Introduction to radiation and its units in radiotherapy

1. RADIATION & ITS UNITS
9-6-2012
By DR K SYED AKRAM

2. 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

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

4. Classification of radiation
• 1. Ionizing Radiation
• 2. Non Ionizing Radiation

5. 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.

6. 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.

8. 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.

9. 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.

10. 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).

11. 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).

13. • 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 37Cl
17 17
• Isobar : nuclide with the same mass number.
• Isotones : nuclide with the same number of neutrons.
• isomer

14. 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.

15. 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

16. 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

17. 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-Curie
Pierre Curie

18. 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

19. 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)

20. 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

21. 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)

22. thank
you