Radiation biology and protection in dental radiology Dose

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 m. Sv CT head Dental pan 2 dental intraoral films Using 70 k. V rectangular Collimation and long cone 8. 0 0. 26 0. 02

Various sources of radiation • - 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 • • Dental intraorals (2) Dental panoramic Lateral ceph ALARA principle 1 in 2 000

Radiation protection measures • • • 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 k. V -100 mm for sets operating below 60 k. V

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