Ionizing radiation protection

Ionizing radiation...Effects
and Safety
Dr/Ahmed Bahnassy
Consultant radiologist
Alexandria Urology Hospital
what every health worker must know
Alexandria Urology
Hospital AUH

Aims of lecture
 To become familiar
with the mechanisms
& biological effects
following exposure to
ionizing radiation.
 To be aware of the
risks of ionizing
radiation .
 To know main safety
issues of protection.

RADIATION:-
Radiation is the energy that comes from a source and
travels through some material or space as waves or
photons.
IONIZING RATIATION:-
This kind of radiation on interaction with matter produce
charged particles called ions.
This type of radiation has enough energy to break
chemical bonds.
NON-IONIZING RATIATION:-
Radiation that does not have enough energy to break
chemical bonds but can vibrate atom. It cannot produce
ions.

UNITS OF RADIATION:-
1)Roentgen (R):- Radiaton exposure in a volume of air.
2) Rad:-
It is the unit of absorbed dose.
The SI unit of absorbed dose is Gray (Gy)
1 Gy=100 rad
3) Rem:-
It is the unit of effective dose.
Used only in radiation protection.
The SI unit is Sievert
1 Sv= 100 rem
1 mSv = 0.001 Sv.

0.01 mSv
0.5 Chest
X-ray.
0.02mSv
1 CXR
0.07 mSv
3.5 CXR
1.3mSv
65 CXR
0.7mSv 1.0mSv 2.5mSv 3.0mSv 7.0mSv
35 CXR 50 CXR 125CXR 150CXR 350CXR

2.3mSv 8.0mSv 10mSv
115 Chest 400 CXR 500 CXR
X-rays.

15 mSv
750 CXR
4 mSv
200 CXR
6 mSv
300 CXR

THYROID SCAN RENAL SCAN LUNG PERFUSION
1.0 mSv 1.0 mSv 1.0 mSv
50 CXR 50 CXR 50 CXR
BONE SCAN PET HEAD (FDG) CARDIAC GATED
4.0 mSv 5.0 mSv 6.0 mSv
200 CXR 250 CXR 300 CXR

Ionizing Radiation..How
effects are produced
Ionizing Radiation is the
removal of an electron
from an atom leaving an
unstable molecule which
may then break apart to
form free radicals.
http://www.paradigmlink.com/ionrad.shtml
The weapon

Linear Energy Transfer (LET)
The average energy deposited per unit
length of track.
Measured in kiloelectron volts per micron
(10-6 m)

Low LET / High LET
 Low LET
Low mass, increased
travel distance (gamma rays, x-
rays).
Sparsely ionizing with
random interactions.
Causes damage primarily
through indirect action or
may cause single strand
breaks (which are repairable).
http://staff.jccc.net/PDECELL/biochemistry/dna.gif
e-

Low LET / High LET
High LET
– Large mass, decreased tr
avel distance (alpha parti
cles, protons, low energy
neutrons).
– Causes dense ionization
along its path with a high
probability of interacting
directly with DNA.
http://staff.jccc.net/PDECELL/biochemistry/dna.gif
α++

Ionizing Radiation
The reactions caused by ionizing radiation
occur rapidly, they are nonselective and
random.
The majority of damage caused by
radiation is due to chemical reactions with
water within the cell.
The injury mechanism

H2O
HOH+
H+
OH*
H* OH-
e- + H2O HOH-
water
negatively charged
water molecule
Hydrogen
ion
Hydroxyl
radical
electron water
Positively charged
water molecule
hydrogen
radical
Hydroxyl
ion
The negatively charged
water molecule
dissociates into a
hydrogen radical and a
hydroxyl ion.

Reactions
The previous reactions produce free
electrons (e-), the ions H- and OH-,
the free radicals H* and OH*.
The fate of these products are…….

Free Radicals
A free radical is an atom or
molecule that has an unpaired
electron in its valence shell.
These free radicals are
non-selective when pairing up
with electrons from other
atoms, including those that
make up the DNA molecule.

Direct Action / Indirect Action
Direct Action
Causes damage directly to DNA or other important
molecules in the cell.
More likely when the beam of charged particles
consist of alpha particles, protons, or electrons
Indirect Action
Causes damage by interacting with the cellular
medium producing free radicals which then damage
the DNA molecule.
More likely when x-rays or gamma-rays compose the
beam.

Direct Action / Indirect Action

DNA Damage
 The arrangement of nitrogenous bases
provide a blueprint for DNA for the synthesis
of specific proteins necessary for individual
cell function.
 In the event of a loss or change of one or
more of the nitrogenous bases....base
sequence and normal functioning of the cell
is altered.
 Another form of DNA damage due to
radiation involves a break in the hydrogen
bonds between the Adenine – Thymine and
Cytosine – Guanine base pairs. These bonds
function to keep the DNA strands together
 Bonds can also break between deoxyribose
sugar and the phosphate groups which can
lead to cross-linking of DNA
The target

Chromosome Aberrations
 If the chromosome fragments are
near one another they have a high
chance of reattaching in their
original position – causing no future
damage to the cell.A process known
as restitution.
 In translocations and inversions, no
genetic information is lost, but the
rearrangement of gene sequence
will alter protein synthesis.
 In a deletion, a chromosome
fragment is not replicated during the
next mitosis, the genetic information
is lost. The effects this has on the
cell depends on the amount and
type of information lost.
Translocation
Inversion
Deletion
The effects

Chromosome deletion
Chromosome translocation

IAEA 3 : Biological effects of ionizing radiation3 : Biological effects of ionizing radiation
Outcomes after cell exposure
DAMAGE
REPAIRED
CELL DEATH
(APOPTOSIS)
TRANSFORMED
CELL
DAMAGE TO DNA

IAEA
International Atomic Energy Agency
DNA Mutation
Cell survives
but mutated
Cancer ?
Cell death
Mutation
repaired
Unviable Cell
Viable Cell

Repair of DNA damage
• RADIOBIOLOGISTS
ASSUME THAT THE
REPAIR SYSTEM IS
NOT 100%
EFFECTIVE.

IAEA
CELL INITIATION
An initiating event
creates a mutation in
one of the basal cells

IAEA
DYSPLASIA
More mutations occurred.
The initiated cell has
gained proliferative
advantages.
Rapidly dividing cells
begin to accumulate
within the epithelium.

IAEA
BENIGN TUMOR
More changes within
the proliferative cell line lead
to full tumor development.

IAEA
MALIGNANT TUMOR
The tumor breaks trough
the basal lamina.
The cells are irregularly
shaped and the cell line is
immortal. They have an increased
mobility and invasiveness.

IAEA
METASTASIS
Cancer cells break through
the wall of a lymphatic
vessel or blood capillary.
They can now migrate
throughout the body and
potentially seed new tumors.

IAEA
A simple generalized scheme for multistage oncogenesis
Damage to chromosomal DNA
of a normal target cell
Failure to correct
DNA repair
Appearance of specific
neoplasia-initiating mutation
Promotional growth
of pre-neoplasm
Conversion to overtly
malignant phenotype
Malignant progression
and tumour spread

Radiosensitivity
Actively reproducing cells are more
radiosensitive than mature cells.
During mitosis, the cell is in a stressed
state and shows an increase in damage
caused by radiation.
Cells that have decreased levels of
differentiation are more radiosensitive
than specialized cells.

The Cell Cycle
 An ordered set of events,
culminating in cell growth and
division into two daughter
cells
 Tc, full mitotic cycle
G2
(2nd gap)
M
(mitosis)
S
(DNA Synthesis phase)
G1
(1st gap)
Cells that
cease
division

Radiosensitivity & Mitotic Cycle
 Cell cycle components
 M, G1, S, G2
 Cell cycles times vary largely due to G1
 crypt cells, 9 - 10 hours
 stem cells (mouse skin) 200 hr
 Sensitivity
 Cells most sensitive close to mitosis
 Resistance greatest in latter part of S
 For long G1’s, there is an early resistance period followed by
sensitive one at the end of G1
 G2 ~ M in sensitivity

Radiosensitivity
Muscle
Bones
Nervous
system
Skin
Mesoderm
organs (liver,
heart, lungs…)
Bone Marrow
Spleen
Thymus
Lymphatic
nodes
Gonads
Eye lens
Lymphocytes
(exception to the RS laws)
Low RSMedium RSHigh RS

Fractionation in radiotherapy
 Instead of a single treatment
consisting of a high dose, frac
tionation divides the dose to be de
livered over a period of time, usua
lly 6-8 weeks.
 At low doses of radiation,
normal cells have an increased sur
vival rate because of their ability
to repair sublethal damage before
the next fraction of radiation is
delivered.
 Tumor cells do not possess the
repair enzymes necessary to
keep up with the repairs and
as a result the cell is
overwhelmed and is destroyed.
http://www.usoncology.com/CompanyInfo/PhotoLibrary.asp

 Two effects of radiation
exposure:
 deterministic (threshold)
 stochastic: cancer
 Radiation Standards
 set below threshold
 set to limit stochastic risk
Dose-Response Relationships

Non-Stochastic (Deterministic) Effects
 Occurs above threshold
dose
 Severity increases with
dose
 Alopecia (hair loss)
 Cataracts
 Erythema (skin reddening)
 Radiation Sickness
 Temporary Sterility

Stochastic (Probabilistic) Effects
 Occurs by chance
 Probability increases with dose
 Carcinogenesis
 Mutagenesis
 Teratogenesis

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

Radiation effects and
Syndromes

Injury
Threshold
Dose to
Skin (Sv)
Weeks to
Onset
Early transient erythema 2 <<1
Temporary epilation 3 3
Main erythema 6 1.5
Permanent epilation 7 3
Dry desquamation 10 4
Invasive fibrosis 10
Dermal atrophy 11 >14
Telangiectasis 12 >52
Moist desquamation 15 4
Late erythema 15 6-10
Dermal necrosis 18 >10
Secondary ulceration 20 >6
Skin damage
from prolonged
fluoroscopic
exposure
Skin reactions

Skin injuries

Effects in eye
• Eye lens is highly RS.
• Coagulation of proteins
occur with doses
greater than 2 Gy.
• There are 2 basic
effects:
From “Atlas de Histologia...”. J. Boya
Histologic view of eye:
Eye lens is highly RS,
moreover, it is surrounded by
highly RS cuboid cells.
> 0.155.0
Visual
impairment
(cataract)
> 0.10.5-2.0Detectable
opacities
Sv/year for
many years
Sv single brief
exposure
Effect

IAEA 3 : Biological effects of ionizing radiation3 : Biological effects of ionizing radiation 49
Whole body response: adult
Acute irradiation
syndrome Chronic irradiation
syndrome
Dose
Steps:
1. Prodromic
(onset of
disease)
2. Latency
3. Manifestation
Lethal dose 50 / 30
BONE
MARROW GASTRO
INTESTINAL
CNS
(central nervous
system)
1-10 Gy
10 - 50 Gy
> 50 Gy
•Mechanism:
Neurovegetative
disorder
•Similar to a sick
feeling
•Quite frequent in
fractionated
radiotherapy

Threshold Doses for Deterministic
Effects
• Cataracts of the lens of the
eye 2-10 Gy
• Permanent sterility
• males 3.5-6 Gy
• females 2.5-6 Gy
• Temporary sterility
• males 0.15 Gy
• females 0.6 Gy
Severity of
effect
dose
threshold

Symptoms of Acute Radiation Sickness
 Three categories (E. Hall, 1994)
 Hemopoietic: 3-8 Gy LD50/60
 radiation damages precursors to red/white blood cells &
platelets
 prodromal may occur immediately
 symptoms: septicemia,
 survival mixed
 examples include Chernobyl personnel (203 exhibited
symptoms, 13 died)

Symptoms, continued
 Gastrointestinal : >10 Gy
 radiation depopulates GI epithelium (crypt cells)
 abdominal pain/fever, diarrhea, dehydration
 death 3 to 10 days (no record of human survivors above 10
Gy)
 examples include Chernobyl firefighters
 Cerebrovascular : > 100 Gy
 death in minutes to hours

Delayed Effects
 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)

RADIATION PROTECTION
Based on two components.
A) JUSTIFICATION.
B) OPTIMIZATION.
JUSTIFICATION:-
Applications of ionising radiation are only justified
when they provide a net benefit with minimization of
risks of radiation for people.

GUIDELINES FOR REFERRING PHYSICIANS:-
1) Repeating investigations which have already been
done:
For example at other hospital, in an outpatient department,
or in an accident and emergency department.
HAS IT BEEN DONE ALREADY? Every attempt should be made
to get previous films.
2) Investigation when results are unlikely to affect
patient management:
The anticipated 'positive' finding is usually irrelevant, e.g.
degenerative spinal disease (as 'normal' as white hairs in old
age) or because a positive finding is so unlikely. DO I NEED IT?

3) Investigating too often:-
i.e. before the disease could have progressed or resolved or
before the results could influence treatment. DO I NEED IT
NOW? Or some clinicians tend to rely on investigations more
than others. ARE TOO MANY INVESTIGATIONS BEING
PERFORMED?
4) Doing the wrong investigation:-
Imaging techniques are developing rapidly. It is often helpful to
discuss an investigation with a specialist in clinical radiology or
nuclear medicine before it is requested. IS THIS THE BEST
INVESTIGATION?
5) Failing to provide appropriate clinical information &
questions that imaging Investigation should answer.
Deficiencies here may lead to the wrong technique being used
(e.g. the omission of an essential view). HAVE I EXPLAINED THE
PROBLEM?

OPTIMIZATION:-
Once a practice is
justified, the exposure to
ionising radiation should
be kept as low as
reasonably achievable
(ALARA).

FUNDAMENTAL
PRINCIPLES OF
RADIATION
PROTECTION:
1. Distance.
2. Exposure time.
3. Barriers & Shielding.

DISTANCE
INVERSE SQUARE LAW:
Intensity of radiation is inversely proportional to
the square of the distance from the source of radiation.
In equation form:
For Example: If the
dose is 9 R at 3
feet, stepping back
to a distance of
6 feet will cause
the dose to
decrease to 2.25 R.

57cm from x-ray source 50cm from x-ray source

EXPOSURE TIME
 The amount of radiation received is proportional to
the length of the exposure time.
 Minimized by conducting
procedures as quickly as possible.
 For Example, using short
bursts of fluoroscopy.
Employing image intensifiers &
Intensifying screens.
Using high kVp , low maS
techniques.

BARRIERS & SHIELDING
 The most commonly used protective material is lead. It
has a double advantage of high density and high
atomic number.
 Lead equivalent: it is the thickness of lead which
provide the same degree of protection as the material.
ROOM SHIELDING:
 Should be located as far as away from areas of high
occupancy and general traffic.
 Wall on which primary beam falls should not be less
than 35 cm thick brick or equivalent.
 Shielding of 1.7mm lead (23 cm brick) in front of doors
& windows of x-ray room.

X-RAY CONTROL
ROOM:
Walls & viewing
windows of control
booth should have lead
equivalent of 1.5 mm.
Distance between
control panel & X-ray
unit / chest
stand should be
minimum 3 meters.

PATIENT WAITING ROOM:
 Provided outside X-ray room a proper warning signal
when unit is in use.
 Warning devices may include audible and visual
signs.

LEAD APRON:-
 Typically thickness of 0.5
mm lead equivalent is
used.
 Weight ranges from 2.5 to
7 kg.
 Should cover much of red
bone marrow & breast.
LEAD GLOVES:
 Lead salts or metallic lead
are added to rubber or
plastic.
 Lead equivalent of these
is about ¼ mm.

LEAD GLASS:
 Made by adding lead salts to silicates , in the
manufacturing of glass.
 It is acceptably transparent and a better protective
material.
 Contains 60% of lead by weight.
GONADAL SHIELDING:
 Must be 0.5 mm of lead.
 Must be used when gonads will lie within 5 cm of the
collimated area.
 Separate male vs. female shielding available.

THYROID COLLER
OVARIAN PROTECTION
MALE GONADAL
SHIELD

 Have standard projections for specific indications.
 Additional views - on a case-by-case basis
 Use PA projections, where practical, for chest and spine
radiographs.
 Avoid repeating exposures.
 Use safe exposure factors – high KVp and low mAs
technique.
Never stand in the primary beam.
Always wear protective apparel when not behind a
protective barrier.
Always wear a radiation monitor and position it outside the
protective apron at collar level.
The person holding the patient must wear protective apron
and if possible gloves.
Always collimate to smallest field size appropriate to
examination.

RADIATION MONITORING DEVICES
Non-Self Reading Devices:
1) FILM BADGES:
 Consist of a small dental–sized film wrapped in light proof
paper and mounted in a holder filled with metallic filters of
different thicknesses.
2) THERMOLUMINESCENT DOSIMETERS (TLD):
 They are used to measure external
individual whole body doses from
X-rays , beta rays & gamma radiation.
 It consists of a TLD card loaded in a
cassette (card holder ) having suitable
metallic & plastic filters.

TLD Ring or Finger badges:
 Ring or finger badges are worn by fluoroscopists &
interventional radiologists who usually receive high
doses to their extremities.
 The ring dosimeter contains a small radiation-sensitive
lithium fluoride crystal.

SELF READING DEVICES:
Real time dose information available
Needs frequent Calibration checks
Can be taken from hospital to hospital.
Good for visiting consultants
surgeons, anesthetists,
urologists, gastroenterologists
etc.

Summary
 Ionizing radiation use should be only used
when benefit outweighs possible risks.
 Every examination should be justified.
 Optimized protocols for lowering patient dose
without affecting accurate diagnosis should
be done.
 Use all kinds of radiation protection during
work...It's your life.!

IAEA 3 : Biological effects of ionizing radiation3 : Biological effects of ionizing radiation 75
Where to Get More Information (1)
• The 2007 Recommendations of the International
Commission on Radiological Protection, ICRP 103,
Annals of the ICRP 37(2-4):1-332 (2007)
• UNSCEAR 2008 Report to the General Assembly,
with scientific annexes, United Nations Scientific
Committee on the Effects of Atomic Radiation,
United Nations, Vienna, Austria, 2008
• Avoidance of radiation injuries from medical
interventional procedures. ICRP Publication 85.
Ann ICRP 2000;30 (2). Elsevier

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