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.
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.
