dosimetry-science of studying the radiation exposure

1. DOSIMETRY
By
Dr Vishal Mehrotra
Professor HOD OMDR,RDC,Kanpur

2. DOSIMETRY
Determining the quantity of
radiation exposure or dose is termed
as dosimetry.

3. Introduction
• As the potentially harmful effects of ionizing
radiation became known, the medical community
sought to reduce radiation exposure throughout
the world by developing standards for measuring
and limiting this exposure. To be able to measure
patient and personnel exposure in a consistent
and uniform manner ,diagnostic imaging
personnel should be familiar with the
standardized radiation quantities and units.

4. Units of measurement
• Fundamental units
• Derived units
• SI units

5. FUNDAMENTAL UNITS
• They are independent of each another and
have their own standards(base).
• Units of all physical quantities can be obtained
from fundamental units
• E.g mass(kg) , time(sec)

6. DERIVED UNITS
• These are units which are not having their
own standards(base) and are obtained from
fundamental units.
• E.g. area(meter square), velocity (meter/sec)

7. SI units
• “international d’units”
• More superior and more convenient
• There are fundamental units( meter, kg, sec,
kelvin, ampere, mole) and 2 supplementary
units( radian, steradian )

8. EXPOSURE
• It is the measure of quantity of radiation.
• The beam of x-ray causes ionization of the air
through which it passes and is called exposure
• It is measured in photon flow and is related to
energy transfer from x-rays to a specified
volume and mass of air.
• RADIATION EXPOSURE refers to amount of
radiation that comes out from the x-ray unit
and reaches the person

9. • Traditional unit : Roentgen
• One Roentgen(R) is defined as an exposure which
will produces 2.08x109 ion pair in cubic
centimeter of air under standard temperature
and pressure
• R measures the intensity of radiation to which an
object is exposed.
• 1milliroentgen is 1/1000 of a roentgen
• SI unit: coulomb per kilogram
• It measures the number of electrical charges or
the number of ion pairs in 1kg of air.
• 1R= 2.58X10-4c/Kg; 1C/Kg=3.88x104R

10. RADIATION ABSORBED DOSE:
• It measures the amount of energy absorbed from the
radiation beam per unit mass of the tissue or the
deposition of the energy in patient by the radiation
exposure is called Radiation absorbed dose
• SI unit: Gray(Gy) measured in joules/kg
• SUBUNIT: Milligray (mGy)
• Original unit rad(radiation absorbed dose)it is equal to
deposition of 100 ergs of energy per gram of tissue. It
is ammount of radiation absorbed as a result of
exposure
• 1G=100rads

11. EQUIVALENT DOSE:
• It is the measure which allows the different
radiobiological effectiveness (RBE) of different
types of radiation to be taken into account
• It is sum of the absorbed dose(DT) and radiation
weighing factor(WR)(HT=E WR.DT)
• Equivalent dose tells us about biological effects of
different types of radiation to a tissue or organ
and helps to compare them.
• Equivalent dose= radiation absorbed dose x
quality factor.

12. • SI unit: Sievert(Sv)
• Subunit: millisevert (mSv) , microsievert
• Original unit: Rem(roentgen equivalent in
men)
• It is product of absorbed dose and quality
factor for the type of radiation.
• 1Siveret=100rem.

13. EFFECTIVE DOSE:
• It is the measure which allows doses from
different investigations of different parts of the
body to be compared, by converting all doses to
an equivalent whole body dose. It is required as
some part of the body is sensitive to radiation
than other part
• It is used to estimate risk of radiations in humans
• It is sum of product of equivalent doses(HT) to
each organ or tissue and tissue weighing factor
(WT)(E=EWT.HT)
• Effective dose= equivalent dose x weighing factor
• SI unit= Sievert, subunit = millisievert

14. Collective effective dose or collective
dose
• This measure is used while considering the
total effective dose to a population from a
particular investigation or source of radiation.
• Collective dose=effective dose x population
• SI unit= Man-Sievert (man-Sv)

15. DOSE RATE:
• It is the measure of dose per unit time
• SI unit= Microsievert/hour

16. KERMA
• “Kinetic energy release in material”
• Defined as the kinetic energy released per unit
mass in the medium
• It is measure of kinetic energy transferred to
charged particles.
• Unit: joules/kilogram
• SI unit= Gray and the special unit is rad

17. RADIOACTIVITY
• The term refers to disintegration rate of an
isotope and it is measured by nit curie(Ci)
• One curie is the number of disintegrations per
second(dps) from one gram of radium and it is
found to be 3.7x1010 dps
• Subunit = millicurie, microcurie also used
• 1millicurie= 3.7x1010 dps
• 1microcurie= 3.7x104 dps