Exam 2

• Which of the following are the least radiosensitive...

  lymphocytes

  nerves cells in an embryo-fetus

  adult nerve cells

  immature spermatogonia

  answer: adult nerve cells
• Low LET= High OER
• Alpha radiation is more likely than gamma radiation to cause biological damage
• Muscle tissue and nervous tissue in an adult do not divide
• Muscle cells are considered radioresistant
• When LET increases, the chance of significant biological response in radiosensitive DNA also increases
• True or false.. Free radicals are formed by direct interactions

  answer: false
• An embryo-fetus is most sensitive during 8- 15 weeks after gestation
• Chromosome aberrations happen before DNA synthesis
• Double strand DNA breaks require difficult repair, high probability of gene abnormality, caused by high LET radiation, and requires more than one interaction
• Anoxic cells are 3 times more resistant than cells that are well oxygenated at the time of irradiation
• Xrays and gamma rays are low LET radiation
• The LET for diagnostic x-rays is 3 kev/um
• If the master molecule is destroyed, the normal cell function will cease and the cell will die
• A lethal dose of radiation to humans without treatment is 3-4 Gy
• The LET of alpha particles is 100
• True or false ... As LET increases, RBE decreases

  answer: false
• Approximately 2/3 of all radiation induced damage is believed to be caused by free radicals
• 5-6 Gy will cause permanent sterility in both male and female gonads
• The 3 factors that effect cell response after irradiation:

  1. LET
  2. RBE
  3. OER
• Linear energy transfer (LET)= average amount of energy deposited
• Alpha particles have a high LET
• RBE for x-ray is 1
• RBE is used to determine radiation weighing factor
• Oxygen enhancement ratio (OER)= ratio of radiation dose required to cause response of cells in an oxygen deprived environment to radiation dose required to generate same response in oxygen
• Aerobic= with oxygen

  Anoxic= without oxygen
• Low LET= High OER

  High LET= Low OER
• Direct hit is DNA, RNA, protein, enzymes, etc; higher chance at high LET; harder to repair damage
• Radiolysis of water is from an indirect hit
• Point lesions are caused by free radicals
• Chromosome aberrations happen before DNA synthesis
• Chromotid aberrations happen after DNA synthesis (only 1 cell damage)
• Damage to chromosomes can been seen at metaphase
• Restitution happens when breaks rejoin at the original configuration with no visible damage
• Target theory says for a cell to die, a target molecule must be inactivated by multiple hits (high LET)
• Cell survival curves are used to determine types of cancer cells that will respond to radiation therapy
• LD 50/30 is a lethal dose in 50% of subjects in 30 days (animals)
• LD 50/60 is a lethal dose in 50% of subjects for 60 days (humans)
• The human limit is 3-4 Gy without intervention
• Dose above 50 Gy= death in hours