Biological effect of radiation and radiation safety Al Azhar University Gaza Dr. lama khaled El Banna Faculty of Oral and Dental Medicine

1. Oral Radilogy
Dr. Rawand Samy Mohamed Abu Nahla
Oral Medicine, periodontology& oral Radiology Department.
Dr. Haydar. A. Shafy Faculty Of Dentistry.Dr. Haydar. A. Shafy Faculty Of Dentistry.
El Azhar University.El Azhar University.
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2. Lecture 8
Biological effect of radiation
And radiation protection
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3. Radiobiology
When x-rays enter the body, they interact at
the atomic level to cause ionization.
Radiobiology is the response of living
systems to ionizing radiation.
3

4. threshold
linear
non-linear
Dose-Response Curves
non-threshold
Response
Dose
Dose-Response curves represent the relationship
between the dose of radiation a person receives and
the cellular response to that exposure. These
responses may be linear or non-linear and may, or may
not, have a threshold dose; the responses (effects)
may be stochastic or deterministic. (See next two
slides for definitions of these terms).
4

5. Linear: the response is directly related to the dose. As
the dose increases, the response increases
proportionately.
Non-linear: the response is not proportionate to the
dose. An increase in dose may result in a larger or
smaller increase in the response depending on the
location on the dose-response curve.
Threshold: this represents the dose at which effects
are produced; below this dose, there are no obvious
effects.
Non-threshold: any dose, no matter how small, will
produce a response. 5

6. Stochastic effect: occurs by chance, usually without
a threshold level of dose. The probability of a
stochastic effect is increased with increasing
doses, but the severity of the response is not
proportional to the dose (e.g., two people may get
the same dose of radiation, but the response will
not be the same in both people). Genetic mutations
and cancer are the two main stochastic effects.
Deterministic effect: health effects that increase in
severity with increasing dose above a threshold
level. Usually associated with a relatively high dose
delivered over a short period of time. Skin erythema
(reddening) and cataract formation from radiation
are two examples of deterministic effects. 6

7. DNA
Radiation effects at the cellular level
result from changes in a critical or
“target” molecule. This target molecule
is DNA (deoxyribonucleic acid), which
regulates cellular activity and contains
genetic information needed for cell
replication. The DNA molecule is called
a chromosome. Permanent changes in
this molecule will alter cell function and
may result in cell death.
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8. Direct vs. Indirect Effect
DNA
If an x-ray or some type of particulate radiation
interacts with the DNA molecule, this is
considered a direct effect. Particulate radiation,
because of its mass, is more apt to cause damage
to the DNA by this direct effect. Other molecules
that contribute to cell function, such as RNA,
proteins, and enzymes, may also be affected by
the direct effect.
x-ray or particulate
radiation
Direct effect=
8

9. Direct vs. Indirect Effect
H2O ions and
free radicals
Most of the damage to DNA molecules from x-rays is
accomplished through the indirect effect. When x-rays
enter a cell, they are much more likely to hit a water
molecule because there are a large number of water
molecules in each cell. When the x-ray ionizes the
water molecule, ions and free radicals are produced
which in turn bond with a DNA molecule, changing its
structure. Since the x-ray interacted with the water
molecule before the DNA was involved, this is
considered an indirect effect.
x-ray or particulate
radiation
DNA =
Indirect
effect
9

10. A free radical is an atom or molecule that has
an unpaired electron in the valence shell,
making it highly reactive. These free radicals
aggressively join with the DNA molecule to
produce damage. In the presence of oxygen,
the hydroperoxyl free radical is formed; this is
one of the most damaging free radicals that
can be produced. Free radicals are the
primary mediator of the indirect effects on
DNA.
Free Radical
10

11. Cells undamaged: ionization alters the structure of
the cells but has no overall negative effect.
Sublethal injury: cells are damaged by ionization
but the damage is repaired.
Mutation: cell injury may be incorrectly repaired,
and cell function is altered or the cell may
reproduce at an uncontrolled rate (cancer).
Cell death: the cell damage is so extensive that the
cell is no longer able to reproduce.
Cellular Effects
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12. Sublethal Injury: Cellular Repair
1. Ionization causes damage to DNA
(single-strand break of DNA).
2. Cellular enzymes recognize the damage
and coordinate the removal of the
damaged section.
3. Additional cell enzymes organize
replacement of the damaged section with
new material.
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13. When the DNA is damaged,
cell function may be altered
or reproductive capacity may
be accelerated. Cancer is the
most harmful result of
cellular mutation.
Mutation
Normal
Mutation
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14. Cell Death
If there is extensive damage to the cell following
irradiation or if cell division (mitosis) is disrupted,
the cell may die. This will depend on how
sensitive the cells are to radiation. The loss of a
few cells or small group of cells is usually of no
consequence, since there are so many cells
present in the body. In most cases, the dead cells
will soon be replaced through normal reparative
processes.
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15. Cell Cycle
More damage results when the cell is irradiated during
the G1/early S portion of the cell cycle (before DNA
synthesis); the damaged DNA (chromosome) will be
duplicated during DNA synthesis and will result in a
break in both arms of the chromosome at the next
mitosis.
G1 = gap phase 1 in which nuclear
components are replicated
S = synthesis phase; DNA is
synthesized during the last 2/3 of
this phase
G2 = gap phase 2, a preparatory
stage to cell division
M = mitosis, during which cells
divide
Cell most sensitive
to radiation
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16. 1. High reproductive rate (many mitoses)
2. Undifferentiated (immature)
3. High metabolic rate
Radiosensitive Cells
Cells that are more easily damaged by radiation are
radiosensitive. The characteristics of radiosensitive
cells are:
Lymphocytes, germ cells, basal cells of skin and
mucosa, and erythroblasts are examples of
radiosensitive cells.
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17. Radioresistant Cells
1. Low reproductive rate (few mitoses)
2. Well differentiated (mature)
3. Low metabolic rate
Cells that are not as susceptible to damage from
radiation are radioresistant. The characteristics of
radioresistant cells are:
Nerve and muscle cells are examples of
radioresistant cells.
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18. Radiation Effect Modifiers
The biological response to radiation is dependent on
several different factors. These include:
• Total Dose: the higher the radiation dose, the
greater the potential cellular damage.
• Dose Rate: A high dose given over a short
period of time (or all at once) will produce more
damage than the same dose received over a
longer period of time.
• Total Area Covered: the more cells that are
exposed to radiation, the greater the effects will
be. 18

19. Radiation Effect Modifiers (continued)
• Type of tissue: As discussed earlier,
radiosensitive cells are more likely to be
damaged by radiation than are radioresistant
cells.
• Age: Because the cells are dividing more
frequently in a growing child, young people are
affected more by radiation than are older people.
• Linear Energy Transfer: This measures the rate
of the loss of energy as radiation moves
through tissue. Particulate radiation (alpha
particles, electrons, etc.) has a higher LET
because it has mass and interacts with
tissues much more readily than do x-rays.
19

20. • Oxygen Effect: Radiation effects are more pronounced
in the presence of oxygen. Oxygen is required for the
formation of the hydroperoxyl free radical, which is
the most damaging free radical formed following
ionization.
Radiation Effect Modifiers (continued)
20

21. The amount of exposure a patient receives
from dental diagnostic radiography (effective
dose) is relatively small. Most of the radiation
damage will be repaired. The effects of the
radiation damage that is not repaired may not
show up for many years. The time between the
exposure and the appearance of the effects of
that exposure is called the latent period. In
general, the higher the dose, the shorter the
latent period.
Latent Period
21

22. Since repair of radiation injury is not 100%,
radiation effects are accumulative. However,
these effects will usually not be noticeable,
since they are masked by the normal aging
processes.
The effects from extreme levels of radiation
exposure are potentially life threatening.
22

23. Somatic Cells vs. Germ Cells
There are two general types of cells in the body; these
are somatic and genetic. Somatic cells are all the cells
except for the germ (reproductive) cells. If somatic
cells are irradiated, only the person exposed will be
affected. Germ cells are the sperm and ova. If the germ
cells are irradiated, the offspring of the individual may
be affected.
23

24. Dosimetry
Measuring the dose of radiation emitted
by a radioactive source.
As mentioned previously, radiation effects are
dependent on the total area covered. If the entire body
is exposed, it would be considered whole-body
radiation. If only a localized area is exposed, as in
dental radiography, it would be called specific-area
radiation. The effects from a given dose of radiation
would be expected to be more severe if the whole
body is exposed to that dose rather than a specific
area. 24

25. Traditional Units SI* Units
Roentgen (R) Coulombs per kilogram
rad Gray
rem Sievert
Units of Radiation Measurement
* SI = International System of Units; used worldwide
25

26. Roentgen
The Roentgen (R) is the traditional unit of
measuring radiation exposure. This measures
the ionization of air. (The exact definition of
Roentgen is complicated and not worth
remembering). The Roentgen measures
radiation quantity before the radiation enters
the body. There is no exact SI unit comparable
to the Roentgen, but in keeping with the metric
system it is measured in coulombs per
kilogram.
26

27. The rad (radiation absorbed dose) is the traditional
unit used to measure the energy absorbed by the
body. The SI unit is the Gray (Gy). 1 Gray = 100
rads; 1 cGy (centiGray) = .01 Gray = 1 rad.
rad/Gray
27

28. The rem (roentgen equivalent man) is the traditional
unit used for comparing the effects of different types
of ionizing radiation (electromagnetic and particulate).
The dose (in rads) is multiplied by a quality
(weighting) factor. The quality factor for x-rays is 1.
Therefore the dose in rems (dose equivalent) is the
same as the dose in rads. For alpha particles the
quality factor is 20. Therefore the dose in rems (dose
equivalent) would be 20 times the dose in rads for
alpha particles. The higher the LET, the higher the
qualifying factor.
The SI unit is the Sievert (Sv). 1 Sievert = 100 rems;
1cSv (.01 Sievert) = 1 rem.
rem/Sievert
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29. Effective Dose Equivalent
Exposure and dose are not related to the amount or
type of tissue covered by the x-ray beam. A dose (or
exposure) of 1 Sv could cover just the teeth or the
entire body. Obviously, the overall effects would be
different, even though the dose is the same. The
effective dose equivalent takes into account the
dose, the volume of tissue covered and the
radiosensitivity of the cells. Using the effective dose
equivalent, different types of x-ray examinations can
be more realistically compared regarding the risk
factor of each.
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30. The accepted cumulative dose of ionizing radiation
during pregnancy is 5 rad (.05 Sv).
The decision to order films during pregnancy is a
personal one. Because of the relatively low dose, it is not
expected that there will be any harm to the fetus.
However, my recommendation is to limit the films to
those needed to treat the patient during the pregnancy
(symptomatic teeth or very active caries).
Pregnancy
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31. Radiation Protection
for
Patient and Operator
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32. Maximum Permissible Dose (MPD)
The maximum permissible dose is the amount of
radiation (dose limit) that a person can receive
from artificial radiation (effective dose
equivalent). These dose limits are recommended
by the NCRP* and required by the state in which a
dentist practices. The dose limits may vary
between the NCRP and the state.
There are no dose limits for patients being
radiographed. The dentist should only order films
that are needed for a diagnosis, and thus keep
patient exposure to a minimum (See ALARA).
* National Council on Radiation Protection and Measurements32

33. Dose limits (MPD’s) are set for occupationally
exposed personnel (dentist, dental hygienist, and
dental assistant) and for non-occupationally
exposed individuals (front-office staff, people in
waiting room, etc.). The dose limits are as follows:
Maximum Permissible Dose (MPD)
33

34. Patient Protection
It is important to do everything we can to reduce the
amount of exposure when a patient has dental
radiographs taken. The following slides identify the
ways in which we can do this.
34

35. ALARA
ALARA stands for “As Low As Reasonably
Achievable”. If we assume that there is no threshold for
stochastic effects (mutations and cancer) to occur, then
it is important to keep the exposure to the minimum
needed to provide an accurate diagnosis. In other
words, take only those films needed to properly identify
patient problems.
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36. Equipment Reliability
X-ray equipment must be functioning properly to
insure that the patient does not receive unnecessary
radiation exposure. The settings for the exposure
factors (exposure time, mA, kVp) must accurately
reflect the output
36

37. Direct Current (Constant Potential)
60-cycle Alternating Current
Many machines now convert the alternating current
into a direct current (constant potential). Instead of
cycles going from zero to the maximum, both positive
and negative, the voltage stays at the maximum
positive value, creating more effective x-ray
production. This allows for shorter exposure times and
a 20% reduction in patient exposure.
Constant Potential X-ray Machine
37

38. Filtration
Low-energy x-rays do not contribute to the formation
of an x-ray image; all they do is expose the body to
radiation. Therefore, we need to get rid of them. The
process of removing these low-energy x-rays from
the x-ray beam is known as filtration. Filtration
increases the average energy (quality) of the x-ray
beam. The x-ray beam becomes more penetrating,
providing good image formation on the film with
reduced patient exposure.
Low-energy
x-rays
high-energy
x-ray 38

39. Collimation
Collimation is used to restrict the size of the x-ray beam,
covering the entire film with the x-ray beam but not
exposing unnecessary tissue. By reducing the amount
of tissue exposed, the production of scatter radiation is
also reduced.
The shape of the opening (round or rectangular) in the
collimator determines the shape of the x-ray beam. The
size of the opening determines the size of the beam at
the end of the PID. If you switch from a 7 cm diameter
round PID to a 6 cm diameter round PID, the patient
receives 25% less radiation. Rectangular collimation
results in the patient receiving 55 % less radiation when
compared to what they would receive with a 7 cm round
PID.
39

40. Focus Film Distance
Extending the distance between the target of the x-
ray tube (focal spot) and the teeth makes the beam
less divergent as it passes through the head,
exposing a smaller area of the patient. (The diameter
of the beam at the skin surface is the same for both
distances. The beam from the 8” target-teeth
distance spreads out much more as it passes
through the head).
16” 8”
Target-teeth
16”
Target-teeth
8”
40

41. Using a faster film requires less radiation. Using
F-speed film (Insight) instead of D-speed film
reduces patient exposure by 60%. F-speed film
has larger silver halide crystals, which more
readily intercept the x-rays.
Intraoral Film Speed
41

42. Extraoral Screen Speed
Extraoral films are exposed by light from intensifying
screens; this light is produced when x-rays contact
phosphor crystals on the surface of the screens. The
light is either blue or green, depending on the type of
screen. Intensifying screens have different speeds,
depending on the type of phosphor crystal (rare earth
recommended) and the thickness of the phosphor layer.
The faster the screen is, the less the patient exposure
will be. However, image detail decreases as the speed
of the screens increases.
42

43. The American Dental Association
recommends that a lead apron and
thyroid collar be used on all patients.
The actual exposure from scatter
radiation to other parts of the body is
minimal, but considering the ease of
placing the lead apron and thyroid
collar, there is no reason not to use
them. Patients will appreciate your
efforts in keeping their exposure to a
minimum. (The thyroid collar is not
used for panoramic films).
Lead Apron/Thyroid Collar
43

44. Good technique in taking films is essential in
producing diagnostic radiographs. Proper film
placement and selection of the correct
exposure factors will maximize the value of
the films and will reduce or eliminate the need
for retakes, which would increase the patient’s
overall exposure.
Technique
44

45. Processing
Processing films for the correct amount of time
and at the proper temperature produces films of
good diagnostic quality, assuming the films were
exposed properly. It is necessary to have
appropriate safelighting in a light-tight
darkroom. Inadequate processing will result in
retaking films which will add to the patient’s
overall radiation exposure.
45

46. The operator should never hold films in the
patient’s mouth during an exposure. Some
patient’s, due to physical or mental impairments,
may need help in stabilizing the films, but this
assistance should be provided by a friend or
relative of the patient. This person should wear a
lead apron and leaded gloves when holding films
in the patient’s mouth.
X-ray Protection for the Operator
The photo at right shows a
squamous cell carcinoma on the
finger of a dentist who routinely
held films for the patient.
46

47. The operator should stand behind a protective
barrier if available. It has been determined that
drywall is adequate protection for this purpose.
The operator must be able to observe the patient
during the exposure to make sure the patient
doesn’t move prior to or during the exposure. If a
direct line of sight is not possible, mirrors can be
mounted on a wall opposite the doorway to allow
visualization of the patient.
If barriers are not available, the operator should
follow the position and distance rule (next slide).
X-ray Protection for the Operator
47

48. Position and Distance Rule
The operator should stand at least six feet away from
the patient at an angle between 90 and 135 degrees. As
the tubehead is moved, this safe position will change
relative to the patient’s head (see below).
48

49. Personnel-monitoring devices (film badges) can be
used to determine the exposure an operator receives
during a given period (often quarterly). Film badges
are required in some states if you expect to exceed
25% of the MPD during any calendar quarter (12.5
mSv). Although you should not expect to exceed this
dose following normal safe operating procedures, it is
beneficial to have a dosimetry service. The cost is
minimal and the reports, which hopefully identify the
lack of exposure to the operators, reduces any
apprehension the office staff may have about
radiation exposure.
Film Badges
49