Transcript Radiation biology and protection in dental radiology

Radiation biology and
protection in dental radiology
Dose units and dosimetry
• Radiation-absorbed dose (D)
This is a measure of the amount of energy
absorbed from the radiation beam per unit
mass of tissue
SI unit: Gray,(Gy) measured in joules/kg
conversion: 1 Gray=100 rads
Cont’d
• Equivalent dose (H)
-This is a measure which allows the
different radio-biological (RBE)
effectiveness of different types of radiation
to be taken into account.
-equivalent dose(H)=radiation-absorbed
dose(D)*radiation weighting factor (Wr)
SI unit: Sievert (Sv)
Cont’d
• Effective dose (E)
This measure allows doses from different
investigation of different parts of the body
to be compared by converting all doses to
an equivalent whole body dose
• Effective dose(E)=equivalent dose(H)*
tissue weighting factor(Wt)
Typical effective doses
X-ray examination
mSv
CT head
Dental pan
2 dental intraoral films
Using 70 kV rectangular
Collimation and long cone
8.0
0.26
0.02
Various sources of radiation
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Natural background radiation
Cosmic
Gama form the rocks
Radiation from ingested radioisotops
Radon
Cont’d
• Artificial background radiation
• Medical and dental diagnostic radiation
• Radiation from occupational exposure
The biological effects and risks
associated with X-rays
• Somatic Deterministic effects
• Somatic Stochastic effects
• Genetic Stochastic effects
Somatic deterministic effects
• They are definitely produced by the high
dose of radiation
• Threshold dose
• Examples- skin reddening
Somatic stochastic effects
• They may develop
• Examples- leukemia and certain tumors
• No threshold dose
Cont’d
• Every exposure to ionizing radiation
carries the possibility of inducing a
stochastic effect
• The severity of the damage is not related
to the size of the inducing dose
Genetic stochastic effects
• Mutations result from any change in the
chromosome
• May result from radiation or occur
spontaneously
• No threshold dose
Effects on the unborn child
• Large dose of radiation- congenital
abnormalities
• Mental retardation- low doses of radiation
Harmful effects important in
dental radiology
• In dentistry the size of the doses are
relatively small
• Somatic stochastic effects are the
damaging effects of most concern
How do X-rays cause damage
• Direct damage
• Indirect damage
Direct damage
• Incoming X-ray photon
• An ejected high-energy electron
Effects
• Inability to pass on information
• Abnormal replication
• Cell death
• Only temporary damage
Factors to be considered
• The type and number of nucleic acid
bonds
• The intensity and type of radiation
• The time between exposure
• The ability of the cell to repair the damage
• The stage of the cell’s reproductive cycle
when irradiated
Indirect image
• The damage to cells result from the free
radicals produced by the ionization
process
• The hydrogen peroxide damages the cell
by breaking down DNA or proteins
Estimating the magnitude of the
risk of cancer induction
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Dental intraorals (2)
Dental panoramic
Lateral ceph
ALARA principle
1 in 2 000 000
Radiation protection measures
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X-ray equipment
Processing equipment
Position and distance from the patient
ALARA
Guidelines for prescribing of radiographs
Digital radiography
X-ray equipment
• Collimation- maximum 6 cm of an x-ray
beam
• Filtration-aluminium filter to remove long
waves x-rays from the beam
• Beam-indicating device (BID)- the legal
focus to skin (fsd) distances are:
-200 mm for sets operating above 60 kV
-100 mm for sets operating below 60 kV
Inverse square law
Ways to reducing radiation
exposure to the patients
• ALARA concept
- As Low As Reasonably Achievable
• Digital radiography-80 % dose reduction
Guidelines for prescribing dental
radiographs
• Clinical examination must be performed
first
• Adhere to departmental protocols for xraying patients in the School
Safety measures for operator
protection
• Only the operator and patient are permitted
in the x-ray room
• The operator will stand in a safe place:
-6 feet away NOT in direct beam
-behind an appropriate barrier
-outside the room if you cannot get 6 feet
away
Never hold the film or tubehead during
exposure