biological effects of ionizing radiation & …...biological effects of ionizing radiation 22...
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DR. MOHAMMED MOSTAFA EMAM
INAYA MEDICAL COLLEGE
(IMC)RAD 232 - LECTURE 3, 4 & 5
Biological Effects of Ionizing Radiation & Commonly Used Radiation Units
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.
+
-
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. This
may be
protective or
damaging.
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.
How does this damage from ionizing
radiation effect our bodies?
Cancer
Sufficient Cell Killing Sufficient Genetic
Alterations
Radiation Sickness
RadiationDose
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...
...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
Commonly Used Radiation UnitsAbsorbed 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
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
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
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
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
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
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
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
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
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 produced inair 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
What is the meaning of absorbed dose?
• This is the energy imparted/ given to matter by charged or uncharged ionizing particles.
ABSORBED DOSE
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
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.
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.
Biological effects of ionizing radiation 22
Dose Equivalent
Since different radiations have different harmful effects on
human tissues.
It is measured in Sieverts (Sv).
H = D×Q.F.
H = equivalent dose (Sv)
D = dose (Gy)
Q.F. = radiation quality factor of radiation (no unit)
1 Sv = 1 J/kg = 100 rem
What is the meaning of equivalent dose?EQUIVALENT DOSE
Sievert
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 effect produced by the same absorbed doses of different types of radiation. In older terminology the quality factor was referred to as the Relative Biological Effectiveness (next slides)
rem (roentgen equivalent man): 1 rem = 10-2Sv (= 10-2 J/kg).
This is defined as the amount of radiation which when absorbed by a person, will produce the same biological effects as the absorption of 1 roentgen of x-ray or gamma-ray radiation.
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)
SI unit is Sivert
1rem=10 Sivert
Dose Equivalent
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
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.
What is Radiation Quality factor?EQUIVALENT DOSE
For example:
• The damage produced by 1 Gy of x-radiation is equal to that produced by 1 Gy of gamma radiation. Thus, gamma radiation has a quality factor of 1 or 1 Gygramma rays x 1 =1 Sv.
• The damage produced by 20 Gy of x-radiation is equal to that from 1 Gy of alpha radiation. Alpha radiation has a quality factor of 20 or 1 Gy of alpha radiation x 20 = 20 Sv.
• Quality factors for other types of radiation are between 1 & 20.
What is the meaning of equivalent dose?EQUIVALENT DOSE
To define the rem quantitively, 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
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)?
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.
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
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)
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
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