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Radiation biology and protection in dental radiology

Radiation biology and protection in dental radiology

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Radiation biology and protection in dental radiology

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  1. Radiation biology and protection in dental radiology

  2. 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

  3. 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)

  4. 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)

  5. 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

  6. Various sources of radiation • Natural background radiation • Cosmic • Gama form the rocks • Radiation from ingested radioisotops • Radon

  7. Cont’d • Artificial background radiation • Medical and dental diagnostic radiation • Radiation from occupational exposure

  8. The biological effects and risks associated with X-rays • Somatic Deterministic effects • Somatic Stochastic effects • Genetic Stochastic effects

  9. Somatic deterministic effects • They are definitely produced by the high dose of radiation • Threshold dose • Examples- skin reddening

  10. Somatic stochastic effects • They may develop • Examples- leukemia and certain tumors • No threshold dose

  11. 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

  12. Genetic stochastic effects • Mutations result from any change in the chromosome • May result from radiation or occur spontaneously • No threshold dose

  13. Effects on the unborn child • Large dose of radiation- congenital abnormalities • Mental retardation- low doses of radiation

  14. 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

  15. How do X-rays cause damage • Direct damage • Indirect damage

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

  17. 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

  18. 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

  19. Estimating the magnitude of the risk of cancer induction • Dental intraorals (2) • Dental panoramic 1 in 2 000 000 • Lateral ceph • ALARA principle

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

  21. 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

  22. Inverse square law

  23. Ways to reducing radiation exposure to the patients • ALARA concept • As Low As Reasonably Achievable • Digital radiography-80 % dose reduction

  24. Guidelines for prescribing dental radiographs • Clinical examination must be performed first • Adhere to departmental protocols for x-raying patients in the School

  25. 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