IAEA PGEC
Pre-Study Materials
Biology and Radiation Effects
IAEA
International Atomic Energy Agency
Table of Contents
Topic
Slide
Living Organisms and Cellular Structure………………... 5
Macromolecules………………………….…………............. 9
The Nucleus …………………………….…………………… 14
The Cell Cycle……………………………………………….. 21
Cellular Damage From Radiation…..……………………. 28
Cell Response to Radiation Damage…………………… 40
Cell and Organ Radiosensitivity ……………….............. 52
Relative Biological Effectiveness………………............. 59
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Table of Contents
Topic
Slide
Biological Effects (High Doses)……………………….
63
Deterministic Effects……………………………………
65
Acute Radiation Sickness……………………………...
69
Biological Effects (Low Doses)………………………..
79
Stochastic Effects……………………………………….
80
Linear No Threshold Concept………………………….
84
In Utero Radiation Effects………………………………
86
Review Problems………………………………………..
92
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Living Organisms
and Cellular Structure
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The Human Cell
•
The cell is the basic building block of life and the
structural & functional unit of all living organisms.
•
Human beings originate from a single cell; the zygote.
The zygote is formed by the union of a female egg and
male sperm.
•
Rapid division and differentiation occur during prenatal
development to form organs and tissues made up of many
cells.
•
Humans are multicellular with trillions of cells. Cells can
take in nutrients, produce energy, and perform specialized
functions in the human body.
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Typical Cellular Structure
•
Organelles are subcomponents of
cells with specific functions
analogous to organs of the human
body.
•
The main organelles are the
mitochondria, nucleus,
endoplasmic reticulum, golgi
complex, lysosomes and
ribosomes.
•
The cell membrane is a double
layered membrane that surrounds
the organelles and maintains the
integrity of the cell.
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Cellular Components
•
Cytoplasm is the viscous gel-like
substance that fills the cell and
contains organelles. Most cellular
activities occur in the cytoplasm.
•
Mitochondria are the sources of energy
for cell functions through the
metabolism of carbohydrates, fats, etc.
•
The endoplasmic reticulum processes
molecules and transports them to
specific destinations inside or outside
of cells.
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Cellular Components
•
The golgi apparatus, or complex,
processes and packages
molecules for transport out of cells.
•
Lysosomes break down cellular
waste materials to simpler
compounds.
•
Ribosomes synthesize proteins, a
macromolecule.
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Macromolecules
•
Cells contain macromolecules, organic molecules
consisting of many smaller structural units linked
together.
•
Four essential macromolecules found in the human
body are:
Proteins
Lipids
Nucleic Acids
Carbohydrates
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Proteins
•
Proteins are amino acids linked together by
peptide bonds. They are vital for metabolism
and can function as enzymes to catalyze
biochemical reactions. Proteins are important in
cell signaling, immune response and cell
structural and mechanical integrity.
Protein Structure
Amino Acid
Polypeptide
Intermediate Filament Protein
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Carbohydrates
•
•
Carbohydrates are organic molecules composed of
monosaccharides, simple sugars. They are a source of
energy storage in living organisms. Monosaccharides can
be linked together to form more complex carbohydrates
which are classified as disaccharides, oligosaccharides, and
polysaccharides.
Deoxyribose and
Ribose are
monosaccharides.
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Nucleic Acids
•
Nucleic Acids are linked nucleotides consisting
of a nitrogenous base, a five-carbon sugar and a
phosphate group. Nucleotides joined together
make up the structural units of DNA and RNA.
Nucleotide
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DNA
Lipids
•
Lipids are a fat-like substances that store needed
energy for the human body. Lipids include fats,
oils, steroids, phospholipids, fatty acids, etc.
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The Nucleus
•
The cell nucleus is the
center of activities in a
cell.
•
It is separated from
cytoplasm by an inner
and outer membrane
•
It houses chromosomes
containing DNA.
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Chromosomes
•
Chromosomes are a
condensed form of the
nucleic acids and proteins
in a cell.
•
Chromosomes are only
visible during cell division.
•
Chromosomes have a
constriction point called a
centromere which divide
them into a short arm (p)
and a long arm (q).
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Deoxyribonucleic Acid (DNA)
DNA is a nucleic acid found
in the nucleus of most of
the body's cells. It contains
the genetic instructions
required for cellular
development and function.
(Mature red bloods cells do
not contain DNA since they
do not have nuclei.)
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DNA Molecular Structure
•
DNA exists as two long,
paired strands. The strands
spiral around one another
forming a double helix.
•
The strands are joined by
chemical bases that can be
arranged in countless ways.
•
The four nitrogenous bases
found in DNA are adenine,
thymine, guanine and
cytosine.
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The order of the bases determines the
messages to be conveyed, much as
specific letters of the alphabet combine
to form words and sentences.
DNA Molecules
•
Nearly every cell in a
person’s body has the
same DNA.*
•
Each cell has 46
molecules of doublestranded DNA made up
of 50 to 250 million
bases.
*DNA in cells can be altered due to mutations.
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Genes
•
A gene is a given segment
along the DNA molecule.
•
Genes are found along
chromosomes in linear order
like beads on a string.
•
Each gene carries a particular
set of instructions for the cell.
•
There are about 25,000 genes,
and every gene is made up of
thousands of chemical bases.
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Genes and Cellular Function
•
Cells use genes
selectively.
•
Cells activate only the
genes needed and
suppress the rest. The
unique selection of
genes used by a cell
gives that cell its
character – making a
brain cell different from
a bone cell.
•
Genes also guide the
cell life cycle including
cell division.
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The Cell Cycle
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The Cell Cycle
•
Organisms must create new cells to continue life.
•
The series of events that take place in a cell leading to
cell division and replication is referred to as the Cell
Cycle.
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Stages of the Cell Cycle
The three major phases of the cell cycle are interphase,
mitosis, and cytokinesis.
•
Interphase is a preparation phase when the cell is
taking in nutrients and growing to prepare for cell
division.
•
Mitosis divides the chromosomes in a cell nucleus
into two identical sets of nuclei.
•
Cytokinesis immediately follows mitosis producing
two distinct daughter cells after the cytoplasm
divides.
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Interphase
Interphase occurs in the following three
phases:
•
Gap 1 (G1) – The cell increases
in size as it prepares for DNA
synthesis.
•
Synthesis (S) – DNA replication
occurs in this phase.
•
Gap 2 (G2) – The cell continues to
grow in preparation for cell
division.
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*G0, is a temporary or
permanent resting phase
when a cell is not dividing
or preparing for division.
For example, mature
nerve cells (neurons)
remain in G0.
Mitosis and Cytokinesis
Mitosis occurs in four major phases:
•
Prophase – chromosomes are
visible and the nuclear
membrane and nucleolus
disappear.
•
Metaphase – chromosomes line
up across center and spindle
fibers attach.
•
Anaphase – chromosomes split
and each half is pulled to
opposite side of the cell.
•
Telophase - chromosomes
cluster in the center of each cell
and cell separation begins
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Nuclear membrane
Nucleolus
Chromosomes
Cytokinesis completes the cell
division process when the cytoplasm
splits and two distinct daughter cells
are formed. .
Cell Cycle Checkpoints
•
Cell cycle checkpoints are
found at various phases of
the cell cycle to verify that
the processes have been
completed accurately
before proceeding to the
next phase.
•
Checkpoints assess DNA
damage and can initiate a
delay to allow for DNA
repair or target a cell for
destruction.
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Meiosis
•
Meiosis is a form of cell
division that occurs with
reproductive cells.
•
Two sequential cell
divisions occur during
meiosis resulting in four
daughter cells.
•
The four daughter cells
have half the number of
chromosomes as the
original cell and will
develop into sperm and
egg cells.
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Cellular Damage
from Radiation
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Cellular Damage
•
Studies have shown that the cell nucleus is the
most radiosensitive structure in the cell due to
the damage that can occur to DNA.
•
Ionizing radiation can break bonds in DNA
molecules resulting in mutations, cell death or
carcinogenesis.
•
DNA is considered the critical biological target
for ionizing radiation.
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Radiation Damage
•
Biological effects to the cell result from both
direct and indirect action of radiation.
•
Direct effects are produced by the initial action
of the radiation itself.
•
Indirect effects are caused by the later chemical
action of free radicals and other radiation
products.
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Direct Effect
•
•
When radiation or
secondary ions break the
chemical bonds of
critical biological
molecules in human
cells.
This effect is more
dominate for high linear
energy transfer (LET)
radiations such as alpha
particles or neutrons.
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alpha
++
Indirect Effect
•
When radiation interacts with
cellular water, it can break
bonds that hold the water
molecules together producing
hydrogen (H) and hydroxyl
(OH) free radicals.
•
Free radicals are highly
reactive agents with unpaired
electrons.
•
The free radicals can
recombine or interact with
other radicals and ions to form
compounds that can damage
the cell.
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Indirect Effect
•
One important free radical is
the hydroxyl radical (OH•).
•
Two of these radicals can
combine to form hydrogen
peroxide (OH• + OH•  H2O2);
a powerful oxidizing agent that
can attack and damage DNA
by breaking chemical bonds.
•
Since cells are about 80%
water, the indirect effect is
believed to be more likely to
occur than the direct effect.
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Radiation Damage to DNA
The major types of DNA damage caused by bond
breaks from ionizing radiation are
•
DNA base damage
•
Single - strand breaks
•
Double - strand breaks
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DNA Base Damage
•
DNA base damage is
primarily caused by
interactions of free
radicals from the
indirect effect with
the nitrogenous
bases.
•
DNA base damage
can result in
misrepairs which can
cause mutations.
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Bonds are broken between the bases
Single Strand Breaks
•
Radiation damage can cause a break in the bond
in a single strand of DNA.
•
Single strand breaks are readily repaired using
the opposite strand as template.
•
Incorrect repairs (misrepairs) can lead to
mutations.
Single
strand
breaks
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Single Strand Breaks
Phosphate
Single strand bond
breaks can occur in the
deoxyribose-base bond
or the phosphatedeoxyribose bonds in
DNA.
Deoxyribose or sugar
Phosphate – deoxyribose bond
desoxyribose-base bond
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Double Strand Breaks
•
Breaks in both strands of DNA that are opposite, or
separated by only a few base pairs are called Double
Strand Breaks.
•
They can occur from the same particle, with enough
energy to create two breaks or by two particles, one after
the other, in a short enough time before repair of the first
break.
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Double Strand Breaks
•
The phosphate-sugar
bonds are broken on both
strands of DNA double
strand breaks.
Phosphate –desoxyribose bond
•
High-LET radiations are
responsible for most
double strand breaks.
•
Double strand breaks are
not easily repaired.
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Cellular Response to DNA Damage
Cellular response following DNA damage will vary
depending on the type of damage to the DNA.
•
Cells can repair DNA damage using repair
mechanisms. Repairs are not always successful
and misrepairs can occur.
•
Cellular death can occur resulting in the complete
loss of cell function or a cell’s ability to proliferate.
•
Cells can enter a state of unregulated cell division.
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Cell Response to DNA Damage
Cellular
Metabolism
Cell Cycle
Arrest
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Viral Attacks
Ionizing
Radiation
Transcriptional
Program Activation
Chemical
Exposure
DNA Repair
(Different repair pathways
can repair some DNA
Damage. Misrepairs can
occur leading to
mutations)
Replication
Errors
Apoptosis
Cellular Death
Cellular death can have different meanings depending on the
type of cells affected by the radiation damage.
•
For differentiated cells like muscle & nerve cells, cellular
death is defined as a loss of a specific function.
•
Proliferating cells can loose their ability to divide. The
cell succeeds in dividing for several cycles, but ends up
by decaying and dying. This is refereed to as delayed
cell death or a loss of the cell’s reproductive integrity.
•
Necrosis can occurs when the cell cannot control
subsequent decay.
•
Cells also can die via apoptosis; a programmed cell
suicide process.
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Cell Necrosis
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Cell Response to DNA Damage
Apoptosis, or
programmed cell
death can occur
after radiation
damage.
Damaged cells
are removed
from the cellular
population.
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Mutations and Aberrations
•
Although cells have the
ability to repair DNA
damage and do it
continually, misrepair can
result in mutations.
•
Not all DNA mutations are
manifested as a disease or
defect.
•
Damage to cellular DNA
from radiation-induced
breakage can lead to
chromosome aberrations.
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Chromosome Aberrations
•
•
Ionizing radiation can
cause chromosomal and
chromatid aberrations.
Chromosome aberrations
occur early in interphase
before DNA duplication.
Chromatid aberrations
occur after DNA
replication.
Rings, dicentrics and
fragments are the most
common types of
aberrations observed.
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fragment
dicentric
dicentric
fragment
ring
Hereditary vs. Acquired Mutations
Acquired mutations are caused by environmental
factors such as diet, smoking, and radiation exposure.
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Radiation Induced Cancers
•
Cancer is uncontrolled cell growth.
•
All cancer is triggered by gene mutations. Genes
that control the orderly replication of cells
become damaged, allowing the cells to
reproduce without restraint.
•
Cancer usually arises in a single cell. However,
the cell's progression from normal to malignant
appears to involve a series of mutations or
changes.
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Stages of Cancer Development
The three major stages of cancer
development are :
•
Initiation – Initiators damage
DNA which can lead to a cell
mutation.
•
Promotion - Certain
compounds can promote
proliferation of a mutated
cell which can give rise to a
tumor.
•
Progression is the
transformation of a tumor to
a spreading malignancy.
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Mutations and Cancer
Promotion
Initiation
Progression
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Radiosensitivity of
Different Cells and
Organ Systems
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Cell Radiosensitivity
Generally, cells are more
radiosensitive if they meet the
following criteria:
•
Have high mitotic rate
•
Have a long mitotic future
(i.e., undergo numerous
divisions in the course of
their lifetime)
•
Are of an unspecialized type
(i.e., less differentiated)
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Cell Radiosensitivity
Cells can be arranged in the following order of
sensitivity:
•
•
•
•
Blood forming stem cells
Reproductive and GI stem cells
Skin stem cells
Mature nerve, muscle and brain
cells
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more sensitive
less sensitive
Stem Cells
•
Stem cells are cells that retain the instructions to
either continue developing undifferentiated or to
form specific tissues
•
Their function is to provide specialized cells
while ensuring a means of reproducing
additional stem cells if needed.
•
For example, stem cells in the basal skin layer
produce new skin cells.
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Blood Stem Cells
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Blood Forming Organs
•
Blood cells are produced by cells
in the red bone marrow and
include:
•
Red blood cells (carry oxygen to
cells and carbon dioxide away)
•
White blood cells (fight infection)
•
Platelets (form clots)
•
Damage to stem cells in the red
bone marrow inhibits the
production of blood cells.
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Small Intestine
•
The small intestine contains
stem cells that form epithelial
lining.
•
These epithelial cells are
constantly being replaced.
•
Damage to the stem cells
prevents replacement of the
epithelial lining and thus
inhibits uptake of nutrients.
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Epithelial
Lining
Relative Biological
Effectiveness (RBE)
•
Different types of radiation do not produce the same
biological effects.
•
The ability of a given type of radiation to damage biological
tissue is measured in terms of Relative Biological
Effectiveness (RBE).
•
Radiation with a high linear energy transfer (LET) will
produce a greater biological effect than lower LET radiations.
•
For example, a dose of 1 Gy from neutrons does not produce
the same biological effect as a dose of 1 Gy from x-rays.
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Radiation Weighting Factors
Radiation Weighting Factors are used in radiation
protection to adjust for differing biological effects.
Radiation Type and Energy Range
wR
Photons
1
Electrons and muons
1
Protons and charged pions
2
Alpha particles, fission fragments,
heavy ions
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20
Radiation Weighting Factors
Radiation Type and
Energy Range
Neutrons
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wR
A continuous function of
neutron energy
Equivalent Dose
•
Radiation weighting factors are used to calculate a biological
meaningful quantity called Equivalent Dose.
•
The equivalent dose in a tissue T is calculated using the
following:
HT = 𝑹 wR DT,R
where DT,R is the absorbed dose averaged over the tissue or
organ T, due to radiation R.
•
Absorbed dose is a measure of energy deposited by radiation
in a given mass of any material expressed in the SI unit of
Gray (Gy). Absorbed dose applies to all ionizing radiations at
all energies in all media, including human tissue.
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Biological Effects
from High Doses
of Radiation
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Biological Effects Overview
Radiation damage to DNA begins at the cellular level but can
eventually cause harmful tissue reactions which can effect
organs and the whole body.
Atom
Molecule
Radiation ionizes atoms
(knocks out electrons)
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Deterministic Effects
•
Harmful tissue reactions that occur at relatively high doses are
called deterministic effects.
•
Deterministic effects have a dose threshold and will not occur
at doses below the threshold. The severity of the effect
increases with dose.
•
Radiation damage (serious malfunction or cell death) to
collective populations of cells in given tissue must occur
before the effects appear.
•
Deterministic effects can appear early (days to weeks) or later
(months to years) after exposure.
•
These effects can be prevented altogether if dose is kept below
the threshold.
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Deterministic Effects
•
Doses below 100 mGy delivered over a short period
of time do not result in measurable changes to
biological tissues.
•
Examples of deterministic effects are:
•
•
•
•
•
Blood count changes
Sterility (temporary or permanent)
Skin Burns
Cataracts
Acute Radiation Sickness
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Severity
Deterministic Dose
Response Relationship
The severity of
the effect
increases as
the dose
increases.
For each
deterministic
effect there is a
threshold dose
below which the
effect may not
occur.
Dose
Threshold
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Typical Deterministic Dose Response
Curve
The dose threshold will
vary according to the
health, age and physical
characteristics of the
exposed individuals.
However, there is a
threshold where 100% of
the exposed population
experiences the effect.
Dose (Gy)
Note: Since the threshold values vary, ranges are often
reported. Some ICRP publications publish the threshold doses
for deterministic effects at a 1% incidence rate.
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Acute Radiation Sickness
•
Acute Radiation Sickness (ARS) results from a
large dose of radiation delivered to the whole
body over a very short time period
•
Signs and symptoms of ARS will vary based on
the amount, duration and type of exposure.
•
ARS can be divided into three syndromes:
• Hematopoietic or Blood Syndrome
• Gastrointestinal (GI) Syndrome
• Central Nervous System (CNS) Syndrome
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Hematopoietic (Blood Syndrome)
•
Hematopoietic syndrome develops at doses greater 1 – 2
Gy.
•
Radiation damage halts the ability of blood stem cells to
reproduce. This diminishes the subsequent supply of red
blood cells, white blood cells and platelets.
•
Signs and symptoms include nausea, vomiting, malaise
and fatigue. Loss of hair (epilation) occurs during the 2nd
or 3rd week after exposure. Death is likely to occur within 1
– 2 months after exposure for doses greater than 2 Gy.
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Blood Syndrome
Lymphocytes (Percent of Normal)
A decrease in blood
lymphocytes is the
first sign of
hematopoietic
syndrome. The
decrease appears
within a few hours or
days after irradiation.
50-75% of the
lymphocytes are
destroyed at doses
above 2-3 Gy.
Lymphocyte Changes in Humans from Accidental Radiation
Exposure as a Function of Dose
Time after Exposure (Days)
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GI Syndrome
•
GI syndrome occurs at does above 7 - 10 Gy.
•
The tissue at risk is epithelial lining of small intestine.
•
Effects include nausea, vomiting, and diarrhea.
•
Death is almost certain within 3-14 days at doses over 10 Gy.
•
Causes of death
include infection,
bleeding, dehydration,
electrolyte imbalance,
and circulatory collapse.
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CNS Syndrome
•
CNS Syndrome occurs at doses about 15 Gy.
•
The organ at risk is the brain.
•
Effects include lethargy, convulsions, tremors, loss
of muscle control, and coma (in addition to effects
from other syndromes).
•
Death will occur within hours to a few days for
doses greater than 50 Gy.
•
The causes of death include respiratory and
circulatory collapse.
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Lethal Dose (LD) 50/60
•
The LD 50/60 is defined as the acute dose at which
50% of the exposed population will die within 60 days
without medical treatment.
•
The LD 50/60 for human beings is about 3-5 Gy for a
whole body dose.
•
Acute doses above about 10 Gy are usually fatal,
even with medical treatment.
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LD 50/60
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Range of Deterministic Effects
Dose (gray)
Effect
0.25 - 0.50
Detectable changes in blood chemistry but no
physical symptoms.
1- 3
Some physical symptoms - skin reddening and loss
of hair. at the high end of the range, vomiting is
caused shortly after exposure.
3 - 4.5
Vomiting is first symptom. Major loss in ability to
produce blood.
4-5
(LD50/60)
Death to 50% of the population within 60 days if no
medical treatment.
4.5 - 10
At upper end, bone marrow transplants needed. Fatal
within one month without medical care.
10 - 50
Vomiting, loss of blood production, failure of GI
system. Fatal within several days.
> 50
Central nervous system failure. Death within hours
or days.
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Deterministic Thresholds for Specific Organs &
Tissue After Whole Body Gamma Exposure
Organ or tissue
Absorbed
Dose
(Gy)
Deterministic effects
Type of effect
Time of
occurrence
Skin
3-6
Main Phase of
skin reddening
1 – 4 weeks
Skin
4
Temporary Hair
Loss
2 – 3 weeks
Eyes
1.5
Cataracts (Visual
several years
Impairment)
Ovaries
3
Permanent
Sterility
< 1 week
Testes
6
Permanent
sterility
3 weeks
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Deterministic Effects for Partial
Body Irradiation
•
When only a small portion of the body receives
high doses, local effects will be observed, but
Acute Radiation Sickness will not occur.
•
Critical tissues are the skin, thyroid, lung, lenses
of the eye and gonads, etc.
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Biological Effects
from Low Doses of
Radiation
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Stochastic Effects
•
The principal effects of doses < 100 mSv are nonlethal cell mutations.
•
If the cell is not killed but the DNA is changed, it
may give rise to a mutated cell.
•
If any cell, capable of dividing, is damaged by
radiation, a cancer may eventually develop.
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Stochastic Effects
•
Stochastic effects generally occur without a dose
threshold and the probability of occurrence of the
effect is a function of dose. The severity of
stochastic effects is independent of the dose
received.
•
Stochastic effects include:
•
Radiation Induced Cancers
•
Hereditary genetic effects (not proven in humans)
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Stochastic Cancer Effects
•
Radiation induced cancers have been well
documented from studies of Atomic Bomb
survivors, uranium miners and early users of
radiation in the medical field.
•
Radiation can produce cancers in blood forming
tissues, skin, bone, lung, thyroid and connective
tissues.
•
The majority or radiation induced cancers have
a latency period of at least 10 years. Leukemia,
cancer of the blood, has a shorter latency
period of ~2 - 4 years after exposure.
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Stochastic Hereditary Effects
•
If the damage caused by radiation occurs in the
reproductive cells, it may be transmitted and
become manifested as hereditary disorders in
the descendents of the exposed individual.
•
These effects have not been proven in humans,
but experimental studies on plants and animals
suggest that effects can occur. Health effects
may range from undetectable to gross
malformation, or loss of function to premature
death.
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Linear Non-Threshold Model
•
The Linear Non-Threshold (LNT) Model is a dose
response model, based on the assumption that
in the low dose ranges, the risk or probability of
developing stochastic effects increases with
dose.
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Dose-Response Relationship for
Stochastic Effects
The Linear Non- Threshold
(LNT) Model :
•
Every increment of
radiation, no matter
how small increases
the probability or risk
of developing a
stochastic effect.
•
The dose response is
linear.
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In Utero Radiation
Effects
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In Utero Radiation Effects
•
The human embryo and fetus are
highly sensitive to the effects of
radiation.
•
Radiation sensitivity varies
according to the stage of pre-natal
development. The embryo/fetus is
more sensitive during the period of
organogenesis.
•
In Utero effects are different from
hereditary effects because the
embryo/fetus is being irradiated.
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In Utero Radiation Effects
The principal effects of in utero exposure are:
•
Growth retardation
• Mental retardation
•
Childhood cancer
• Developmental abnormalities
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Growth Retardations
•
With children, growth retardations of the brain and skull
have been found very pronounced after prenatal
radiation doses in the order of 0.5 Gy.
•
The high radiosensitivity of the central nervous system
can be explained by the fact that the development of the
brain takes the longest time and is most complex.
•
For atomic bomb survivors a reduced circumference of
the head has been observed.
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Mental Retardation
•
Severe mental retardation can occur when the brain
is forming during the early stage of pre-natal
development.
•
A study of about 1600 children exposed in-utero at
Hiroshima and Nagasaki to various radiation doses
and at various developmental stages identified
clinically severe mental retardation in some dose
groups.
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Cancer Development from In Utero
Radiation Exposure
•
Studies have shown that there is an increased risk of
developing childhood cancers of all types following inutero irradiation.
•
The lifetime cancer risk following in-utero exposure is
similar to the risk following irradiation in early
childhood, i.e. about three times that of the population
as a whole.
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REVIEW PROBLEMS
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Problem 1
What is the critical biological target for
ionizing radiation?
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Problem 2
The radiation __________ effect occurs
when DNA is damaged by free radicals
or other reactants created by radiation
interaction with cellular water.
a) Direct
b) Indirect
c) Stochastic
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Problem 3
Cells can repair a portion of radiation
damage.
a) True
b) False
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Problem 4
When DNA is damaged by radiation, it is
always manifested as a disease or
defect.
a) True
b) False
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Problem 5
Most cancers originate from how many
cells?
a) One
b) Two
c) Five
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Problem 6
______ is a free radical produced from the
indirect effect of radiation interacting with
cellular water.
a) H2O2
b) OH
c) H2O
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Problem 7
______ is an oxidizing agent that is
produced from the chemical actions
associated with the indirect effect of
radiation.
a) H2O2
b) OH
c) H2O
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Problem 8
Cells are more radiosensitive if they
have a ______ division rate.
a) low
b) moderate
c) high
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Problem 9
Cells are more radiosensitive if they are
a) unspecialized
b) more differentiated
c) specialized
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Problem 10
_____ and ____ are examples of
stochastic effects of radiation exposure.
a) Cancer and hereditary genetic effects
b) ARS and cancer
c) Erythema and hereditary genetic effects
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Problem 11
The linear non-threshold concept means
the probability of ___________ effects
occurring increase with dose.
a) Deterministic
b) Indirect
c) Stochastic
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Problem 12
Hematopoietic, GI and _________
syndromes are all part of acute radiation
sickness.
a) Central Nervous System
b) Erythema
c) Cancer
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Problem 13
What is the approximate value of LD
50/60?
a)
b)
c)
d)
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1 - 2 gray
2 - 3 gray
3 - 5 gray
9 - 10 gray
Problem 14
Hereditary genetic effects are _________
effects of ionizing radiation exposure.
a) threshold
b) deterministic
c) stochastic
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Review Problem Solutions
1.
2.
3.
4.
5.
6.
7.
DNA
b) Indirect
True
False
a) one
b) OH
b) H2O2
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8.
9.
10.
11.
12.
13.
14.
c) high
a) unspecialized
a) cancer and hereditary genetic effects
c) stochastic
a) Central Nervous System
C) 3 - 5 gray
C) stochastic
END OF
BIOLOGY AND
RADIATION EFFECTS
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