BIOLOGICAL EFFECT OF RADIATION

1. PRINCIPLES

The gamma radiation is energy in the form of electromagnetic waves which interact with matter producing ionization

The IONIZATION causes significant changes in the matter and in the case of living organisms cause changes in cells, tissues, organs and the whole individual.

The type and magnitude of DAMAGES depend on the type of radiation, its energy, ABSORBED DOSE, the affected area and the exposure time.

1. PRINCIPLES

The ability of ionizing radiation to interact with the material is utilized for various

applications

Industry Agriculture

Medical Treatment

1. PRINCIPLES

There are two mechanisms by which radiation ultimately affects cells. These two mechanisms are commonly called direct and indirect effects.

ATOMS which may affect MOLECULES which may affect CELLS which may affect TISSUES which may affect ORGANS which may affect THE WHOLE BODY

Although we tend to think of biological effects in terms of the effect of radiation on living cells, in actuality, ionizing radiation, by definition, interacts only with atoms by a process called ionization. Thus, all biological damage effects begin with the consequence of radiation interactions with the atoms forming the cells.

As a result, radiation effects on living organisms proceed from the lowest to the highest levels:

Radiation Causes Ionizations of:

If radiation interacts with the atoms of the DNA molecule, or some other cellular component critical to the survival of the cell, it is referred to as a direct effect. Such an interaction may affect the ability of the cell to reproduce and, thus, survive. If enough atoms are affected such that the chromosomes do not replicate properly, or if there is significant alteration in the information carried by the DNA molecule, then the cell may be destroyed by “direct” interference with its life-sustaining system.

EFFECT OF THE IRRADIATION ON THE CELL

CLASIFICATION OF THE BIOLOGICAL EFFECT

Somatic and Genetic effects

Somatic effects appear in the exposed person.  Somatic effects may be divided into two classes based on the rate at which the dose was received. Prompt somatic effects are those that occur soon after an acute dose (typically 10 rad or greater to the whole body in a short period of time), Delayed somatic effects are those that may occur years after radiation doses are received.

Genetic, or heritable effects appear in the future generations of the exposed person as a result of radiation damage to the reproductive cells. Genetic effects are abnormalities that may occur in the future generations of exposed individuals. 

a) Depending on the type of cells found in organisms

Deterministic effects: has a threshold of dose, the severity of the effect is dose-relatedStochastic effects: the probability of an effect increases with dose, it has no dose threshold and the severity of the effect is not dose related

CLASIFICATION OF THE BIOLOGICAL EFFECT

Deterministic and Stochastic effects •

b) According to their probability of occurrence

Radiosensitivity & law of Bergonié and Tribondeau

Bergonié and Tribondeau stated their law in 1906 which is:

“The radiosensitivity of a tissue is directly proportional to its reproductive capacity and inversely proportional to its degree of differentiation”

Law of Bergonie and Tribondeau

This law established the relationship between metabolic state and radiosensitivity

The law specifically states that:

• Stem cells are radiosensitive.

• Immature or young cells and tissues are more radiosensitive; resistance to radiation increases with increased cell maturity.

• Low metabolic rate decreases radiosensitivity and high metabolic rate increases radiosensitivity.

• High proliferation (reproductive) rate for cells and fast growth rate increases the radiosensitivity of those cells.

Eggs Larvae Pupae Adult

0

20

40

60

80

100

AgeCelular Transformation

Rad

iose

nsib

ility

RADIOSENSIBILITY: The radiosensibility is a function of the metabolic

stage of the irradiated tissue.

Virus

Bacter

ia

Insec

tM

en

0.11

10100

100010000

Resistence

Complexity Biological Cycle

Dos

e (

Kra

d)

SUMMARY:

The more complex the organism is more sensitive to radiation

shorter life cycle of the organism =

greater resistance