1) Radiation is the emission or transmission of energy through space or matter and comes in the form of waves or particles. The various quantities of radiation include activity, exposure, kerma, absorbed dose, relative biological effectiveness (RBE), effective dose, and equivalent dose. 2) Activity refers to the number of unstable nuclei that decay per unit time and is measured in becquerels (Bq) or curies (Ci). Exposure is a measure of ionization in air due to radiation. Kerma measures the kinetic energy transferred to charged particles per unit mass. Absorbed dose measures energy absorbed per unit mass. 3) Effective dose takes into account RBE, which varies by radiation type and biological factors

1. RADIATION
QUANTITIES AND UNITS
SAIKAT ROY
DRT STUDENT
TATA MEDICAL CENTER

2. What Is Radiation?
Radiation is the emission or transmission of energy in the form of
waves or particles through space or through a material medium.
Energy
Particle
Radioactive
Atom

3. The Various Radiation Quantities Are:
Activity Exposure Kerma
Absorbed
Dose
REB
(Relative Biological
Effectiveness)
Effective
Dose
Equivalent
Dose

4. Activity
Activity refers to the number of unstable nucleus present in a
radionuclide which regains stability through radio-disintegration per
unit time.
The Quantity of radiation released from the radioactive material is directly proportional to the Activity.

5. Curie(Ci)
The quantity of 3.7 × 10¹⁰ Disintegrations per second from 1 gram of
Radium-226 is called Curie(Ci), Which is the older unit of radioactivity.
Becquerel(Bq)
This is the SI unit of activity and its is equal to 1 Disintegration per
Second(DPS).
1 Ci = 3.7 × 10¹⁰ Bq

6. Exposure
Radiation Exposure is a measure of the ionization of air in a small
volume around a point due to ionizing radiation.
Small area filled
with air
Ionization of air molecule
due to radiation exposure

7. Roentgen(R)
The amount of ionizing radiation producing one electrostatic unit of
positive or negative ionic charge in one cubic cm of air under standard
conditions.
1 cc of Air
(0.001293 gm at STP)
Ionizing Radiation
1 ESU
Charge

8. KERMA
Kerma is an acronym for “Kinetic Energy Released per unit Mass”
Karma is defined as the sum of the initial kinetic energy of all the charged ionizing
particles, liberated by photons in a material of unit mass.
Kerma
(Kinetc Energy)
Delta rays
Absorbed Dose

9. Gray(Gy)
The SI unit of Kerma is Gray and is defined as the absorption of one joule of radiation energy
per kilogram of matter.
Rad(R)
This is the special unit of Kerma.

10. Abosrbed Dose(D)
The term absorbed dose(D) refers to the amount of energy absorbed
per unit mass of the medium.
1 unit mass of
medium
Radiation abosorbed
in the medium

11. Gray(Gy)
Gray(Gy) the absorption of one joule of radiation energy per kilogram of matter.
It is a SI based Unit and name after Louis Harold Gray.
1Gy = 1 J⋅kg−1
Rad(R)
Rad is defined as the dose causing 100 ergs* of energy to be absorbed by one gram of matter.
It is a SI based unit.
1 rad = 0.01 Gy = 0.01 J/kg.
*The erg is a CGS unit of energy equal to 10⁻⁷ joules.

12. Relative Biological Effectiveness
It is the ratio of biological effectiveness of one type of ionizing radiation relative to
another, given the same amount of absorbed energy.
RBE
Dose of 250 kVp X-rays required to produce certain biological effect
Dose of reference radiation required to produce the same effect

13. RBE depends on
1. Liner Energy Transfer
• The RBE depends upon the liner energy transfer.
• The LET is a parameter the describe the average energy deposition per unit path length of the incident radiation.
• LET expressed in keV/µm.
2. RBE also depends on the biological end point.
3. And the nature and conditions of the biological system.
• Physiological state
• Temperature
• Oxygen Concentration
• Pressure
• The absence of free radicals
4. Total dose.
5. Dose rate.
6. Fractionation.
6. Dosse distribution.

14. Radiation Weighting Factor(WR)
A radiation weighting factor is an estimate of the effectiveness per unit
dose of the given radiation relative a to low-LET standard.
Radiation Type Radiation Weighting Factor
Photons 1
Electrons 1
Protons 2
Alpha particle, Heavy ions 20
Neutrons 2.5-20

15. Equivalent Dose(H)
The product of the absorbed dose and Radiation weighting factor is
called Equivalent Dose(H)
Equivalent Dose(H) = Absorbed Dose(D) × Radiation weighting factor (WR)

16. Sievert(Sv)
The SI unit of Effective dose is Sievert (Si) And 1Sv = 1J/KG.
Rontgen Equivalent Men(rem)
Rem is an older, CGS unit of Effectivet dose and 100rem = 1Sv

17. Tissue Weighting Factor(WT)
To account for the variation of radiosensitivity of different tissue, ICRP has established
Tissue Weighting Factor(WT) (ICRP-103,2007)
Tissue Tissue Weighting Factor
Lung 0.12
Stomach 0.12
Colon 0.12
Bone Marrow 0.12
Breast 0.12
Reminders* 0.12
Gonads 0.08
Thyroid 0.04
Esophagus 0.04
Bladder 0.04
Liver 0.04
Bone surface 0.01
Skin 0.01
Brain 0.01
Salivary Gland 0.01
Total 1.0

18. Effective Dose(HT)
The sum of the products of the equivalent dose to each tissue
irradiated (HT) and the corresponding weighting factor of tissue is
called effective dose (E).
Effective Dose(H) = Sum of Radiation weighting factor × Tissue weighting factor (WR)

19. Thank You