Radiation Protection Course For Radiologists Lecture 3 of 8 Radiation Hazards

1. Radiation Protection Course For Radiologists
Lecture 3 of 8
Radiation Hazards
Prof Amin E AAmin
Dean of the Higher Institute of Optics Technology
&
Prof of Medical Physics
Radiation Oncology Department
Faculty of Medicine, Ain Shams University

2. The Need For Radiation Protection
The need for radiation protection exists
because exposure to ionizing radiation can
result in deleterious effects that manifest
themselves not only in the exposed
individual but in his descendants as well.

3. ❖ 1895 X-rays discovered by Roentgen
❖ 1896 First skin burns reported
❖ 1896 First use of x-rays in the treatment of cancer
❖ 1896 Becquerel: Discovery of radioactivity
❖ 1897 First cases of skin damage reported
❖ 1902 First report of x-ray induced cancer
❖ 1911 First report of leukaemia in humans and lung cancer from
occupational exposure
❖ 1911 94 cases of tumour reported in Germany (50 being radiologists)
Early Observations Of The Effects Of
Ionizing Radiation

4. First Medical Findings
• First skin-burn attributed
to radiation - 1901
• First radiation induced
leukemia described -1911
• First publication
describing “a clinical
syndrome due to atomic
bomb” - 1946

5. Reporting of Radiation Effects
• Later, in 1896, Walkhoff succeeded in
making extra-oral pictures with an
exposure time of 30 min.
• He noticed a loss of hair on the side of
the head of some of the patients he
irradiated, but as there was no mention
of blisters on the skin it is assumed that
the absorbed dose was less than 300
rads.

6. Reporting of Radiation Effects
• John Daniel described scalp epilation during
a diagnostic exposure in 1896.
• In February 1896 a child who had been
accidentally shot in the head was brought to
the laboratory at Vanderbilt University
(Tennessee, USA).
• Before attempting to locate the bullet in the
child, Professor Daniel and Dr Dudley
decided to undertake an experiment.
Physics professor
John Daniel

7. Reporting of Radiation Effects
• Dr Dudley, lent himself to this experiment.
• A plate holder containing the sensitive plate
was tied to one side of Dudley’s head and
the tube attached to the opposite side of the
head.
• The tube was placed 0.5 inches away from
Dudley’s hair and activated for 1 h.
• After 21 days all the hair fell out from the
space under discharge, which was
approximately 2 inches in diameter.
William Lofland
Dudley

8. Skin Reaction
• On 12 August 1896, Electrical Review reported that Dr HD
Hawks, gave a demonstration with a powerful X-ray unit in
the vicinity of New York.
• After 4 days, he was compelled to stop work.
• He noticed a drying of the skin, which he ignored.
• The hand began to swell and gave the appearance of a deep
skin burn.
• After 2 weeks the skin came off the hand, the knuckles
become very sore, fingernail growth stopped and the hair on
the skin exposed to X-rays fell out.

9. Skin Reaction
• His eyes were bloodshot and his vision became considerably
impaired.
• His chest was also burnt.
• Mr Hawks’ physician treated this as a case of dermatitis.
• Hawks tried protecting his hands with petroleum jelly, then
gloves and finally by covering it with tin foil.
• Within 6 weeks Hawks was partially recovered and was making
light of his injuries.
• Electrical Review concluded by asking to hear from any of its
readers who had had similar experiences.

10. Skin Reaction
• GA Frei of Frei and Co., a Boston manufacturer of Xray tubes,
replied the next day: Mr K, an employee of the company,
complained of peculiar itching and burning in his left hand and
thought it was due to poisoning with chemicals.
• Mr K used to regularly attend to testing of tubes during and
after the exhausting process at the rooms.
• The same phenomenon also appeared on Frei’s hand.
• The letter concluded by stating that further developments would
be carefully monitored.

11. Early occupational exposures
• The X-ray pioneers took repeated
X-rays of their own hands to see if
the tube was ready for patients.
• In 1895 Frank Austin, x-rayed his
own hand.

12. Testing X-ray Sets – The Early Days

13. X-Ray Early Days

14. First Reports of Injury
• In November 1896 Elihu Thomson, conducts
experiments on x-ray burns.
• He purposely exposed the little finger of his left hand
for half an hour close to an x-ray tube.
• He induced a dermatitis on his own finger, and
concluded that the rays themselves had caused it.
• Over a period of a week or two the finger became
swollen, sensitive and painful.
• He was convinced that the effects were caused by the
“chemical activity” of the rays and issued a caution.
• (One of his recommendations was “Do not expose
more than one finger”)
• Most disregarded his warnings.
Elihu Thomson

15. Thomas Edison
Edison’s assistant - hair
fell out & scalp became
inflamed & ulcerated

16. Clarence Dally
• Clarence Dally (1865-
1904), assistant to
industrialist Thomas Alva
Edison. The first
recognized American X
ray fatality.

17. Dr Rome Wagner
And Assistant

18. Edmund Kells
• April 1896 built own X-ray
machine, packed films in
rubber and took X-ray of his
dental assistant
• 10 years on, cancer of right
hand
• 42 operations in next 20 years
– lost hand, arm and shoulder.

19. • Mihran Kassabian
meticulously noted and
photographed his hands during
progressive necroses and serial
amputations, hoping the data
collected might prove useful
after his death.
• He died of skin cancer related
to his repeated exposure to
high doses of radiation.
Mihran Kassabian (1870-1910)

20. First Reports of Injury
• March 1896 - The Lancet - L R L Bowen, in a talk to the London
Camera Club, warned that x-rays might produce effects like
sunburn.
• March 3rd - First reports of X-Ray injury; damage to eyes.
• In April 1896 - BMJ - L G Stevens reported that people exposed to
x-rays suffered sunburn and dermatitis.
• April 10th - Epilation noted from X-Ray exposure.
• April 18th - Skin effects first noted.
• July - Reports of accidental injury [burns].

21. Radiation Hazards
•1896, Frank Harrison: probably first to
report occurrence of radiation hazard
•1896, March 23 : Dr. John Daniel
mentioned about hair loss from head of
colleague that was photographed with
radiography.
•1896, July 22: W. Marcuse published first
microscopic study of effect of radiation
on tissues. Frank Harrison

22. Early Radiation Exposure
◼ While performing a fluoroscopic study,
radiologists received a full dose of
transmitted primary beam to upper torso
and face
◼ Many radiologists developed leukemia
and died, thus becoming martyrs for
radiologic science

23. ❖Concerns first raised about possible injuries
from x-ray exposures.
❖The first recorded biologic effect of radiation
was seen by Becquerel, who developed
erythema and subsequently ulceration when
radium container was left accidentally in his left
pocket.
Possible Injuries

24. Monument For The Victims Of
The X-ray

25. Neils Ryberg Finsen
• Neils Ryberg Finsen
1893 On the influence
of light on the skin
showed UV caused
sunburn and not radient
heat. (1903 Nobel Prize
for UV treatment of
lupus vulgaris)

26. How Does Radiation Cause Harm?
• LD(50/30) = 4 Gy
 280 J to 70 kg man
 1 milli-Celsius rise in body temp.
 drinking 6 ml of warm tea
•i.e. not caused by heating, but ionisation
•Damages DNA.

27. Radiation Action
❖When radiation is incident upon a biological system, it is
important to realize that the incident radiation may;
➢pass through the system without producing any damage,
or
➢be totally or partially absorbed within the system resulting
in some degree of damage

28. Ionizing Radiation Effects
Absorption of Radiation
Ionization
Chemical Change
Repair or Damage
High Dose Effects
Cell killing
Tissue or organ effects
Whole body effects
Low Dose Effects
Mutations
Cancer
Effects to unborn

29. Radiation Causes Ionizations of:
ATOMS
which may affect
MOLECULES
which may affect
CELLS
which may affect
TISSUES
which may affect
ORGANS
which may affect
THE WHOLE BODY
Ionizing Radiation Effects

30. Summary of Biological
Effects

32. Radiation damage: Time course

33. 1. Fast Reactions 10-10 to 10-3 sec
• energy absorbed
• free radicals produced
• DNA attacked
• chemical repair
2. Biological Processing 10-3 to 104 sec
• enzymatic Repair of DNA
• turnover of damaged non-DNA molecules
• mis-repair DNA damage fixed into genome
3. Biological Consequences 104 to 109 sec
• genetic effects in future generation (heritable)
• somatic effects (cell death, cancer)
Cellular Radiation Effects : Time course

34. Fate Of The Photon Beam
• The photon beam may undergo the following four processes –
Attenuation , Absorption , Scattering and Transmission .
• Attenuation refers to the removal of radiation from the beam by the
matter . Attenuation may occur due to scattering and absorption .
• Absorption refers to the taking up of energy from the beam by the
irradiated material .It is the absorbed energy which is important in
producing the radiobiological effects .
• Scattering refers to the change in the direction of photons and it
contributes to both attenuation and absorption .
• Any photon which does not suffer the above processes is
transmitted.

35. Interactions Of X-Rays With Matter
• No interaction: X-ray
passes completely and get
to film
• Complete absorption:
no x-rays get to film
• Partial absorption with
scatter

36. The Five Interactions Of X and Gamma
Rays With Matter
• Coherent scatter
– Not important in diagnostic or therapeutic radiology
• Photoelectric effect
– Very important in diagnostic radiology
• Compton scatter
– Very important in diagnostic radiology
• Pair production
– Very important in therapeutic radiology
• Photodisintegration
– Very important in therapeutic radiology

37. Two Forms of X-ray Interactions
Important to Diagnostic X-ray
Only two types of interactions of photons with matter
have impact in diagnostic X-ray
• Photoelectric Effect
• Compton Effect

38. Coherent Scattering
• Classical scattering or Rayleigh
scattering
– No energy is changed into electronic
motion
– No energy is absorbed in the medium
– The only effect is the scattering of the
photon at small angles.
• In high Z materials and with photons
of low energy


••
••
•
•
•
•
•
•

39. Photoelectric Effect
• Low energy photons, up to about 100 keV.
• Important in diagnostic radiology, contrast
is due to different mass absorption
coefficient in tissues.
• The probability of photoelectric absorption
depends not only on the energy of the
photon but also on the atomic number of
the atoms with which it interacts.
• Mass absorption coefficient Z3/E3
(bones highly absorb x-ray)

40. Compton Effect
❖ Photon interacts with an atomic
electron as though it were a free
electron. Practically this means that
energy of the incident photon must be
large compared with the electron
binding energy.
❖ The electron receives some energy
from the photon and is emitted at an
angle Φ while the photon with reduced
energy is scattered at an angle θ .

41. Compton Effect

42. Dependence Of Compton Effect On
Energy
• As the photon energy
increase, the photoelectric
effect decreases rapidly and
Compton effect becomes
more and more important.
• The Compton effect also
decreases with increasing
photon energy.

43. Pair Production
• When the photon with energy in excess of 1.02 M e V passes
close to the nucleus of an atom, the photon disappears, and a
positron and an electron appear. This effect is known as pair
production.
• Pair production results in attenuation of the beam with absorption.

44. Pair Production
• The positron created as a result
loses its energy by interaction
with an electron to give rise to
two annihilation photons, each
having 0.511 M e V energy.
• Again because momentum is
conserved in the process two
photons are rejected in
opposite directions. This
reaction is known as an
annihilation reaction.

45. Photonuclear Reaction
• This reaction occurs when the photon
has energy greater than the binding
energy of the nucleus itself. In this case,
it enters the nucleus and ejects a particle
from it. The photon disappears
altogether, and any energy possessed in
excess of that needed to remove the
particle becomes the kinetic energy of
escape of that particle.
• The threshold energy for this effect is
10.8 M e V.

46. Cellular Effects of Ionising
Radiation
Ionising radiation can cause chemical reactions in the
body’s cells which may
• do no harm
• kill the cell
• cause the cell to multiply out of control (cancer)
• cause the cell to malfunction in some other way

47. X-ray passes straight
through cell

No change to cell
Cellular Effects of Ionising
Radiation

48. X-ray causes a
chemical reaction in
cell, but no damage
done or damage
repaired by cell

No change to cell
*
Cellular Effects of Ionising
Radiation

49. DNA damaged in a
“fatal” way”

Cell killed
*
Cellular Effects of Ionising
Radiation

50. DNA damaged,
causing cell to
reproduce
uncontrollably

Cancer?
*
Cellular Effects of Ionising
Radiation

51. X-ray passes straight
through cell

No change to cell
X-ray causes a
chemical reaction in
cell, but no damage
done or damage
repaired by cell

No change to cell
DNA damaged in a
“fatal” way”

Cell killed
DNA damaged,
causing cell to

Cancer?
*
*
*Cellular Effects of
Ionising Radiation

52. Radiation chemistry

53. Radiation Chemistry
❖Radiation chemistry is the study of the chemical
effects of radiation on matter.
❖It is also defined as the study of radiation
molecular effects i.e. the interaction of radiation
with molecules (chemical compounds).

54. Molecular Damage
A fundamental assumption in radiobiology is that
radiation damage to a living organism begins with
molecular damage to that organism.

55. Molecular Damage
Since the basic unit of a living organism is the cell,
significant damage to vital molecules can be seen at the
cellular level.

56. Principal Types of Molecules
Within A Cell
• The five principal types of molecules within a cell are;
– water,
– proteins,
– lipids,
– carbohydrates and
– nucleic acid.
• The last four types are called macromolecules or very large
molecules.

57. Water
Water is the most abundant molecule in the body
and makes up about 75% (65-90%) of the weight.

58. Macromolecules
Macromolecules can consist of over several hundred
thousand atoms.

59. DNA
• There is substantial evidence
that the most important target
in the irradiated cell is the
DNA molecule.
• DNA is generally thought to be
the most critical and
radiosensitive molecule and is
found in the nucleus of a cell.

60. DNA - The Target Of
Radiation Protection
The double-helical structure
of DNA carries the genetic
code for the cell. Breakage of
the strand by radiation plus an
error in its rejoining, may
cause the cell to proliferate in
an erroneous mode (cancer)
or to die.

61. Radiation Molecular Effects
In the 1920’s researchers found that biological effects
from radiation were due mostly to two different processes.
These processes are called direct and indirect effects

62. Initial Physical Events
❖The initial event is the transfer of ~ 7 - 100
eV, an amount of energy sufficient to cause
(multiple) ionizations or excitations in water
molecules.
❖Transfer of energy to the medium in biological
systems usually involves ionization of a water
molecule, but can also involve the cellular
macromolecules (e.g., DNA) directly.

63. How Does Ionizing Radiation
Damage DNA?

64. Direct And Indirect Action Of Radiation
❖Direct action:
secondary e- resulting from absorption of a
photon interacts directly with the DNA,
dominant process for radiations with high
LET: neutrons, α-particles, heavy ions
❖Indirect action:
secondary e- interacts with another molecule,
e.g. H2O generation of free radicals which
produce the damage to the DNA, dominant
process for radiations with low LET: X-, γ-
rays.

65. Direct Effects
➢ Interaction of ionizing radiation directly with
DNA is named as direct effect.
➢ Atoms in DNA may ionized or excited which
leads to biological change.
➢ When DNA directly affected by radiation, energy
absorbed by DNA undergoes to Strand breaks
➢ Direct Effect is proportional to LET of Radiation.
➢ A quarter to a third of the damage produced in
cellular macro-molecules by radiation is due to its
direct effect.

66. Initial Physical Events
– Through ionizations and excitations the passage of a charged
particle through biological medium creates three species in
the local vicinity of the particle track:
– Direct ionization of water produces a radical ion and a free
subexcitation electron (E < 7.4 eV).
𝐻2 𝑂
𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛
𝐻2 𝑂.+
+ 𝑒−

67. Initial Physical Events
– Energy transfer can produce a water molecule in an excited
state.
𝐻2 𝑂
𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛
𝐻2 𝑂∗
– The time scale for the creation of these species is on the
order of 10-16 seconds.

68. Prechemical Reactions
• The actual concentrations of the radicals are
very small, especially when compared to the
concentrations of ions present from the
dissociation of water.
• Thus, the three initial species:
H2O*, H2O·+ and e¯,
react further to produce chemically reactive
species:
HO·, H·, and , e-
aq

69. Prechemical Reactions
The electron is captured by water through dipolar
interactions, becoming solvated, and referred to as
an aqueous electron or a solvated electron:
e¯ + H2O → e-
aq surrounded by a “cage” of water;
e¯ + H+ → H· or it can react with H+ to form a radical.

70. Prechemical Reactions
• The excited water molecule can dissipate excess energy by
bond breakage to produce hydroxyl and hydrogen radicals.
H2O* → HO· + H·
• It takes ~ 5 eV to break the O-H bond.

71. Prechemical Reactions
• The radical ion of water can dissociate to produce a hydroxyl
radical and a hydrogen ion.
H2O·+ → H+ + HO

72. Prechemical Reactions
• The three initial species begin to diffuse and react with each
other or other molecules in the medium.
• Some of these reactions produce radicals.

73. Free Radical
➢A free radical is an atom or molecule that has an unpaired
electron in the valence shell, making it highly reactive
➢ Radicals are highly reactive.
➢ Radicals can be neutral or charged.

74. ❖ Free radicals aggressively join with the DNA molecule to
produce damage.
❖ In the presence of oxygen, the hydroperoxyl free radical is
formed; this is one of the most damaging free radicals that
can be produced.
❖ Free radicals are the primary mediator of the indirect
effects on DNA.
Free Radical

75. Chemical Stage
• After ~10-12 sec, the chemically reactive species are still
located in the vicinity of the original H2O*, H2O·+ and e¯
species that caused their creation.
• Three of the new species created are radicals: HO·, H·, e-
aq.
• These species now begin to migrate randomly about their
initial positions. As this diffusion proceeds, individual pairs
may come close enough together to react with each other.

76. Chemical Stage
• Most of these reactions remove chemically reactive
species from the system.
• With time (by ~ 10-6 sec) all of the reactive species have
diffused sufficiently far that further reactions are
unlikely.
• The chemical development of the track is over by 10-6
sec.

77. Radiation Action
• Low LET radiation (e.g., x-rays and gammas) tend to be more
penetrating but produce their damage via indirect action which
is more likely to be repaired perfectly.
• This assumes low level, chronic exposure from an external
source.

78. Direct Action
• Direct effects occur when radiation directly ionizes and
damages a macromolecule such as DNA.
• In this case the irradiated radiosensitive molecule is said
to be the target molecule.

79. Direct Action
The DNA can be damaged by direct energy deposition in
the molecule leading to breakage of chemical bonds and to
structural changes of the molecule.

80. Direct Ionization Damage to DNA
• Ionizing Radiation may
directly break bonds in
the DNA molecule.
• Damage remains when
the DNA cannot repair
the bond breaks

81. Radiation Action
High LET radiations (e.g., low energy neutrons, fission
fragments, and alphas) tend to pose more of an internal
radiation hazard due to the increased likelihood of damage via
direct action which is less likely to be repaired perfectly.

82. DNA Damage And Its Consequences
DNA
Damage
Repair No Repair Misrepair

83. DNA Damage And Its Consequences
DNA Damage
Repair No Repair
Chromosome
Aberration
Cell Death
Misrepair
Mutation
Cancer

84. Classification Of Cells
Classification
of cells
Somatic
cells
Gonadal
cells

85. Gonadal Cells
• Gonadal cells are found in ovaries and testicles.
• Gonadal cells divide by meiosis.
• They are rapidly proliferating cells.

86. Somatic Cell
• A somatic cell is generally taken to mean any cell
forming the body of an organism.
• The word "somatic" is derived from the Greek word
sōma, meaning "body".
• Somatic cells, by definition, are not germline cells.
• Somatic cells divide by mitosis.
• They are devided according to degree of differentiation and
proliferation.

87. Somatic Cell
• Every other cell type in the mammalian body—apart
from the sperm and ova, ___ is a somatic cell: internal
organs, skin, bones, blood, and connective tissue are all
made up of somatic cells.

88. Somatic Cell
Highly Differentiated Cells
Highly Proliferating Cells
Cells of Intermediate Degree of
Differentiation & Proliferation
Somatic Cell

89. Highly Differentiated Cells
• A differentiated cell is one that is specialized
functionally and/or morphologically (structurlly).
• It can be considered a mature cell, or end cell, in a
population.
• e.g. brain, nerve cells

90. Undifferentiated Cells
• Udifferentiated cell has few specialized morphologic or
functional characteristics.
• It is an immature cell whose primary function is to divide, thus
providing cells to maintain its own population and to replace
mature cells lost from end cell population.
• Udifferentiated cell can be considered precursor, or stem, cells
in a population.

91. Highly Proliferating Cells
• Cells that show poor degree of differentiation and high
proliferation.
• They are rapidly dividing cells.
• e.g. B.M, epithelia, mucosal cells, cells of peripheral
blood as RBCs, WBCs, etc.

92. Factors Involved In Development Of
Radiation Induced Cell Injury
• Radiation absorbed dose by the cell.
• Types of molecules involved in injury.
• Number of molecules involved in injury.
• Site of radiation injury in the cell.
• Degree of molecular repair.
• Type of cell population involved in the injury.
• Degree of cell differentiation.
• Degree of cell proliferation and stage of cell cycle.

93. Cellular Radiosensitivity
• Radiosensitivity is the relative susceptibility of cells,
tissues, organs or organisms to the harmful effect of
ioniing radiation.

94. Law Of Bergonie And Tribondeau
• Not all cells in the human body respond the same to radiation.
• In 1906, the law of Bergonie and Tribondeau stated: The radio-
sensitivity of a tissue is directly proportional to its reproductive
capacity and inversely proportional to its degree of
differentiation.
• In short, this means that actively dividing cells or those not
fully mature are at most risk from radiation.

95. Cellular Radiosensitivity
The most radio-sensitive cells are those which:
• have a high division rate
• have a high metabolic rate
• are of a non-specialized type
• are well nourished

96. Relative Sensitivity Of Cell
And Tissue
➢Lymphocytes
➢Spermatogonia
➢Hematopoietic (Blood Forming)
➢Intestinal Epithelium
➢Skin
➢Nerve Cells
➢Muscle Tissue
➢Bone
➢Collagen

97. Examples Of Various Tissues And Their
Radiosensitivity
Radiosensitive Cells Radioresistant Cells
Reproductive cells Bone, Cartilage, Muscle
Blood forming tissues Liver
Epithidium of skin Kidney
Epithidium of
gastrointestinal tract
Nerve tissue

98. Examples Of Various Tissues And Their
Radiosensitivity
High Radiosensitivity
Lymphoid organs, bone marrow, blood, testes, ovaries, intestines
Fairly High Radiosensitivity
Skin and other organs with epithelial cell lining (cornea, oral cavity, esophagus,
rectum, bladder, vagina, uterine cervix, ureters)
Moderate Radiosensitivity
Optic lens, stomach, growing cartilage, fine vasculature, growing bone
Fairly Low Radiosensitivity
Mature cartilage or bones, salivary glands, respiratory organs, kidneys, liver,
pancreas, thyroid, adrenal and pituitary glands
Low Radiosensitivity
Muscle, brain, spinal cord

99. Tissue Weighting Factor
Tissue or Organ Tissue weighing factor - wT
Gonads 0.20
Bone marrow – red 0.12
Colon 0.12
Lung 0.12
Stomach 0.12
Bladder 0.05
Breast 0.05
Liver 0.05
Oesophagus 0.05
Thyroid 0.05
Skin 0.01
Bone surface 0.01
Remainder 0.05

100. Cell Cycle

101. RadiosensitivityDetailes
AbbreviationDescriptionState
RadioresistantA resting phase where the cell has left the cycle
and has stopped dividing.
G0Gap 0quiescent/
senescent
RadioresistantCells increase in size in Gap 1. The G1 checkpoint
ontrol mechanism ensures that everything is ready
for DNA synthesis.
G1Gap 1Interphase
Most
Radioresistant
DNA replication occurs during this phase.SSynthesis
RadiosensitiveDuring the gap between DNA synthesis and
mitosis, the cell will continue to grow. The G2
checkpoint control mechanism ensures that
everything is ready to enter the M (mitosis) phase
and divide.
G2Gap 2
Most
Radiosensitive
Cell growth stops at this stage and cellular energy
is focused on the orderly division into two daughter
cells. A checkpoint in the middle of mitosis
(Metaphase Checkpoint) ensures that the cell is
ready to complete cell division.
MMitosisCell
division
Cell Cycle

102. Factors Affecting
Radiosensitivity
of Cells
Physical
Factors
Biological
Factors
Chemical &
Biochemical
Factors

103. Factors Affecting
Radiosensitivity
of Cells
Physical
Factors
Radiation Related
Factors
Biological
Factors
Cells & Tissues
Related Factors
Chemical &
Biochemical
Factors
Chemistry of
Tissues Related
Factors

104. Physical Factors
• Type of radiation involved.
• Size of dose received.
• Dose fractionation.
• Rate the dose received.
• Physical T1/2 of radionuclide (in case of internal
exposure).

105. Type Of Radiation Involved
• All kinds of ionizing radiation can produce health effects.
• The main difference in the ability of alpha and beta particles
and Gamma and X-rays to cause health effects is the amount of
energy they have.
• Their energy determines how far they can penetrate into tissue
and how much energy they are able to transmit directly or
indirectly to tissues.

106. Size Of Dose Received
• The higher the dose of radiation received, the higher the
likelihood of health effects.

107. Dose Rate
• Tissue can receive larger dosages over a period of time. If the
dosage occurs over a number of days or weeks, the results are
often not as serious if a similar dose was received in a matter of
minutes.

108. Biological Factors
• Degree of proliferation of exposed cells.
• Degree of differentiation of exposed cells.
• Volume of irradiated part of the body.
• Nature of irradiated tissue.
• The age of the individual.
• Biological differences.
• Repair mechanism.
• Phase of cell regeneration cycle.

109. Degrees Of Proliferation And
Differentiation Of Exposed Cells
The law of Bergonie and Tribondeau
The radio-sensitivity of a tissue is;
➢directly proportional to its reproductive capacity and
➢inversely proportional to its degree of differentiation.

110. Volume Of Irradiated Part Of The Body
The Larger the exposed volume is the higher
the effected part of the body.

111. Nature Of Irradiated Tissue
• Extremities such as the hands or feet are able to receive a
greater amount of radiation with less resulting damage than
blood forming organs housed in the torso.

112. Examples Of Various Tissues And Their
Radiosensitivity
Radiosensitive Cells Radioresistant Cells
Reproductive cells Bone, Cartilage, Muscle
Blood forming tissues Liver
Epithidium of skin Kidney
Epithidium of
gastrointestinal tract
Nerve tissue

113. The Age Of The Individual
• As a person ages, cell division slows and the body is less
sensitive to the effects of ionizing radiation. Once cell division
has slowed, the effects of radiation are somewhat less damaging
than when cells were rapidly dividing.

114. Biological Differences
• Some individuals are more sensitive to the effects of radiation
than others.
• Studies have not been able to conclusively determine the
differences.

115. Chemical And Biochemical
Materials
• H2O
• O2
• Blood supply
• Metabolic and biochemical activity of the cells

116. Radioprotective Materials
• Drugs used to depress the radiation effects.

117. Radioprotective Materials
• Radioprotective materials include Vitamins A, C, E and
Vitamin E +.
• They are important in high dose exposures
(radiotherapy).
• Their effect in low level exposure is very poor.

118. Radiosensitizers
• Drugs used to enhance the effect of radiation treatment.

119. Radiosensitizers
• These drugs are mainly including oxidizing agents e. g.
– O2
– Ozone O3
– H2O2
– Vitamin K

120. Type Of Radiation
Damage

121. Systemic Effects
• Effects may be morphological and/or functional
• Factors:
– Which Organ
– How much Dose
• Effects
– Immediate (usually reversible): < 6 months e.g.: inflammation,
bleeding.
– Delayed (usually irreversible): > 6 months e.g.: atrophy,
sclerosis, fibrosis.

122. Systemic Effects
• Categorization of dose
– < 1 Gy: LOW DOSE
– 1-10 Gy: MODERATE DOSE
– > 10 Gy: HIGH DOSE
• Regeneration means replacement by the original tissue while
Repair means replacement by connective tissue.

123. Classification Of Radiation Damage
• Radiation damage to mammalian cells is divided into three
categories:
❖Lethal damage
❖Sublethal damage
❖Potentially lethal damage

124. Lethal Damage
•It is irreversible, irreparable and leads to cell death.
•Non repairable injury associated with double strand breaks
•Increases with LET up to a point
•Increases with higher doses

125. Sublethal Damage
• It can be repaired in hours unless additional sublethal damage is
added that eventually leads to lethal damage.
• i.e. It is repairable injury to the DNA

126. Repair of Radiation Injury
• Cellular mechanisms are in place which can repair most if not
all types of radiation injury to the DNA.
• Repair is a time sensitive process
• Repair is a cell cycle dependent process
• Repair is a dose rate dependent process
• Repair is dose dependent
• Repair is radiation type dependent

127. Potentially Lethal Damage
• Damage which is lethal unless modified by post irradiation
events

128. Potentially Lethal Damage
• Not repaired and lethal under normal circumstances.
• Repair increased by conditions which are suboptimal to the
division of the cell
➢Reduced temperature
➢Hypoxia
➢Low pH
➢Others

129. Specific Effects Of Radiation
Ionizing radiation causes two types of effects;
❖ Deterministic (Non-stochastic) effects of radiation: Those
are the effects that occur only above a threshold dose. Once
the threshold is exceeded, the severity of the effect increases
with dose.
❖ Stochastic effects of radiation: Those are the effects that
have a certain probability of occurring, and the probability
increases as the radiation dose increase. The stochastic
effects don’t need a threshold to occur.

130. Deterministic
(Non-stochastic)
effects of radiation
Stochastic effects
of radiation
e.g. Lens opacities, skin injuries,
infertility, epilation, etc
Cancer, genetic effects.

131. Deterministic (Non-Stochastic)
Radiation Effects
Deterministic effects result from the killing
of cells which, if the dose is large enough,
causes sufficient cell loss to impair the
function of the tissue. i.e. exposure to high
doses of radiation can damage large
number of cells which produce
deterministic effects .
Severity
Radiation Dose
Threshold

132. Deterministic Health Effects
• A radiation effect for which generally a
threshold level of dose exists above
which the severity of the effect is
greater for a higher dose
– many cells die or have function altered
– occurs when the dose is above given
threshold (characteristic for the given
effect) (below this dose, the effect is not
observable)
– severity increases with the dose
– A large number of cells are involved
Acute dose
Probability
> ~1000 mSv
100%

133. Deterministic (Non-Stochastic)
Radiation Effects
❖ Some of these effects occur quite quickly - within days or
weeks after the exposure.
❖ For such effects to occur a minimum radiation dose - a
threshold - has to be exceeded. Once the threshold is exceeded,
the severity of the effect increases with dose.
❖ This means that; the probability of causing such harm will be
zero at small doses (the threshold for clinical effect) the
probability will increase steeply to unity (100%).
❖ Thresholds for these effects are often at doses of a few Gy or
dose rates of a fraction of a Gy per year.

134. Note On Threshold Values
• Depend on dose delivery mode:
– single high dose most effective
– fractionation increases threshold dose in most
cases significantly
– decreasing the dose rate increases threshold in
most cases
• Threshold may differ in different persons

135. Deterministic (Non-stochastic)
Radiation Effects
The most common non-stochastic effects are;
1-Radiation sickness
2-Skin burns
3-Hair loss
4-Sterility
5-Damage to the eye

136. Deterministic Health Effects
Organ or tissue
Dose in less
than 2 days,
Gy
Deterministic effects
Type of effect
Time of
occurrence
Whole body (bone
marrow)
1
Acute Radiation
Syndrome (ARS)
1 – 2 months
Skin 3 Erythema 1 – 3 weeks
Thyroid 5 Hypothyroidism 1st – several years
Lens of the eye 2 Cataract
6 months - several
years
Gonads 3 Permanent sterility weeks

137. Tissue Reactions
(Deterministic effects)
Very large doses only
The bigger the dose, the more severe the effect
5000
3500
3000
2500
2000
500 500
150
0
1000
2000
3000
4000
5000
6000
Cataracts
Perm.male
sterility
Temp.
epilation
Female
sterility
Transient
erythema
Detectable
opacities
(lens)
Supressionof
bonemarrow
Temp.male
sterility
milli-sieverts
Staff doses never this big

138. Skin Injuries
• Radiation effects on
the skin can appear
several weeks after
the irradiation and
can be progressive

139. Skin Effects
• Skin effects are:
– Erythema: 1 to 24 hours after irradiation of about 3-5 Gy
– Alopecia: 5 Gy is reversible; 20 Gy is irreversible.
– Pigmentation: Reversible, appears 8 days after irradiation.
– Dry or moist desquamation: traduces epidermal hypoplasia
(dose  20 Gy).
– Delayed effects: teleangiectasia, fibrosis.

140. Hair Loss
Hair loss is another non-stochastic radiation
effect which may occur after a dose to the scalp
of 3Sv or more. Recovery takes place in the
months following the exposure unless the hair
follicles have been exposed to high doses.

141. Sterility
❖ A dose to the tests as low as 0.1 Sv can
depress sperm production for up to a year. 2.5
Sv will produce sterility for three years or
longer.
❖ The ovary is not as sensitive to radiation as
the testes, but doses of 1 to 2 Sv will cause
temporary sterility.

142. Damage To The Eye
Radiation to the lens of the eye
can cause cataract. The threshold
radiation dose for production of
detectable damage to the lens is
between 0.5 to 2 Sv, and for
production of visual impairment
is about 5 Sv.

143. DeterministicEffects In Children
Radiation dose of less than 0.1 Sv may cause
mental and growth retardation in children. The
younger children were more susceptible to these
effects than the older ones.

144. Stochastic Effects
Stochastic (Non-Threshold)
❑Generally occurs with a single cell (cell mutation) leading to cancer or
hereditary disease
❑Current theory says, no threshold
❑Probability of the effect (but not the severity) increases with dose

145. Stochastic Effects Of Radiation
❖ Low doses of radiation may affect only a few cells, perhaps
just one cell usually produce stochastic effects.
❖ Stochastic effects may result when an irradiated cell is
modified rather than killed.
❖ These effects appear after an interval of years or even
decades.
❖ There is no threshold for a stochastic effect, and the
probability of the effect occurring increases steadily as the
dose increases.

146. Stochastic Effects Of Radiation
The Stochastic effects of radiation are;
❖ Production of cancer,
❖ Genetic effects and
❖ Effect on life span.
Radiation Dose
Risk

147. Health Detriment For Stochastic
Effects
Includes these quantities:
❖the probability of fatal cancer,
❖the weighted probability of incurring a non fatal cancer,
❖the weighted probability of severe hereditary effects,
❖the length of lifetime lost.

148. Radiation Induced Cancer
❖ The production of cancer is the most important stochastic
effect of radiation.
❖ Modified somatic cells may subsequently, after a prolonged
delay, develop into a cancer.
❖ There are repair and defence mechanisms that make this a
very improbable outcome.
❖ The probability of cancer resulting from radiation increases
with increments of dose, probably with no threshold.
❖ The severity of the cancer is not affected by the dose.

149. Cancer Risk
• For adult worker, average risk of inducing fatal cancer is
4% per Sv
• i.e. risk from 0.1 mSv
= 0.04 x 0.0001
= 0.000004
= 1 in 250,000

150. Based upon studies of Hiroshima atomic bomb
survivors, statisticians predict that an effective dose
of 10 mSv (1 rem) given to a population of one
million would result in 400 additional cancer
deaths!
Cancer Risk

151. Radiation Induced Cancer
❖ The unborn child in the womb is more susceptible
to radiation-induced cancer.
❖ Children under the age of ten are more susceptible
to radiation-induced cancer than adults.

152. 0 10 20 30 40 50 60 70 80
(age at exposure)
20
15
10
5
0
Male
Female
Risk (%/ Sv) For Cancer Induction
By Age At Exposure And Sex
❖ The diagram illustrates the
increased risk for children
and young people.
❖ It shows the importance of
having special diagnostic
methods for kids and why
workers <18 year are not
allowed in the department.

153. Cancer Risks
❖It is assumed that any dose of radiation could potentially cause
cancer.
❖The bigger the dose, the more likely the effect will occur, (but
it will probably never occur).
❖i.e. a bit like crossing the road - the more times you cross the
more likely you are to be run over, but probably never will.

154. 0
10
20
30
40
50
0 10 20 30 40 50 60 70 80 90
Probability Of Fatal Cancer
(Atom bomb “survivors”)
• i.e. children risk  3 x adult risk
Risk per million per mGy

155. Effect On Life Span
There have been some suggestions that exposure
to ionizing radiation accelerates the process of
aging and accordingly reduce the life span.

156. Acute Versus Late Tissue Or
Organ Effects
• An organ or tissue expresses response to radiation damage
either as an acute effect or as a late (chronic) effect.
• Acute effects manifest themselves soon after exposure to
radiation and are characterized by inflammation, oedema,
denudation of epithelia and haemopoietic tissue, and
haemorrhage.
• Late effects are delayed and are, for example, fibrosis, atrophy,
ulceration, stenosis or obstruction of the intestine.

157. Effects of Ionizing Radiation
Early and Delayed Mnifestions of Radiation injury
Tissue/Cell Type Early Delayed
Radiosensitive epithelial and
parenchymal cells
Vessels
Stroma
Necrosis, primarily of stem
cells
Dilatation; necrosis of
endothelial cells; increased
vascular permeability
Edema
Ischemic atrophy; ulceration;
impaired stem cell reserves;
atypia, dysplasia and neoplasia
Sclerosis of small arteries and
arterioles; capillary
telangiectasia; hypertrophy of
endothelial cells
Fibrosis; collagen deposition;
abnormal fibroblasts

158. Human Responses To Ionizing Radiation
Early Effects
Acute Radiation
Syndrome
Hematologic Syndrome
Gastrointestinal syndrome
Central nervous system
Local Tissue damage Skin
Gonads
Extremities
Hematologic
depression
Cytogenic damage

159. Human Responses To Ionizing Radiation
Late Effects
Acute Radiation Syndrome Hematologic Syndrome
Gastrointestinal syndrome
Central nervous system
Other malignant disease Bone cancer
Lung cancer
Breast cancer
Leukemia
Genetically significant
dose
Lifespan shortening

160. Late Effects
• Late effects may be generic and caused by absorption of
radiation directly in the target tissue, or consequential to acute
damage in overlying tissues such as mucosa or the epidermis.

161. Delayed Effects Of Radiation
The effects of radiation on the human population can
be classified as either somatic or genetic:
• 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)

162. Somatic Effects
• Somatic effects are harm that exposed individuals suffer
during their lifetime, such as radiation induced cancers
(carcinogenesis), sterility, opacification of the eye lens
and life shortening.

163. Genetic Or Hereditary Effects
• Genetic or hereditary effects are radiation induced
mutations to an individual’s genes and DNA that can
contribute to the birth of defective descendants.
– Anemia
– Epilepsy
– Diabetes
– Asthma

164. Genetic Effects (Hereditary Effects)
❖ The hereditary effects of radiation result from damage
to a cell whose function is to transmit genetic
information to later generation (reproductive cells).
❖ This damage takes the form of genetic mutations in the
hereditary material of the cell.
❖ These effects may be of different kinds and severity.
❖ The risk of serious hereditary illhealth within the first
two generations following the irradiation of either
parent is about 10 per million per mSv.

165. Sensitive Subgroups
❖Highly radiosensitive persons are less than
0.1-1% of the population
❖The main problem occurs in radiotherapy
and not in diagnosis

166. Dose Splitting (Fractionation)
❖ The threshold doses given here are for
single acute exposure to radiation.
❖ In general the body is more able to tolerate a
given dose of radiation when the radiation
dose is split (fractionated) into smaller doses
and delivered over longer period of time.

167. In Fact A Little Bit Of Radiation ‘May’ Be
Good For You
• the physiological benefits of a low dose of IR have been
demonstrated in plants and animals
• benefits include
❖life lengthening
❖Growth
❖more offspring

168. Hormesis
• Some data indicate that low doses of
radiation are beneficial
• Not widely accepted
– Conservative is better
• But not impossible
Dose
DetrimentBenificial
Risk

169. Hormetic Effects Of Radiation
In contrast to the radiation hazards there have
been some claims that exposure to low levels of
ionising radiation might be beneficial. Effects of
this kind are often referred to as hormetic effects.
Possible hormetic effects are:
❖ An increased life span.
❖ A reduction in cancer frequency.
❖ Increased growth and fertility.