This document discusses dosimetry and radiation protection. It begins with a brief history of radiation discovery and the first radiograph. It then discusses key concepts in radiation protection including dose limits for different exposure groups, the ALARA (As Low As Reasonably Achievable) philosophy, and the basic methods of reducing radiation exposure through time, distance and shielding. The document also covers external and internal radiation sources, dose and exposure concepts, and methods for reducing radiation exposure in dental radiography through proper equipment selection, technique choice, processing and interpreting images. Protection of patients, personnel and the public is emphasized throughout.

1. DOSIMETRY AND
RADIATION
PROTECTION
Dr. Vibhuti Kaul

2. HISTORY
• Wilhelm Conrad
Roentgen
• Accidentally
discovered
• Working with cathode
rays tube
• Fluorescence of
screens
• Observation of bones
of hand

3. • 1st radiograph of hand of Bertha,
Roentgen’s wife

4. Introduction
• Radiation protection deals with dose received
by populations, and avoidance of effects
• Radiological protection, is the science of protecting people
and the environment from the harmful effects of ionizing
radiation, which includes both particle radiation and high
energy electromagnetic radiation.
• The doses involved are measurable even if the
effects are not

5. Sources of Radiation

6. SOURCES
• We are exposed to radiation everyday of
our lives
• Background radiation comes from natural
sources
• 2 types of sources:
1. External
2. Internal

7. External Sources
• Cosmic & Terrestrial radiation
• Cosmic radiation includes:
- energetic subatomic particles
- photons of extraterrestrial origin
- interactions of primary cosmic radiation with atoms & molecules of
earth’s atmosphere
# Also greater at higher altitudes
# Exposure from airline travel

8. • Terrestrial radiation:
Radioactive nuclides in soil

9. Experiments are impossible, but scientific
panels
have evaluated the cumulative data, assessed
the
risks and developed standards
• International Commission on Radiological Protection
– report ICRP 60 (1991)
• National Council on Radiation Protection – report
NCRP 91 (1987)

10. Exposure groups
Dose limits are governed by laws and
regulation:
to cover three distinct exposure groups
1. Occupational
2. Medical – patients who benefit from
radiation exposure for diagnosis or
treatment
3. Non-intentional – the public who do not
benefit from exposure

11. The ALARA philosophy
As low as
reasonably
achievable

12. Basic methods of protection against
exposure to ionizing radiation
Three basic
factors
• time
• distance
• shielding

13. Time
Distance
Shielding

14. TIME
• The less time that people are exposed
to a radiation source, the less the
absorbed dose.
• It's easy to understand how to
minimize the time for external (direct)
exposure.
• Gamma and x-rays are the primary
concern for external exposure.

15. Time
Exposure rate
=10mGy/h
X Time = Total dose
1 hour = 10 mGy
2 hours = 20 mGy

16. Distance

17. DISTANCE
• The farther away people are from a
radiation source, the less their
exposure.
• It depends on the energy of the
radiation and the size (or activity) of
the source.
• Distance is a prime concern when
dealing with gamma rays.
• As a rule, if the distance is doubled,
the exposure is reduced by a factor of
four.

18. DISTANCE

20. Inverse square law
150 mSv/h
0.06 mSv/h
d=50cm

21. SHIELDING
• Used when neither time nor distance is
effective method to reduce the exposure.
• Interposing a material between source of
radiation & the point at which the it is desired
to reduce the exposure.
• The greater the shielding around a radiation
source, the smaller the exposure.

22. SHIELDING
• Degree of exposure reduction
depends on physical
characteristics of material:
1. Atomic number
2. Density
3. Thickness
• For fixed X-ray imaging facilities
most common materials are lead
and concrete

23. SHIELDING
• Standard design practice evaluating
shielding is to measure the halving thickness
of a material, the thickness that reduces
gamma or x-ray radiation by half.

24. Penetrating power of radiation

25. Shielding photons

26. • The aim of radiation protection in dentistry is to obtain the
desired clinical information with minimum radiation
exposure to patients, dental personnel and the public.
• National council on radiation protection (NCPR) and
International council on radiation protection (ICPR).
MPD (Maximum Permissible Dose)
Maximum dose that a person or specified parts thereof
shall be allowed to receive in a period.

27. • MPD differs for nonoccupationally & occupationally
exposed persons.
• Non occupationally exposed– 0.005 Sv/year
• For occupationally exposed persons, the MPD is
calculated by using formula,
MPD = (Age – 18) x 5 rem
• Occupationally exposed: 0.05 Sv/year

28. Exposure & Dose Concept
• Exposure is the property of the x-ray beam.
• It is measure of the no. of x-rays making
up the beam of radiation and the energy
transferred from x-rays to molecules of air
under very standardized conditions
• Old unit: Roentgen (R)
• SI unit: Air kerma (Gy)
• 1 Gy = 1 joule/kg

29. Exposure & Dose Concept
What is absorbed dose?
• It is a measure of energy
absorbed by any type of
ionizing radiation per unit
mass of any type of matter
• Old unit rad (radiation absorbed dose)
• SI is Gray where 1 Gray = 1 J/kg
• 1 Gy = 100 rads

30. Exposure & Dose Concept
Incident dose
• Incident dose = the dose
measured on the intended
surface of the patient, but
without the presence of
the patient
• The SI unit used to measure
the incident dose is the
Gray, where 1 Gy = 1 J/kg

31. Exposure & Dose Concept
Surface dose
• The surface dose is measured
with the body in the path of
the beam by including the
amount of scattered
radiation.
• Surface dose =
incident dose + scattered
radiation from the body
The SI unit is the Gray (Gy)

32. Exposure & Dose Concept
Body dose and effective dose
• The body dose is the comprehensive
concept for the organ or partial-body
dose equivalent and the effective
dose.
• Body dose = sum of all organ or
partial-body doses
• Effective dose <= patient dose limit
• The SI unit = sievert
• 1 sievert = 1 Sv = 1 Joule/kilogram = 1
Gray

33. Methods of exposure & dose reduction
• The guiding principle of diagnostic
radiology in dentistry is to enhance the
diagnostic benefits of dental radiographs
and minimize the associated risks to
patients and staff**
** from ADA Council on Scientific Affairs

34. There are four main concerns when dealing
with radiation hazards.
• First, patients should not be
subjected to unnecessary dental
radiography.
• Second, patients need to be
protected from unnecessary
exposures.
• Third, personnel in dental facilities
be protected from unnecessary
exposure to radiation in the course
of their work.
• Finally, the public requires adequate
protection.

35. Methods of exposure & dose reduction
Patient selection
• Professional judgment
• Radiographic selection criteria to guide are
clinical or historical findings
• Must justify taking any radiographs, not a
blanket screening for all patients.
• There are disadvantages and risks - must
weigh up benefits against risks.

36. Conduct of examination
1. Choice of equipment
2. Choice of technique
3. Operation of equipment
4. Processing & Interpretation
of radiographic image

37. Choice of equipment
1) Selection of image receptor
• Faster films should be used
• E speed Ekta speed group

38. Choice of equipment
2) Intensifying screens
• For all extra oral radiographs
• Reduce patient exposure by 55%
• Two types of crystals calcium
tungstate
& rare earth

39. Choice of equipment
3) Focal spot to film distance
• 32% decrease in surface
exposure with longer distance
• X- ray beam is less divergent

40. Choice of equipment
4) Collimation
• Limits size of X-ray beam
• Reduces patient exposure
• Increased image quality
• Scatter radiation is decreased

41. Choice of equipment
5) PID
Film fog is decreased with
the Use of rectangular position
indicating device & film
holders with rectangular
collimators

42. Choice of equipment
6) FILTRATION
• Selective filtration of low
energy radiation
• Decreased patient exposure
• With no loss of radiological
information
• Aluminum

43. Choice of equipment
7) Leaded aprons & collars
• Minimize patient exposure
to radiation
• ALARA principles
• Attenuate 98% scatter
radiation to gonads
• Thyroid collar – 92% dose
reduction to thyroid gland

44. Choice of Technique
1) BISECTING ANGLE TECHNIQUE
An early method for
aligning the x-ray beam
and film with the teeth
and jaws the bisecting
angle technique.

45. Choice of Technique
2)PARALLELING TECHNIQUE
In this method placing film
parallel with long axis to the
tooth. In this technique film
is positioned towards the
midline of oral cavity
away from the teeth.

46. Choice of Technique
Film holders to position the receptor
BISECTING ANGLE
TECHNIQUE
PARALLELING TECHNIQUE

47. Operating the equipment
• Selection of x-ray generating units
Exposure settings be established
• Kilovoltage – 70-90 kVp
Decrease Kilovoltage – image contrast
increases, vice versa
• Milliampere- Seconds
Image density is controlled by quantity of
X-ray, this is controlled by mAs
2.2 mAs – E speed film – 90 kVp
4.2 mAs – E speed film – 70 kVp

48. Processing the film
• Proper processing equipment
• Darkroom with safelights
• Automatic processor with
appropriate safelight hood
• Saves needless exposure of patient
& operating costs

49. Interpretation of Images
• Semi darkened room
with light transmitted
only through films
• Variable intensity light
source
• Magnifying glasses

50. Protection of Personnel
• Leave room & take position
behind suitable barrier or wall
• Walls of sufficient density and
thickness,10.4-15.4 cm
• Gypsum wallboard Lead
between layers of wood
• Thickness of 1.3-2.4 mm lead
used for 60-70 kVp
• Barium plaster or
barium concrete

51. Protection of Personnel
Position and Distance Rule
If no barriers are available,
you should stand at least six
feet away from the patient at
an angle of 90-135 degrees
to the direction of the x-ray
beam.

52. Protection of Personnel
• Operator should never hold
films in place, film holding
instruments should be used.
• Neither patient nor operator
should hold radiographic
tube housing

53. Protection of Personnel
Personnel monitoring devices
• Film Badges
Thermo luminescent
dosimeters (TLD)

54. Protection for General Public
• Radiation area should
be at corner of building
• One extra brick with
barium plaster for walls
• No person is allowed
while exposing
• Warning board
and light

55. SOURCES OF RADIATION

56. 1. Primary beam is defined as radiation originating from
the focal spot.
2. Scattered or secondary radiation is the radiation
originating from the irradiated tissues of the patient.
3. Leakage or stray radiation is the radiation from the X-
ray tube had housing.
4. Scattered radiation is the radiation from filters and
cones.
5. Scattered radiation is the radiation coming from the
objects other than the patient such as the walls and
furniture that the primary beam may strike.

57. MEANS OF
PROTECTION
FOR
OPERATOR
FOR PATIENT
FOR
ENVIRONMENT

59. Sources of Radiation
1. Primary X-ray beam
2. Scattered radiation
Other Sources of Lesser Importance Include:
• Leakage through the head housing
• Scattered X-ray from the filters, cones
• Scattered radiation coming from the
objects other than the patient, such as
walls and furniture that the primary beam
may strike.

61. • Secondary Barriers
- for surfaces receiving
secondary or leakage radiation
LEAD standard material
- Viewing windows : lead glass
- Lead salts or metallic lead
added to rubber or plastics :
protective gloves or aprons
made

62. PROTECTION AGAINST
PRIMARY BEAM
Primary beam: It is defined as radiation emitted by the focal spot of
the target

63. i. Effort must be made so that the operator can
leave the room or take a suitable position
behind a barrier or wall during exposure.
ii. Dental Operatory should be designed and
constructed to meet the minimum shielding
requirements.
iii. Position Distance rule- states that the operator
should stand at least six feet away from the
source of radiation or the operator should be at
an angle of 90o to 135o, with respect to the
direction of the central ray.

64. This rule takes advantage of the
inverse square law to reduce the
intensity and also considers that
in this position the patient’s
head will absorb the most
scattered radiation.

66. iv. Behind a barrier, made of suitable material, or
v. If there is no shield or barrier the operator
should use a lead apron
vi. The film should never be held by the operator
vii. There should be no use of fluorescent mirrors
in the oral cavity at the time of exposure
viii. Avoid holding the X-ray tube head of the
machine.

67. PROTECTION AGAINST
LEAKAGE RADIATION
Leakage or Stray radiation is defined as radiation emitted by any
other part of the X-ray tube other than the focalspot.

68. i. Neither the tube housing nor the cone should be hand
held during the exposure.
ii. The machine should be periodically checked for
leakage.

69. PROTECTION AGAINST
SECONDARY AND
SCATTERED RADIATION
Secondary radiation is defined as the radiation emitted by a
substance through which X-rays are passing. Scattered radiation is
defined as that radiation that has under gone change in direction
during passage through a substance.

70. i. Use of high speed films
ii. Replace the short plastic cone with an open
ended lead lined cone
iii. Adequate filtration of the primary beam
iv. Use of collimator, to reduce the diameter of the
beam
v. Use of film badge/ TLD badge/ Pocket
Dosimeter, for personnel radiation monitoring ,
to avoid accumulated over exposure.

72. PATIENT SELECTION
• High yield or referral criteria, which is the
clinical or historical findings that identify
patients for whom a high probability exists
that a radiographic examination will
provide information affecting their Rx &
prognosis.

73. CONDUCT OF THE
EXAMINATION
1. Selection of the Image Receptor:
a. Use of high speed films
b. Use of screen films

74. 2. Use of Intensifying Screens
3. Focal Spot Film Distance: As X-rays are less divergent
at a longer distance, there is a decrease in the volume
of the patient exposed tissue volume.
Longer FSFD results in 32% reduction in exposed
tissue volume.

75. 4. Collimation of the beam: collimation helps to control the
size and shape of the X-ray beam, allowing only the
useful mean to emerge.
The beam should be limited to as small as an area
possible for a particular radiographic examination.
The recommended beam size is not more than 2 ¾” in
diameter at the patient’s face, when the source film
distance is 18 cm or more. Collimation decreases the
risk of radiation and decreases the fog, with a sharper
image and better contrast.

77. Collimation
Types of collimators
1. Diaphragm
2. Rectangular
3. Tubular
• Using rectangular PID – reduces the
area of the patient’s of skin surface
exposed by 60% over that of a round
• Reduction in beam size makes aiming
the beam difficult
• Film holders

78. 5. Filtration: Filtration preferentially absorbs low energy
photons which are undesirable as they add to the
patient’s skin dose but do not have enough energy to
penetrate the tissue and bring about the image
formation.
Operating range of
machine
Amount of filtration
Below 50 kVp 0.3 to 0.5 mm of Al
50-70 kVp 1.2-1.5 mm of Al
Above 70kVp 2.1-4.1 mm of Al

80. 6. Use of high kVp: Higher kVp is used to keep the
incident skin doses acceptable. The equipment should
be capable of operating at a kilo voltage of 60 kVp or
higher.
7. Use of positioning indicating device: These help to
minimize the volume of tissue irradiated in intraoral
radiography, it is necessary to increase the target film
distance by using longer position indicating devices to
direct the X-ray beam.

81. 8. Film holding devices: These offer protection to the
patient, because
- their use often reduces frequency of retakes, as the
film can be positioned more accurately in the patient’s
mouth.
- they also provide an external guide to indicate the film
position.
- The possibility of cone-cuts is also reduced.
-Some of the holders also collimate the beam to the
size of the film being used.
- Exposure to the patient’s fingers is also reduced.

82. 9. Timers: Most equipment are provided with ‘dead man’
timers. This timer requires a continuous pressure on
the button (switch) during the exposure cycle in order to
continue the operation of the X-ray machine. If the
button is released the exposure is terminated.
Dental X-ray machine timers generally automatically
reset once the exposure has been terminated. Care
should be taken that they are not capable of initiating
another exposure until the switch is pressed again.
Also, it should not make an exposure if the timer set to
zero or off position.

83. 10. USE OF PROTECTIVE BARRIERS:
a. Leaded aprons
b. Gonadal shields
c. Thyroid shields

84. DOSIMETRY

85. TERMS
• Determining the quantity of radiation
exposure or dose is termed dosimetry.
• The term dose is used to describe the
amount of energy absorbed per unit mass
at a site of interest.
• Exposure is a measure of radiation based
on its ability to produce ionization in air
under standard conditions of temperature
and pressure (STP).

86. UNITS OF MEASUREMENT
• EXPOSURE
Exposure is a measure of radiation
quantity, the capacity of radiation to ionize
air.
SI unit: air kerma
(kinetic energy released in matter)
Traditional unit: roentgen

87. UNITS OF MEASUREMENT
• ABSORBED DOSE
Absorbed dose (DT)is a measure of the
energy absorbed by any type of ionizing
radiation per unit mass of any type of
matter.
SI unit: Gray (Gy)
Traditional unit: rad
(radiation absorbed dose)

88. UNITS OF MEASUREMENT
• EQUIVALENT DOSE
Equivalent dose (HT) is used to compare
the biologic effects of different types of
radiation to a tissue or organ.
Relative biologic effectiveness of different
types of radiation is called the radiation-
weighting factor (WR).
TYPE OF RADIATION WEIGHTING FACTOR
Photons 1
5 keV Neutrons/Protons 5
α particles 20

89. UNITS OF MEASUREMENT
• EQUIVALENT DOSE
SI unit: Sievert (Sv)
Traditional unit: rem
(roentgen equivalent man)
1 Sv = 100 rem

90. UNITS OF MEASUREMENT
• EFFECTIVE DOSE (E)
Estimate the risk in humans
Allows comparison of risk of exposure to
one region with another in body.
Considers radiosensitivity of different
tissues for cancer formation or heritable
effect.
Comparative radiosensitivities of different
tissues are measured by tissue-weighting
factor (WT).

91. TISSUES TISSUE WEIGHTING
FACTOR
Red bone marrow, breast, colon,
lung, and stomach
0.12
Gonads 0.08
Bladder, esophagus, liver &
thyroid
0.04
Bone surface, brain, salivary
glands & skin
0.01
Others 0.12

92. UNITS OF MEASUREMENT
• RADIOACTIVITY
The measurement of radioactivity (A)
describes the decay rate of a sample of
radioactive material.
SI unit: Becquerel (Bq)
= 1 disintegration/second
Traditional unit: Curie (Ci)
=> activity of 1 g of radium (3.7 x 1010
disintegrations/second)
1 mCi = 37 megaBq
1 Bq = 2.7 x 10-11 Ci

94. • Dosimetry tracks exposures and monitors
external radiation exposures.
• Dosimetry use ensures that we are following
the principle of ALARA, keeping exposures as
low as reasonably achievable.
• Dosimetry only measures external radiation
exposure and offers no protection from
radiation.

95. Dosimetry
• A Whole Body Dosimeter
at all times when working
with or around radiation
sources.
• Where to wear dosimetry?
• whole body dosimeter should
be worn on the torso, closest
to the source of radiation.

96. Dosimetry
• TLD rings are worn on the
hand used most often to
handle radioactive
materials
• Most dosimeters (Whole Body
and Finger Ring) are issued
for three months

97. • Badges are slim & lightweight
• Can be worn on the body or
extremities.
• Film encased in a specially
designed molded plastic holder.
• Multi-filter system
• radiation will reach the exposed
film after penetrating the five
different filter areas: open
window (OW), aluminum (Al),
copper (Cu), lead/tin (Pb/Sn),
and plastic (Pl).
• A complex algorithm is deployed
to analyze the results of these
filter areas and report dose.
Film badges

98. The badge has six filters:
1. An open window which allows all incident
radiation that can penetrate the film wrapping
to interact with the film.
2. A thin plastic film which attenuates beta
radiation but passes all other radiations
3. A thick plastic filter which passes all but the
lowest energy photon radiation and absorbs
all but the highest beta radiation.
4. A dural filter which progressively absorbs
photon radiation at energies below 65keV as
well as beta radiation.
5. A tin/lead filter of a thickness which allows an
energy independent dose response of the
film over the photon energy range 75keV to
2Mev.
6. A cadmium lead filter where the capture of
neutrons by cadmium produces gamma rays
which blacken the film thus enabling
assessment of exposure to neutrons.

100. TLD (Thermoluminiscent
Dosimetry)
• Some materials absorb energy from ionizing
radiation, store it such that later it can be recovered
in the form of light when the materials are heated.
• Amount of light released is directly proportional to
the energy absorbed from the ionizing radiation
• Hence to the absorbed dose the material received.
• Lithium fluoride (LiF) and calcium fluoride

101. TLD (Thermoluminiscent Dosimetry)
• Higher sensitivity,
• Wider range of exposure
measurement,
• Greater precision,
• Extended wear period (3
months)
• Can measure gamma/x-
ray exposures down to 1
mrem and beta exposures
down to 10 mrem.

102. TLD
• Have a precision for approximately 15%
for low doses, improves to 3% for high
doses.

103. MECHANISM OF TLDs
• When a TLD is exposed to ionizing
radiation at ambient temperatures, the
radiation interacts with the phosphor
crystal and deposits all or part of the
icident energy in that material.
• Some of the atoms in the material that
absorb that energy become ionized
producing free electrons and areas lacking
one or more electrons, called holes.
• Imperfection in the crystal lattice structure
act as sites where free electrons can
become trapped and locked into place.

104. MECHANISM OF TLDs
• Heating the crystal causes the crystal
lattice to vibrate releasing the trapped
electrons in the process.
• Released electrons return to the original
ground state, releasing the captured
energy from ionization as light. Hence, the
name thermoluminiscent.
• Released light is counted using
photomultiplier tubes and the number of
photons counted is proportional to the
quantity of radiation striking the phosphor.

105. MECHANISM OF TLDs
• Instead of reading the optical density
(Blackness) of a film, as is done with the
film badges, the amount of light released
vs the heating of the individual pieces of
thermoluminiscent material is measured.
• The glow curve produced by this process
is then related to the radiation exposure.
• The process can be repeated many times.

107. ADVANTAGES
• Small in size & light in weight
• Chemically inert
• Almost tissue equivalent
• Usable over wide range of radiation qualities &
dose values
• Accurate & reproducible readings
• Automation compatible
• No wet chemistry reqd
• Reusable
• Economical
• Read out simple & quick
• Apart from initial fading, can store dose over long
period of time

108. DISADVANTAGES
• Read out is destructive, giving no
permanent record, results cannot be
checked or reassessed.
• Only limited information provided on type
of energy of the radiation
• Dose gradients are not detectable.

109. Finger dosimeters
• For those who handle
radioisotopes or who
perform interventional
radiographic procedures
• Single use
• Can be worn under surgical
gloves

110. IONIZATION CHAMBER
• An ionization chamber is used to determine the radiation
exposure of a room.
• It consists of two oppositely charged plates, separated
by a known volume of air.
• The plates are connected to a galvanometer to measure
the charge.
• Before using, standard charge is applied to the plates.
• When the X-ray beam exposes the air, there is formation
of ion-pairs. The positive & negative ions get attracted to
the oppositely charged plates thus resulting in the partial
discharges.
• Accordingly the radiation exposure depends on the
number of ion pairs produced & dropped in the potential.

111. IONIZATION CHAMBER

112. THANK YOU