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RADIOBIOLOGY

RADIOBIOLOGY. Principles of Radiobiology based on. Random nature of radiation interactions how radiation interacts at cellular level factors that can alter these interactions. REMEMBER. All radiation damage occurs at cellular or subcellular level

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RADIOBIOLOGY

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  1. RADIOBIOLOGY

  2. Principles of Radiobiology based on • Random nature of radiation interactions • how radiation interacts at cellular level • factors that can alter these interactions

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

  4. Characteristics of ionizing radiation • Charge • Mass • Energy Vary among different types of radiation

  5. Ionizing radiation causes injury through these concepts • LET • RBE • OER

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

  7. 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

  8. 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

  9. OER The ratio of radiation damage done with oxygen vs. without oxygen

  10. 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?

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

  12. IONIZING RADATION AND BIOLOGIC DAMAGE • Direct or indirect • occurs more with high LET radiation • Relative Biologic Effectiveness

  13. Direct • Can be fatal to cell • high LET

  14. A FREE RADICAL • Hydroperoxl • Hydroxyl • H2O2 • 2/3 of all biologic damage is from H2O2 which is… • hydrogen peroxide

  15. 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

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

  17. 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

  18. TARGET THEORY ADDRESSES LETHAL DAMAGE THERE ARE AREAS ON THE DNA CHAIN THAT, IF DAMAGED, ARE LETHALTO THE CELL

  19. 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

  20. Principles of Radiobiology based on • Random nature of radiation interactions • how radiation interacts at cellular level • factors that can alter these interactions

  21. 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

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

  23. Radiation damage • Cannot be distinguished from other sources (chemical, heat or trauma)

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