Basic Biological Interaction of Radiation

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Basic Biological Interaction of Radiation

• Ling Li
• September, 2000

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Basic Biological Interaction of Radiation

• Basic interaction of radiation in cell
• LET and RBE
• Radiation effect on cell

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Basic Interaction of Radiation in Cell
x-rays photon
free electron
ion radicals
free radicals
chemical change from the breakage of
bonds biological effects

• Indirect action
• Direct action

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LET RBE

• LET
• RBE
• Definition
• Factors that determine RBE
• Radiation dose
• Number of dose fractions
• Biological system or endpoint
• Radiation quality (LET)
• Dose rate

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Definition of RBE
RBE is defined as the comparison of a dose of
test radiation to the dose of 250 keV x-ray that
produce the same biologic response.
dose in Gy from 250 keV x-ray
REB dose in Gy from another
radiation delivered under the
condition that produces the same biologic effect

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Radiation dose Number of dose
fractions
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Biological system on RBE
1. Mouse bone marrow 2. Ly.leuk.mouse L5178Y 3.
Tissue cultured cell of human kidney
origin 4. Rat rhabdomyosarcoma cells 5.
Mouse crypt cells
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Radiation quality
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Radiation effect on cells

• Radiation effect on DNA
• Radiation effect on chromosomes
• Radiation effect on other cellular constituents

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Radiation effect on DNA

• Base damage
• Single-strand breaks (ssb)
• Double-strand breaks (dsb)
• Crosslinks

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Radiation effect on DNA
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Dsb and mammalian cell death

• Dsb in Dna are the most common type of radiation
  lesions that lead to mammalian cell death
• Dsb rejoining

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Radiation effects on chromosomes

• General chromosomes effects
• Structure changes
• Changes in the sequence of genetic information
  translocations and inversions

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General chromosome effects

• The over all result breakage of the chromosome,
  producing chromosomal fragments
• Gross structure change aberrations
• Chromosome aberration
• Chromatid aberration
• Consequence to cell of the structure change
• Restitution
• Deletion
• Distorted chromosome ring, dicentric,
  anaphase bridge
• Mutation

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Chromosome Structure Changes

• Acentric fragments and dicentric rings
• Ring chromosomes
• Chromosome stickness

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Acentric fragments and dicentric rings
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Ring chromosomes
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Changes in the Sequence of Genetic
InformationTranslocation and Inversions
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• Upper line (from left to right)
• 1 chromatid lesions
• 2 chromatid breaks
• 3 isochromatid fragments
• Translocation
• Lower line (from left to right)
• 1 Dicentrics
• 2 Rings
• 3 Quadriradius (middle)
• endoreduplication (left)
• triradius (right)

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Radiation Effects on Other Cellular Constituents

• Carbohydrates
• Proteins
• Lipid
• Enzyme
• Membrane