3. CONTENTS:
•DEFINITION
•TYPES OF RADIATINON
•SOURCES OF RADIATION
•RADIATION EFFECTS ON DIFFERENT BIOLOGICAL
TISSUES
•MAXIMUM PERMISSIVE DOSAGE OF RADIATION
•ACUTE AND CHRONIC DOSAGE
•EFFECTS OF ACUTE AND CHRONIC EXPOSURE
•EFFECTS OF WHOLE BODY IRRADIATION
•RADIATION PROTECTION:
PATIENT
CLINICIAN
•ALARA PRINCIPLE
•RECENT ADVANCES.
•CONCLUSION
4. DEFINITION:
• Radiation is defined as the energy that comes from a source
and travels through some material or through space.
or
The emission of energy as electromagnetic waves or as
moving sub-atomic particles, especially high energy particles
which cause ionization.
or
Radiation is the emission or transmission of energy in the form
of waves or particles through space or through a material
medium. This includes:-
•Electromagnetic radiation – radio waves, visible light, x-rays.
•Particle radiation – such as a,b,g radiation.
•Acoustic radiation – ultrasound, seismic radiation.
7. RADIATION EFFECTS ON DIFFERENT BIOLOGICAL
TISSUES:-
•The study of effects of ionizing radiation on living systems is
termed as “radiobiology”.
•Initial interaction b/w ionizing radiation &matter occurs at the
level of the electrons within the first 10-13 seconds after
exposure.
•These changes result in modification in biologic molecules
within the following seconds to hours.
The molecular changes may lead to alterations in cells and
organisms that persist ranging from hours, decades and
possibly generations which may result in cell injury or death
8. •When the energy of a
photon or secondary electron
ionizing biologic
macromolecules, the effect is
termed as “direct effect”.
•Alternatively a photon may be absorbed by water in an organism,
ionizing some of its water molecules resulting in free radicals that
interact with surrounding cells and produce changes in the biologic
molecules.
•Because water molecules are required to alter the biologic molecules
this series of events is termed as “indirect effect”.
•RADIATION
CHEMISTRY
9. Main changes seen are:-
•Break in 1 or more strands of DNA.
•Cross linking of DNA strands within the helix to other DNA strands or
to proteins.
•Change or loss of base.
•Disruption of hydrogen bonds
b/w DNA strands.
• Radiation may also cause
clusters of double stranded
breakage.
10. EFFECTS ON INTRACELLULAR STRUCTURES:
•The changes seen in the intra cellular organisms are both structural and
functional.
NUCLEUS:
•Nucleus is radio-sensitive in terms of lethality.
CHROMOSOMALABBERATIONS:-
•Chromosomes serve as useful markers for radiation injury. Extent of
their damage is related to cell survival.
•Type of damage depends on the stage of the cell in cell cycle at the time
of irradiation.
•Irradiation of cell after DNA synthesis results in single-arm
(CHROMATID) aberrations.
•Irradiation before synthesis results in a double-arm aberrations.
11. CELL REPLICATION:
•Radiation is damaging to rapidly dividing cell systems such as skin,
intestinal mucosa and hematopoietic tissues.
•Irradiation of such cells leads to inhibition of progression of the cells
through cell cycle and reproductive cell death.
•Cells that are
damaged by radiation
release substances that
kill the nearby cells.
This is termed as
“bystander effect”.
12. APOPTOSIS:
•Also known as programmed cell death.
•Seen commonly in lymphoid and haemopoitic tissues.
Radiation induces apoptosis in both normal and tumor tissues
13. HIGH INTERMEDIATE LOW
Bone Fine vasculature Neurons
Testes Growing cartilage muscle
mucous membranes growing bone erythrocy
tes
intestines salivary glands Squamou
s
epithelial
cells
Lungs
kidney, liver, thyroid
(parenchymal cells)
•RELATIVE RADIO-SENSTIVITY OF VARIOUS CELLS:
15. ACUTE DOSAGE:-
• Caused when exposed to large amounts of radiation in a short period of
time.
•It has a greater effect on the body as well as there is no time to repair or
replace damaged body cells.
•Possible effects include:-
•Lowering of WBC count.
• Redding of skin.
•Fatigue.
•Hair loss.
•Possible sterility.
•Nausea and vomiting
•Diarrhea.
•Loss of apatite.
•Possible sterility.
16. CHRONIC DOSE:-
• Caused when exposed to small amounts of radiation over a long period
of time.
•Body can tolerate chronic dose better than an acute dose.
•Possible effects include:-
•Risk of developing cancer and cataract.
17. EFFECTS OF IRRADIATION IN THE ORAL CAVITY:
•The oral cavity is exposed to large doses of radiation when radiation
therapy is used to treat oral cancer (usually squamous cell carcinoma).
•Radiation therapy in the oral cavity is indicated when the lesion is radio
sensitive or advanced, or deeply invasive and cannot be approached by
surgically.
• Radiation treatment is administered as small doses(fractions).
•Usually 2Gy is delivered daily for a weekly exposure of 10Gy.
•The radiation continues for 6-7 weeks until a total of 60 to 70Gy is
administered.
18. ORAL MUCOUS MEMBRANE:-
•Oral mucous membrane contains a basal layer composed of rapidly
dividing, radiosensitive stem cells.
•At the end of 2nd week of therapy as some of these cells die. The
mucous membranes begin to show areas of redness and inflammation
(mucositis).as the therapy continues, the irradiated mucous membrane
begins to separate from the underlying connective tissue with the
formation of a white-yellow pseudomembrane(the desquamated
epithelial layer).at the end of therapy, the mucositis is usually in severe
form, discomfort is at a maximum and food intake is difficult.
19.
20.
21. TASTE BUDS:-
•Taste buds are sensitive to radiation.
•Doses in therapeutic range cause extensive degeneration of normal
architecture of taste buds.
•There is always loss of acuity during the 2nd or 3rdweek of radio therapy.
•Posterior 2/3rds irradiated causes loss of bitter and acid flavors.
•Anterior 1/3rd irradiated causes loss of salt and sweet taste.
•Taste acuity usually decreases by a factor of 1000 to 10,000 during
course of radiotherapy.
•Taste loss is reversible and recovery takes 60-120days.
22. SALIVARY GLANDS:
•Major salivary glands are exposed to
20Gy to 30Gy during radiotherapy in
the cancer of oral cavity or
oropharynx.
•The mouth becomes dry and tender,
and swallowing is difficult and
painful.
•There is also variation in PH of saliva
i.e:5.5( normal-6.5).
•The buffering capacity of saliva falls
to 44% during radiation therapy.
Due to low ph there may be initiation
of decalcification of normal enamel
23. TEETH:
•Children receiving radiation therapy to the jaws may show defects in the
permanent dentition such as retarded root development, dwarfed teeth, or
failure to form one or more teeth.
•If exposure precedes calcification, irradiation may destroy the tooth bud.
Irradiation after calcification has begun may inhibit cellular
differentiation causing malformations and arresting general growth.
•Radiation has no discernible effect on the crystalline structure of
enamel, dentin, cementum and radiation does not increase their
solubility.
24. RADIATION CARIES:
•Radiation caries is a rampant form of dental decay that may occur in
individuals who receive a course of radiotherapy that includes exposure
of salivary glands.
•Caries results from changes in salivary glands and saliva, including
reduced flow decreased ph reduced buffering capacity, increased
viscosity, and altered flora.
•There is reduced ca+2 ion in., leading to greater solubility of the tooth
structure and reduced demineralization.
25. BONE:
•The marrow tissue becomes hypovascular, hypoxic , hypocellular. the
endosteum becomes atrophic showing lack of osteoblastic and
osteoclastic activity an indication of necrosis.
•The degree of mineralization may be reduced, leading to brittleness.
When these changes are severe it results in death of bone and bone is
exposed , this is known as “osteoradionecrosis”.
MUSCULATURE:
•Radiation may cause inflammation and fibrosis resulting in contracture
and trismus in the muscles of mastication.
•Restricted mouth opening is seen after 2 months of irradiation.
26. DOSE (Gy) MANIFESTATION
1-2 prodromal symptoms.
2-4 mild haematopoietic symptoms.
4-7 severe haemopoietic symptoms.
7-15 Gastrointestinal symptoms
50 cardiovascular and central nervous
Symptoms.
EFFECTS OF WHOLE BODY IRRADIATION:
ACUTE RADIATION SYNDROME:-
•It is collection of signs and symptoms experienced by persons after
acute whole body exposure to radiation.
27.
28. RADIATION EFFECTS ON EMBRYOS AND
FETUSES:
•Embryos and fetus are considerably more radiosensitive than adults
because most embryonic cells are relatively undifferentiated and rapidly
mitotic activity is seen.
•Exposures in the range of 1-3Gy during the first days after conception
are thought to cause undetectable death of embryo.
•Radiation exposure is contraindicated in 1st trimester as it is the period
of organogenesis, when the major organ systems form.
•These effects are deterministic in nature and are believed to have a
threshold of about 0.1Gy.
29. RADIATION PROTECTION:
•Dentist must be prepared to discuss with the patients the benefits and
possible hazards involved with the use of x-rays, the steps taken to
reduce these hazards.
•Recognition of the harmful effects of radiation and the risks involved
with its use led the international commission on radiological protection
(ICRP) to establish guidelines for limitations on the amount of radiation
received by both occupationally exposed individuals and public.
30. Reducing dental exposure:
There are 3 principles in radiation protection:
Justification decision making if diagnosis needs any radiographs.
Optimization as low as reasonably achievable.
Dose limitation applies to dentist and staff.
•Use of E/F films or digital sensors.
•Use of position indication device.
•Use of rectangular collimators to decrease the area of exposure.
•Filtration of beam for elimination of low energy photons.
•Generous use of leaded aprons and thyroid collars.
•Optimal operating potential unit should be 60-70 kVp.
31.
32. CLINICIAN PROTECTION:
•Operators of radiographic equipment should use barrier protection when
possible, and the barriers should contain a leaded glass window to enable
the operator to view the patient during exposure.(ADA 2006).
•Dental operatories should be designed and constructed to meet the
minimal shielding requirement.
When shielding is not possible, the operator should stand at least 2
meters from the tube head and out of path of primary beam.
33.
34. ALARA PRINCIPLE:
•Position and distance rule :-
•The operator should stand at least 6 feet from the patient, at an angle of
90-135 degrees to the central ray of x-ray beam.
•When applied this rule not only takes advantage of the inverse square
law to reduce the exposure but also the position of the patients head
absorbs most of the scattered radiation.
•Use of personal dosimeter badges to access the extent of exposure
annually.
•Quality assurance protocols for x-ray machine, imaging receptor, film
processing , dark room, and patient shielding should be accessed
periodically to for safety of both operator and patient.
38. CONCLUSION:
Radiation has both advantages and disadvantages, so
use of radiation in a judicious way in both medical
and dental field may reduce risk of long term
effects to both operator and patient.
39. REFERENCES:
•STUART C.WHITE.MICHAEL.J PHAROAH, 1stedition- Text book of
Oral Radiology – principles of interpretation.
•GUPTA, MEHTA, SAHU, 2nd edition- Dental radiology.
•KARJODKAR- 2nd edition- text book of dental and maxillofacial
radiology.
•JOEN IANNUCCI RARRIN, 2nd, 3rd edition- Dental radiography
principles and techniques.
