Objectives of radiation protection
• The International commission of Radiation protection (ICRP)
Stated that “the overall objectives of radiation protection is to
provide an appropriate standard of protection for man
without unduly limiting the beneficial practices giving rise to
• NCRP (1993)- “The goal of radiation protection is to prevent
the occurrence of serious radiation induced conditions in
exposed persons & to reduce stochastic effects in exposed
persons to a degree that is acceptable in relation to the
benefits to the individual & society from activities that
generate such exposure”.
• From What?
• Whom to protect?
• How to protect?
• ROENTGEN– unit of
radiation exposure that
will liberate a charge of
• Independent of the
area or field size
• Deposition of energy in pt by radiation exposure
• Independent of composition of irradiated
material and energy of beam
• RAD: unit of absorbed dose
• GRAY: SI unit of absorbed dose
• Gray defined as the quantity of radiation that
results in an energy deposition of 1 joule per
• I GRAY = 100 RAD
• 1RAD = 1 cGY
• It is a measure of biological effectiveness of radiation
• REM: unit of absorbed dose equivalent
• SIEVERT : SI unit
• 1 sievert = 100 rems
• Dose equivalent=Absorbed dose x QF.
• REM = RADS X QUALITY FACTOR
• It is the parameter used to describe the quality of beam.
• Gives the amount of energy deposited per unit length travel.
Expressed in KEV per micron.
Type of radiation Q factor
X rays 1
Gamma rays 1
Beta particle 1
Thermal neutrons 5
Other neutrons 20
Alpha particle 20
EFFECTIVE DOSE EQUIVALENT
• Purpose – to relate exposure to risk
• It is calculated by multiplying the dose equivalent
received by each individual organ or tissue (DT) by an
appropriate tissue weighting factor (WT) and
summing for all the tissues involved.
for each organ and tissue estimate the
multiply by the
RADIATION WEIGHING FACTOR Wr
OR QUALITY FACTOR
for the radiation used
to the organ in msv
multiply by the
TISSUE WEIGHING FACTORWt
for the tissue or organ concerned
sum of all the organs and tissues irradiated
to the pt in msv
• From What?
• Whom to protect?
• How to protect?
Radiation - We live with
Natural Radiation: Cosmic rays, radiation within our
body, in food we eat, water we drink, house we live
in, lawn, building material etc.
Human Body: K-40, Ra-226, Ra-228
e.g. a man with 70 kg wt. 140 gm of K
140 x 0.012%
0.0168 gm of K-40
0.1 Ci of K-40
Radiation - We live with
New Delhi 700
(in narrow coastal strip)
SOURCES OF RADIATION
• Natural radiation:
1. External: Cosmic and gamma radiation
2. Internal: radionuclides with in the body
ingested or inhaled
• Medical procedures:
• Nuclear weapons/industry/accidents
Low ENERGY High
Radiation health effects
CELL DEATH BOTH
Radiation health effects
in the exposed
somatic & hereditary
attributable in large
in the foetus, in the live
born or descendants
• Existence of a dose threshold
value (below this dose, the effect
is not observable)
• Severity of the effect increases
• A large number of cells are
Radiation injury from an industrial source
Threshold Doses for Deterministic Effects
• Cataracts of the lens of the eye 2-10 Gy
• Permanent sterility
• males 3.5-6 Gy
• females 2.5-6 Gy
• Temporary sterility
• males 0.15 Gy
• females 0.6 Gy dose
– No threshold
– Probability of the effect increases with dose
– Generally occurs with a single cell
– e.g. Cancer, genetic effects
Repair of DNA damage
S ASSUME THAT
SYSTEM IS NOT
Outcomes after cell exposure
DAMAGE REPAIRED CELL NECROSIS OR
DAMAGE TO DNA
Diffusion, chemical reactions
Initial DNA damage
Proliferation of "damaged" cells
Initial particle tracks
DNA breaks / base damage
CHAIN OF EVENTS FOLLOWING EXPOSURE TO IONIZING
(MEMBRANES, NUCLEI, CHROMOSOMES)
MAY BE SOME REPAIR
• RS = Probability of a cell,
tissue or organ of suffering an
effect per unit of dose.
RS laws (Law of Bergonie & Tribondeau)
Radiosensitivity of living tissues varies with
maturation & metabolism;
1. Stem cells are radiosensitive. More mature cells
are more resistant
2. Younger tissues are more radiosensitive
3. Tissues with high metabolic activity are highly
4. High proliferation and growth rate, high
High RS Medium RS Low RS
(exception to the RS laws)
• Mechanism is cell killing
• Has a threshold dose
• Deterministic in nature
• Severity increases with dose
• Occurs only at high doses
• Can be completely avoided
• Causal relationship between
radiation exposure and the effect
• Sure to occur at an adequate
Mechanism is cell modification
Has no threshold
Probabilistic in nature
Probability increases with dose
Occurs at even at low doses
Cannot be completely avoided
Causal relationship cannot be
established at low doses
Occurs only among a small
percentage of those exposed
• Radiation Sickness
• Radiation syndromes
– Haematopoietic syndrome
– GI syndrome
– CNS syndrome
• Damage to individual organs
• Late damage
• Chromosomal damage
• Cancer Induction (Several
years after exposure to
• Genetic Effects
(Hereditary in future
• Somatic Mutations
OBJECTIVES OF RADIATION
• PREVENTION of deterministic effect
• LIMITING the probability of stochastic effect
HOW? Up to what point?
We live with
Where to stop, where is the safe point?
Changes in Dose Limit (ICRP)
1931 1947 1977 1990
Dose Limits (ICRP 60)
Effective dose 20 mSv/yr averaged* 1 mSv in a yr
over 5 yrs.
• Lens of eye 150 mSv 5 mSv
• Skin 500 mSv 50 mSv
• Hands & Feet 500 mSv
* with further provision that dose in any single yr > 30 mSv (AERB) and
=50 mSv (ICRP)
PRINCIPLES OF RADIATION PROTECTION
1. Justification of practices
2. Optimization of protection by
keeping exposure as low as
3. Dose limitation
Justification of procedure
versus the net benefit
i.e. no practice involving exposures to radiation
should be adopted unless it provides sufficient
benefit to offset the detrimental effects of
Optimization of protection
Protection should be optimized in relation to
the magnitude of doses,
number of people exposed
for all social and economic strata of patients.
• Optimization of protection can be achieved by
optimizing the procedure to administer a radiation
dose which is
as low as reasonably achievable,
so as to derive maximum diagnostic information with
minimum discomfort to the patient
All doses should be kept
HOW TO APPLY
THESE PRINCIPLES IN
How much time one works with radiation?
Radiation ON Time
CxR = 50x50 m sec = 2500 = 2.5s
LS = 50x800 m sec = 40000=40s
Total time = 45 sec/day
Not greater than 1 min/day
Dose limit ICRP = 20 mSv/yr.
Radiography work 0.1 mS/yr.
i.e. 1/200th of
Relative Dose Received
0 50 100 150 200
number of chest x-rays
Arm, head,ankle & foot (1)
Head & Neck (3)
Head CT (10)
Thoracic Spine (18)
Mammography, Cystography (20)
Abdomen, Hip, Upper & lower femur (28)
Ba Swallow (30)
Obsteric abdomen (34)
Lumbo-sacral area (43)
Lumber Myelography (60)
Lower abdomen CT male (72)
Upper Abdomen CT (73)
Ba Meal (76)
Angio-head, Angio-peripheral (80)
Chest CT (136)
Lower Abd. CT fem. (142)
Ba enema (154)
Radiation Doses in Radiological Exam.
(as multiple of chest x-ray)
IS IT POSSIBLE TO GET
DETERMINISTIC EFFECTS IN
RADIOGRAPHIC WORK ?
For staff, for patient..??
Risk of Staff Patient Public
Radiation emitted by the X Ray tube
• Primary radiation: before interacting photons
• Scattered radiation: after at least one interaction;
• Leakage radiation: not absorbed by the X Ray tube
• Transmitted radiation: emerging after passage
X-ray Tube Position
• Position the X-ray tube
under the patient not above
• The largest amount of
scatter radiation is
produced where the x-ray
beam enters the patient.
• By positioning the x-ray
tube below the patient, you
decrease the amount of
scatter radiation that
reaches your upper body.
FACTORS AFFECTING X Ray BEAM
• TUBE CURRENT
• TUBE POTENTIAL
• HIGH OR LOW Z TARGET MATERIAL
• TYPE OF WAVEFORM
• Determines the quantity of the photons which
also contribute to the patient dose.
• Increased exposure time also contributes to
an increased patient dose.
X Ray spectrum: tube current
Change of QUANTITY
NO change of quality
Effective kV not changed
X Ray spectrum: tube potential
Change in QUANTITY
Change in QUALITY
- spectrum shifts to higher
- characteristic lines appear
• use of high KV technique and low mAs (using the
shortest exposure time)
• The high KV beam has higher energy photons,
which undergo a lesser degree of beam attenuation
and greater penetration of the beam through the
• Therefore the tissue deposition of photons is
reduced, which reduces the radiation dose to the
A. At high KVp, majority of the photons are of high energy;
therefore minimum number of photons are deposited in the patient
B. At low KVp, a large number of photons are of low energy;
therefore larger number are deposited in the patient (dark area).
X Ray spectrum: Target Z
X Ray Energy (keV)
Number of X
Rays per unit
What is beam filtration?
X Ray spectrum at 30 kV for an X Ray tube
with a Mo target and a 0.03 mm Mo filter
10 15 20 25 30
Number of photons (arbitrary normalisation)
Absorber placed between
Source and object
Will preferably absorb
the lower energy photons
Or absorb parts of spectrum
• Inherent filtration (always present)
– reduced entrance (skin) dose to the patient (cut off the
low energy X Rays which do not contribute to the
• Additional filtration (removable filter)
– further reduction of patient skin and superficial tissue
dose without loss of image quality
• Total filtration (inherent + added)
• Total filtration must be > 2.5 mm Al for a > 110 kV
Change in QUANTITY
Change in QUALITY
spectrum shifts to higher energy
1- Spectrum out of anode
2- After window tube housing
3- After ADDITIONAL filtration
Collimate tightly to the
area of interest.
Reduces the patient’s
total entrance skin
Scatter radiation to
the operator will also
• Antiscatter grids
Antiscatter grids reduce scattered radiation reaching
the film thus improving the quality of the resulting
the radiograph and reducing chances of repeat
Source of -rays
Scattered X Rays Lead
Useful X Rays
Film and cassette
• Correct filtration
– 0.5 mm Al equivalent (inherent)
– Added filtration is good
– Minimum total filtration (inherent + added) must
be 2.5 mm Al equivalent
– Accurate collimation
• Minimum repeats
• Good technique to avoid re-takes:
– use of correct film for the view intended
– use of appropriate film holder
– correct film placement within film holder
– correct placement (angulation) of film holder in
– correct tube angulation
– correct exposure time
AMOUNT & TYPE OF RADIATION EXPOSURE
• The exposure time is related to radiation exposure
and exposure rate (exposure per unit time) as
• Exposure time = Exposure
Exposure = Exposure rate x Time
The algebraic expressions simply imply that if the
exposure time is kept short, then the resulting dose
to the individual is small
- Take foot off fluoro pedal if physician is not viewing the TV monitor
- Use last image hold (freeze frame)
- Five-minute timer
- Use pulsed fluoro instead of continuous fluoro
- Low-Dose mode: 40% dose of Normal fluoro
- Pulsed Low-Dose provides further reduction with respect to Normal Dose
- Use record mode only when a permanent record is required
- Record beam-on time for review
• The second radiation protection action relates to
the distance between the source of radiation and
the exposed individual.
• The exposure to the individual decreases inversely
as the square of the distance. This is known as the
inverse square law, which is stated mathematically
I ~ ———
- One step back from tableside:
cuts exposure by factor of 4
- Move Image Int. close to patient:
less patient skin exposure
less scatter (more dose interception by tower)
- Source to Skin Distance (SSD):
38 cm for stationary fluoroscopes
30 cm for mobile fluoroscopes
Equipment to Control Distance
• In case of X-ray equipment operating up to
125 kVp, the control panel can be located in
the X-ray room.
AERB recommends that the distance between
control panel and X-ray unit/chest stand
should not be less than 3 m for general
purpose fixed x-ray equipment.
• In mobile radiography,
where there is no fixed protective control booth, the
technologist should remain at least 2 m from the
patient, the x-ray tube, and the primary beam
during the exposure.
• In this respect, the ICRP (1982), as well as the NCRP
(1989a), recommended that the length of the
exposure cord on mobile radiographic units be at
least 2 m long
• Shielding implies that
(concrete, lead) will
(reduce its intensity)
when they are placed
between the source of
radiation and the
• Lead is used as a radiation shielding material as it has
a high atomic number (i.e. 82)
• Atomic number of an element is the number of
protons in the nucleus (which is equal to the number of electrons
around the nucleus)
• For the photoelectric process, the mass absorption
coefficient increases with the cube of the atomic
• It is known that
• 0.25 mm lead thickness attenuates 66% of the
beam at 75kVp
• and 1mm attenuates 99% of the beam at same kVp.
• It is recommended that for general purpose
radiography the minimum thickness of lead
equivalent in the protective apparel should be
- Lead aprons: cut exposure by factor of 20
distant scatter: 0.25 mm Pb eq
direct involvement: 0.5 mm Pb
Gamma and X-rays
Paper Plastic Lead Concrete
Four aspects of shielding in diagnostic radiology
1. X-ray tube shielding
2. Room shielding
(a) X-ray equipment room shielding
(b) Patient waiting room shielding.
3. Personnel shielding
4. Patient shielding (of organs not under
1) X-ray tube shielding (Source Shielding)
• The x-ray tube housing is lined with thin sheets of
lead because x-rays produced in the tube are
scattered in all directions.
• This shielding is intended to protect both patients
and personnel from leakage radiation.
• Leakage radiation is that created at the X-ray tube
anode but not emitted through the x-ray tube
• Rather, leakage radiation is transmitted through
• According to AERB recommendations
manufacturers of x-ray devices are required to
shield the tube housing so as to limit the leakage
radiation exposure rate to
0.1 R/ hr at a distance of 1 meter
from the tube anode.
2) Room shielding (Structural Shielding)
The lead lined walls of Radiology department are
referred to as protective barriers because they are
designed to protect individuals located outside the
X-ray rooms from unwanted radiation.
• There are two types of protective barriers.
(a) Primary Barrier:
is one which is directly struck by the primary or the
(b) Secondary Barrier:
is one which is exposed to secondary radiation
either by leakage from X-ray tube or by scattered
radiation from the patient.
The shielding of X-ray room is influenced by the nature
of occupancy of the adjoining area. In this respect two
types of areas have been identified.
• Is defined as the area routinely
occupied by radiation workers
who are exposed to an
• For control area, the shielding
should be such that it reduces
exposure in that area to
• Are those areas which are
not occupied by
• For these areas, the
shielding should reduce the
exposure rate to
• AERB has laid down GUIDELINES for shielding of
X-ray examination room and patient’s waiting room
which are as follows.
• The room housing an X-ray unit is not less than
18m2 for general purpose radiography and
conventional fluoroscopy equipment.
• In case the installation is located in a residential
complex, it is ensured that
1. Wall of the x-ray rooms on which primary x-ray
beam falls is not less than 35 cm thick brick or
2. Walls of the x-ray room on which scattered x-rays
fall is not less than 23 cm thick brick or equivalent
3. There is a shielding equivalent to at least 23 cm
thick brick or 1.7 mm lead in front of the doors
and windows of the x-ray room to protect the
adjacent areas, used by general public
• Unshielded openings in an X-ray room for
ventilation or natural light, are located above a
height of 2 m.
• Rooms housing fluoroscopy equipment are so
designed that adequate darkness can be achieved
conveniently, when desired, in the room.
Rooms housing diagnostic X-ray units and related
equipment are located as far away as feasible from
• areas of high occupancy and general traffic,
• maternity and paediatric wards
• and other departments of the hospital that are not
directly related to radiation and its use.
• Shielding of the Xray control room :
• The control room of an X-ray equipment is a
secondary protective barrier which has two
• (a) The walls and viewing window of the control
booth, which should have lead equivalents of
(b) The location of control booth, which should not
be located where the primary beam falls directly,
and the radiation should be scattered twice before
entering the booth
• The AERB recommends the following shielding for
the Xray control room:
• The control panel of diagnostic X-ray equipment
operating at 125 kVp or above is installed in a
separate room located outside but contiguous to
the X-ray room and provided with appropriate
shielding, direct viewing and oral communication
facilities between the operator and the patient
• Patient waiting area
• Patient waiting areas are provided outside the X-ray
• A suitable warning signal such as red light and a
warning placard is provided at a conspicuous place
outside the X-ray room and kept ‘ON’ when the unit
is in use to warn persons not connected with the
particular examination from entering the room
• 3) Personnel shielding
• Shielding of occupational workers can be achieved
by following methods:
• Personnel should remain in the radiation
environment only when necessary (step behind the
control booth, or leave the room when practical)
• Lead aprons are shielding apparel recommended
for use by radiation workers. These are classified as
a secondary barrier to the effects of ionizing
• These aprons protect an individual only from
secondary (scattered) radiation, not the
primary beam .
• The thickness of lead in the protective apparel
determines the protection it provides.
• It is recommended that women radiation workers
should wear a customized lead apron that reaches
below midthigh level and wraps completely around
• This would eliminate an accidental exposure to a
Care of the lead apparel:
• It is imperative that lead aprons are not abused,
such as by
– dropping them on the floor,
– piling them in a heap
– improperly draping them over the back of a chair.
• Because all of these actions can cause internal
fracturing of the lead, they may compromise the
apron’s protective ability.
• When not in use,
– all protective apparel should be hung on properly
• Protective apparel also should be radiographed for
defects such as internal cracks and tears at least
once a year
• Other protective apparel include eye glasses
with side shields, thyroid shields and hand
• The minimum protective lead equivalents in
hand gloves and thyroid shields should be
• 4)Patient shielding
• Most radiology departments shield the worker and
the attendant, paying little attention to the
radiation protection of the patient.
• It has been recommended that the thyroid, breast
and gonads be shielded, to protect these organs
especially in children and young adults
Only authorized users may
have access to x-ray devices
Energized equipment must be
attended at all times
Lock lab door when
equipment not attended
Notification of hazard presence
Signs, Posting, Warning signs
To sum up……
Exposure to X-ray radiation is reduced if:
TIME exposed to source is decreased
DISTANCE from source is increased
SHIELDING from source is increased
Notable Changes: FDA regs.
For equipment manufactured after 10 June 2006:
• Warning Label – “WARNING: This x-ray unit may be
dangerous to patient and operator unless safe exposure
factors, operating instructions and maintenance scheduled
• Timer: audible signal every 5 min of irradiation time until reset
Irradiation time display at fluoroscopist’s working position:
- means to reset display at zero for new exam/procedure
• Last Image Hold (LIH) after exposure termination
- indicate if LIH = radiograph or ‘freeze-frame’ image
• It has been estimated that although CT accounts for
less than 50% of all x-ray examinations it
contributes upto 40% of the collective dose from
diagnostic radiology .
• CT Scanners have scattered radiation levels that
may prove hazardous.
• The dose unit used in CT is the
computed tomography dose index “CTDI”.
• This measurement is defined in relation to the
radiation field delivered at a specific point (x, y) by
the CT Scanner.
• CTDI is usually expressed in terms of absorbed dose
to air and is called CTDI air.
• Absorbed dose to tissue (Dtissue) is related to
absorbed dose to air (Dair) by a mathematical
coefficient which has a value of about 1.06 and an
error not greater than ± 1%.
• Such measurements are made using a special pencil
ionisation chamber or by a thermoluminescent
dosimeter (TLD) .
• Langer et al evaluated scattered radiation in a CT
suite and documented that the radiation on the
floor of the C.T. suite could be as high as 0.3 Gy/day.
It was concluded that
• adequate shielding should be provided for the floor
and roof areas of a CT suite depending on which
floor the CT is located.
• It was proposed an additional thickness of 2.5mm
of lead or 162mm of concrete to shield the front
and rear reference points, so as to reduce the dose
to 1 mGy/year
• The highly collimated X-ray beam in CT results in
markedly non uniform distribution of absorbed
dose perpendicular to the tomographic plane
during the CT exposure.
• Therefore the size of the CT room housing the
gantry of the CT unit as recommended by AERB
should not be less than 25m2
• The greatest risk to the fetus of chromosomal
abnormalities and subsequent mental retardation is
between 8 and 15 weeks of pregnancy and
examinations involving radiation to the fetus should
be avoided during this period.
• For examinations which may involve rather heavy
doses of radiation such as Barium enemas, pelvic or
abdominal CT, the examination should be carried
out during the first 10 days of the menstrual cycle
to avoid irradiating any possible pregnancy
If Pelvic Area in Beam:
• No possibility of pregnancy - proceed
• Probably pregnant - radiologist decides
– delay X-ray until after delivery, or
– use non-X-ray technique (e.g. ultrasound), or
– go ahead with X-ray but keep dose low
• Possibly pregnant, low dose procedure - proceed if
period is not overdue.
• High dose procedure (10s of mGy, e.g. pelvic CT)
– X-ray in first 10 days of menstrual cycle .
Pregnancy and Mammography
“There is no requirement to enquire
about pregnancy prior to
mammography as there is no
significant dose to the fetus”
NHBSP Dec 02
For pregnant staff,
• a risk assessment must be performed,
• dose to fetus < 1 mSv for rest of pregnancy.
• The instruments used to detect radiation are
referred to as
radiation detection devices.
• Instruments used to measure radiation are called
Devices monitor and record
ionizing radiation doses
Must distinguish from
• Personnel Dosimetry
Personnel dosimetry refers to the monitoring of
individuals who are exposed to radiation during the
course of their work.
Personnel dosimetry policies need to be in place for
all occupationally exposed individuals.
The data from the dosimeter are reliable only when
the dosimeters are properly worn, receive proper
care, and are returned on time.
The radiation measurement is a time-integrated
dose, i.e., the dose summed over a period of time,
usually about 3 months.
The dose is subsequently stated as an estimate of
the effective dose equivalent to the whole body in
mSv for the reporting period.
Dosimeters used for personnel monitoring have
dose measurement limit of 0.1 - 0.2 mSv
Proper care includes
• not irradiating the dosimeter except during
• and ensuring proper environmental conditions
Monitoring is accomplished through the use of
personnel dosimeters such as
• the pocket dosimeter,
• the film badge
• the thermoluminescent dosimeter
• Outwardly resembles a
fountain pen .
It consists of
• a thimble ionization
chamber with an eyepiece
and a transparent scale,
• a hollow charging rod
• a fixed and a movable fiber.
The ability of radiation to produce ionization in air is
the basis for radiation detection by the ionization
It consists of an electrode positioned in the middle
of a cylinder that contains gas.
When x-rays enter the chamber, they ionize the gas
to form negative ions (electrons) and positive ions
The electrons are collected by the positively charged
rod, while the positive ions are attracted to the
negatively charged wall of the cylinder.
The resulting small current from the chamber is
subsequently amplified and measured.
The strength of the current is proportional to the
• Is sensitive for exposures upto 0.2 R
– Easily damaged
– Unreliable in inexperienced hands
– Does not provide a permanent record
Film Badge Monitoring
• These badges use small x-ray films sandwiched
between several filters to help detect radiation.
• The photographic effect, which refers to the
ability of radiation to blacken photographic films,
is the basis of detectors that use film.
Wearing the badge
-wear the badge on the collar region, because the collar region
including head, neck, and lens of the eyes are unprotected.
• Each member of staff wears film badge for a period of 4
• At the end of period the film inside is changed.
• The exposed film is sent to BARC.
• Useful for detecting radiation at or above 0.1 msv (10 mrem)
– easy to use,
– permanent record of exposure,
– wide range of sensitivity ( 0.2 – 2000 msv),
– identifies type and energy of exposure,
• they are not sensitive enough to capture very low
levels of radiation( < 0.15 msv),
• Their susceptibility to fogging caused by high
temperatures , humidity and light means that they
cannot and should not be worn for longer than a 4-
week period at a stretch,
• Enormous task to chemically process a large
number of small films and subsequently compare
each to some standard test film.
Thermo luminescent dosimetry (TLD)
• The limitations of the film badge are overcome by
the thermo luminescent dosimeter (TLD).
• Thermo luminescence is the property of certain
materials to emit light when they are stimulated
• Materials such as lithium fluoride (LiF), lithium
borate (Li2B4O7), calcium fluoride (CaF2), and
calcium sulfate (CaSO4) have been used to make
• When an LiF crystal is exposed to radiation, a few
electrons become trapped in higher energy levels.
For these electrons to return to their normal energy
levels, the LiF crystal must be heated.
As the electrons return to their stable state, light is
emitted because of the energy difference between
two orbital levels.
The amount of light emitted is measured (by a
photomultiplier tube) and it is proportional to the
• The measurement of radiation from a TLD is a two-step
• In step 1, the TLD is exposed to the radiation.
• In step 2, the LiF crystal is placed in a TLD analyzer,
where it is exposed to heat.
• As the crystal is exposed to increasing
temperatures, light is emitted.
• When the intensity of light is plotted as a function
of the temperature, a glow curve results.
• The glow curve can be used to find out how much
radiation energy is received by the crystal because
the highest peak and the area under the curve are
proportional to the energy of the radiation.
• The TLD can measure exposures to individuals as low as 5 mR can
withstand a certain degree of heat, humidity, and pressure
• Their crystals are reusable
• Is very compact ( suitable even for finger dosimetry)
• And instantaneous readings are possible if the department has a TLD
• Response to radiation is proportional upto 400 R
• Very expensive
• No permanent record ( other than glow curves)
• Cannot distinguish radioactive contamination.
The greatest disadvantage of a TLD is its cost
Storing TLD Badges
• Badge must not be left in an area
where it could receive a radiation
exposure when not worn by the
individual (e.g. On a lab coat or
left near a radiation source)
• Store badges in a dark area with
low radiation background (in low
light away from fluorescent or uv
lights, heat and sunlight)
• Lost or damaged badges should
be reported immediately to the
radiation safety officer and a
replacement badge will be issued
• There are various Regulatory Bodies at the
international and National level, which lay down
norms for radiation protection.
• These are
• the International Commission for Radiation
Protection ( ICRP),
• the National Commission for Radiation Protection
(NCRP ) in America,
• and the Atomic Energy Regulatory Board (AERB) in
• The International Commission of Radiation
Protection (ICRP) was formed in 1928 on the
recommendation of the first International Congress
of Radiology in 1925.
• The commission consists of 12 members and a
chairman and a secretary who are chosen from
across the world based on their expertise.
• The first International Congress also initiated the
birth of the ICRU or the International Commission
on Radiation Units and measurements
• The Indian regulatory board is the AERB, Atomic
Energy Regulatory Board.
• The Atomic Energy Regulatory Board was
constituted on November 15, 1983
• by the President of India by exercising the powers
conferred by Section 27 of the Atomic Energy Act,
to carry out certain regulatory and safety functions
under the Act.
• Radiation safety in handling of radiation generating
equipment is governed by section 17 of the Atomic
Energy Act, 1962, and the Radiation Protection
• The “Radiation Surveillance Procedures of Medical
Applications of Radiation,” specify general
requirements for ensuring radiation protection in
installation and handling of X-ray equipment.
Guidance and practical aspects on implementing
the requirements of this Code are provided in
revised documents issued by AERB in the year 2001
Dose Limits Recommended by ICRP (1991)
Exposure Dose Limit (mSv per year)
Occupational Apprentices Public
Whole body: 20 mSv per year, 6 mSv in a year 1 mSv in a year,
(effective dose) averaged over defined averaged over
period of 5 years with 5 years,
no more than 50 mSv
in a single year
Parts of the body:
Lens of the eye 150 mSv per year 50 mSv in a year 15 mSv in a year
Skin* 500 mSv per year 150mSv in a year 50 mSv in a year
Hands and feet** 500 mSv per year 150 mSv in a year 50 mSv in a year
*Averaged over areas of no more than any 1 cm2 regardless of the area exposed. The nominal depth is 7.0 mg cm-2
**Averaged over areas of the skin not exceeding about 100 cm2
Note 1.Dose limit for Women upon declaration of pregnancy - 2 mSv measured on the surface of the abdomen and
1/20th of ALI for exposure to internal emitters.
Note 2.Dose limits do not apply to medical exposures, to natural sources of radiation and under conditions resulting from
• The responsibility for establishing a radiation
protection programme rests with the hospital
administration / owners of the X-ray facility
• The administration is expected to appoint a
Radiation Safety Committee (RSC), and a Radiation
Safety Officer (RSO).
• It is recommended by NCRP that the RSC should
comprise of a radiologist, a medical physicist,, a
senior nurse and an internist. It is the duty of RSC to
perform a regular radiation protection survey
This survey has 5 phases which are:
1. Investigation: To obtain information regarding
layout of the department, workload, personnel
monitoring and records.
2. Inspection: Each diagnostic installation in the
department is examined for its protection status
with respect to its operating factors, control booth
and availability of protection devices.
3. Measurement: Measurements are conducted on
exposure factors. In addition scattered radiation
and patient dose measurements in radiography
and fluoroscopy are performed.
4. Evaluation: The radiation protection status of the
department is evaluated by examination of records,
equipment working, status of protective clothing
and the radiation doses obtained from phase-3.
5. Recommendations: A report is prepared on the
protection status of the department and the
problem areas if any identified, for which
recommendations are made regarding corrective
Thin-window GM (Geiger-Mueller) survey meter
may be used to
- Check leaking radiation
- Indicate x-ray production
- Monitor routine operation
Ion chamber is used to determine dose rate at the x-ray
Survey meters are calibrated annually.
Depicts the organizational flow chart and the administrative
and functional components of radiation protection program.
• Protect patient, public and staff
• Remember dose is cumulative
• Benefit/risk ratio
• Principles of radiation protection
• Dose reduction = time, distance, shielding
High speed film Lead coats to
reduced exp. time steps away stop scatter radiation