Biological Effects of Radiation Long and Short Essays

Radiation Biology Important Notes

  • The action of radiation can be direct or indirect
    • Direct effect occurs when energy of a photon is transferred directly to biological molecules.
    • Indirect effect occurs when photon is absorbed by water and from free radicals which in turn reacts with biologic macromolecules.
    • About two – third of radiation induced biologic damage results from indirect effects.
  • The order of tissue susceptibility affected by radiation are:
    • Spermatozoa and oogonia (most susceptible)
    • Bone marrow with immature cells including lymphocytes
    • Intestinal mucosa
    • Epithelium of skin
    • Muscle cells
    • Nerves
  • For osteoradionecrosis to occur, three factors should be present. They are:
    • Radiation at the site
    • Injury at the site and
    • Infection at the site
  • Susceptibility of different tissues to radiation induced cancer

Oral Radiology Radiation Biology Different tissues of radiation

  • Linear Energy Transfer (LET): The rate of loss of energy from a particle as it moves through the irradiated material is called LET.
    • The does required to produce a certain biologic effect is reduced as the Linear Energy Transfer (LET) of the radiation is increased.
  • The amount of radiation necessary to produce a noticeable skin reaction is called as Erythema dose.
    • The skin erythema dose is 300 – 400R.

Radiation Biology Long Essays

Question 1. Enumerate hazards of radiations. Discuss effects of radiation on oral tissues.
Or
What is ionizing radiation? Descrine biological effects of excessive radiation on orofacial tissues.
Or
What are the effects or radiation in the oral cavity? Write in detail about osteo – radionecrosis.
Or
Describe in detail the effects of radiation on oral cavity.
Answer.

Ionizing Radiation:

  • It is defined as radiation that is capable of producing ions by removing or adding electrons to an atom

Hazards Of Radiation:

  • Biologic changes
    • Changes in DNA:
      • Change in base
      • Disruption of hydrogen bonds
      • Breakage of DNA strands
      • Cross – linking of DNA strands
    • Proteins:
      • Denaturation of proteins
  • Cellular changes:
    • Nuclear changes
    • Chromosome aberration
    • Cytoplasmic changes
  • Tissue changes:
    • Non stochastic Effects
    • Stochastic Effects

Radiation Effects On Oral Tissues:

  • Oral Mucous Membrance:
    • Mucositis
    • Desquamation of epithelial layer
    • Infection of oral cavity
    • Candidiasis
    • Atrophic mucosa
    • Ulceration
    • Radiation necrosis

Read And Learn More: Oral Radiology Question and Answers

  • Taste buds:
    • Degeneration
    • Loss of taste sensation
  • Salivary glands:
    • Xerostomia
    • Loss of salivary secretion
    • Difficult & painful swallowing
    • Decreased buffering capacity
    • Susceptibility to radiation caries
  • Teeth:
    • Retards growth of teeth
    • Inhibit cellular differentiation
    • Premature eruption
    • Retard root formation
    • Fibroatrophy of pulp

Radiation Caries:

Pathogenesis:

Oral Radiology Radiation Biology Pathogenesis

Types:

    • Superficial
    • Involving cervical region
    • Dark pigmentation
  • Bone:
    • Osteoradionecrosis
    • Hypocellularity
    • Hypoxia
    • Hypovascularity

Osteoradionecrosis:

  • It is a radiation induces pathologic process characterized by the chronic and painful infection and necrosis is accompained by the late sequestration and sometimes permanent deformity.
  • This is one of the most serious complication of radiation to head and neck seen frequently

Factors Leading To Osteoradionecrosis:

  • Irradiation of an area of previous surgery before adequate healing has taken place
  • Irradiation of lesion in close proximity to the bone
  • Poor oral hygiene and continued use of irritants
  • Poor patients cooperation in managing irradiated tissue
  • Surgery in irradiated area
  • Failure to prevent trauma to irradiated area

Clinical Features:

  • Non healing dead bone
  • The bone becomes hypovascular, hypocellular and hypomineralized
  • Mandible is more effected than maxilla

Treatment:

  • Debridement of necrotic tissue should be done along with removal of sequestrum
  • Administration of intravenous antibiotic and hyperbaric oxtgen therapy
  • Maintenance of oral hygiene is necessary

Radiation Biology Short Essays

Question 1. Osteoradionecrosis
Answer.

Osteoradionecrosis

  • It is a radiation induces pathologic process characterized by the chronic and painful infection and necrosis is accompained by the late sequestration and sometimes permanent deformity.
  • This is one of the most serious complication of radiation to head and neck seen frequently

Factors Leading To Osteoradionecrosis

  • Irradiation of an area of previous surgery before adequate healing has taken place
  • Irradiation of lesion in close proximity to the bone
  • Poor oral hygiene and continued use of irritants
  • Poor patients cooperation in managing irradiated tissue
  • Surgery in irradiated area
  • Failure to prevent trauma to irradiated area

Osteoradionecrosis Clinical Features:

  • Non healing dead bone
  • The bone becomes hypovascular, hypocellular and hypomineralized
  • Mandible is more effected than maxilla

Osteoradionecrosis Treatment:

  • Debridement of necrotic tissue should be done along with removal of sequestrum
  • Administration of intravenous antibiotic and hyperbaric oxtgen therapy
  • Maintenance of oral hygiene is necessary

Question 2. Effects of radiation
Or
Hazards of radiation.
Answer.

Effects of radiation

  • Biological effects:
    • Nucleic acids
      • X-ray damages the DNA molecules causing cellular death by the following changes
      • Change in the base
      • Disruption of H+ bond
      • Breakage of DNA strand
      • Crosslinking of the DNA Strands
    • Proteins
      • Causes
      • Breakage of hydrogen bonds
      • Denaturation of proteins
      • Crosslinking
  • Cellular effects:

Oral Radiology Radiation Biology Cellular effects

    • Effects at tissue and organ level
      • Non – stochastic effects
        • It is specific damaging effects to the body of the person exposed to the high dose of radiation
        • Ex: reddening of skin, cataract
      • Stochastic effects
        • It refers to the radiation that may/may not affect the person
    • Short term effects
      • It depends on the radiosensitivity of cells
      • More injury occurs to the proliferating tissues
      • Ex: bone marrow
      • While less proliferating cells has no sign of injury
      • Ex: muscles
    • Long term effects
      • Depends on the radiosensitivity of cells
      • Proliferating tissues are more effected compared to that of less proliferating tissues
      • Example: more injury occurs to bone marrow as compared to that of muscles

Question 3. Effects of radiation on oral tissues.
Answer.

  • Oral Mucous Membrance
    • Mucositis
    • Desquamation of epithelial layer
    • Infection of oral cavity
    • Candidiasis
    • Atrophic mucosa
    • Ulceration
    • Radiation necrosis
  • Taste buds:
    • Degeneration
    • Loss of taste sensation
  • Salivary glands:
    • Xerostomia
    • Loss of salivary secretion
    • Difficult & painful swallowing
    • Decreased buffering capacity
    • Susceptibility to radiation caries
  • Teeth:
    • Retards growth of teeth
    • Inhibit cellular differentiation
    • Premature eruption
    • Retard root formation
    • Fibroatrophy of pulp

Radiation Caries:

Pathogenesis:

Oral Radiology Radiation Biology Pathogenesis

Types:

    • Superficial
    • Involving cervical region
    • Dark pigmentation
  • Bone:
    • Osteoradionecrosis
    • Hypocellularity
    • Hypoxia
    • Hypovascularity

Question 4. Radiotherapy
Answer.

Radiotherapy

  • It is the treatment of the disease using ionizing radiation

Principle:

  • Rapidly proliferating cells are more sensitive to ionizing as compared to the normal cells

Advantages:

  • No function loss
  • Cosmetic
  • Protect adjacent uninvolved area
  • Possible to treat in inaccessible areas

Disadvantages:

  • Development of secondary tumours
  • Mucositis
  • Dysguea
  • Xerostomia

Types Of Therapy:

  • Curative
    • It permanently eradicate the disease
  • Palliative
    • It leads to temporary improvement in the patient’s condition

Types Of Radiation:

  • External radiation
  • Internal radiation
  • Brachytherapy

Question 5. Radiation hazards of jaws.
Answer.

Radiation hazards of jaws

  • The marrow is replaced by fatty marrow and fibrous connective tissue
  • The endosteum becomes atrophic
  • The bone becomes hypovascular, hypocellular and hypomineralized
  • The complication following irradiation i.e. “Osteoradionecrosis”
  • Necrosis of bone may result in nonhealing ulcer which may occur after tooth extraction
  • Lack of osteoblastic and osteoclastic activity in endosteum
  • Mandible is more commonly effected than maxilla
  • On the radiograph, osteoradionecrosis does not show any periosteal reaction as that seen in the case of osteomyelitis

Question 6. Radiation Caries:
Answer.

Radiation Caries

Pathogenesis:

Oral Radiology Radiation Biology Pathogenesis

Types:

    • Superficial
    • Involving cervical region
    • Dark pigmentation
  • Bone:
    • Osteoradionecrosis
    • Hypocellularity
    • Hypoxia
    • Hypovascularity

Radiation Biology Short Answers

Question 1. Effects of radiation on developing tooth.
Answer.

Effects of radiation on developing tooth

Oral Radiology Radiation Biology Developing tooth

Question 2. Radiation mucositis.
Answer.

Radiation mucositis

  • Oral mucous membrane contains the basal layer of differentiating inter mitotic cells which are highly radiosensitive at the end of second week of therapy the mucous membrane begins to show areas of redness and inflammation, this state is called as “Mucositis”
  • As the therapy continues the mucous membrane breaks down with the formation of white or yellow pseudo-membrane
  • At the end of the therapy the mucositis is severe, painful leading to difficulty in talking, eating and swallowing
  • After termination of therapy, the healing may be complete after about two months, but the mucous membrane tends to become thin, atrophic and relatively avascular
  • Secondary infection by candida albicans is a very common complication
  • Patient is usually prone to oral ulcerations and unable to tolerate dentures

Question 3. Types of radiation caries.
Answer.

Types of radiation caries

  • Primarily involving cementum and dentin in the cervical areas
    • This lesion progresses around the teeth circumference and ultimately results in amputation of the crown
  • Generalized superficial lesions attacking the Buccal, occlusal, incisal and palatal surfaces of the teeth
  • Dark pigmentation of the crown

Question 4. Acute radiation syndrome.
Answer.

Acute radiation syndrome

Collective signs and symptoms occuring after whole body radiation exposure

Oral Radiology Radiation Biology Active radiation syndrome

Question 5. Units of radiation
Answer.

Units of radiation

  • Exposure:
    • It refers to the measurement of ionization in air produced by x-rays
    • The unit of exposure is roentgen [R]
    • One roentgen is the quantity of gamma radiation that produces an electrical charge of 2.58 x 10-4coulombs in a kilogram of air at standard temperature and pressure
    • It is also defined as the amount of gamma radiation that will produce in 1 cc of air
    • It is used to measure the intensity of radiation to which an object is exposed
      1R = 2.58 x 10-4 C/kg
      1C/kg = 3.88 x 103 R
  • Absorbed dose:
    • It it the amount of energy absorbed by a tissue
    • Radiation absorbed dose or rad is the unit of dose
    • It is equal to the deposition of 100 ergs of energy per gram of tissue
    • In SI system, the unit of measurement of dose is Gray (GY)
      1Gy = 1 joule/kg or 100 rads
      1 rad = 100 ergs/g of absorber
  • Dose equivalent:
    • It is used to compare the biologic effects of different types of radiation
    • Its unit is roentgen equivalent – man, rem
    • In SI system, the unit of dose – equivalent is the Sievert {Sv}
      1 rem = 0.01 Sv
  • Quality factor:
    • It refers to its biologic effect relative to standard exposure of X-ray
  • Relative biological effectiveness:
    • It is similar to quality factor
  • Radioactivity:
    • It refers to the decay rate of a sample of radioactive material
    • Its traditional unit of radioactivity is curie [Ci]
    • SI unit is Becquerel [Bq]
      1 mCi = 37 mega Bq
      1 Bq = 2.7 x 10-11 Ci

Radiation Biology Viva Voce

  • Unit of measurement of radiation exposed to the patients during dental x-ray procedure is Roentgen
  • SI unit of measuring radioactivity is Becquerrel
  • Most radio-susceptible organ for radiation cancer is stomach
  • Tissue most susceptible to radiation is blood forming cells
  • The most sensitive period in humans for inducing developmental abnormalities is during the period of organogenesis (18 – 45 days of gestation)
  • The sensitive sites within the nucleus are DNA and chromosomes
  • The order of cell cycle is G1 S G2 M
  • If the exposure to radiation occurs after DNA synthesis [i.e. in G2 or late S], only one arm of affected chromo some will be broken.
  • If the radiation exposure occurs before DNA replication [i.e. in G1 or early S], the damage occurs in both arms.
  • Most sensitive phase to radiation is G2 phase while least sensitive phase is ‘S’ phase
  • Mean exposure of radiation from one IOPA is 300 mR
  • Mean exposure from dental X-ray can be reduced to as low as 1 – 10 mR by using improved techniques
  • Mean exposure of radiation to gonads from one IOPA is 1/1000 x 300 mR = 0.03 mR
  • In treatment of oral cancers, the fraction of total dose given in each appointment is in the range of 150 rads

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