RADIATION & ITS UNITS

9-6-2012By DR K SYED AKRAM

Radiation Oncology

• Radiation oncology is that discipline of human medicine concerned with the generation, conservation, and dissemination of knowledge concerning the causes, prevention, and treatment of cancer and other diseases involving special expertise in the therapeutic applications of ionizing radiation

Radiation

• Radiation is propogation of energy through medium or through space in the form of electro-magnetic waves or particulate matter.

Classification of radiation

• 1. Ionizing Radiation

• 2. Non Ionizing Radiation

Non ionizing radiation

o They are electromagnetic waves incapable of producing ions while passing through matter, due to their lower energy

o Examples :Visible light, Microwaves, Radio waves, Tv waves etc.

Ionizing radiation

• capable of producing ionization in substances through which it passes.

• High enough energy to pull electron from orbit.• can ionize matter either directly or indirectly.—Directly ionizing radiation (charged particles):

electrons, protons, alpha particles and heavy ions.

—Indirectly ionizing radiation (neutral particles): photons (X rays and gamma rays), neutrons.

Directly ionizing radiation

• deposits energy in the medium through direct coulomb interactions between the directly

ionizing charged particle and orbital electrons of atoms in the medium.

Indirectly ionizing radiation

● Deposits energy in the medium through a two step process:

● In the first step a charged particle is released in the medium (photons release electrons or positrons, neutrons release protons or heavier ions);

● In the second step the released charged particles deposit energy to the medium through direct Coulomb interactions with orbital electrons of the atoms in the medium.

Atomic structure

• The constituent particles forming an atom are protons, neutrons and electrons.

• Protons and neutrons are known as nucleons and form the nucleus of the atom.

• The electron is constantly spinning around the center of the atom (called the nucleus).

Basic definitions

● Atomic number Z : number of proton in an atom.

● Atomic mass number A: number of nucleons in an atom (i.e. number of protons Z plus number of neutrons N in an atom: A = Z + N).

• Atomic mass M : expressed in atomic mass units u, where 1 u is equal to 1/12 of the mass of the 12C atom or 931.5 MeV/c2.

• Atomic g-atom (gram-atom): number of grams that correspond to NA atoms of an element, where NA = 6.022 × 1023 atoms/g-atom (Avogadro’s number).

• Isotopes : Atoms with the same number of protons, but different numbers of neutrons.

Isotopes of chlorine

35Cl 37Cl17 17

• Isobar : nuclide with the same mass number.• Isotones : nuclide with the same number of neutrons.• isomer

Radioactivity

• transformation of an unstable nucleus into a more stable entity that may be unstable and will decay further through a chain of decays until a stable nuclear configuration is reached.

• Number of spontaneous nuclear transitions from one particular energy state to other per unit interval of time.

Units of radioactivity

• Old unit is Disintegration per second(dps).• SI unit is Becquerel(Bq). 1Bq= 1dps• Special unit is Curie(Ci).

1Ci=3.7 x 1010dps = 3.7 x 1010 Bq 1Bq=27 x 10-12 Ci

Becquerel

• One Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second.

• Bq is named for Henri Becquerel, who shared a Nobel Prize with Pierre and Marie Curie in 1903 for their work in discovering radioactivity.

Antoine Henri Becquerel

Curie(Ci)• Non-SI unit of radioactivity, named after Marie and Pierre Curie. 1 Ci = 3.7 × 1010 decays per second.• One Curie is roughly the activity of 1 gram of the radium isotope

226Ra, a substance studied by the Curies.• Marie curie shared her 1903 Nobel Prize in Physics with her

husband Pierre Curie and with the physicist Henri Becquerel.

Marie Skłodowska-CuriePierre Curie

Units of Radiation Exposure

SI Unit is C/Kg 1 Roentgen = amount of X or gamma radiation

that produces ionization resulting in 1 electrostatic unit of charge in 1 cm3 of dry air.

1R(Roentgen)=2.58 X 10-4 C/Kg(air). Prof. Roentgen , on 8 November 1895, produced

and detected electromagnetic radiation in a wavelength range today known as X-rays or Röntgen rays, an achievement that earned him the first Nobel Prize in Physics in 1901.

Wilhelm Conrad Röntgen

KERMA

• Kinetic energy released per unit mass.• It is the sum of the initial kinetic energies of all

charged ionizing particles liberated by uncharged ionizing radiation in a unit mass.

• Kerma(K)=dE/dm dE=sum of the initial kinetic energies of all charged

secondaries.dm=mass of material

• SI unit = joule per kilogram (J/kg)

Absorbed dose

• It is the amount of energy imparted by ionizing radiation in the unit mass of matter.

• D=dE/dm• SI Unit is J/Kg(Special name of this unit is Gray)• Another special unit is rad.1Gray=1J/Kg=104 ergs/gm=100rad

Harold Gray

Equivalent dose

• Factors affecting the biological effects of radiation– Dose– Type of radiation

• Dose equivalent (H)– The dosimetric quality relevant to radiation protection

H = D • Q D = absorbed dose Q = the quality factor or radiation weighting factor (Wr)

• Units– Sivert (Sv)

• SI unit • 1 Sv = 1 J/kg

– Rem

• 1 rem = 10-2 J/kg (Sv)

thank you