RADIOBIOLOGY

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RADIOBIOLOGY
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Principles of Radiobiology based on

• Random nature of radiation interactions
• how radiation interacts at cellular level
• factors that can alter these interactions

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REMEMBER

• All radiation damage occurs at cellular or
  subcellular level
• visible effects are seen after millions of cells
  are impacted

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Characteristics of ionizing radiation

• Charge
• Mass
• Energy
• Vary among different types of radiation

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Ionizing radiation causes injury through these
concepts

• LET
• RBE
• OER

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LET

• High and low LET (chart 6-1, pg 108 Sherer)
• LET IS AVERAGED DUE TO POLYENERGETIC NATURE OF
  IONIZING RADIATION

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RBEBackground information

• QF-How much biologic damage one type of radiation
  does vs. type of radiation
• What is the QF of x-rays?
• What about Alpha?
• QFrounded estimate of RBE

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RBE (Pg. 495-Bushong)

• Compares
• dose of standard radiation necessary to
  produce a given effect
• dose of test radiation necessary to produce
  same effect
• Standard radiation is 250 KeV
• RBEs of diagnostic is 1
• Max. is approx. 3
• As LET increases so does RBE
• Alpha and Beta have high RBE

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OER

• The ratio of radiation damage done with oxygen
  vs. without oxygen

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OXYGEN EFFECT

• Tissue more sensitive to rad when oxygenated or
  in aerobic state
• VS
• anoxic or hypoxic
• Oxygen produces free radicals
• Why would this be important in radiation therapy?

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• Alpha-insensitive to oxygen (Low OER)
• Gamma and x-rays more sensitive (High OER)
• Therefore Low LET is associated with ____OER (LOW
  OR HIGH)

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IONIZING RADATION AND BIOLOGIC DAMAGE

• Direct or indirect
• occurs more with high LET radiation
• Relative Biologic Effectiveness

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Direct

• Can be fatal to cell
• high LET

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A FREE RADICAL

• Hydroperoxl
• Hydroxyl
• H2O2
• 2/3 of all biologic damage is from H2O2 which is
• hydrogen peroxide

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INDIRECT

• RADIOLYSIS OF WATER
• Breakdown of H2O
• produces an ion pair of HOH and e-
• These can attach to uncharged water molecules
  (unstable) free radical

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CHROMOSOMAL EFFECT

• Biologic damage occurs during breakage of
  chromosomal backbone or to DNA
• Point mutations
• Frameshift mutation

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RADIATION MUTATION CHARACTERISTICS

• Germ cells-carry on to future generations
• Somatic cells-effect only occurs once
• undesirable
• probably cumulative
• threshold
• effects are not specific to radiation

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TARGET THEORY

• ADDRESSES LETHAL DAMAGE
• THERE ARE AREAS ON THE DNA CHAIN THAT, IF
  DAMAGED, ARE LETHALTO THE CELL

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UNDERSTANDING THE TARGET

• CELLS ARE MADE UP MOLECULES
• OVERABUNDANCE OF MOLECULES
• CRITICAL MOLECULE
• WHEN RADIATION INTERACTS WITH OR NEAR A CRITICAL
  MOLECULE, THIS SENSITIVE AREA IS CALLED
  TARGET.
• NUCLEUS VS CYTOPLASM

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Principles of Radiobiology based on

• Random nature of radiation interactions
• how radiation interacts at cellular level
• factors that can alter these interactions

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NOW ON TO THE THEORIES

• DNA SEQUENCE VITAL-DAMAGE TO ANY TARGET(SEQUENCE)
  WILL KILL THE CELL
• NO SINGLE SEQUENCE IS IMPORTANT-2 TO 3 TARGETS
  (SEQUENCES) NEED TO BE HIT

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• TARGET ONLY NEEDS ONE HIT TO CAUSE FETAL DAMAGE
• TARGET NEEDS TO BE HIT TWICE OR MORE TO CAUSE
  DAMAGE

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Radiation damage

• Cannot be distinguished from other sources
  (chemical, heat or trauma)