DIAGNOSTIC ULTRASOUND IN MAXILLOFACIAL IMGING

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RADIATION BIOLOGY
Christos Angelopoulos, DDS, MS
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Radiation Biology is the study of the effects of
ionizing radiations on living tissues
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BIOLOGIC EFFECTS OF RADIATION
DNA, RNA, ADP, ATP, NAD, cytochrome oxidase,
glucokinase, proteins and many more
Injury to the chemicals of life
Direct effects
Indirect effects
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BIOLOGIC EFFECTS OF RADIATION
The very first interaction between the ionizing
radiation and matter occurs at subatomic level
(electrons) within the first 10-13 sec.
Excitation
Ionization
Breaking of molecular bonds
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DIRECT EFFECTS OF RADIATION
When the energy of the ionizing radiation is
deposited directly in the chemicals of life
DNA, RNA, proteins, enzymes, etc.
Approximately 1/3 of the biologic effects of
x-ray exposure result from direct effects
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INDIRECT EFFECTS OF RADIATION
When the energy of the ionizing radiation is
deposited on water molecules first, causing the
formation of free radicals, and then the free
radicals act upon the biologic macromolecules
(chemicals of life)
Approximately 2/3 of the biologic effects of
x-ray exposure result from indirect effects due
to the abundance of water in the living tissues
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RADIOLYSIS OF WATER
Free radicals molecules that result from the
irradiation of water, containing an unpaired
electron and very active chemically
H2O
H2O
H
H2O
H2O
O
H2O
H2O
HO2
H
H2O
H2O
HO-
H
H2O
H2O
H2O
H2O
O-
O-
HO2
H2O2
HO
H2O
H2O
H2O
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THE TARGET THEORY
Strand breakage
HO2
Change or loss of a base
Hydrogen bond breakage
HO2
HO2
HO
Cross-linking
HO2
HO
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RADIATION EFFECTS AT CELLULAR LEVEL
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Chromosome aberration

THE CELL CYCLE
G1
S
M
G2


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Chromatid aberration
G1
S
M
G2

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CELL SURVIVAL CURVES
Survived cells
Radioresistant
Radiosensitive
Radiation dose
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RADIOSENSITIVITY CELL TYPE
BERGONIE TRIBONDEAU (1906) The higher the
mitotic rate of a cell, the more radiosensitive
it is The more primitive (undifferentiated) a
cell, the more radiosensitive it is
Except oocytes lymphocytes
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RADIOSENSITIVITY CELL TYPE
RADIOSENSITIVE CELLS
RADIORESISTANT CELLS

• Germinal cells of ovary
• Seminiferous epithelium of testes
• Lymphocytes
• Erythrocytes
• Myeloblasts
• Epithelium (skin,intestines)
• Connective tissue cells

• Glandular cells
• Kidney tubule cells
• Bone cells
• Brain cells
• Nerve cells
• Muscle cells
  

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RADIATION EFFECTS ON TISSUES ORGANS
HIGH SENSITIVITY
Small lymphocyte Bone marrow Reproductive
cells Intestinal mucosa
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RADIATION EFFECTS ON TISSUES ORGANS
FAIRLY HIGH SENSITIVITY
Skin Lens of the eye Oral mucosa
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RADIATION EFFECTS ON TISSUES ORGANS
MEDIUM SENSITIVITY
Connective tissue Small blood vessels Growing
bone, cartilage
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RADIATION EFFECTS ON TISSUES ORGANS
FAIRLY LOW SENSITIVITY
Mature bone, cartilage Salivary glands Thyroid
gland Kidney Liver
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RADIATION EFFECTS ON TISSUES ORGANS
LOW SENSITIVITY
Muscle Nerve
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RADIATION EFFECTS ON TISSUES ORGANS
Organs that if damaged by radiation have a
greater potential for reducing the quality of life
CRITICAL ORGANS
Lens of the eye Gonads Fetus Bone marrow
Thyroid gland Salivary glands Skin Bone
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RADIATION EFFECTS ON TISSUES ORGANS
Short-term exposures
direct loss of parenchymal cells
Long-term exposures
indirect loss of parenchymal cells due to damage
to fine vasculature
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RADIATION EFFECTS ON TISSUES ORGANS
Latent period
Time interval between irradiation and development
of an observed effect
Cumulative effects of radiation
multiple exposures to ionizing radiation produce
an additive effect
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FACTORS AFFECTING RADIATION INJURY

• Type of radiation
• Total dose
• Acute VS chronic exposure (dose rate)
• Whole body VS local exposure
• Oxygen effect

• Chemical protectors
• Host factors (age, sex)
• Type of tissue
• Phase of cell cycle
• Species differences

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LETHAL DOSE (LD) 50/30
The radiation dose which will result in death of
the 50 of the irradiated population in 30 days
Humans 300
rads Monkeys 600
rads Rats 750
rads
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LONG-TERM EFFECTS OF RADIATION
Tumors Leukemia Cataracts Life span
shortening Genetic mutations
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RADIATION DOSE-RESPONSE CURVE
The graphic relationship between levels of
radiation dose and the magnitude of a radiation
effect or injury
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RADIATION DOSE-RESPONSE CURVES
Tissue damage
Linear threshold response
D
Radiation dose
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RADIATION DOSE-RESPONSE CURVES
Tissue damage
Linear non-threshold response
Tumors Life span shortening Genetic mutations
Radiation dose
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RADIATION DOSE-RESPONSE CURVES
Tissue damage
Linear quadratic response
Leukemia
Radiation dose
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RADIATION DOSE-RESPONSE CURVES
Tissue damage
Non linear threshold response
Cataracts
D
Radiation dose
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RADIATION UNITS MEASUREMENT
Exposure
how much exposure comes out of the x-ray machine
count ionizations in the air at the cone of the
radiographic machine
Roentgen (old system) Exposure unit or Culomb/Kg
(SI)
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RADIATION UNITS MEASUREMENT
Dose
the amount of x-ray energy absorbed by a unit
mass of tissue
exposure DOES NOT equal dose
rad (old system) Gray (Gy) (SI)
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RADIATION UNITS MEASUREMENT
Dose equivalent (H)
allows a comparison of biologic effects of
different types of ionizing radiation
equal doses of different types of
radiation produce different amounts of biologic
damage
rem (old system) Sievert (Sv) (SI)
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RADIATION UNITS MEASUREMENT
Dose equivalent (H)
takes into consideration differences between
radiation by using a radiation Quality factor
(QF), HDose X QF
Radiation
QF
X-rays 1 Gamma rays
1 L.E. protons 5 Alpha
10
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RADIATION UNITS MEASUREMENT
H (dose equivalent) D (dose) X QF
if we want to compare the biological effects of
0.5 Gys of x-rays to 0.5 Gys of alpha
particles H (dose equiv.) x-rays 0.5 X 1 0.5
Sv H (dose equiv.) alpha p 0.5 X 10 5 Sv
Radiation
QF
X-rays 1 Gamma rays
1 L.E. protons 5 Alpha
10
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RADIATION UNITS MEASUREMENT
if we want to compare the biological damage of
0.5 Gys of x-rays to the (R) hand with 0.5 Gys of
x-rays to the breast.or a local exposure VS a
whole body exposure OUR UNITS ARE NOT GOOD ENOUGH
Effective dose (E) helps us understand the
assessment of biologic consequences (risk) of
radiation to a localized part of the body and the
degree to which this local exposure would
increase a persons whole body risk of
developing Ca
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EXPOSURE DOSE IN RADIOGRAPHY
Effect that increases in severity as radiation
dose increases, after a threshold dose has been
reached
Deterministic effect
The effect whose probability of occurrence
rather than its severity is increased with
increased dose (no threshold)
Stochastic effect
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SOURCES OF RADIATION EXPOSURE
AVERAGE ANNUAL EFFECTIVE DOSE TO US POPULATION
NATURAL (BACKGROUND)
83
Cosmic
8
Terrestrial
8
Internal
67
Radon gas
56
ARTIFICIAL (MEDICAL)
15
Medical x-rays
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Nuclear Medicine
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CONSUMER PRODUCTS
2
3.60 mSv
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SOURCES OF RADIATION EXPOSURE
VARIATIONS FROM AVERAGE
NATURAL (BACKGROUND)
Cosmic 0.27 mSv/yr
0.50 mSv/yr (Colorado)
Terrestrial 0.28 mSv/yr
0.90 mSv/yr (Colorado)
Internal
Radon gas
3.00 mSv
3.85 mSv
ARTIFICIAL (MEDICAL)
Medical x-rays
Nuclear Medicine
CONSUMER PRODUCTS
8 mSv daily
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EXPOSURE TO CRITICAL ORGANS FROM DENTAL
RADIOGRAPHY
Increased risk/ tissue damage
FMS, round cone, D-speed film
Panoramic
Lens of the eye 200,000 mrads 60
mrads 8 mrads
Bone marrow 5,000 mrads 9-14
mrads 17 mrads
Thyroid gland 6,000 mrads
23 mrads 32 mrads
Skin 25,000 mrads
1,300 mrads 632 mrads
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EXPOSURE FROM INTRAORAL RADIOGRAPHS (D-film)
70 kVp 215-365 mrads/film
75 kVp 200-325 mrads/film
90 kVp 100-200 mrads/film
Higher kVp reduces exposure
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EXPOSURE FROM INTRAORAL RADIOGRAPHS
70 kVp D-speed film
300 mrads/film
70 kVp E-speed film
150 mrads/film
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EXPOSURES FROM DENTAL RADIOGRAPHS
EQUIVALENT NATURAL EXPOSURE
EXAM
E (mSv)
FMS (Round cone-D) 150
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FMS (Rectan. cone-E) 33
4
Panoramic 26
3.3
CT mandible 761-3,324
95-415
Chest 80
10
8 mSv daily
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THE RISKS FROM DENTAL RADIOGRAPHY
CANCER
In 2002 almost 1,300,000 new cases of cancer
were diagnosed and over 550,000 people died from
cancer
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THE RISKS FROM DENTAL RADIOGRAPHY

• Latent period
• Indistinguishable from other cancers
• Insufficient human data at diagnostic doses
• Local vs whole body exposures
• Single vs multiple exposures
• Radiation sensitive populations

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THE RISKS FROM DENTAL RADIOGRAPHY
ICRP
International Commission on radiological
Protection
Probability co-efficient for developing Ca and
hereditary effects from low doses of radiation is
0.073 ca/Sv
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EXPOSURES FROM DENTAL RADIOGRAPHS
PROBABILITY OF CANCER/1,000,000 CASES
EXAM
E (mSv)
FMS (Round cone-D) 150
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FMS (Rectan. cone-E) 33
2.4
Panoramic 26
1.9
CT mandible 761-3,324
55-242
Chest 80
5.8
8 mSv daily
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ONE IN A MILLION RISKS

• To smoke 1.4 cigarettes and develop cancer
• To drink 30 cans of diet soda and develop cancer
• To have a panoramic radiograph and develop cancer