3. RADIATION EFFECTS
• Can be divided into high doses and
low doses
• High doses of radiation over a short
periods of time, producing acute or
short term effects (eg: CT scan)
• Low doses: low exposure doses over
a long period of time producing
chronic effects (example of chest x-
ray or orthodontic radiographs)
4. • High doses radiation tend to kill
cells, it causes immediate problems
to any body organ
• These are several effects of high
doses radiation:
- Skin burn
- Hair loss
- Sterility
- cataracts
HIGH DOSE
6. • Low doses radiation damage the
cells and spread out over long
periods of time
• Effects of exposure to low doses of
radiation:
- Genetic: (suffer by offspring)
- Somatic (cancer)
- In utero (suffer by a developing
embryo is seen after birth)
LOW DOSE
8. Acute Radiation Syndrome
• When the whole body is exposed to low or
moderate doses of radiation, characteristic
changes (acute radiation syndrome) develop
• Acute Radiation Syndromes include
– Hematopoietic Syndrome
– Gastrointestinal Syndrome
– Cardiovascular and Central Nervous System
Syndrome
9. Acute Radiation Syndrome
• A collection of signs and symptoms experienced
by persons after acute whole-body exposure to
radiation.
• Information comes from :
animal experiments
human exposures (medical radiotherapy, atom bomb
blasts, and radiation accidents)
• Individually, the clinical symptoms are not unique
to radiation exposure, but taken as a whole, the
pattern constitutes a distinct entity.
10. White, S. and Pharoah, M. (2009). Oral radiology.
1st ed. St. Louis, Mo.: Mosby/Elsevier.
11. 1. Prodomal Period
• Within the first minutes to hours after exposure to
whole-body irradiation of about 1.5 Gy, symptoms
characteristic of gastrointestinal tract disturbances may
occur.
• Individual may develop anorexia, nausea, vomiting,
diarrhea, weakness, and fatigue.
• Cause is not clear but probably involves the autonomic
nervous system.
• Severity & time of onset may be significant prognostic
value as they are dose-related
• Higher dose, more rapid the onset & greater the
severity of symptoms.
12. 2. Latent Period
• Occurs after prodromal period where no signs or
symptoms of radiation sickness occur.
• The extent of the latent period is also dose-
related
• Extends from hours or days at supralethal
exposures (> approximately 5 Gy) to a few weeks
at sublethal exposures (< 2 Gy).
• Symptoms follow the latent period when
individuals are exposed in the lethal range
(approximately 2 to 5 Gy) or supralethal range
13. Hematopoietic Syndrome
• Whole-body exposures of 2 to 7 Gy cause injury
to the hematopoietic stem cells of the bone
marrow and spleen.
• Bone marrow is a highly radiosensitive tissue due
to the high mitotic activity of these cells & the
presence of many differentiating cells.
• Doses in this range cause a rapid and profound
fall in the numbers of circulating granulocytes,
platelets, and finally erythrocytes
14. Hematopoietic Syndrome
• Mature circulating granulocytes, platelets, and
erythrocytes themselves are very radioresistant
• However, since they are nonreplicating cells, paucity in
the peripheral blood after irradiation reflects the
radiosensitivity of their precursors
• Rate of fall in the circulating levels of a cell depends on
the life span of that cell in the peripheral blood
• Granulocytes, short lives in circulation, fall off in a
matter of days,
• Red blood cells, long lives in circulation, fall off only
slowly
15. White, S. and Pharoah, M. (2009). Oral
radiology. 1st ed. St. Louis, Mo.:
The
shorter
the life
span of a
cell, the
faster the
rate the
cells fall
off
16. Hematopoietic Syndrome
• Clinical signs of the hematopoietic syndrome
include infection (in part from the lymphopenia
and granulocytopenia), hemorrhage (from the
thrombocytopenia),and anemia (from the
erythrocyte depletion).
• Individuals may survive exposure in this range if
the bone marrow and spleen recover before the
patient dies of one or more clinical complications.
• Death results from the hematopoietic syndrome,
usually occurs 10 to 30 days after irradiation.
17. Gastrointestinal Syndrome
• Whole-body exposures in the range of 7 to 15
Gy cause extensive damage to the
gastrointestinal system.
• Such exposure causes injury to rapidly
proliferating basal epithelial cells of the
intestinal villi and leads to a loss of the
epithelial layer of the intestinal mucosa.
• Turnover time for cells lining the small
intestine is normally 3 to 5 days.
18. Gastrointestinal Syndrome
• Because of the denuded mucosal surface, plasma
and electrolytes are lost therefore efficient
intestinal absorption cannot occur. Ulceration
also occurs, with hemorrhaging of the intestines.
• All these changes are responsible for the
diarrhea, dehydration, and loss of weight.
• Endogenous intestinal bacteria readily invade the
denuded surface, producing septicemia.
• Death occurs before the full effect of the
radiation on hematopoietic systems can be
evidenced
19. Gastrointestinal Syndrome
• The combined effects on these stem cell
systems cause death within 2 weeks from a
combination of factors that include :
fluid and electrolyte 'loss' infection
possibly nutritional impairment.
20. Cardiovascular and CNS Syndrome
• Exposures in excess of 50 Gy usually cause death
in 1 to 2 days.
• The few human beings who have been exposed at
this level showed collapse of the circulatory
system with a precipitous fall in blood pressure in
the hours preceding death.
• Autopsy revealed necrosis of cardiac muscle
• Victims also may show intermittent stupor,
incoordination, disorientation, and convulsions
suggestive of extensive damage to the nervous
system.
21. Cardiovascular and CNS Syndrome
• Syndrome is irreversible, and the clinical
course may run from only a few minutes to
about 48 hours before death occurs.
• Cardiovascular and central nervous system
syndromes have such a rapid course
• Irradiated individual dies before the effects of
damage to the bone marrow and
gastrointestinal system can develop
22. Cardiovascular and CNS Syndrome
• Antibiotics are indicated when infection
threatens or the granulocyte count falls.
• Fluid and electrolyte replacement is used as
necessary.
• Whole blood transfusions are used to treat
anemia, and platelets may be administered to
arrest thrombocytopenia
23. Syndromes Whole Body
Exposure
(Gy)
Length of
Time to
Death
Signs &
Symptoms
Site of Injury Length of
Time to
Recover to
Survive
Hemapoietic
Syndrome
2 - 7 10 – 30
Days
Infection,
Hemorrhage,
Anemia
Hematopoietic
stem cells of
the bone
marrow and
spleen
Before 10 –
30 days
Gastrointesti
nal Syndrome
7 - 15 Within 14
Days
Diarrhea,
Dehydration,
Lose of weight
Basal epithelial
cells of the
intestinal villi
3 – 5 days
Circulatory &
CNS
Syndrome
50 Few
minutes to
48 hours
Stupor,
Incoordianation,
Disorientation,
Convusions
Cardiac
muscle,
Nervous
system
Confirmed
death
25. Radiation sickness
• is illness and symptoms resulting from
excessive exposure to ionizing radiation.
• results when humans (or other animals) are
exposed to very large doses of ionizing
radiation.
26. Cancer
• Carcinogenesis is the actual formation of a
cancer, whereby normal cells are transformed
into cancer cells.
• Radiation causes cancer by modifying DNA.
• Radiation induced gene mutation.
• Radiator acts as initiator (it induces change in
the cells so that it no longer undergoes
terminal differentiation) and also promoter (
stimulating cells to multiply ).
27. Thyroid Cancer
• is a disease that a person gets when abnormal
cells begin to grow in the thyroid gland.
• The incidence of thyroid carcinomas that arise
from the follicular epithelium increases in
human beings after exposure.
• Only about 10% of individuals with such
cancers die from their disease.
28. • Susceptibility to radiation-induced thyroid
cancer is greater early in childhood than at
any time later in life, and children are more
susceptible than adults.
• Females are 2 to 3 times more susceptible
than males to radiogenic and spontaneous
thyroid cancers.
29.
30. Esophageal Cancer
• Esophageal cancer is malignancy of the
esophagus.
• . Esophageal cancer usually begins in the cells
that line the inside of the esophagus.
• Esophageal tumors usually lead to difficulty
swallowing, pain and other symptoms.
31.
32. Brain and Nervous System Cancers
• are the second most common type of childhood
cancer.
• A brain tumor is a collection (or mass) of abnormal
cells in the brain.
• Patients exposed to diagnostic x-ray examinations in
utero and to therapeutic doses in childhood or as
adults (average midbrain dose of about 1 Gy) show
excess numbers of malignant and benign brain
tumors.
33.
34. Salivary Gland Cancer
• is a rare form of cancer that begins in the
salivary glands.
• can begin in any of the salivary glands in your
mouth, neck or throat.
• The incidence is increased in
patients treated with irradiation for diseases
of the head and neck,
Japanese atomic bomb survivors, and
persons exposed to diagnostic x radiation.
35. • the risk being highest in persons receiving full-
mouth examinations before the age of 20
years.
• Only individuals who received an estimated
cumulative parotid dose of 500mGy or more
showed a significant correlation between
dental radiography and salivary gland tumors.
36.
37. Leukaemia
• the most common cancer
• The incidence of leukaemia rises after
exposure of the bone marrow to radiation.
• Leukaemia's appear sooner than solid tumors
because of the higher rate of cell division and
differentiation of hematopoietic stem cells
compared with the other tissues.
• Persons younger than 20 years are more at
risk than adults.
38.
39. Mental Retardation
• a condition diagnosed before age 18 that
includes below-average intellectual function
and a lack of skills necessary for daily living.
• Studies of individuals exposed in utero have
shown that the developing human brain is
radiosensitive.
40. • An estimated 4% chance of mental retardation
per 100mSv exists at 8 to 15 weeks of
gestational age, with less risk occurring from
exposure at other gestational ages.
• During this period, rapid production of
neurons and migration of these immature
neurons to the cerebral cortex occur.
41. Cataract
• A cataract is a clouding of the lens in the eye that
affects vision.
• The most common symptoms of a cataract are:
- Cloudy or blurry vision.
- Poor night vision.
- Double vision or multiple images in one eye.
(This symptom may clear as the cataract gets
larger.)
- Frequent prescription changes in your
eyeglasses or contact lenses.
42. • The threshold for induction of cataracts ranges
from about 2 Gy when the dose is received in
a single exposure to more than 5 Gy when the
dose is received in multiple exposures over a
period of weeks.
• Most affected individuals are unaware of their
presence.
45. • Biological effects of ionizing radiation divided into 2 major
categories:
A) Deterministic effects: the effects in which the severity
of response is proportional to the dose. These effects, usually cell
killing, occur in all people when the dose is large enough. A dose
threshold below which the response is not seen.
B) Stochastic effects: the effects in which is the probability
of the occurrence of a change, rather than its severity. It is either
all-or-none: a person either has or does not have the condition.
46. Changes in biological molecules
1) Nucleic Acid
• The damage to the deoxyribonucleic acid (DNA)
molecule is the primary mechanism for radiation-
induced cell death, mutation, and carcinogenesis.
• Radiation produces a number of different types of
alterations in DNA, including the following:
1) breakage of one or both DNA strands,
2) cross-linking of DNA strands within the helix, to
other DNA strands, or to proteins,
3) change or loss of a base,
4) disruption of hydrogen bonds between DNA
strands.
47. • The most important types of damage are single- and
double-strand breakage.
• Most single-strand breakage is of little biologic
consequence as the broken stand is repaired using the
intact second strand as a template.
• However, misrepair of a strand can result in a mutation
and consequent biologic effect.
• Double-strand breakage occurs when both strands of a
DNA molecule are damaged at the same location or
within a few base pairs.
• In this instance repair is greatly complicated by the lack
of an intact template strand and misrepair is common.
• Double-strand breakage is believed to be responsible for
most cell killing and carcinogenesis as well as mutation.
48. 2) Cells
A) Cells are undamaged by the dose
– Ionization may form chemically active substances which in
some cases alter the structure of the cells.
– These alterations may be the same as those changes that
occur naturally in the cell and may have no negative effect.
B) Cells are damaged, repair the damage and operate
normally
– Some ionizing events produce substances not normally found
in the cell.
– These can lead to a breakdown of the cell structure and its
components.
– Cells can repair the damage if it is limited.
– Even damage to the chromosomes is usually repaired.
– Many thousands of chromosome aberrations (changes) occur
constantly in our bodies.
– We have effective mechanisms to repair these changes.
49. C) Cells are damaged, repair the damage and operate
abnormally
– If a damaged cell needs to perform a function before it has
had time to repair itself, it will either be unable to perform
the repair function or perform the function incorrectly or
incompletely.
– The result may be cells that cannot perform their normal
functions or that now are damaging to other cells.
– These altered cells may be unable to reproduce themselves
or may reproduce at an uncontrolled rate.
– Such cells can be the underlying causes of cancers.
D) Cells die as a result of the damage
– If a cell is extensively damaged by radiation, or damaged in
such a way that reproduction is affected, the cell may die.
– Radiation damage to cells may depend on how sensitive the
cells are to radiation.
50. 3) Tissues
• Generally , the radiation sensitivity of a tissue is:
I. proportional to the rate of proliferation of its cells
II. inversely proportional to the degree of cell differentiation
• This also means that a developing embryo is most sensitive to
radiation during the early stages of differentiation, and an
embryo/fetus is more sensitive to radiation exposure in the first
trimester than in later trimesters
• Blood-forming organs
• Reproductive organs
• Skin
• Bone and teeth
• Muscle
• Nervous system
Sensit-
ivity
51. 4) Organs
Organ
Relative Radio
sensitivity
Chief Mechanism of Parenchymal Hypoplasia
Lymphoid organs; bone marrow;
testes and ovaries; small
intestines
High
Destruction of parenchymal cells, especially the
vegetative of differentiating cells
Skin; cornea & lens of eyes;
gastrointestinal organs; cavity;
esophagus; stomach; rectum
Fairly High
Destruction of vegetable and differentiating cells
of the stratified epithelium
Growing cartilage; the
vasculature; growing bones
Medium
Destruction of proliferating chondroblasts or
osteoblasts; damage to the endothelism;
destruction of connective tissue cells &
chondroblasts or osteoblasts
Mature cartilage or bone; lungs;
kidneys; liver; pancreas; adrenal
gland; pituitary gland
Fairly Low
Hypoplasia secondary damage to the fine
vasculature and connective tissue elements
53. Radiosensitivity
• is the relative susceptibility of cells,
tissues, organ to the harmful action of
radiation.
It denotes the level of harm which
radiation can cause to certain types
of cells in the body.
54. • The most radiosensitive cells are those
that
(1) have a high mitotic rate
(2) undergo many future mitoses
(3) are most primitive in
differentiation.
• Mammalian cells may be divided into
five categories of radiosensitivity on the
basis of histologic observations of early
cell death.
Oral Radiology Principle and Interpretation (Fifth
Edition), White Pharoah
55. Vegetative intermitotic
cells
• most radiosensitive,
• divide regularly, have long
mitotic futures, and do not
undergo differentiation
between mitoses.
• Examples include
spermatogenic or
erythroblastic series, and
basal cells of the oral
mucous membrane.
Differentiating intermitotic
cells
• they divide less often than
vegetative intermitotic
cells.
• Examples of this class
include the inner enamel
epithelium of developing
teeth, cells of the
hematopoietic series that
are in the intermediate
stages of differentiation,
spermatocytes, and
oocytes.
Sources:
Oral
Radiology
Principle
and
Interpretat
56. Multipotential connective
tissue cells
• intermediate
radiosensitivity.
• They divide irregularly,
usually in response to a
demand for more cells,
and are also capable of
limited differentiation.
• Examples are vascular
endothelial cells,
fibroblasts, and
mesenchymal cells.
Reverting postmitotic
cells
• radioresistant because
they divide infrequently.
• They also are generally
specialized in function.
• Examples include the
acinar and ductal cells of
the salivary glands and
pancreas as well as
parenchymal cells of the
liver, kidney, and thyroid.
Sources:
Oral
Radiology
Principle
and
Interpretat
57. Fixed postmitotic cells
• most resistant to the direct action of radiation.
• They are the most highly differentiated cells
and, once mature, are incapable of division.
• Examples of these cells include neurons,
striated muscle cells, squamous epithelial cells
that have differentiated and are close to the
surface of oral mucous membrane, and
erythrocytes.
Sources: Oral Radiology Principle and
Interpretation (Fifth Edition), White Pharoah
59. Radiosensitivity
• the level of harm which radiation can cause to
certain types of cells in the body
• 3 levels:
1. high
2. Intermediate
3. low radiosensitive
60. High Radiosensitivity
• organs, cells or structures are highly
susceptible to the harmful effects of radiation
1. Lymphoid organs
2. Bone marrow
3. WBC
4. Testes
5. Ovaries
6. intestines
7. relatively HIGH: skin &
organs with epithelial cell
lining (cornea, oral cavity,
esophagus, rectum,
bladder, vagina, uterine
cervix, ureters)
61. Intermediate Radiosensitivity
• This organs, cells or structures are moderately
susceptible to the harmful effects of radiation
• neither severely affected nor completely
unaffected
• show moderate signs of radiation injury
65. What is Radioresistance?
• Radioresistance is the relative resistance to
ionizing radiation
• Applicable to cells, tissues, organs, or
organisms to the injurious effects of ionizing
radiation
• Examples of highly radioresistant cells are
fibrocytes, chondrocytes, myocytes and nerve
cells.
66. Induced radioresistance
• 2 ways
• either protecting against a subsequent
exposure to radiation that may be
substantially larger than the initial
'conditioning' dose.
• or by influencing the response to single doses
so that small acute radiation exposures.
70. 1. Somatic deterministic effect
Definitely result from high dose of radiation
Eg : skin reddening , cataract formation
Severity of effect = dose received
Below threshold = no effect
71. 2. SOMATIC STOCHASTIC EFFECT
Development is random, depends on probability
no threshold dose
Eg : Leukemia , tumors
May induced when exposed to any dose of radiation
Every exposure have possibility of stochastic effect
72. 3. GENETIC STOCHASTIC EFFECT
Mutation result from sudden change in gene / chromosome
Caused by external factor : radiation
Radiation to reproductive organ
No threshold dose
73. Effect on unborn child
• Major problem :
a. congenital abnormality / death (high dose)
b. mental retardation (low dose)
74. Harmful effect important in dental
radiology
Size of dose is small
Below threshold
= x cause Somatic deterministic effect
Dental radiology x involve radiation to reproductive organ
= x cause Genetic stochastic effect
Most concern = somatic stochastic effect
77. • Dosimetry : Determining the quantity
of radiation exposure or dose
• Dose : used to describe the amount of
energy absorbed per unit mass at a
site of interest
• Exposure : a measure of radiation
based on its ability to produce
ionization in air under standard
conditions of temperature and
pressure (STP)
78. • Radiation dosimetry is the calculation and
assessment of the ionizing radiation dose
received by the human body due to both external
irradiation and the ingestion or inhalation of
radioactive materials
• Internal dose is calculated from a variety of
physiological techniques, whilst external dose is
measured with adosimeteror inferred from other
radiological protection instruments
• Dosimetry is used extensively forradiation
protectionand is routinely applied to
occupational radiation workers, where a radiation
dose is expected, but regulatory levels must not
be exceeded
79. 2. Types of Units for
Measuring Quantities of
Radiation
80. 1. Exposure
• A measure of radiation quantity, the
capacity of radiation to ionize air
• SI unit : KERMA (kinetic energy released
per unit mass)
• KERMA: the sum of the initial kinetic
energies of all the charged particles
liberated by uncharged ionizing radiation
(neutrons and photons) in a sample of
matter, divided by the mass of the sample.
81. 2.Radioactivity
• The measurement of radioactivity
(A) describes the decay rate of a
sample of radioactive material.
• SI unit: becquerel (Bq)
• The traditional unit is the curie
(Ci)
84. Radiation-absorbed Dose (D)
• measure of the amount of energy absorbed
from the radiation beam per unit mass of
tissue
• SI unit: Gray, (Gy) measured in joules/kg
• Subunit: milligray, (mGy) (x 103)
• original unit: rad
• conversion : 1 Gray = 100 rads
85. Equivalent Dose (H)
• measure which allows the different
radiobiological effectiveness (RBE) of different
types of radiation to be taken into account
• radiation weighting factor WR represents the
biological effects of different radiations
• common unit allowing comparisons to be
made between one type of radiation and
another
86.
87. Equivalent dose (H) = radiation-absorbed dose
(D) X radiation weighting factor (WR)
• SI unit : Sievert (Sv)
• subunits : millisievert (mSv) (x 103)
• original unit : rem
• conversion : 1 Sievert =100 rems
88. Effective Dose (E)
• allows doses from different investigations of
different parts of the body to be compared, by
converting all doses to an equivalent whole
body dose
• some parts of the body are more sensitive to
radiation than others -> tissue weighting
factor (Wτ)
89.
90. Effective dose (E) = equivalent dose (H) X tissue
weighting factor (Wτ)
• SI unit : Sievert (Sv)
• subunit : millisievert (mSv)
91.
92. Collective Dose
• used when considering the total effective dose
to a population
Collective dose = effective dose (E) x population
• SI unit : man-sievert (man-Sv)
93. Dose Rate
• measure of the dose per unit time
• E.g: dose/hour
• Convenient and measurable
• SI unit : microsievert/hour
95. 1) The average annual dose for radiation sources
from x-ray machine is 54 millirem/year
(Adapted from NCRP Report No. 94. Exposure of
the Population in the United States and Canada
from Natural Background Radiation. National
Council on Radiation Protection and
Measurements, Bethesda, MD, 1987.)
2)Dose limit values with upper limit should not be
exceeded.
• Because of radiation, a person would experience
significant adverse or become ill.
• Therefore, upper limit is used as a reference so
that any unnecessary exposure should be
avoided and acceptance should be sought as
low-dose.
96. • Value to the general public dose limit - 5
mSv per year.
• For pregnant women - 10 mSv during
pregnancy.
3) In local irradiation on specific parts of the
body, the average dose in each organ or tissue
affected by patient should not be > 50 mSv
• The maximum annual dose recommended
for health care operators - 50 mSv.
• Lifetime maximum allowable - 10 mSv
multiplied by the person's age in years.
97. 4)Medical uses of radiation are by far the
largest source of man-made exposure of the
public; the global yearly average dose - 0.3
mSv.
5)The National Radiological Protection Board
(NRPB) and the Royal College of Radiologists'
document Guidelines on Radiological
Standards for Primary Dental Care, published
in 1994, provides examples of typical
effective doses for a range of dental
examinations using different equipment and
image receptors.
