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 8.0

Dental pan 0.26

2 dental intraoral films

Using 70 kV rectangular

Collimation and long cone 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 1 in 2 000 000

• Lateral ceph

• ALARA principle

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 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 x-raying 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