RADIOBIOLOGY. Principles of Radiobiology based on n Random nature of radiation interactions n how...
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Transcript of RADIOBIOLOGY. Principles of Radiobiology based on n Random nature of radiation interactions n how...
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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? QF=rounded 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 RBE’s 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)