Injuries from radiations

Dr. Umar Tauqir

What is Radiobiology?• The study of effect of ionizing

radiation on biological tissues

What is cell theory?• Cell are basic functional unit of all

plants and animals

What is cell theory?

Cells are the basic functional

units in all plants and animals.

What do macro

molecules consist

of?

carbohydrates

lipids

nucleic acids

Proteins

DNA is the most sensitive structure to be

affected by radiations It regulates cellular activity and contain

genetic information needed for cell replication. Permanent changes alter the cell function and

result in cell death.

which cell effect by which type of radiations.

Direct effect

Indirect effect

Effect of Radiations

In an X-RAY or some other type of radiation

interact with DNA molecules. Particular radiation because of its mass cause more damage to DNA molecule.

Other particles like RNA enzymes and proteins can also be affected by direct effect of radiations

DIRECT EFFECT OF RADIATIONS

Most of the damage to DNA molecules take

place through indirect effect. When X-rays enter a cell, they most likely hit a water molecule because there are large number of water molecules inside a cell. The x-ray ionizes a water molecules. Ions, free radicals are produced which in turn bond with DNA molecule changing its structure. Since the x-ray interacted with water molecule before the DNA Was involved, this is called indirect effect

INDIRECT EFFECT

A free radical is any atom or molecule that

has a single unpaired electron in an outer shell. While a few free radicals such as melanin are not chemically reactive, most biologically-relevant free radicals are highly reactive. It is the primary mediatory of indirect effect of radiation

FREE RADICAL

Change or loss of base

Disruption of hydrogen bonds between DNA

strands

Breakage of one or both DNA strands

What effects happen on DNA due to radiations

Ionization alters the

structure of cell but has no negative effect

Cells are damaged by ionization but damage is

repaired

Mutation can be occurred as well

cell damage is so extensive that it can damage the cell

CELLULAR EFFECTS

Greatest dose of radiation which is not

expected to cause detectable bodily injury to people at anytime during their life

The amount of ionizing radiation a person may exposed to supposedly without being harmed

The limits of ionizing radiation set for general public by international commison on radiological protection. For radiological workers this limit is 50msv

MAXIMUM PERMISSIBLE DOSE

The amount of ionizing

radiation that will kill 50% of population in a specified time

MEDIAN LETHAL DOSE

Stochastic effects occur by chance and can

be compared to deterministic effects which result in a direct effect.

The damaging effects may be induced when body is exposed to any dose of radiations. Experimentally it is not possible to establish a safe dose. It is therefore assumed that there is no thresh-hold dose so that every exposure does carry a stochastic effect

Stochastic effects

Non-stochastic (deterministic effects) are

somatic effects that have a threshold that increase in severity with the absorbed dose

Examples of non-stochastic effect include erythema, loss of hair, cataract formation and decreased fertility

Compared to stochastic effects, deterministic effects required a large dose to cause serious impairment of health

DETERMINISTIC EFFECTS

Following the latent period, effects that are seen

within minutes, days, or weeks are termed short-term effects. Short-term effects are associated with large amounts of radiation absorbed in a short time (e.g., exposure to a nuclear accident or the atomic bomb).

Acute radiation syndrome (ARS) is a short-term effect and includes nausea, vomiting, diarrhea, hair loss, and hemorrhage.

Short-term effects are not applicable to dentistry

Short term effects

Effects that appear after years, decades, or

generations are termed long-term effects. Long-term effects are associated with small

amounts of radiation absorbed repeatedly over a long period. Repeated low levels of radiation exposure are linked to the induction of cancer, birth abnormalities, and genetic defects

Long term effects

All the cells in the body can be classified as

either somatic or genetic. Somatic cells are all the cells in the body

except the reproductive cells. The reproductive cells (e.g., ova, sperm) are

termed genetic cells. Depending on the type of cell injured by

radiation, the biologic effects of radiation can be classified as somatic or genetic.

SOMATIC AND GENETIC EFFECTS

Somatic effects are seen in the person who

has been irradiated. Radiation injuries that produce changes in somatic cells produce poor health in the irradiated individual.

Major somatic effects of radiation exposure include the induction of cancer, leukemia, and cataracts.

These changes, however, are not transmitted to future generations

SOMATIC EFFECTS

The developing fetus is particularly sensitive to the effects of

radiation, especially during the period of organogenesis (2–9 weeks after conception).

Exposures in the range of 2 to 3 Gy during the first few days after conception are thought to cause undetectable death of the embryo.

The period of maximal sensitivity of the brain is 8 to 15 weeks after conception.

The major problems are: 1.Congenital abnormalities or death associated with large doses of radiation 2.Mental retardation associated with low doses of radiation. As a result, the maximum permissible dose to the abdomen of a

woman who is pregnant is regulated by law.

EFFECT ON THE UNBORN CHILD

1. Skin: The reaction of the skin to radiation may be categorized as: i. Early or acute signs:• Increased susceptibility to chapping.• Intolerance to surgical scrub.• Blunting and leveling of finger ridges.• Brittleness and ridging of finger nails. ii. Late or chronic signs:• Loosening of hair and epilation.• Dryness and atrophy of skin, due to destruction of the sweat glands.• Progressive pigmentation, telangiectasis and keratosis.• Indolent type of ulcerations.• Possibility of malignant changes in tissue.

RADIATION EFFECTS ON CRITICAL ORGANS

All these changes in the skin are due to

radiation trauma to:1-The blood vessels.2- Connective tissue.3- Epithelium. Early erythema may appear from a single dose

of about 450 rads. With lower doses no erythema occurs

13 mR for full mouth intraoral periapical radiographs. A maximum dose of 200 R is required for any damage

to the marrow or blood forming organs. Hence, the risk of bone marrow damage from dental

X-rays is small. The primary somatic risk from dental radiography is

leukemia induction,especially in young individuals. This is because at birth all bones contain only red

bone marrow. younger individuals are at a greater risk of developing leukemia.

BONE MARROW

THYROID 40 mR for full mouth intraoral periapical radiographs. A dose of 10 R will produce thyroid cancer. Gonadal – a single intraoral radiograph gives 100 to 900

mR to the face. From this; Male gonads receive 0.3 mR. Female gonads receive 0.03 to 0.001 mR, Eye – a series of full mouth intraoral periapical

radiographs, will give only a few mR. Cataract of the lens is produced after 500 R of exposure