Ionizing radiation

• Direct effects of ionizing radiation


  The energy is directly absorbed by important macromolecules in the body like nucleic acid, enzymes, hormones, modifying their structure by breaking hydrogen bridges or disulfide bridges
• Direct effect of ionizing radiation ex

  1. Excitation or ionization of the molecule

  2. Molecule returns to the bottom state
• Direct effects of ionizing radiation

  • Alteration of nitrogenous bases (thymine dimerization) that leads to errors in transcribing genetic information
  • Single or multiple breaks in the DNA strand
  • Formation of peroxides
  • Amino acid modification
  • Tyrosine polymerization
  • Ruptures of hydrogen and disulfide bridges
  • Rupture of the polypeptide chain
• Indirect effects of ionizing radiation

  The direct action of the radiations is focused on the water molecules, as a result of radiolysis, free radicals are produced which indirectly affect important macromolecules in the body
• Liquid/Liquid chromatography is where the stationary phase is an immobilized material, which has only a mechanical interaction with the analyte
• Optic radiations


  The action of optic radiations is mainly directed to the exposed parts: the skin and the eyes, producing thermal and photochemical changes
• Effects of optic radiations


  • Pigmentations, erythema, cancer
  • Photo cataract, lesion of retina and cornea
  • Heating of the body surface
• Infrared radiations


  Are caloric radiations, the main way of heat exchange of bodies with the environment, used in spectroscopic analysis, can produce insolation, caloric shock, muscle cramps, vasodilatation, change the sensitivity of nervous terminations (analgesic and regeneration effects), high intensity can produce burns and cataract
• Visible radiations


  Wavelengths between 390 nm and 780 nm, stimulate the brain activity, activate the metabolism, the circadian rhythm, can make the skin photosensitive, responsible for seeing
• Radiosensitivity

  Some tissue respond faster to lower doses than others, there is a relationship of dose response, the radiosensitivity of a tissue varies with maturation and metabolism, stem cells are radiosensitive while more mature cells are more resistant, younger tissue are more radiosensitive, tissue with high metabolic activity are highly radiosensitive, the radiosensitivity of a tissue increases with the pH (basic tissue are more radiosensitive), hydration, oxygenation and temperature
• Factors influencing radiosensitivity

  • Linear energy transfer
  • Relative biological effectiveness
  • Fractionation (dividing the dose into smaller doses) and protraction (prolonging the time interval of applying the doses)
• Dose fractionation

  1. Same dose applied in smaller consecutive doses with rest periods in between

  2. Increases the survival of cells due to cell repair mechanisms which repair damages DNA, proteins, or other important biomolecules

  3. Used for radiation therapy in cancer treatment to divide the dose so healthy cells can recover and minimise negative side effects
• Maximum admissible dose


  The annual dose that can be absorbed by human body without any noticeable lesions, excluding genetic effects, set by the international commission on radiological protection
• Average annual effective dose

  • Cosmic rays: 1 mSv/year
  • Natural earth radioactive sources: 0.378 mSv/year
  • Medical procedures: 0.62 mSv (0.27 mSv for long X-rays)
  • Radiotherapy: 0.38 mSv/year
  • Nuclear medicine: 0.007 mSv/year
• Somatic effects of ionizing radiation


  Depend on the radiosensitivity of the tissues
• Genetic effects of ionizing radiation


  Don't have a threshold and are the result of chromosomes lesions in the reproductive cells, can produce genetic diseases in the next generation, mutations and even death
• Specific effects of ionizing radiation

  • Thyroid - absorbs radioactive iodine 131
  • Lungs - inflammation and fibrosis
  • Red blood cells - sudden bleeding, decrease of thrombocytes number
  • Stomach and small intestine - internal bleeding
  • Bone marrow - 50% destruction in 48 hours
• Methods of radioprotection

  • Physical methods (distance, time, shielding)
  • Chemical methods (dehydration, temperature/metabolic rate reduction, deoxygenation, free radical inhibition/fixation)
  • Biochemical methods (use biologically active products that diminish destructive effects and favour cell repair)
  • Biological methods (introduce viable cells to favour hematopoietic function)
• Absorbed dose ranges and effects

  • D < 5 rad: no immediate effects
  • 50 rad > D > 5 rad: slight blood composition changes, no symptoms
  • 150 rad >> D > 50 rad: severe blood changes, symptoms like tiredness, vertigo, vomiting for 1-2 days
  • 200 rad > D > 1000 rad: immediate initial symptoms, gastrointestinal system destroyed, intensive care useless
  • 1100 rad > D > 1500 rad: severe blood changes, death in 2 weeks, 50% mortality at 300-500 rad
  • D > 2000 rad: sure death in hours or days, D > 5000 rad: central nervous system failure, intensive care useless