NUCMED Quiz 1

• Cell


  Basic biological structure
• Cell exposed to radiation

  Undergoes ionization
• Ionization


  Breaking down of components to negative and positive ion
• Radiolysis


  Breaking down of water while absorbing radiation
• Radicals


  Components that are highly reactive (like oxidizers)
• Ejected electron interacts with ionized water

  Returns to ordinary water
• 2 Ionized water combined

  Creates H2O2 (Hydrogen peroxide)
• Hydrogen Peroxide


  Antiseptic, Kills the cell
• Killing cells can be good or bad depending on the situation
• Hepatocytes are millions in number, if only a few are killed, then there are still many cells left
• If a fertilized egg is killed then it is considered bad
• Biggest organs


  • Skin
  • Liver
• Radioimmunoassay


  Using radioisotopes as labels to detect the product of the reaction with a specific antibody
• Types of radioactive sources


  • Open - Contamination and irradiation
  • Sealed - Irradiation
• Types of radiation emission


  • Alpha - Easily stopped by material, can cause ejection of neutrons
  • Beta - Negative beta emitters easily stopped by low density materials, create Bremsstrahlung with high density materials
  • Gamma - Easily stopped by high density materials
• If cell is irradiated


  1. DNA can be damaged

  2. Cell damage can be repaired - No effect

  3. If incorrectly repaired, cell remains viable but with faulty genetic information - Stochastic/Hereditary effect

  4. If incorrectly repaired, cell remains viable and triggered into division and multiplication - Stochastic/Cancer effect

  5. Unrepairable damage cell at reproduction, enough cells killed to inhibit tissue function - Deterministic effects
• Somatic effects


  Effects seen on exposed individuals, Acute - large doses in short period, Chronic - low doses over long period
• Radiation is not considered as carcinogen, it only induces cancer
• Carcinogen


  Materials that causes cancer
• Examples of carcinogens


  • Diet soft drinks
  • Nicotine in cigarettes
• Genetic effects


  Not seen on exposed individual but on the children/children's children of the exposed individual
• Types of biological effects


  • Stochastic - probability of effect, linear relationship without threshold
  • Deterministic - severity of effect, linear relationship with threshold
• Hormesis


  Beneficial effects due to receiving low doses
• Factors that influence radiation effects


  • Type of emission
  • Amount
  • Area involved
  • Age
  • Sex
  • Weight
  • BMR (Basal metabolic rate)
• LD/50


  Lethal dose that will kill 50% of exposed organisms
• LD/50 for man is 4 Gy
• Cockroach has LD/50 more than 4 Gy because it does not have interdependent body parts
• LD/50 (30) means the dose that will kill 50% of organisms within 30 days
• 4 Gy = 67 calories, equivalent to a 3ml sip of 60 coffee
• 30 - 100 Trillion Cells at Risk from 4 Gy
• Distribution of responsibilities


  • Referring physician - Efficacy of test
  • NucMed physician - Control of all aspects of conduct & extent of exam
  • Medical Physicist - Physical & technical aspects of dosimetry, NM instrumentation, radiation protection, QA/QC
  • Technologists & other staff - Carry out exam under supervision
  • Committee on Radiation Protection - Provide advice on radiation protection of patients
• ICRP System of Dose Limitation


  Recommendatory body, does not regulate use of radiation but only suggests, Justification - Positive net benefit, Optimization - ALARA (As low as reasonably achievable)
• Dose Limit does not apply for patients who undergo medical procedures
• Types of effects following irradiation in utero


  • No deterministic or stochastic in first 3 weeks
  • Potential for malformation of organs in 3rd to 8th week
  • Potential for severe mental retardation in 8th to 25th week
  • Cancer in childhood or adult life from 4th week throughout pregnancy
• Pelvimetry - X-ray done on mother in 7th month to see if normal delivery, no ultrasound yet
• Factors affecting radiation dose in nuclear medicine


  • Amount administered
  • Biokinetics
  • Decay scheme of radionuclide
• Diagnostic doses in nuclear medicine result in a few tens of mGy
• Therapeutic applications result in the order of tens to hundreds of Gy
• Misapplication of radiopharmaceuticals in diagnostic levels can carry small risks, inappropriate application or dosimetric error in therapy may result in unacceptable tissue damage or inadequate treatment
• Effective half-life


  Combination of physical and biological half-life