Radiobiology

Summary

• Radiation is energy in the form of waves and particles that are emitted from a source.
  • It comes in many forms.
  • It is not necessarily a dangerous thing.
• Visible light divides the electromagnetic spectrum into general regions.
  • infrared and below — non-ionizing radiation
  • visible light — able to excite electrons in normal atoms
  • ultraviolet and above — ionizing radiation
• The forms of radiation that are especially dangerous to living things are those with energy sufficient to penetrate tissues and then ionize the atoms they pass along the way.
  • They generally have energies on the order of 1 MeV.
  • They damage tissues by disrupting normal cellular chemistry.
  • They are mutagenic (can damage genes) and carcinogenic (can cause cancer).
• The absorbed dose (D) is the energy of the ionizing radiation (E) absorbed by some object per mass (m).
  • It only provides a first approximation of the radiobiological damage in a human.
  • The SI unit of absorbed dose is the gray, which is equal to a joule per kilogram [Gy = J/kg].

    D =	E
    	m

• The equivalent dose (H) is the absorbed dose (D) multiplied by the radiation weighting factor (w_R) — a number that varies according to the type of radiation.

  H = wRD

  • It relates the absorbed dose to the equivalent radiobiological damage in a human.
  • The SI unit of equivalent dose is the sievert, which is equal to a joule per kilogram [Sv = J/kg].
• The effective dose (E) is the equivalent dose (H) multiplied by the tissue weighting factor (w_T) — a number that varies according to the organ or tissue exposed.

  E = wTH

  • It relates the equivalent dose to the effective radiobiological damage in a human.
  • The SI unit of effective dose is the sievert, which is equal to a joule per kilogram [Sv = J/kg].
• Dose units summarized
  • The SI unit of absorbed dose is the gray [Gy].
  • The SI unit of equivalent dose and effective dose is the sievert [Sv].
  • The gray and the sievert are each equal to a joule per kilogram, but they are not equal to each other.
  • The gray was named in honor of the English physicist Louis Gray (1905–1965) who developed the concept of relative biological effectiveness, which was later quantified as the weighting factor
  • The sievert was named in honor of the Swedish physicist Rolf Sievert (1898–1966) who developed the basic techniques for measuring absorbed dose
  • The weighting factors are unitless.