Radiation Therapy


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Preview to radiobiology and radiation effects at the molecular level.

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Radiation Therapy

  1. 1. Radiobiology A Preview By: Katherine Walz Callie Widmayer
  2. 2. Ionizing Radiation <ul><li>Ionizing Radiation is the removal of an electron from an atom leaving an unstable molecule which may then break apart to form free radicals. </li></ul>http://www.paradigmlink.com/ionrad.shtml
  3. 3. Linear Energy Transfer (LET) <ul><li>The average energy deposited per unit length of track. </li></ul><ul><li>Measured in kiloelectron volts per micron (10 -6 m) </li></ul>
  4. 4. Low LET / High LET <ul><li>Low LET </li></ul><ul><ul><li>Low mass, increased travel distance (gamma rays, x-rays). </li></ul></ul><ul><ul><li>Sparsely ionizing with random interactions. </li></ul></ul><ul><ul><li>Causes damage primarily through indirect action or may cause single strand breaks (which are repairable). </li></ul></ul>http://staff.jccc.net/PDECELL/biochemistry/dna.gif e -
  5. 5. Low LET / High LET <ul><li>High LET </li></ul><ul><ul><li>Large mass, decreased travel distance (alpha particles, protons, low energy neutrons). </li></ul></ul><ul><ul><li>Causes dense ionization along its path with a high probability of interacting directly with DNA. </li></ul></ul>http://staff.jccc.net/PDECELL/biochemistry/dna.gif α ++
  6. 6. Ionizing Radiation <ul><li>Alpha particles </li></ul><ul><ul><li>The alpha particle has a large mass and consists of two protons, two neutrons and no electrons (+2) </li></ul></ul><ul><ul><li>The alpha particle deposits a large amount of energy in a short distance of travel (about 1-2 inches) </li></ul></ul><ul><ul><li>Most alpha particles are stopped by a few centimeters of air, a sheet of paper, or the dead layer (outer layer) of skin. </li></ul></ul><ul><li>Beta particles </li></ul><ul><ul><li>The beta particle has a small mass and is negatively charged (-1)  </li></ul></ul><ul><ul><li>Beta radiation causes ionization by displacing electrons from their orbits. </li></ul></ul><ul><ul><li>Because of its negative charge, the beta particle has a limited penetrating ability.   Range in air is about 10 feet. </li></ul></ul>The following are the most common types of ionizing radiation: http://www.paradigmlink.com/ionrad.shtml
  7. 7. Ionizing Radiation <ul><li>Gamma rays/x rays </li></ul><ul><ul><li>Gamma/ x ray radiation is an electromagnetic wave or photon and has no electrical charge </li></ul></ul><ul><ul><li>Gamma/ x ray radiation can ionize as a result of direct interactions with orbital electrons and  is transmitted directly to its target.  Because Gamma/ x ray radiation have no charge and no mass, it has a very high penetrating power.   </li></ul></ul><ul><li>Neutron particles </li></ul><ul><ul><li>Neutron radiation consists of neutrons that are ejected from the nucleus and have no electrical charge </li></ul></ul><ul><ul><li>Due to their neutral charge, neutrons interact with matter either directly or indirectly </li></ul></ul><ul><ul><li>Because of the lack of a charge, neutrons have a relatively high penetrating ability and are difficult to stop.  </li></ul></ul>http://www.paradigmlink.com/ionrad.shtml
  8. 8. Ionizing Radiation <ul><li>The reactions caused by ionizing radiation occur rapidly, they are nonselective and random. </li></ul><ul><li>The majority of damage caused by radiation is due to chemical reactions with water within the cell. </li></ul>
  9. 9. H 2 O HOH + e - water electron Positively charged water molecule Radiation reacts with water to produce an electron and a positively charged water molecule.
  10. 10. H 2 O HOH + e - + H 2 O HOH - water negatively charged water molecule electron water Positively charged water molecule The electron reacts with another water molecule to produce a negatively charged water molecule
  11. 11. H 2 O HOH + H + OH * e - + H 2 O HOH - water negatively charged water molecule Hydrogen ion Hydroxyl radical electron water Positively charged water molecule The positively charged water molecule dissociates into a hydrogen ion and a hydroxyl radical.
  12. 12. H 2 O HOH + H + OH * H * OH - e - + H 2 O HOH - water negatively charged water molecule Hydrogen ion Hydroxyl radical electron water Positively charged water molecule hydrogen radical Hydroxyl ion The negatively charged water molecule dissociates into a hydrogen radical and a hydroxyl ion.
  13. 13. Reactions <ul><li>The previous reactions produce free electrons (e - ), the ions H - and OH - , the free radicals H* and OH*. </li></ul><ul><li>The fate of these products are……. </li></ul>
  14. 14. HOH + + e - H 2 O The positively charged water molecule and the electron recombine to form water. H 2 O HOH + H + OH * H * OH - e - + H 2 O HOH -
  15. 15. H + + OH - H 2 O The ions combine to form water. H 2 O HOH + H + OH * H * OH - e - + H 2 O HOH -
  16. 16. H * + OH * H 2 O The radicals combine to form water. H 2 O HOH + H + OH * H * OH - e - + H 2 O HOH -
  17. 17. H 2 O HOH + H + OH * H * OH - e - + H 2 O HOH - OH* OH* + OH* H 2 O 2 The hydroxyl radical reacts with another hydroxyl radical to form hydrogen peroxide.
  18. 18. Free Radicals <ul><li>A free radical is an atom or molecule that has an unpaired electron in its valence shell. </li></ul><ul><li>These free radicals are non-selective when pairing up with electrons from other atoms, including those that make up the DNA molecule. </li></ul>
  19. 19. Direct Action / Indirect Action <ul><li>Direct Action </li></ul><ul><ul><li>Causes damage directly to DNA or other important molecules in the cell. </li></ul></ul><ul><ul><li>More likely when the beam of charged particles consist of alpha particles, protons, or electrons </li></ul></ul><ul><li>Indirect Action </li></ul><ul><ul><li>Causes damage by interacting with the cellular medium producing free radicals which then damage the DNA molecule. </li></ul></ul><ul><ul><li>More likely when x-rays or gamma-rays compose the beam. </li></ul></ul>
  20. 20. DNA Damage <ul><li>The arrangement of nitrogenous bases provide a blueprint for DNA for the synthesis of specific proteins necessary for individual cell function. </li></ul><ul><li>In the event of a loss or change of one or more of the nitrogenous bases, base sequence and normal functioning of the cell is altered. </li></ul><ul><li>Another form of DNA damage due to radiation involves a break in the hydrogen bonds between the Adenine – Thymine and Cytosine – Guanine base pairs. These bonds function to keep the DNA strands together </li></ul><ul><li>Bonds can also break between deoxyribose sugar and the phosphate groups which can lead to cross-linking of DNA </li></ul>
  21. 21. http://www.greenfacts.org/glossary/def/dna.htm
  22. 22. Chromosome Aberrations <ul><li>If the chromosome fragments are near one another they have a high chance of reattaching in their original position – causing no future damage to the cell. A process known as restitution. </li></ul><ul><li>In translocations and inversions, no genetic information is lost, but the rearrangement of gene sequence will alter protein synthesis. </li></ul><ul><li>In a deletion, a chromosome fragment is not replicated during the next mitosis, the genetic information is lost. The effects this has on the cell depends on the amount and type of information lost. </li></ul>Translocation Inversion Deletion
  23. 23. Radiosensitivity <ul><li>Actively reproducing cells are more radiosensitive than mature cells. </li></ul><ul><li>During mitosis, the cell is in a stressed state and shows an increase in damage caused by radiation. </li></ul><ul><li>Cells that have decreased levels of differentiation are more radiosensitive than specialized cells. </li></ul>
  24. 24. Fractionation <ul><li>Instead of a single treatment consisting of a high dose, fractionation divides the dose to be delivered over a period of time, usually 6-8 weeks. </li></ul><ul><li>At low doses of radiation, normal cells have an increased survival rate because of their ability to repair sublethal damage before the next fraction of radiation is delivered. </li></ul><ul><li>Tumor cells do not possess the repair enzymes necessary to keep up with the repairs and as a result the cell is overwhelmed. </li></ul>http://www.usoncology.com/CompanyInfo/PhotoLibrary.asp
  25. 25. References <ul><li>Leaver, D., Washington C.M. (2004) Principals and Practice of Radiation Therapy. Second Edition pp. 55-84 St Louis, Mosby </li></ul><ul><li>Statkiewicz Sherer, M.A., Ritenour, E.R., Visconti, P.J. (2002) Radiation Protection in Medical Radiography. Fourth Edition, pp85-154, St. Louis, Mosby. </li></ul><ul><li>Ott, M.E. (2006, April 12) Radiation and why it is bad for humans. A videotaped lecture describing Radiation Types, Effects & Sources http://video.google.com/videoplay?docid=-1764500297917980309&q=radiation </li></ul><ul><li>Gwozdz, J. T. (2002, July 20). IMRT - Intensity Modulated Radiation Therapy. A powerpoint presentation of IMRT Intensity Modulated Radiation Therapy. http://drjohng.com/Talk/IMRT/Slide1_GIF.html </li></ul><ul><li>Low Dose Radiobiology Slideshows (n.d.) http://lowdose.tricity.wsu.edu/radiobio_slideshows.htm </li></ul>
  26. 26. References <ul><li>Radiation Therapy. (2003, February). Merck Research Laboratories http://www.merck.com/mmhe/au/print/sec15/ch182/ch182c.html) </li></ul><ul><li>How Radiation Therapy Works. (n.d.) Physics Students Web Project of How Radiation Therapy Works http://www.unc.edu/~taleb84/phys25/therapy.html </li></ul><ul><li>Großmann, V. (2004). Radiation Biology and Nanodosimetry http://www.ptb.de/en/publikationen/jahresberichte/jb2004/nachrdjahres/s22e.html </li></ul><ul><li>Medical Physics. (2004). from Johns Hopkins University. http://www.radonc.jhmi.edu/html/medical_physics.html </li></ul><ul><li>Radiation Therapy (n.d.) from Wikipedia. http://en.wikipedia.org/wiki/Radiation_therapy#How_it_works </li></ul>