Radiation biology and protection in dental radiology

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Radiation biology and protection in dental
radiology
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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 Gray100 rads

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Contd

• 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)

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Contd

• 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)

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Typical effective doses

• X-ray examination mSv
• CT head
  8.0
• Dental pan
  0.26
• 2 dental intraoral films
• Using 70 kV rectangular
• Collimation and long cone 0.02

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Various sources of radiation

• Natural background radiation
• Cosmic
• Gama form the rocks
• Radiation from ingested radioisotops
• Radon

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Contd

• Artificial background radiation
• Medical and dental diagnostic radiation
• Radiation from occupational exposure

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The biological effects and risks associated with
X-rays

• Somatic Deterministic effects
• Somatic Stochastic effects
• Genetic Stochastic effects

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Somatic deterministic effects

• They are definitely produced by the high dose of
  radiation
• Threshold dose
• Examples- skin reddening

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Somatic stochastic effects

• They may develop
• Examples- leukemia and certain tumors
• No threshold dose

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Contd

• 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

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Genetic stochastic effects

• Mutations result from any change in the
  chromosome
• May result from radiation or occur spontaneously
• No threshold dose

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Effects on the unborn child

• Large dose of radiation- congenital
• abnormalities
• Mental retardation- low doses of radiation

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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

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How do X-rays cause damage

• Direct damage
• Indirect damage

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Direct damage

• Incoming X-ray photon
• An ejected high-energy electron
• Effects
• Inability to pass on information
• Abnormal replication
• Cell death
• Only temporary damage

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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 cells reproductive cycle when
  irradiated

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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

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Estimating the magnitude of the risk of cancer
induction

• Dental intraorals (2)
• Dental panoramic 1 in 2 000 000
• Lateral ceph
• ALARA principle

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Radiation protection measures

• X-ray equipment
• Processing equipment
• Position and distance from the patient
• ALARA
• Guidelines for prescribing of radiographs
• Digital radiography

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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

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Inverse square law
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Ways to reducing radiation exposure to the
patients

• ALARA concept
• As Low As Reasonably Achievable
• Digital radiography-80 dose reduction

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Guidelines for prescribing dental radiographs

• Clinical examination must be performed first
• Adhere to departmental protocols for x-raying
  patients in the School

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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