Hazards & protection

Radiation Hazards and Protection
30 January 2015 1Dr Saad Wahby Al Bayatti

X- ray Dose Measurements
X- ray Dose Units

Radiation Absorbed Dose
• This is a measure of the amount of energy
absorbed from the radiation beam per unit mass of
tissue
• Unit of measurement:
• SI unit : Gray, (Gy) measured in joules/kg
• original unit : rad, measured in ergs/gm
• 1 Gray = 100 rads

Equivalent Dose
• A measure which allows comparison between
different types of radiation in regard to their
absorbed doses in the body (RBE radiobiological
effectiveness)
• Unit of measurement (SI unit) : Sievert (Sv)
• subunits : millisievert (mSv) ( ×1/1 000)
• : microsievert ( µSv) ( ×1/1 000 000)
• original unit : rem
• 1 Sievert = 100 rems

Quality Factor (Q)
• Represents the biological effects of each
type of radiation:
• X- rays, gamma rays and beta particles
Q = 1
• Fast neutrons protons Q = 10
• Alpha particles Q = 20

Equivalent Dose
• equivalent dose = radiation absorbed dose (Gy)×
Q
• Since Q for x -ray = 1, then
equivalent dose = radiation absorbed dose
(Sv) = (Gy)

Effective Dose
• Each body tissue is affected differently by
radiation
• Effective dose: This is a measure that allows doses
from different investigations of different parts of
the body to be compared , by converting all doses
to an equivalent whole body dose

Weighing Factor (W)
• Measures the radiosensitivity, i.e.the risk of
the tissue being damaged by radiation.
• The higher the damage, the higher is W

Weighing factors for different body tissues
Tissue Weighing factor
Testes and ovaries 0.20
Red bone marrow, colon, lung,
stomach
0.12
Breast, bladder, liver, thyroid 0.05
Bone surfaces , skin 0.01
Remainder 0.01

Effective Dose
• Effective dose = equivalent dose × weighing factor
= radiation absorbed dose(Gy)×Q ×W
• SI unit : Sievert (Sv)
• subunit : millisievert (mSv)
• Effective dose (whole body) = sum of W

Absorbed dose
Multiplied by a factor to reflect harm by a specific radiation
Equivalent dose
Multiplied by a factor to reflect sensitivity of a specific tissue
Effective dose, commonly called “dose”

Effective doses
X -ray examination
X- ray exam. Effective dose (mSv)
• CT cest 8.0
• barium meal 7.7
• lumbar spine 2.2
• CT head 2.0
• skull 0.1
• chest 0.04
• OPG 0.007
• 2 intra oral films (E speed) 0.002

The frequency of taking films is based on
the following factors:
1. Patient’s oral hygiene
2. Caries activity
3. Dental history
4. Reliability of patient
5. ADA Guidelines

ADA Guidelines
Full-mouth Series
1 - 5 years
Bitewings
6 months - 3 years
Panoramic
1 - 5 years

Biological Effects of X-ray

Radiobiology
The response of living systems to
ionizing radiation

Biological Effects of X-ray
• X-Rays interact with living tissues and can cause
biological changes.
• These changes are mediated directly by excitation
or ionization of atoms or indirectly as a result of
chemical changes occurring near the cells.
• Affected cells may be damaged or killed.

Biological Effects of X-ray (cont’d)
• Genetic effects involve chromosomal damage or
mutation in the reproductive cells and will affect
future generations.
• Somatic effects involve damage to other tissues and
result in changes within the individual’s lifetime
(e.g. radiation burns, leukemia).
• Radiation is a particular hazard because its effects
are painless, latent and cumulative

Incoming
photon
Excited electron
Excitation

Incoming
photon
Ejected electron
Photon
Positive Ion
Ionization
Photon

Ionization
The process of removing an electron from an electrically
neutral atom to produce an ion. An ion is an atom or
subatomic particle with a positive or negative charge.

Ionization negative ion
positive ion

Attenuation
Reduction of x-ray beam intensity (that
reaches film) by interaction with matter.
1. Coherent scattering
2. Compton scattering
3. Photoelectric absorption

Coherent Scattering
Low-energy x-ray interacts with outer-
shell electron and causes it to vibrate
briefly. Scattered x-ray of same energy
as primary x-ray is then emitted, going
in a different direction than primary x-
ray. Electron not ejected from atom. (No
ionization).

Compton Scattering
Outer shell electron ejected
(Ionization)
Scatter radiation results
Occurs majority of the time
30% of scatter exits head

recoil electron
scattered x-ray
Compton Scattering
primary x-ray
The primary x-ray strikes an outer-shell electron,
knocking it out of its orbit (ionization). The primary x-
ray loses some of its energy and continues in a different
direction as a scattered x-ray.

Inner-shell electron ejected
(Ionization)
Complete absorption
Photoelectric Absorption

photoelectron
primary x-ray
Photoelectric Absorption
The primary x-ray strikes an inner-shell electron,
knocking it out of its orbit (ionization). The x-ray loses
all of its energy and disappears. There is no scatter.

Dose-Response Curves
threshold
linear
non-linear
non-threshold
Response
Dose
Linear: the response is directly
related to the dose.
Non-linear: the response is not
proportionate to the dose.
Threshold: the dose at which effects
are produced; below this dose, there
are no obvious effects.
Non-threshold: any dose produces a
response.

Critical Molecule
(Target)
DNA

Radical
Atom or molecule that has an
unpaired electron in the valence
shell, making it highly reactive.
(Most damaging).

Mutations
Cell death
Sublethal injury
Biologic Effects

DNA altered; cell function
altered or development
changed. It is unclear which
critical lesion/s in DNA may
lead to cancer.
Mutation
Normal
Mutation

Loss of capacity for mitosis
Cell Death

Cellular Repair
1. Damage to biologic molecules
(single-strand break of DNA)
2. Removal of damaged section by
cell enzymes
3. Placement of new material by
other cell enzymes

Radiation Effects Influenced by:
Total dose
Dose rate
Total area covered
Type of tissue
Age

Sources of Radiation

Sources of Radiation
• Natural background radiation
- cosmic rays
- gamma rays from rocks & soil 87%
- ingested radioisotops in certain foods
- radon decay products (granite )
• Artificial background radiation
- fallout from nuclear explosions > 1%
- radioactive waste
• Medical and dental diagnostic radiation 12%
• Occupational exposure > 1%

Biologic Effects Of Ionizing Radiation
Stochastic
• The probability of occurrence
of the change, rather than its
severity, is dose dependant
• All or non, the person either has
the condition, or not
• No threshold
e.g.
• Radiation induced cancer,
greater exposure of population
to radiation increases cancer
probability, but not its severity
Deterministic
• The severity of response is
proportional to the dose
• Occur in all people when the
dose is large enough
• There is a dose threshold below
which the response is not seen
e.g.
• Oral effects after radiation
therapy
• Radiation sickness after whole
body radiation

Radiation Hazards

Radiation Hazards
Nuclerar boms
nueclear reactors leaks
Whole body
radiation
Medical
(diagnostic & theraputic)
Dental
X- rays
Specific area
radiation
Radiation exposure

Specific Versus Whole-Body Radiation

Radiation Hazards
Indirect Direct
Somatic
Affects individual
No effect on offspring
Genetic
Do not affect individuial
Offspring is affected
Radiation damage

Radiation Hazards
Direct Damage
RH +Radiation R
+
+ H
+
+ e
-
R
+
Dissociation
R
+
X + Y
Cross-linking
R
+
+ S RS

Radiation Hazards
Direct Damage
Radiation
• DNA /RNA molecule nuclear acid
breakdown
• Nuclear acid breakdown
Somatic cells radiation induced
malignancy
Genetic cells radiation induced
congenital abnormality

Radiation Hazards (indirect damage)
Water Hydrolysis
• H 2 O H
+
+ OH
-
• H
+
+ H
+
H2
• OH
-
+ OH
-
H 2 O 2
Radiation

• H2O2 + DNA Molecular
breakdown
• H2O2 + Proteins
• Molecular breakdown Cell damage
Radiation Hazards (indirect damage)
Water Hydrolysis

Radiation Hazards
Direct
DNA /RNA hit
Radiation induced malignancy
Indirect
H2O2 formation
TOXIC
breakdown of large molecules(protiens/DNA)
Somatic
Radiation damage

Radiation Hazards
Direct
DNA/RNA hit
Radiation induced congenital
abnormality
Indirect
H2O2 formation
TOXIC
breakdown large molecules ( proteins/ DNA)
Genetic
Radiation damage

Factors Affecting Radiosensitvity
• Dose: the amount of radiation
received. The higher the dose,
the greater is the effect
(consider the threshold)
• Dose rate: the rate of exposure.
e.g. a total dose of 5Gy can be
given as
- 5Gy/min (single dose) is more
destructive
- 5mGy/min(fractionized), less
destructive, injured cells can
recover
• Oxygen: the higher the O2 level
in irradiated cells, the greater is
the damage. (H2O2 formation)
• Linear Energy Transfer
(LET): the rate of loss of
energy from a particle as it
moves in its track through
matter (tissue)
e.g. alpha particles vs. X-ray

X- ray Protection

X- ray Protection
Follow ALARA , keep exposure
A = As
L = Low
A = As
R = Reasonably
A = Achievable

Patient Staff public
X- ray protection

X- ray Protection
Patient
• Radiographs are only taken when necessary
• Number, frequency and type of radiographs is the
responsibility of the dentist
• Use high output DC x- ray generators
• Minimum kilovoltage should be 60kV
• Minimum milliamperage should be 8 mA
• Minimum filtration should be 1.5 mm Al

X- ray Protection
Patient
• Maximum Beam diameter should be 7 cm
(circular beams)
• Use rectangular collimation for intra oral films
• Minimum target – skin distance should be 20 cm
• Accurate timer
• Use open- ended lead lined cylindrical cones
(PID)
• Do not use close ended pointed plastic cones

X- ray Protection
Patient
• Use high speed films (D or E )
• Use film holders and beam-aiming devices
• Avoid retakes, master radiographic
techniques
• Avoid retakes, master film processing
techniques
• Use lead aprons
• Use thyroid collars30 January 2015 61Dr Saad Wahby Al Bayatti

Lead Aprons

Lead Apron/Thyroid Collar
Psychology
Protection

Adult Patient’ s Lead apron
with a thyroid collar
Separate thyroid collar

Child Patient’ s Lead apron
with and without thyroid collar

Operator’s Lead apron

Proper placement of the Lead
apron with a thyroid collar

Correct way of hanging
the Lead apron

Lead apron
Without a thyroid collar

Correct way of hanging lead apron and thyroid collars

Lead apron
hangers

X- ray Protection
Staff
• Never hold the x- ray head during exposure
• Never hold the film during exposure
• Never stand in the path of the primary beam
• Stand behind a lead barrier (2 mm thickness)
• Watch the patient through leaded glass during
exposure
• Stand minimum 2 M from the x-ray beam behind
the patient’s head

X- ray Protection
Public
• Warning/Informative signals to indicate
hazardous x- radiation
• Patients should be seated away from x- ray
rooms
• Patients are not allowed to wait in corridors
next to x- ray rooms

Open –ended cylindrical
Close ended plastic
7 cm
7 cm

Mobile lead barriers

Open-end cylindrical coneClose-end pointed cone
√X

Rectangular modifications for an
Open-end cylindrical cone

Rectangular collimatorsCircular collimators
Area of exit of the x-ray beam
Area of exit of
the x-ray beam
Metal shield

Long cylindrical Open-end cone
Short cylindrical Open-end cone
Long rectangular cone
Short rectangular cone

Patient
90-135
o o
90-135
X- ray
head
90
o
90
o
180
o
Operator
Safe position
Operator
Safe position
Scattered rays Scattered rays
DangerDanger
Safe operator’s position
No barrier used

Patient
90-135
o
o
90-135
90
o
90
o
180
o
Operator’s
Safe position
Operator
Safe position
Scattered rays
Scattered rays
Danger
Danger
No barrier used

1 M
2 M
A
B
Source
Inverse square law
I 1/D
Intensity of radiation at B =1/4 at A
2

Inverse-square law states that the
intensity (quantity) of X-ray is inversely
proportional to the square of the
distance from the source of radiation

2 M
minimum .
Operator `
Patient
Danger
X -ray

Operator `
Lead barrier
Using a lead barrier allows less than
2 M distance
X- ray
Patient
Danger

Patient
Operator `
Leaded wall room
Leaded
glass
Danger
X- ray

Patients’
Waiting rooms
X- ray room
X- ray room
Restricted areas
Restrictedareas
Safe patients waiting rooms

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