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RADIATION PHYSICS
DR. MOHAMMED MOSTAFA EMAM
INAYA MEDICAL COLLEGE (IMC)NMT 232
1
Radiation:
It is defined as the process by which
energy is emitted from a source and
propagated through the surrounding
medium.
2
• This appear is a nucleus; the red ones aregoing to be the protons and the blue ones aregoing to be the neutrons.
NUCLEUS CHARACTERISTICS
3
• If we look at the periodic table, we can see neon has same number of proton and neutron, similar way calcium also has same no. of neutrons and protons.
Stable atoms
NUCLEUS CHARACTERISTICS
4
• Uranium have 92P and 146N.
Why is that???
Nucleus is held together by a strongnuclear force; All these nucleons are heldtogether by this force (came fromneutrons) which hold the nucleustogether.
NUCLEUS CHARACTERISTICS
5
Radioactivity : It is the act of emitting radiation
spontaneously from the unstable atoms.
Unstable atoms differ from stable atoms
because they have an excess of energy or
mass or both.
Unstable atoms are known as radioactive
atoms.
E.g. Carbon 14, Uranium 238
6
7
CLASSIFICATION OF RADIATION
Radiation
Non-ionizing Ionizing
Directly ionizing;
(charged particles)
electrons, protons, etc
Indirectly ionizing
8
NON-IONIZING RADIATION
Non-ionizing radiation refers to any type of
electromagnetic radiation that does not carry
enough energy to ionize an atom or molecule.
Examples:
Near ultraviolet radiation
infrared radiation,
microwave,
radio waves, etc
9
IONIZING RADIATION
Ionizing radiation has sufficient energy to ionize anatom or molecule.
Ionization is a process in which a charged portionof a molecule (usually electron) is given enoughenergy to break away from the atom.
Ionization results in the formation of chargedparticles or ions; the molecule with net positivecharge and the free electron with a net negativecharge.
All ionizing radiation is capable, directly andindirectly of removing electrons from most of themolecules.
Ionizing radiation has enough energy to damageDNA in cells which in turn may lead to cancer.
10
ALPHA RADIATION
11
12
Characteristics of alpha radiation:
Alpha radiation is not able to penetrate skin.
Alpha emitting materials can be harmful to
humans if the materials are inhaled, swallowed
or absorbed through open wounds.
13
Characteristics of alpha radiation:
Alpha radiation is not able to penetrate skin.
Alpha radiation is the least penetrating.
It can be stopped (or absorbed) by a sheet of paper.
14
Characteristics of alpha radiation:
When alpha particles are emitted outside our bodies, virtually all of their ionizing radiation is harmlessly absorbed by the nonliving outer layer of our skin.
This means that alpha radiation doesn’t have much effect on our health unless radioactive isotopes get inside our bodies and emit radiation internally .
15
Alpha radiation travels a very short distance
through air.
A variety of instruments have been
designed to measure alpha radiation.
Instruments can not detect alpha radiation
even a thin layer of water, blood, dust, paper
or other material, because alpha radiation is
not penetrating
16
USES OF ALPHA RADIATIONS
Alpha particles are most commonly used in
smoke alarms (smoke detectors). The alpha
particles ionize air between a
small gap. A small current is
pass through the ionized air.
Smoke particles from fire that
enter the air gap reduces the current flow,
sounding the alarm.
Alpha decay can produce safe power sources
for radioisotope thermoelectric generators
used for space probes and artificial heart
pacemakers.
17
BETA RADIATION
Beta radiation is a stream of electrons called beta
particles. When a beta particle is ejected, a neutron
in the nucleus is converted to a proton, so the mass number of nucleus is unchanged, but the atomic number increases by one unit.
18
Thorium undergoes radioactive decay to form Protactinium and beta particle.
19
Beta radiation is more hazardous because it can
also cause ionization of living cells. If the particles
hits a molecule of DNA it can cause spontaneous
mutation and cancer.
Characteristics of beta radiation:
20
Beta emitting contaminants may be harmful if deposited
internally.
Beta radiation may travel meters in air and is moderately
penetrating, so It can penetrate human skin to “germinal
layer” where new cells are produced.
Characteristics of beta radiation:
21
Beta radiation is more hazardous because it can
also cause ionization of living cells. If the particles
hits a molecule of DNA it can cause spontaneous
mutation and cancer.
Characteristics of beta radiation:
22
Beta radiation is more hazardous because it can
also cause ionization of living cells. If the particles
hits a molecule of DNA it can cause spontaneous
mutation and cancer.
Characteristics of beta radiation:
23
Beta radiation cannot be detected with an ionization
chamber such as a CD V-715.
Clothing and turnout gear provide some protection
against most beta radiation. Turnout gear and dry
clothing can keep beta emitters off of the skin.
24
USES OF BETA RADIATIONS
Beta radiation are widely used in medicine. In
brachytherapy, beta radioisotopes can be used to
irradiate areas inside a patient to prevent the growth
of certain tissues.
Beta particles are also used in some forms of
therapy to kill cancer cells.
25
USES OF BETA RADIATIONS
• Brachytherapy is a procedure that involves placing radioactive material inside your body.
• Brachytherapy is one type of radiation therapy that's used to treat cancer.
26
USES OF BETA RADIATIONS
• Brachytherapy is sometimes called internalradiation.
• Brachytherapy allows doctors to deliverhigher doses of radiation to more-specificareas of the body, compared with theconventional form of radiation therapy(external beam radiation) that projectsradiation from a machine outside of yourbody.
27
USES OF BETA RADIATIONS
• Brachytherapy may cause fewer side effectsthan does external beam radiation, and theoverall treatment time is usually shorter withbrachytherapy.
28
USES OF BETA RADIATIONS
Beta radiation is used in leak detection
in the pipeline. This is achieved by
adding small amount of beta radiation
to the fluid.
The area above the ground where high
intensity of beta radiation is detected
will pin point the leak sources in the
pipeline.
29
USES OF BETA RADIATIONS
• Carbon-14 is used as tracers in
chemical and biological research.
• The age of the ancient organic
materials can also be found by
measuring the amount of Carbon-14that is left.
30
GAMMA RADIATION
Gamma radiation is electromagnetic radiation of
high frequency and therefore high photons with a
very short wavelength.
31
GAMMA RADIATION
The emission of gamma radiation results from an
energy change within the atomic nucleus.
32
GAMMA RADIATION
• It should be noted that the emission of gamma rays does not change the mass number or atomic number of the nucleus.
33
GAMMA RADIATION
• Alpha and beta emission are often accompanied by
gamma emission, as an excited nucleus drops to a
lower and more stable energy change.
34
X-RAYS
X-ray photons carry enough energy to ionize atoms
and disrupt molecular bond.
This makes it a type of ionizing radiation and
thereby harmful to living tissues.
X-ray machine sends individual x-ray particles
through the body. The image is recorded on a
computer or film.
35
Characteristics of gamma radiation and x-rays:
Gamma radiation and X-rays are electromagnetic
radiation like visible light, radio waves, and
ultraviolet light. These electromagnetic radiations
differ only in the amount of energy they have.
Gamma rays and X-rays are the most energetic of
these.
X-rays are like gamma rays. They, too, are
penetrating radiation.
36
Gamma radiation is able to travel many meters in air
and many centimeters in human tissue.
Radioactive materials that emit gamma radiation and
X-rays constitute both an external and internal hazard to
humans
Gamma radiation or X-rays frequently accompany the
emission of alpha and beta radiation
37
Gamma radiation is detected with survey
instruments, including civil defense instruments.
Low levels can be measured with a standard Geiger
counter, such as the CD V-700. High levels can be
measured with an ionization chamber, such as a CD
V-715.
Instruments designed solely for alpha detection will
not detect gamma radiation
Pocket chamber (pencil) dosimeters, film badges,
thermo luminescent, and other types of dosimeters
can be used to measure accumulated exposure to
gamma radiation.
38
USES OF GAMMA RADIATIONS
Even after it has been packaged, gamma rays can
be used to kill bacteria, mould and insects in food.
This process prolongs the shelf-life of the food, but
sometimes changes the taste.
Gamma rays are also used to sterilise hospital
equipment, especially plastic syringes that would be
damaged if heated.
39
The most common tracer is called Technetium-99 and is
very safe because it only emits gamma rays and doesn't
cause much ionization.
• Radioisotopes can be used for medical purposes, such
as checking for a blocked kidney.
To do this a small amount of Iodine-123 is injected into
the patient, after 5 minutes 2 Geiger counters are placed
over the kidneys.
• Also radioisotopes are used in industry, to detect leaking
pipes. To do this, a small amount is injected into the pipe.
It is then detected with a GM counter above ground.
40
Checking welds. If a gamma source is placed on
one side of the welded metal, and a photographic
film on the other side, weak points or air bubbles will
show up on the film, like an X-ray.
Because Gamma rays can kill living cells, they are
used to kill cancer cells without having to resort to
difficult surgery. This is called "Radiotherapy", and
works because cancer cells can't repair themselves
when damaged by gamma rays, as healthy cells can
41
USES OF X-RAYS
X-rays are used in medicine for medical analysis.
Dentists use them to find complications, cavities and
impacted teeth. Soft body tissue are transparent to
the waves. Bones also block the rays.
X-rays are used in industry to inspect
products made by various kinds of
materials. X-ray machines are used
in airports to check luggage etc.
42
In Science x-rays are used to analyze the
arrangement of atoms in many kinds of substances,
particularly crystals. Archaeologists used X-rays to
examine ancient objects covered by a crust of dirt.
X-rays are also used in consumer goods the
manufactures treat certain kinds of plastic to check
the quality of many mass produced products.
43
How does radiation injure people?
• High energy radiation breaks chemical
bonds or DNA molecules.
• This creates free radicals, like those produced
by other insults as well as by normal cellular
processes in the body.
• The free radicals can change chemicals in the body.
• These changes can disrupt cell function and may kill
cells.
+
-
44
Genomic
Instability
Sometimes DNA
damage produces
later changes
which may
contribute to
cancer.
Gene
Expression
A gene may
respond to the
radiation by
changing its
signal to
produce
protein.
Effects of DNA Damage
DNA is the most important moleculethat can be changed by radiation
Studies have shown that most radiation-induced DNA
damage is normally repaired by the body
Gene
Mutation
Sometimes a
specific gene is
changed so that
it is unable to
make its
corresponding
protein
properly
Chromosome
AberrationsSometimes the damage effects
the entire chromosome,
causing it to break or recombine in
an abnormal way. Sometimes parts of two different chromosomes
may be combined
Cell Killing
Damaged DNA
may trigger
apoptosis, or
programmed
cell death. If
only a few
cells are
affected, this
prevents
reproduction of
damaged DNA
and protects
the tissue.
45
How does this damage from ionizing
radiation effect our bodies?
Cancer
Sufficient Cell Killing Sufficient Genetic
Alterations
Radiation Sickness
46
RadiationDose
47
Radiation Dose
One of the most confusing things about
understanding radiation effects is visualizing “how
much” radiation is involved. It is very difficult to keep
the units which measure radiation straight. A number
describing the amount of radiation means nothing
without evaluating the units, but this is not easy.
For example...
48
...try to match the letter with the amount of radiation involved in each example
• Amount of potassium 40 in the body
• Dose to Atomic bomb survivors
• You can safety hold this amount of alpha radiation
• One coast to coast flight
• A diagnostic X-ray
A. Billions of becquerels
B. About 250 picocuries
C. 2-10 millirem
E. 2
millirads
D. 0-5 Gy
49
Commonly Used Radiation Units
Absorbed dose (Gray or rad)
Average dose
Organ dose
Dose commitment
Collective dose
Effective dose (Sievert or rem)
Committed effective dose
Equivalent dose
Collective equivalent dose
Committed equivalent dose
Uniform equivalent dose
Dose equivalent
Collective dose equivalent
Ambient dose equivalent
Directional dose equivalent
Individual dose equivalent
Individual dose equivalent, penetrating
Individual dose equivalent, superficial
Dose and dose-rate effectiveness factor
Man-gray
Man-sievert
Tissue weighting factor
Relative biological effectiveness (RBE)
Quality factor (Q)
Fatality probability coefficient
Nominal fatality probability coefficient
Radiation weighting factor (wR)
Linear energy transfer (LET)
Radioactivity (Becquerel or curie)
Each of these units has a
different technical meaning.
All are used by experts to talk
about radiation. With so many
terms, you can see why it is
important to know what the
unit means when you are
evaluating radiation
information.
RAD
BecquerelSievert
50
ActivityThe number of times, each second, a radioactive material decays and releases radiation.
Exposure Amount of ionization per mass of air due to x and gamma rays.
Dose (Absorbed)The amount of radiation energy absorbed into a given mass of tissue.
Dose (Equivalent) H & Effective dose equivalent (HE )Measures the energy per unit mass times adjustments for the type of radiation;
Involved Radiation (quality factor) and the biological response in the tissue (a weighting factor).
* Equivalent dose converts dose into a measure of risk.
Understanding Radiation Units
51
Activity• Disintegration/sec=1 Becquerel (Bq)
• 37 billion Bq = 1 curie
Exposure
• Roentgen
Dose (Absorbed)
• 1 joule/kg=1 Gray(Gy)
• 1Gray=100 rad =100,000 mrad
Dose (Equivalent)
• Gray x quality factors= Sievert (Sv)
• 1 Sievert =100 rem =100,000 mrem
Understanding Radiation Units
Standard Units
S.I. Units
52
What is the meaning of activity?
This is the expectation rate of spontaneous nuclear transitions in a source.
Becquerel = 1 disintegration/second.
• This is the SI unit for measuring radioactivity.
Curie.
• Defined as 3.7 x 1010 disintegrations per second= 3.7 x 1010 Bq.
This is the activity of 1 gram of radium
in equilibrium with its decay products
• The Rutherford. 1 Rd = 106Bq.
ACTIVITY
53
More curies = a greater amount of radioactivity.
A large amount of material can have a very small amount
of radioactivity; a very small amount of material can have
a lot of radioactivity.
54
How much is a Becquerel (Bq)?
• The natural 40K activity in the body of an adult human of normal weight is4000-6000 Bq.
• There is an average of about 50 Bq per cubic meter of air inside a homefrom radon.
• Even though a 60Co source of strong gamma radiation containing billions ofBq can kill you if you are standing 5 meters from it, it is harmless at adistance of 100 meters.
• A Bq has 27 times more disintegrations than a pCi, but is still a very smallamount of radiation.
ACTIVITY
55
How much is a picocurie (pCi)?
•Many times the media reports excess radiation in picocuries. It takes 1,000,000,000,000 pCi to make 1 Curie.
A Becquerel is 1 disintegration/second. It takes 27 pCi to make one Bq, so a pCi represents less radioactivity that a Bq and results in very, very little dose.
ACTIVITY
56
What is the meaning of exposure?
• The quantity of X- or gamma-radiation to which an object is exposed.
• This electromagnetic radiation produces ionization within the object.
Amount of ionization per mass of air due to x and gamma rays. This is the amount of ionization produced by photons in air.
• Since it is impossible to directly measure the absorbed dose in tissue, the measurement of radiation is performed in air.
• It is measured in roentgen (R) and Sieverts (Sv).
Exposure
57
What is the meaning of exposure?
• Roentgen.
• Röntgen or Roentgen may refer to:
• Roentgen (unit), unit of measurement for ionizing radiation, named after Wilhelm Röntgen
• Wilhelm Röntgen (1845–1923), German physicist, discoverer of X-rays
Exposure
58
What is the meaning of exposure?
• Roentgen.
• This is defined as the amount of gamma radiation that produces 1 cm3 of air ionization equal to 1 electrostatic unit (esu).
• 1 esu = 3.3 x 10-10 coulombs = 2 x 109 ion pairs/cm3 of air.
• Equivalent to 2.58 x 10-4 C/kg air (0.0087 J/kg of air).
• 1R is approximately 10-2 Sv.
Exposure
59
ROENTGEN
• Roentgen was defined as 1R=1 electrostatic unit (esu)/cm3 airat standard temp and pressure(STP) = Δ Q by Δ m;
Where:
Δ Q is the absolute value of total charge of ions of one sign producedin air when all the electrons liberated by photons in air of mass (Δ m).
X = Δ Q/ Δ m
Conventional units is Roentgen
SI unit : c/kg
1R=2.58*10-4 c/kg
60
What is the meaning of absorbed dose?
• This is the energy imparted/ given to matter by charged or uncharged ionizing particles.
ABSORBED DOSE
61
What is the meaning of absorbed dose?
Gray
1Gy = 1 J/kg.
This is the SI unit for absorbed dose of ionizing radiation.
The Rad. 1 rad = 10-2Gy (= 10-2 J/kg).
• This is defined as the amount of radiation that deposits 100 ergs (10-5 J) in each gram of tissue it traverses.
• Two different types of radiation may, however, produce different degrees of biological damage even though they are both rated as 1 rad.
ABSORBED DOSE
62
How much radiation is an X-ray?ABSORBED DOSE
• 1Gray=100 rad =100,000 mrad
• So, the average chest X-ray may give a dose;
10 millirads = 0.01 rads = 0.0001 Gray.
• A millirad is comparatively small. Average normal background
level of radiation is 370 mrad/year.
• One Gray is a relatively large amount of radiation. If 3-4 Gray
are delivered over a short time to the whole body, they can be
deadly.
63
What is the meaning of equivalent dose?EQUIVALENT DOSE
This is the quantity used to express on a common scale the risk to exposed persons from all ionizing radiations.
64
65
Dose Equivalent
Different radiations have different harmful effects on
human tissues.
Dose Equivalent is measured in Sieverts (Sv).
H = D×Q.F.
H = equivalent dose (Sv)
D = dose (Gy)
1 Sv = 1 J/kg = 100 rem
Q.F. = radiation quality factor for the particular type
of ionizing radiation (no unit);
What is Radiation Quality Factor?EQUIVALENT DOSE
Different types of radiation behave in different ways. In order to compare the amount of risk or biological change that occurs, quality factors are introduced.
Biologic effects of radiation depend not only on dose but also on the type of radiation.
66
What is Radiation Quality factor?EQUIVALENT DOSE
For example:
• The damage produced by 1 Gy of x-radiation is equalto that produced by 1 Gy of gamma radiation. Thus,Gamma radiation has a quality factor of 1 or 1 Gygamma rays x 1 =1 Sv.
• The damage produced by 20 Gy of x-radiation isequal to that from 1 Gy of alpha radiation. Thus,Alpha radiation has a quality factor of 20 or 1 Gy ofalpha radiation x 20 = 20 Sv.
• Quality factors for other types of radiation are between 1 & 20.
67
RADIATION Q.F.
X-rays & gamma rays 1.0
Electron (incld. β-rays) of energy >30kv
1.0
Thermal ( slow) neutron 5
Fast neutrons 20
Conventional unit is Roentgen equivalent in man (rem)
Dose Equivalent
68
Radiation Q. Factors Illustration
Type and Energy Range Q. Factor
X and γ rays, electrons, positrons and muons 1
Neutrons <10 keV 5
Neutrons 10 keV to 100 keV 10
Neutrons >10 keV to 2 MeV 20
Neutrons > 2 MeV to 20 MeV 10
Neutrons >20 MeV 5
Protons, other than recoil protons and energy >2 MeV 2
Alpha particles, fission fragments, nonrelativistic heavy nuclei 20
EQUIVALENT DOSE
69
What is the meaning of equivalent dose?EQUIVALENT DOSE
Sievert (Sv)
1 Sv = 1 J/kg. The Sievert is equal to the absorbed dose in tissue (Gy)multiplied by the 'quality factor' for the particular type of ionizing radiation.The quality factor is a dimensionless number representing the relative effectproduced by the same absorbed doses of different types of radiation.
Rem (Roentgen Equivalent Man):
1 rem = 10-2 Sv (= 10-2 J/kg). This is defined as the amount of radiation whichwhen absorbed by a person, will produce the same biological effects as theabsorption of 1 roentgen of x-ray or gamma-ray radiation.
In older terminology the quality factor was referred to as the RelativeBiological Effectiveness.
number of rem = number of rad x RBE;
70
Radiation induced cancers have been seen in the atomic bomb survivors exposed to as low as 0.2 Sieverts.
A Sievert is a relatively large amount of radiation.
The annual background radiation exposure for a typical American is 0.0037 Sv, 3.7 mSv or 370 millirem.
1 Sv = 100 rem1000 mSv = 100,000 mrem
EQUIVAENT DOSE
How much is a Sievert (Sv)?
71
EQUIVAENT DOSE
How much is a millirem (mrem)?
• The annual background radiation exposure for a typical
American 370 mrems.
• The average dose from watching color TV is 2 mrem each
year.
• The granite from Grand Central Station exposes its
employees to 120 mrem of radiation each year.
• People in Denver receive 50 mrem more each year than those
in LA because of the altitude.
• The nuclear industry contributes to less than 1 mrem /year to
an individual’s background radiation.
• A millimrem is a small unit of measure.
72
What is the meaning of equivalent dose?EQUIVALENT DOSE
In older terminology the quality factor was referred to as the RelativeBiological Effectiveness.
number of rem = number of rad x RBE;
73
What is the meaning of equivalent dose?EQUIVALENT DOSE
To define the rem quantitatively, a Relative Biological Effectiveness(RBE) has been established
(number of rem) = (number of rad) x RBE. The following table gives RBE for the usual types of radiation.
RELATIVE BIOLOGICAL EFFECTIVENESS
Type of radiation rad x RBE = rem
x-rays and gamma-rays 1 1 1
Beta radiation 1 1 1
Protons 0.1 10 1
Alpha particles 0.05 20 1
Fast Neutrons 0.1 10 1
Slow Neutrons 0.3 3 1
74
EQUIVALENT DOSE EFFECTIVE (HE)
• Whole body exposures are rarely uniform.
• Tissues vary in sensitivity to radiation induced effects
• Effective dose is a measure of radiation and organ system specific damage in man
• The effective dose equivalent HE =Sum of Ht x Wt
• Ht = mean dose equivalent received by the tissue t• Wt =weighing factor of tissue t
75
Tissue Weighting Factors Illustration
0.01 0.05 0.12 0.20
Bone surface Bladder Bone Marrow Gonads
Skin Breast Colon
Liver Lung
Esophagus Stomach
Thyroid
Remainder
EQUIVALENT DOSE EFFECTIVE (HE)
76
The effectiveness of the dose is dependent on the dose-rate
Dose
1 bottle of Aspirin
or
250,000 mrem of
Radiation
Dose -Rate
Over 50 seconds??
Or over 50 years??
Over 50 seconds??
Or over 50 years??
Dose-rate
Death
Minimal health risk
Death
Minimal health risk
77
DR. MOHAMMED MOSTAFA EMAM
Biological Effects of Ionizing Radiation
78
79
Objective
To become familiar with the mechanisms of
different types of biological effects following
exposure to ionizing radiation.
To be aware of the models used to derive risk
coefficients for estimating the damage.
80
Contents
• Basic concepts, cellular effects
• Deterministic effects
• Stochastic effects
• Effects on embryo and fetus
• Risk estimates
Biological Effects
81
82
• 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
83
Information comes from:
studies of diseases propagation (epidemiology)
Experimental Radiobiology (studies of animals and
plants)
Fundamental studies of cells and their components
(cellular and molecular biology)
The key to understanding the health effects of
radiation is the interaction between these sources of
information.
Effects of Radiation Exposure
84
Radiation exposure affects
the center of life:
the cell
Chromosomes
85
86
radiation
hit cell
nucleus!
No change
DNA mutation
Exposure of the Cell
87
DNA Mutation
Cell survives
but mutated
Cancer?
Cell death
Mutation
repaired
Unviable Cell
Viable Cell
Outcomes after cell exposure
88
Repair
The human body contains about 1014 cells. An
absorbed dose of 1 mGy per year (natural sources)
will produce about 1016 ionizations, which means
100 per cell in the body.
If we assume that the mass of DNA is 1% of the
mass of the cell, the result will be one ionization in
the DNA-molecule in every cell in the body each
year.
89
… order of magnitudes
• 999 of 1000 harms are repaired
• 999 of 1000 damaged cells die (not a major
problem as millions of cells die every day
in every person)
• many cells may live with damage (could be
mutated)
90
Cell killing
Radio-Sensitivity
• RS = Probability of a cell, tissue
or organ of suffering an effect per
unit of dose.
• Bergonie and Tribondeau (1906):
“RS LAWS”: RS will be greater if
the cell:
• Is highly mitotic.
• Is undifferentiated.
91
RADIOSENSITIVITY
High RS Medium RS Low RS
Bone Marrow
Spleen
Thymus
Lymphatic
nodes
Eye lens
Lymphocytes
Skin
Mesoderm
organs (liver,
heart, lungs…)
Muscle
Bones
Nervous system
92
Biological Effects at Cellular Level
Possible mechanisms
of cell death:
• Physical death
• Functional death
• Death during
interphase
• Mitotic delay
• Reproductive failure
Cellular effects of ionizing radiation
are studied by cell survival curves
% s
urv
ival cell
s (
sem
i lo
gari
thm
ic)
Dose
Dq
D0
(threshold)
(radiosensitivity)
100%
Hereditary
Linear Energy Transfer (LET)
(Term used in Dosimetry)
- LET (Linear Energy Transfer) is the
amount of energy (MeV) a particle will
lose in traversing a certain distance (m)
of a material.
- It describe the action upon matter.
93
Linear Energy Transfer (LET)
(Term used in Dosimetry)
- It is identical to the retarding force
acting on a charged particle travelling
through the matter by unit distance.
- LET is a positive quantity and depends
on the nature of the radiation as well as
on the material traversed.
94EXTRACT
Schematic of the cell cycle (Mitosis)
95
outer ring: I = Interphase, M = Mitosis; inner ring: M = Mitosis, G1 = Gap 1, G2 –Gap 2, S = Synthesis; not in ring: G0 = Gap 0/Resting.
96
Stages of Mitosis
97
Meiosis
98
• Meiosis occurs during the formation of
gametes.
• Gametes are haploid reproductive cells, the
egg and sperm cells.
• Meiosis reduces the chromosome number by
½. Ex. 23 + 23 = 46
• 2n = diploid, 1n = haploid
99
In cells without a nucleus (prokaryotic), the cell
cycle occurs via a process termed binary fission.
In cells with a nucleus (eukaryotes), the cell cyclecan be divided into three periods: interphase, themitotic (M) phase, and cytokinesis.
100
• Physical• LET (linear energy transfer): RS
• Dose rate: RS
• Temperature: RS
• Chemical• OXYGEN, cytotoxic drugs: RS
• SULFURE (cys, cysteamine…): RS
• Biological• Cycle status:
• G2, M: RS
• S: RS
G1
S
G2
M
G0
Factors Affecting Radio-Sensitivity
EXTRACT
101
.....
.....
.............
Låg LET
Hög LET
low LET
high LEThigh LET
low LET
Absorbed dose
Surviving fraction
LET (linear energy transfer) is the amount of energy (MeV) a particle will loose
in traversing a certain distance (m) of a material.
Cell Survival
Radiation Quality
102
Direct
effects
Indirect
effects
Cell death
Primary
damage
Modified
cell
Damage
to organ
Somatic
cells
Germ
cells
Hereditary
effects
Cancer
Leukemia
Death of
organism
Repair
Deterministic
effects
Stochastic
effects
Biological Effects
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Definition
• A free radical is a molecule oratom, which is not combined toanything (free) and carries anunpaired electron in its outershell. It is in a state associatedwith a high degree of chemicalreactivity.
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Indirect Action of free radical
• In indirect action the radiationinteracts with other moleculesand atoms (mainly water, sinceabout 80% of a cell iscomposed of water) within thecell to produce free radicals,which can, through diffusion inthe cell, damage the criticaltarget within the cell.
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Indirect Action
• In indirect action the radiationinteracts with other moleculesand atoms (mainly water, sinceabout 80% of a cell iscomposed of water) within thecell to produce free radicals,which can, through diffusion inthe cell, damage the criticaltarget within the cell.
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Indirect Action
• In interactions of radiation withwater, short lived yetextremely reactive freeradicals such as H2O
+ (waterion) and OH* (hydroxyl radical)are produced.
• The free radicals in turn cancause damage to the targetwithin the cell.
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• If the water molecule is ionized
H2O = H2O+ + e-
(H2O is the water molecule ; H2O+
is an ion radical )
• Ion meaning it is electricallycharged, because it has lost anelectron and a radical because ithas an unpaired electron in theouter shell, making it veryreactive.
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• Ion radicals have a short life,usually no more than 10-10 s,before they decay to form freeradicals
• Free radicals are not charged,
but do have an unpaired electron
in the outer shell.
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• The water ion radical can, for
example, do the following:
H2O+ + H2O = H3O
+ + OH*
(H2O+, H3O
+ are the ion radicals
H2O is a water molecule)
• OH* is a highly reactive hydroxyl radical, with 9 electrons, therefore one is unpaired.
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• Hydroxyl radicals (OH*), are
highly reactive and can go on to
react with DNA;
It is estimated that 2/3 of the x-ray
damage to mammalian DNA is by
hydroxyl radicals.
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Biological Response to Radiation
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Cellular Repair
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Radiation Protection
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Rational for Radiotherapy
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