Radiation hazards..!!!!

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

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.

TYPES OF RADIATION:-•Mainly of two types:•a) Ionizing.•b) Non ionizing.

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

•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

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.

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.

CHROMOSOMAL ABBERATIONS:-•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.

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”.

APOPTOSIS: •Also known as programmed cell death.

•Seen commonly in lymphoid and haemopoitic tissues.

Radiation induces apoptosis in both normal and tumor tissues

HIGH INTERMEDIATE LOW Bone Fine vasculature Neurons

Testes Growing cartilage muscle mucous membranes growing bone erythrocy

tes

intestines salivary glands Squamous epithelial cells

Lungs kidney, liver, thyroid

(parenchymal cells)

•RELATIVE RADIO-SENSTIVITY OF VARIOUS CELLS:

MAXIMUM PERMISSIVE DOSAGE OF RADIATION:

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

RECENT ADVANANCES TO REDUCE RADIATION EXPOSUE: •USG- ultrasound +elastography.•COMBINATION SYSTEMS.•MAGNETIC PARTICLE IMAGING.•SPECT.•PET.

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.

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.

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