

35. Dose-length product DLP
DLP Dose-length product for a complete examination: [mGy • cm]
where:
i represents each serial scan sequence forming part of an examination
N is the number of slices, each of thickness T (cm) and radiographic exposure C (mAs), in a particular sequence.
N.B.: Any variations in applied potential setting during the examination will require corresponding changes in the value of CTDIW used. C N T
CTDI =
DLP w i × å

36. Reference dose quantities
In the case of helical (spiral) scanning [mGy • cm]:
where, for each of i helical sequences forming part of an examination:
T is the nominal irradiated slice thickness (cm)
A is the tube current (mA)
t is the total acquisition time (s) for the sequence.
N.B.: CTDIW is determined for a single slice as in serial scanning. t A T
CTDI =
DLP w n i × å

37. Part No...., Module No....Lesson No
Module title
Summary
Dosimetric quantities are useful to know the potential hazard from radiation and to determine radiation protection measures to be taken.
The old, non-S.I. quantities and units are mentioned, since these are still used in some countries, notably the United States of America.
Let’s summarize the main subjects we did cover in this session. (List the main subjects covered and stress again the important features of the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

38. Biological effects of radiation

39. Radiation health effects
TYPE OF
EFFECTS
CELL DEATH
CELL TRANSFORMATION
BOTH
ANTENATAL
somatic and hereditary expressed in the foetus, in the live born or descendants
DETERMINISTIC
Somatic
Clinically attributable in the exposed individual
STOCHASTIC
somatic & hereditary
epidemiologically attributable in large populations

40. Part No...., Module No....Lesson No
Module title
Radiation Effects (1)
Three types of potential effect:
Stochastic : probability of effect related to dose, down to (?) zero dose
Deterministic : threshold for effect - below, no effect; above, certainty, and severity increases with dose
Hereditary (genetic)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

41. Part No...., Module No....Lesson No
Module title
Stochastic Effect
Probability of Effect
Examples :
carcinogenesis
leukaemogenesis
Involves DNA/chromosome
damage
Dose
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

42. The Linear No-Threshold Hypothesis (LNT)
Part No...., Module No....Lesson No
Module title
The Linear No-Threshold Hypothesis (LNT)
Above the prevalent background dose, an increment in dose results in a proportional increment in the probability of incurring stochastic effects. Risk is also regarded as additive.
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

43. Part No...., Module No....Lesson No
Module title
Probability of stochastic effects, p
Background
incidence
D p
5% / Sv
In this zone the relationship
is irrelevant
D D
Annual dose, D
average 2.4 mSv
typical 10 mSv
high 100 mSv
Background dose
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

44. Models of Stochastic Effects
Part No...., Module No....Lesson No
Module title
Models of Stochastic Effects
Probability of Effect
Linear
Supralinear
Linear-quadratic
Dose
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

45. Deterministic Effect (or non-stochastic)
Part No...., Module No....Lesson No
Module title
Deterministic Effect (or non-stochastic)
Severity of Effect
Examples :
epilation
radiation sickness
erythema
Involves cell death
Dose
Threshold
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

46. Deterministic effect thresholds
Cataracts of the lens of the eye Gy
Permanent sterility
males Gy
females Gy
Temporary sterility
males Gy
females Gy

47. Deterministic effects
Radiation injury from an industrial source

48. Severe Deterministic Effect - 48 y.o. woman following RFA
Part No...., Module No....Lesson No
Severe Deterministic Effect - 48 y.o. woman following RFA
Module title
3 weeks following RFA months months
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

51. Effects in eye Eye lens is radiosensitive.
Coagulation of proteins occur with doses greater than 2 Gy.
There are 2 basic effects:
Histologic view of eye:
Effect
Effect
Effect
Effect
Effect
Effect
Effect
Effect
Effect
Effect
Sv single brief exposure
Sv single brief exposure
Sv single brief exposure
Sv single brief exposure
Sv single brief exposure
Sv single brief exposure
Sv single brief exposure
Sv single brief exposure
Sv single brief exposure
Sv single brief exposure
Sv/year for many years
Sv/year for many years
Sv/year for many years
Sv/year for many years
Sv/year for many years
Sv/year for many years
Sv/year for many years
Sv/year for many years
Sv/year for many years
Detectable opacities
Detectable opacities
Detectable opacities
Detectable opacities
Detectable opacities
Detectable opacities
> 0.1
> 0.1
> 0.1
> 0.1
> 0.1
> 0.1
> 0.1
> 0.1
From “Atlas de Histologia...”. J. Boya
Eye lens is highly RS, moreover, it is surrounded by highly RS cuboid cells.
Visual impairment (cataract)
Visual impairment (cataract)
Visual impairment (cataract)
Visual impairment (cataract)
Visual impairment (cataract)
5.0
5.0
5.0
5.0
> 0.15
> 0.15
> 0.15

52. Delayed effects of radiation
Classification:
SOMATIC: they affect the health of the irradiated person. They are mainly different kinds of cancer (leukemia is the most common, with a delay period of 2-5 years, but also colon, lung, stomach cancer…)
GENETIC: they affect the health of the offspring of the irradiated person. They are mutations that cause malformation of any kind (such as mongolism)

53. Latency - The Time for Stochastic Effects to Become Apparent
Part No...., Module No....Lesson No
Latency - The Time for Stochastic Effects to Become Apparent
Module title
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

54. Links Between Radiation and Effects
Part No...., Module No....Lesson No
Module title
Links Between Radiation and Effects
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

55. Lethal dose 50 / 30
“Dose which would cause death to 50% of the population in 30 days”.
Its value is about 2-3 Gy for humans for whole body irradiation.

56. Radiation and Pregnancy
Part No...., Module No....Lesson No
Module title
Radiation and Pregnancy
Three relevant stages of gestation :
preimplantation (0 - 9 days post conception)
organogenesis (10 days - 6 weeks)
major organogenesis is however weeks
foetal (6 weeks to term)
Main radiation effects are failure to implant, organ malformation, carcinogenesis, foetal death
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

57. Part No...., Module No....Lesson No
Module title
Preimplantation
Undetectable embryonic death (failure to implant) is deterministic effect, requiring ~ 100 mGy (low LET radiation)
Malformations do not occur
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

58. Post-Implantation Death
Part No...., Module No....Lesson No
Module title
Post-Implantation Death
Spontaneous abortion, or foetal death
Difficult to prove unless at high doses
Deterministic effects, with threshold probably at least 100 mGy and probably much higher
Highest risk period ~16 days PC
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

59. Part No...., Module No....Lesson No
Module title
Foetal Death
Days PC Threshold ?
mGy
mGy
mGy
< 500 mGy
> > 1000 mGy
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

60. Part No...., Module No....Lesson No
Organogenesis
Module title
Sensitive period is > 21 days PC when the CNS and heart develop
A-bomb survivors have shown some problems, mainly related to brain development, and seeming to have a threshold but with a risk factor of ~30 IQ points Sv-1
These relate to high dose/high dose rate, and probably an overestimate
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

61. Severe Mental Retardation
Part No...., Module No....Lesson No
Module title
Severe Mental Retardation
Greatest risk 8-15 wks PC
Risk factor about 0.04% / mGy to foetus
Equates to 0.03 IQ points / mGy
Could be threshold of ~100 mGy
Lower risk wks PC (0.01% / mGy), with possible threshold of > 500 mGy
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

62. Part No...., Module No....Lesson No
Module title
Carcinogenesis
Due to risk of cell damage, we assume the risk exists from ~3 weeks to term
Data is not consistent, and has high uncertainty
Thus assume that the risk factor is higher than for adults (ICRP 103 says “about 3 times”)
This is the only radiation risk which can easily be greater than the spontaneous risk (~ 0.1 % / mSv)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

63. Normal Risks of Pregnancy - Keep these in mind
Part No...., Module No....Lesson No
Module title
Spontaneous abortion 15%
Major malformation 3%
Severe mental retardation (SMR) 0.5%
IUGR %
Genetic disease %
Childhood cancer %
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

64. Proportion of Fatal Cancers Attributable to Different Agents
Part No...., Module No....Lesson No
Module title
Proportion of Fatal Cancers Attributable to Different Agents
Agent or Class Percentage of all Cancer
Best estimate Range
Smoking
Alcoholic beverages
Diet
Medicines, medical practices
Electromagnetic radiation
Ionizing (85% natural)
Ultraviolet
Industrial products <1 <1 - 2
Pollution 2 <1 - 4
Doll, R. (1996) Risk of cancer attributable to industry with special reference to the effects of ionising radiation, The Hazards Forum, No 1B January, 2-3.
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

65. Does Low Level Radiation Produce Genetic Effects?
Part No...., Module No....Lesson No
Module title
Does Low Level Radiation Produce Genetic Effects?
No conclusive human data
Risk estimates based on animals - difficult to extrapolate to humans
Hiroshima/Nagasaki survivors have shown no genetic effects as of the third generation
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

66. What is the relevance to radiology?
Basic philosophy of diagnostic radiology is :
Appropriately high (NOT best) image quality
At minimum reasonable (NOT lowest) dose
Avoid deterministic effects
Limit stochastic effects (CANNOT eliminate)
Patient diagnosis and treatment is of primary importance

67. Thank you!