Lecture-2

 

objective

žBiological effect of ionizing radiation.

              Deterministic effect.

              Stochastic effect.

žObjective of radiation protection program

žLegal and ethical responsibilities

The effects of radiation on the human body as a whole arise from damage to individual cells, but the two types of change have quite different results.

1.Deterministic effect.

2.Stochastic effect.

 

Deterministic effect.

oCaused early death of the cell or the prevention or delay of cell division.

oThey are biologic somatic effects that can be directly related to the dose received.

oThreshold exists.

oA threshold dose below which no effect is seen

oThe severity of certain effects on human beings will increase with increasing doses.

 

žDeterministic effect has two type:

1.Acute radiation effect

2.Late deterministic effect

Acute radiation effect(early effect):
ØThe acute radiation effects are those
that occur within a few hours, days or
weeks after the receipt of a large dose
in a relatively short period of time.
ØThe main effects are attributable to
bone marrow, gastrointestinal or
neuromuscular damage depending on the
dose received.
ØAcute absorbed doses above about 1 Gy
give rise to nausea and vomiting, this
known as radiation thickness and it
occurs a few hours after exposure.
ØAbsorbed doses  above about 2 Gy can
lead to death, probably 10-15 days after
exposures.

Late deterministic effects
ØThey are effects that appear
months or years after exposure to
ionizing radiation.
ØThese effects may result from
previous whole- or partial- body
acute, high radiation doses, or they
may be the product of individual
doses sustained over several years.

Stochastic Effects

žStochastic effects account for

the remaining late effects:

žThere is no threshold and the

probability of having the effects

is proportional to the dose

absorbed. They increase in

likelihood as dose increase

žTheir severity is not dose-related

žProbability of occurrence depends on absorbed dose

žStochastic effects include radiation carcinogenesis and hereditary effects

Genetic effects do not

produce any significantly

observable effect in the

exposed individual but may

appear in descendants of the

exposed individual. The

effects may lie dormant for

several generations.

It is unlikely that any worker

in the medical environment

would be exposed to

ionizing radiation at a level

high enough to cause genetic

effects.

žAren't children more

sensitive to radiation than

adults?

žYes, because children are

growing more rapidly, there

are more cells dividing and a

greater opportunity for

radiation to disrupt the

process. EPA's radiation

protection standards take

into account the differences

in the sensitivity due to age

and gender.

žFetuses are also highly

sensitive to radiation. The

resulting effects depend on

which systems are

developing at the time of

exposure

 

Risks

Exposure to ionizing radiation affects various organs and tissues in the body and may result in a finite possibility for radiation-induced disease in persons exposed to the radiation, and in their descendants. Health effects are know to be influenced by radiation characteristics and biological factors .

Some factors that can affect the probability and significance of potential effects are:

žAge: Response to radiation differs with age. Children are more sensitive to exposure than most adults.

žAcute or chronic exposure: Was exposure delivered over a short period of time or spread over an extended period?

žInternal or external exposure: External means the source of radiation is outside the body and internal means the source of radiation was ingested, inhaled, absorbed, or injected.

žWhat part and how much: Was the exposure localized to a specific area?

žType of radiation: Forms of radiation differ in their penetrating power and ability to cause damage to biological tissues.

 

Objective of radiation protection program

Industrial radiography sources emit X rays and gamma radiation which produce dose rates of the order of hundreds of milligrays per hour at one meter. These high dose rates at close distances can cause severe injuries such as radiation burns following exposures of a few seconds. Workers using such sources must achieve the protection objective to prevent doses arising from acute and chronic accidental exposures and unsafe work practices likely to cause injuries to develop. Safe work practices will protect not only the individual worker but also others in the vicinity and the public from serious consequences arising from the loss or uncontrolled use of these sources.

The primary aim of radiation protection and safety is to provide appropriate standards of protection and safety for people without unduly limiting the benefits of practices giving rise to exposure.

   This primary aim is expressed by the following:

1.Protection objectives

2.Safety objectives

Protection objectives: to prevent the occurrence of deterministic effects in individuals by keeping doses below the relevant threshold and to ensure that all reasonable steps are taken to reduce the occurrence of stochastic effects in the population at present and in the future.

Safety objectives: to protect individuals, society and the environment from harm by establishing and maintaining effective defences against radiological hazards from sources.

Any practice resulting in increased exposure to radiation should be carefully planned in accordance with the three basic radiological protective principles as set out by the International Commission on Radiological Protection (ICRP) in 1991 (ICRP Publication No. 60). These basic principles are:

Justification of a practice- any practice involving exposure should be justifiable, i.e. it produces more benefit to the exposed individual or society than harm

Principles for radiation protection

Optimization of protection- the magnitude of individual doses and the number of people exposed should be kept as low as reasonably achievable, economic and social factor being taken into account; and

Individual dose limits- the exposure of individuals will be subjected to dose limit to ensure that no individual is exposed to radiation risks that are judged to be unacceptable.

žThese radiation protection and safety objectives apply to the design, manufacture or construction, commissioning, operation, maintenance and decommissioning of exposure devices, sealed sources and fixed facilities for industrial radiography.

žThey also apply to the development, application and review of all operating procedures.

  

žOverall, the aim of radiation protection, as stated by the ICRP, is to prevent deterministic effect and to limit the probability of stochastic effects to levels deemed to be acceptable.

 

Legal and ethical responsibilities

Responsibility for an effective radiation safety program.

 Employers responsibilities

i.Implement and maintain an effective radiation safety program in which to execute ALARA by providing:

1)Necessary resources.

2)Appropriate environment for ALARA program

ii.Make a written policy statement describing the ALARA program and identifying the commitment of management to keep all radiation exposure ALARA available to all employees in the workplace.

Radiation workers’ responsibilities

i. Be aware of rules governing the workplace

ii.Perform duties consistent with ALARA

  Organizational responsibilities

    The safe performance of industrial radiography relies on the people and organizations involved meeting certain responsibilities. These organizations are the Regulatory Authority, the operating organization responsible for carrying out the work, the industrial radiographers, device manufacturers, qualified experts and the client responsible for hiring the operating organization. It is necessary for all concerned to co-operate.

    The Radiation Protection Program is responsible for other protection activities too. For example, there is a team of expert that respond to involving radioactivity. There is also a laboratory that monitors the environment to determine how much radiation is in the air.

                           The End