Transcript 5_Physical, chemical, and physiological protection of people from

Physical, chemical, and
physiological protection of
people from radiation
Dr. Igor M. Leskiv, MD
Department of Oncology & Radiology
What are the biological
effects of ionizing radiation?
 One characteristic of ionizing radiation on human body
is that the energy absorbed is low but the biological
effects are serious. For example after receiving a lethal
dose of 10 Gy, the body temperature will only increase
by 0.02 oC but the dose may lead to death of all the
exposed entities.
 The second characteristic is the latent biological effects
of radiation. Acute biological effects can occur within
several hours to several days while the long term
effects usually appear several years after the
exposure.
Type of effects
Characteristic of
effects
Occurring
time
Object
Effects on organs
Skin damage
Acute Effects
Deterministic
Effects
Somatic
Effects
Damage of reproductive
system
Damage of blood forming
system
Damage of digestive system
Damage of central nervous
system
Cataract
Damage of immunization
system
Cancer
Latent Effects
Stochastic
Effects

Genetic Effects
Heredity effects
The biological effects of ionizing radiation can be classified according to
the characteristics of effects, occurring times and the object that shows
the effects.
The effects of critical organs
Different organs have different sensitivity to ionizing radiation. For example, gonad
and bone marrows are more sensitive organs, but the bones are less sensitive
Deterministic effects and stochastic effects
From the biological effects of radiation on human body, radiation effects are
generally divided into two categories: "Deterministic effects" and "Stochastic
effects".
Threshold for deterministic effects (Sv)
Effects
One single absorption
(Sv)
Prolong absorption (Sv-year)
testis
permanent infertility
3.5 - 6.0
2
ovary
permanent infertility
2.5 - 6.0
> 0.2
Lens of
eyes
milky of lens
cataract
0.5 - 2.0
5.0
> 0.1
> 0.15
Bone
marrow
Blood forming
deficiency
0.5
> 0.4
According to the time for the effects to occur, the
biological effects of radiation can be divided into
two categories:
a) acute effects and b) latent effects
Acute effects: There are three types of acute effects
of radiation:
 1. Haematopoietic syndrome
2. Gastrointestinal syndrome
3. Central Nervous syndrome
Latent effects: Latent effects of radiation refer to
those which occur 6 months after the exposure. It
consists of two categories: somatic effects and
genetic effects. The former refers to the effects
occur on the exposed individuals (e.g. cataracts,
radiation sickness, cancers, etc.) while the latter
occurs in their future generations because of
mutations of the genetic cells.
An acute radiation dose is defined as a large dose (10 rad or
greater, to the whole body) delivered during a short period
of time (on the order of a few days at the most). If large
enough, it may result in effects which are observable within
a period of hours to weeks
 Acute doses can cause a pattern of clearly identifiable
symptoms (syndromes). These conditions are referred to in
general as Acute Radiation Syndrome. Radiation sickness
symptoms are apparent following acute doses >100 rad.
Acute whole body doses of >450 rad may result in a
statistical expectation that 50% of the population exposed will
die within 60 days without medical attention.
 As in most illnesses, the specific symptoms, the therapy that
a doctor might prescribe, and the prospects for recovery vary
from one person to another and are generally dependent on
the age and general health of the individual.
Acute effects:
 Blood-forming organ (Bone marrow) syndrome (>100 rad) is
characterized by damage to cells that divide at the most rapid
pace (such as bone marrow, the spleen and lymphatic tissue).
Symptoms include internal bleeding, fatigue, bacterial infections,
and fever.
 Gastrointestinal tract syndrome (>1000 rad) is characterized by
damage to cells that divide less rapidly (such as the linings of the
stomach and intestines). Symptoms include nausea, vomiting,
diarrhea, dehydration, electrolytic imbalance, loss of digestion
ability, bleeding ulcers, and the symptoms of blood-forming organ
syndrome.
Acute effects:


Central nervous system syndrome (>5000 rad) is characterized by damage
to cells that do not reproduce such as nerve cells. Symptoms include loss of
coordination, confusion, coma, convulsions, shock, and the symptoms of the
blood forming organ and gastrointestinal tract syndromes. Scientists now have
evidence that death under these conditions is not caused by actual radiation
damage to the nervous system, but rather from complications caused by
internal bleeding, and fluid and pressure build-up on the brain
Other effects from an acute dose include:
200 to 300 rad to the skin can result in the reddening of the skin (erythema),
similar to a mild sunburn and may result in hair loss due to damage to hair
follicles.
125 to 200 rad to the ovaries can result in prolonged or permanent
suppression of menstruation in about fifty percent (50%) of women.
600 rad to the ovaries or testicles can result in permanent sterilization.
50 rad to the thyroid gland can result in benign (non cancerous) tumors.
According to the subjects on which the effects
occur, the biological effects of radiation are
classified into: "Somatic effects" and "Genetic
effects".
Somatic effects: This is the biological effects that occur on the exposed individuals.
 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). One
example of a prompt effect is the temporary hair loss which occurs about
three weeks after a dose of 400 rad to the scalp. New hair is expected to
grow within two months after the dose, although the color and texture may
be different.
 Delayed somatic effects are those that may occur years after radiation doses
are received. Among the delayed effects thus far observed have been an
increased potential for the development of cancer and cataracts. Since some
forms of cancer are among the most probable delayed effects, the
established dose limits were formulated with this risk in mind. These limits
are set such that the calculated risk of cancer in radiation workers is an
increase of a very small fraction of the normal cancer risk. (More on risk in a
moment)
Genetic effects or heritable effects : Genetic effects refer to
biological changes on the descendants of the exposed individuals
due to mutation of their genetic cells.
When genetic cells are irradiated, the chromosomes or DNA of the
cells may be affected which may lead to genetic mutations,
chromosome aberrations or changes in the number of
chromosomes in the cells. As a result, the probability of genetic
changes will increase, bringing detrimental effects to the
descendants of the exposed persons.
Genetic effect 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. They have been extensively
studied in plants and animals, but risks for genetic effects in
humans are seen to be considerably smaller than the risks for
somatic effects. Therefore, the limits used to protect the exposed
person from harm are equally effective to protect future
generations from harm
Sensitivity of body organs to radiation
 Gonad: The probability of cancer induction in this organ is
comparatively low. The main concern is the genetic effects due to
irradiation of this organ and the probability is proportional to the
absorbed dose.
 Red bone marrow: The effect on bone marrow plays an important role
in the induction of leukemia. Based on statistical data from radiotherapy
patients and atomic bomb survivors in Japan, the induction of leukemia
has a maximum at several years after the irradiation and will return to
the normal incident level after about 25 years.
 Bone: The radiosensitive cells in bone are endosteal cells and epithelial
cells on the bone surfaces. The sensitivity of bone is less than that of
the breast, red bone marrow, lung and thyroid.
 Lung: Cancer of the lung has been observed in miners exposed to high
concentration of radon and its decay products. External irradiation can
also induce lung cancer and the risk is about the same as that for the
development of leukemia.
 Thyroid: Radiation can induce thyroid cancer. However, the mortality of
this type of cancer is much lower than that of leukemia primarily
because of the success in the treatment of thyroid cancer.
Sensitivity of body organs to radiation
 Breast: During reproductive life, the female breast may be one of the
more radiosensitive tissues of the human body. The risk for breast
cancer is about one half of that of leukemia.
 Skin: The effects on skin depend on absorbed dose and the area of
irradiation. Major effects are erythema and ulceration of the skin. The
probability of induction of skin cancer is less than the above organs.
 Lens: The effects of radiation on the eyes are causing cataract, which
is the opacity of the lens. The lens is 5 to 10 times more sensitive to
neutrons than to x-ray. Thresholds exist with lower values for children
than those for the adults.
 Fetus: Effects depend on the stage of pregnancy at the time of
exposure. At the early stage of pregnancy when the cells are still not
differentiated, it usually causes death of the embryo. It is generally
believed that exposure of fetus at the first 3 weeks of pregnancy should
not cause any deterministic and stochastic effect to the embryo. Later
stage irradiation of the fetus may leads to malformation of body organs
and increase in cancer risk of the child.
 The local radiation damages are divided into early and late ones.
Damages developed in the process of radiation therapeutics or
within 3 months after its completion belong to early ones.
Damages, which appear at any period after the expiry of 3 month
after radiation therapeutics belong to late radiation damages. The
early damages are observed mainly in those cases, when the total
radiation dose exceeds the tolerance of irradiated tissues by 3050% . If the total dose does not exceed the tolerance of tissues or
exceeds its slightly, the radiation damages can develop during the
remote periods, especially under the unfavorable additional
circumstances (the action of mechanical or chemical trauma on
irradiation field, insolation etc.). The disturbances of vital activity of
skin in these conditions result in arising of radiation necrosis and
then ulcer.
The radiation ulcers are characterized by their stability and quite often
require the surgical treatment - skin transplantation on the surface of
granulations or dissection of injured area with the following plasty.
 The treatment of local radiation damages must be complex. It
consists of generally roborant therapeutics and local application of
anti-inflammatory and resorptive medicinal preparations. At the
unsuccessful long-term conservative treatment apply the surgical
interference. The strict clinic-dissymmetric and radiobiological
substantiation and flexible planning of the process of radiation
therapy allow avoiding the severe complications in most cases.
But, taking into consideration the long period of rehabilitation, the
radiation therapeutist together with physicians of corresponding
specialties must observe the patients for a long time, realizing the
measures, directed on prevention and treatment of possible
consequences. The cost of radiation curing of the tumors must not
be too high. After the rehabilitation period the patient can be in
usual for him living home or working conditions, but he has to
follow the doctor’s recommendations and recurrently examination.