explains all basic radiation protection guidelines for operator, patient and environment with a brief on dosimeters and dosimetry terminologies

2. Department of oral medicine and radiology
Radiation protection
and Dosimetry
Dr Mammootty Ik
Ist year MDS

3. CONTENTS
 INTRODUCTION
 Historical perspectives
 NCRP and MPD
 ALAARA concept
 Sources of radiation in dental radiology
 Protection for the operator
 Protection for the patient
 Radiation monitoring devices
 Dosimetry
 References

4. INTRODUCTION

5. HISTORICAL PERSPECTIVE
 Dr. William Herbert Rollins(1852-1929)
◦ Father of Radiation protection. Often referred to
as “ Dentistry’s forgotten man”.
◦ He experimented with guinea pigs(1901),
inferred that the adverse physiological effects
related with x-ray exposure were a result of x-ray
beams themselves and he suggested:
 Use of radiopaque leaded glasses to protect the eyes
 Encompass the x-ray tube in a leaded housing
 Expose only the area of interest of the patient
 Suggested the use of collimators to reduce the beam size
and proposed a long target-film distance
 First to use selective filtration of the x-ray beam to
remove the dangerous low-energy x-rays

6. History(cont’d)
 In 1902 x-ray induced skin-cancer was
reported
 In 1915 the British Roentgen Society made
the first radiation protection
recommendations
 In 1921 British X-ray and Radium protection
committee was formed.
 It was made as an international committee in
1928 and in 1950 transformed as
“International Commision on Radiological
Protection”.(ICRP)
 National Council on Radiation Protection
(NCRP) was formed in 1946(US).

7. MPD
 NCRP has made maximum permissible dose(MPD)
recommendations that are published periodically in a
handbook
 MPD is the amount of radiation that an individual is allowed to
receive from artificial sources of radiation such as x-ray
machines except when the individual is a medical/dental
patient
 Since the first recommendation by NCRP in 1931 of 50
roentgens per year MPD has been lowered on 3 occasions.
 Now, its only 1/10th of its initial level
 MPD is defined for two groups of people :
◦ Occupationally exposed i.e. people who are expected to use or work
around radiations as normal part of their jobs
◦ Non-occupationally exposed people people who do not work with
radiations

8. MPD(cont’d)
 X ray machines should not cause any occupational or non-
occupational person to receive anywhere near the MPD
 IF a dental office recieves even 1/10th of the MPD , radiographic
procedure and machinery should carefully evaluated
 When calculating MPD, radiation received from environmental
background and diagnostic medical and dental exposures (for the
individuals personal health care) are specifically excluded from
calculations
 As per the most recent report of NCRP
◦ MPD for occupationally exposed: 5rem/year or 0.05Sv /year
◦ MPD for non-occupationally exposed : 0.1rem/year or 0.001Sv
/year
◦ MPD for occupationally exposed pregnant woman is same as that
for non occupationally exposed

9. ALARA Concept
 It is an important radiation concept. Stands for As Low As
Reasonably Achieveable.
 Every reasonable measure will be taken to assure that
occupationally and non-occupationally exposed persons will
receive the smallest amount of radiation possible.
 Does not specify a specific level of radiaition dose for
exposed person as the MPD concept does.

10. Sources of radiation in a dental
radiology dept:
2 main sources the operator is exposed to:
• Primary x-ray beam: originating from the
focal spot.
• Scattered or secondary radiation : Radiation
originating from the irradiated tissues of the
patient.
Other sources of lesser importance
include:
• Leakage radiaton through tube-head housing
• Scattered radiations from filters and cones
• Scattered radiation coming from objects other
than the patient , such as walls and
furnitures.

11. PROTETCTION FOR THE
OPERATOR:
 3 basic methods to reduce the occupational dose
from the x-rays:

12.  If the radiographer cannot stand at least 6 ft away from the
patient, should stand behind a leaded protective barrier or
behind a gypsum wall board (dry wall)
 Should not hold film in the patients mouth squamous cell
carcinoma of the fingers can be caused.
 The tubehead or cone should NEVER
be held or stabilised during exposure
 When a patient has to be restrained, patie
nt’s bystander should do so. The bystander
should be provided with lead apron and g
loves for maximum protection.

13. Sheilding for the operator
 Minimal shielding requirement is periodically updated by NCRP
 Appropriate personnel sheilding can be achieved by having
◦ A lead protective barrier of 1.5mm b/w operator and x-ray
tube
◦ Lead apron and gloves of 0.25mm thickness
◦ For any specialised radiological investigation minimum
0.5mm of lead equivalence protection device is
recommended
Protection against secondary / scattered radiation:
 Use of high speed films
 Replace the short plastic cone with an open ended lead –lined
cone
 Adequate filtration of primary beam
 Use of collimator to reduce the diameter of the beam.
 Use of film badge/ TLD badge / pocket dosimeter for personnel
radiation monitoring, to avoid accumulated over-exposure.

14. PROTECTION FOR THE
PATIENT:
1. PATIENT SELECTION:
• Operator should expose no one to x-rays without a good
reason.
• Radiographs prescribed without considering the patient’s
clinical finding and history should not be taken. Includes
routine FMR or OPG for every new patient
• If a radiograph wouldn’t change the diagnosis or rx or is
highly unlikely to provide any additional helpful information,
should not be taken.
• Post- operative radiographs should be taken only if there is a
clinical indication

15.  Using high KVp:
• Should be operated at highest Kvp consistent with a
good image( ususaly 70 to 90 kvp)
• An x- ray machine that is incapable of operating even at 60
kvp should not be used.
• High kvp produces more “useful” x-rays and fewer low
energy rays that are absorbed by the patient without
contributing to the image.

16.  Using constant potential x-ray machines:
◦ Converts alternating current(AC) to DC
◦ Produces a homogenous beam of similar
wavelengths during exposure rather bursts of
radiation.
◦ Reduces exposure by 20% over conventional

17.  Filtration
• X-ray beam should be properly filtered to preferentially
remove soft, low-energy long-wavelength x-rays from the
beam.
• When an x-ray beam is filtered with 3mm of Al the surface
exposure is reduced to 20%of that with no filtration.
• Half value layer(HAL) is the thickness of the material used
for filtration at which the incident radiation entering it is
reduced to half
X-RAY TUBE
VOLTAGE(KVp)
MIN HALF-VALUE
LAYER(mm of Al)
30 to 70 1.5
71 2.1
80 2.3
90 2.5
100 2.7

18. Filtration(cont’d)
 Patient exposure can be further reduced by
removing both very-high and very –low energy
photons leaving only mid-range photons for
exposure.
 This is done by using the combination of Al and
rare earth elements such as samarium , yttrium,
niobium etc.
 Disadvantages of filtration: increase in the
exposure time and decrease in contrast.

19.  COLLIMATION
• Helps in restricting the field of radiation at the patient’s skin
surface to a circle having diameter of no more than 7cm ie
2.75inches.
• Done with a lead diaphragm(collimator) within the
tubehead or at the end of the lead lined p.i.d.
• It is highly recommended that instead of using round
collimator , rectangular collimator which restricts the beam
to approx the size of No.2 intraoral film should be used
• Rectangular collimators reduces the dose by 55%.
• Also improves image quality by reducing fog from scatter
resulting in better resolution and contrast

20.  Rectangular collimation in intraoral radiography
can be accomplished by one or a combination of
methods
◦ Dentsply/rinn xcp film holders in conjunction with a
rectangular PID
◦ Round PID with a Dentsply/ Rinn Universal collimator
attached to the round PID
◦ Using Masel precisio
n intruments.

21.  Narrow slit collimators are used in opgs
• Collimators in CBCT machines are generally designed as
variable diaphragms composed of movable pieces of metal.
They include two movable pieces of metal in the longitudinal
direction (perpendicular to the plane of X-ray source
trajectory) and two in the transverse direction (tangential to
the circle of X-ray source trajectory)

22. • Use of long PID
Serves to show the radiographer where the beam strikes the
patient
3 lengths of PIDs used: 8 inches
12 inches
16 inches
A lead-lined long open ended PID is preferred as they result
in less divergence
Pointed plastic cones causes more scattered radiation.

23.  Use of electronic timers:
◦ Mechanical timers are imprecise for short
exposures .
◦ “dead man “ control: shuts the machine
off immediately regardless of time –
setting, unless finger or foot pressure is
held continously on the switch throughout
the desired exposure.

24.  Use of high speed film:
• Fastest and the most appropriate film
should be used.
• E- speed film requires half the exposure
that D-speed film requires to produce the
same amount of image density.
• E- speed is more difficult to process ,
tighter quality control needed.

25.  Use of rare earth intensyfying screens:
◦ Intensyfying screens converts x-ray energy into visble light energy
which inturn exposes the screen film.
◦ It is the sum effect of x-rays and visible light emitted by the
screens that exposes the x-ray film.
◦ Thus the image receptor system is 10 to 60 times more sensitive
to x-rays
◦ Smooth plastic sheet coated with minute fluorscent crystal called
phosphors.
◦ Phosphors can be in the form of Catungstate crystals or rare
earth intensyfing screens using terbium-activated gadolinium
oxysulphide and thelium-activated lanthanum oxybromide.
◦ rare earth intensifying screens are four times more efficient than
catungstate screens and thus less exposure is required.

26.  Use of film holding devices
◦ Helps in avoiding using patient’s fingers to hold
the film in place.
◦ To more accurately align the film with the teeth
hence avoiding retakes
◦ Essential if rectangular collimators are used
since smaller narrow beam leaves no room for
error in aiming the PID.

27.  Use of leaded aprons and thyroid collars and shields:
◦ Leaded apron provides shielding and further reduces
genetic and carcinogenic risks to pelvis, abdominal and
thoracic tissues
◦ Leaded apron will reduce genetic exposure by 98% for
panoramic radiography
◦ For intraoral radiography a thyroid shield will reduce the
dose to the thyroids by approx 50%

28.  Proper technique
◦ Proper technique helps ensure the diagnostic
quality of images and reduce the amount of
exposure a patient receives.
◦ The radiographer must have a thorough
knowledge of the techniques most often used in
dental radiography.
◦ An organised routine is important for the effective
application of a technique

29.  Proper processing techniques:
◦ Helps in avoiding retakes
◦ Dark room lighting precautions:
 Must be kept free from light-leaks
 Use of appropriate safelight filters
 Light lamp should be placed 4 feet away from the
working area
◦ Processing solution should be changed regularly,kept
covered to prevent oxidation, stirred thoroughly twice each
day
◦ Depleted or contaminated chemicals can result in non-
diagnostic radiographs – necessitates retake- doubles
pateints exposure.

30. Protection for the
environment:
 Surrounding environment must be protected from radiation to avoid
exposure to persons in the environment.
 Primary beam should never be directed at any one other than the
patient.
 Patient should be positioned such that x-ray beam is aimed at the wall of
the room and not through a door or other opening.
 X- ray equipment room features:
 Minimum dimension of x-ray equipment room is 18 sq.mts
 Walls made of 3” of concrete , 3” x 16” of steel or 1mm of lead will suffice to
protect adjacent rooms.
◦ An alternative to lead is barium in the form of barium plaster or
barium concrete
◦ Altenatively , lead plywood(0.25mm of lead sandwiched between
layers of wood) can be used.
◦ Primary barrier should be incorporated in floor or ceiling where
primary beam is fired—must be of minmum 35cm thick brick
◦ Secondary barrier in the walls provide protection against scattering
and leakage radiation – must be of 23 cm thick brick

31.  Shielding of x-ray control panel:
◦ Based on operating potential;
 If < 125 kVp, panel should be within the x-ray
room with a minimum distance of 3m
 If > 125 KVp control panel installed outside the
equipment room with appropriate sheilding for
the room
 Location should be such that primary beam
scatters twice before entering the room
 Control booth wall and window sheilding should
be of 1.5 mm lead thickness

32.  Patient waiting area
◦ Should be outside the waiting room
◦ Suitable alert signal in the form of red light
should be placed outside the x-ray room .
Kept ON during the procedure
◦ A warning placard should be attached at
the eye-catching place

33. RADIATION MONITORING
DEVICES
Measuring of the x-ray exposure of operators or
associated personnel as a protective measure.
Various typres of radiation monitoring devices:
• Electrical:
• Ionization chamber
• Thimble chamber
• Geiger counter
• Chemical:
• Film
• Chemical dosimeter
• Light
• Scintillation counter
• Thermoluminescence:
• TLD

34. Ionization Chamber
Consists of :
A pair of collecting plates each with an opposite
charge.
Separated by a std volume of air.
Plates are connected by a electrometer.
Advantages:
Most accurate.
Direct read out- immediate information.
Disadvantages:
No permanent record.
No indication of type of energy.
Not sensitive to low energy radiation.

35.  Thimble chamber:
◦ Consist of a thimble shaped Argon-gas filled glass chamber that
houses a –vely charged metalic cylinder encompassing a
centrally placed metal plate(+ve charged)
◦ When x-ray is incident on it, the ionization of air within the gas
chamber takes place causing drop in potential which proprotional
to incident x-ray.

36.  Geiger counters:
◦ Hand-held radiation survey instrument
◦ Consist of geiger-muller tube which detects the radiation
and the processing electronics, that displays the circuit
◦ It is filled with an inert gas such as argon at low pressure to
which high voltage is applied
◦ Briefly conducts electrical charge when a particle or photon
of incident radiation makes the gas conductive.
◦ The ionisation is amplified to produce an easily measured
detection pulse which is then fed into processing and
display electronics.

37.  Scintillation counter:
◦ A scintillation is an instrument for detecting and measuring
ionizing radiation by using excitation effect of incident
radiation on a scintillator material and detecting the
resultant light pulse.
◦ Consist of a scintillator which generates photon of light in
response to incident radiation , a sensitive
photomultiplier tube which converts the light to an
electric signal and electronics to process the signal.

38.  Pocket dosimeters:
◦ a pen-like device that measures the cumulative dose
of ionising radiation received by the device. It is usually
clipped to a person's clothing and worn to measure one's
actual exposure to radiation.
◦ Must be recharged at the start of every work shift
◦ Are of 2 types :Minometer /condensor type / Indirect
read dosimeter and Direct read dosimeter

39.  Indirect pocket dosimeters
◦ It is an ion chamber that has voltage potential placed in it
by insertion into a charger.
◦ Radiation penetrating causes the current to leak off which
is proportional to the incident radiation.
◦ By re-inserting the dosimeter into the charger at the end of
the day, the drop in the voltage potential is calibrated in
terms of milliroentgens(mR)
◦ It is imperative to recharge the dosimeter after every
reading

40.  Direct reading pocket dosimeters:
◦ Generally of the size and shape of a fountain pen.
◦ Consist of a small ion-chamber of volume of approx 2cubic mm
◦ Inside the chamber , central wire anode at the end of which is metal-
coated quartz fiber attached.
◦ When the anode is charged to a positive potential , the charge is
distributed between the wire and the fiber-----electrostatic repulsion
deflects the fiber
◦ Electrons produced due to ionizing radiaiton, gets attracted to the
positive anode . As a result of net +ve charge in the fiber decreases
◦ Fiber moves back to its original position
◦ Change in the position is proportional to the ionization produced
which is in-turn proportional to the x-ray radiation.
◦ By pointing the dosimeter at a light source the position of fiber may
be observed through use of lens
◦ Typical industrial pocket dosimeter has full scale reading of 200 mR.

41.  Advantages of pocket dosimetry:
◦ Provides immediate reading of the
exposure
◦ Reusable
 Diadvantages
◦ Limited range of exposure
◦ Inability to provide a permanent record
◦ Potential for discharging or reading-loss
resulting due to dropping or bumping.
◦ Must be recharged and recorded at the
start of each working shift.

42.  Film badges:
 Dental film enclosed in a light tight cover in
a metal framework containing various filters.
 6 quadrants: open, Al, Cd, Cu2+, Cu3+, Pb
 X-rays blacken photographic films.
 Degree of darkening – densitometer.
 Blackening in the open part of film indicates quality of radiation.
 Both portions are equally blackened-high energy x-rays.
 Blackening of open part is greater-low energy x-rays
 The ratio of blackness in open to different regions of filters quality
of radiation

43.  Advanatges of film badge:
◦ Good for measuring any type and energy of radiation
◦ Continous assessment is possible
◦ Accumulated dose can be calculated
◦ Provides a permanent record of dose received
◦ Simple robust and relatively inexpensive.
 Disadvantages of film badges:
◦ Accuracy is only 10 to 50%
◦ Range of exposure is less
◦ The results are very technique-sensitive – may lead to
errors
◦ No immediate indication of exposure-all info are
retrospective
◦ Film may also be affected by visible light
◦ Prone to filter loss

44.  Thermoluminiscent dosimeter(TLD):
◦ Measures ionizing radiation exposure by measuring the
intensity of visible light emitted from a crystal when the
crystal is heated after being exposed to
radiation.(Thermoluminiscence).
◦ Principle:
 Radiation interacts- causes excitation of electrons in the
crystal
 Excited electrons stay trapped in excited state due to
intentionally introduced impurities(manganese and
magnesium componds)
 heating --- causes electron to fall back to ground state---
emits a photon of energy equal to difference between the
trapped state and ground state

45. ◦ Two common types of crystals used in TLDS are:
 LiF (used for x and gamma rays)
 CaF2 (used for gamma and neutrons)
 TLD badge in INDIA supplied by BARC consist of:
 Card holder cassette of a high impact plastic
 TLD card consist of Ni-coated Al plate having 3 symmetrical
holes of 12mm dm over which 3 identical CaSO4 embedded
teflon disks are clipped
 These 3 disks are coated with 3 different filters:
 First disk coated with Al-Cu combination filters(cuts off
beta-radiation and detects x-ray and gamma radiaiton)
 Second disc is plastic filter coating (cuts off soft beta
radiation and detects hard beta , x-ray and gamma
radiation)
 Third disc is not coated with any filters. Therefore
detects all radiaitons

46. ◦ TLD(cont’d)
 Advt:
 Small in size and light in weight
 Chemically inert
 Usable over wide range of dose value(100uSv to 10Sv)
 Sensitivity is independent of the dose rate
 Almost tissue equivalent
 Reusable
 Economic
 Disadvt:
 Limited info provided
 Dose gradients are not detectable

47. DOSIMETRY
 Scientific sub-speciality in the field of health physics and
medical physics where it is the calculation and assessment of
radiaton dose received by the human body.
 Used extensively for radiation protection and is routinely
applies to occupational workers where irradiation is expected.
 The more important terms in dosimetry are:
◦ Radiation absorbed dose(D)
◦ Equivalent dose(H)
◦ Effective dose(F)
◦ Collective effective dose
◦ Commited dose
◦ Dose rate

48. Radiation Absorbed Dose(D)
 This is the measure of the amount of
energy absorbed from the radiation
beam per unit mass of tissue.
◦ SI unit: gray(Gy) measured in joules/kg
◦ Subunit : milligray(mGy)
◦ Original unit: rad, measured ergs/g.
◦ Conversion: 1Gy=100 rads

49. Equivalent dose(H)
 This measure allows the different radiobiological effectiveness of
different types of radiation to be taken into account
 For eg, the biologic effect of a particlular radiation-absorbed
dose of alpha particles would be considerably more severe than
a similar radiaion absorbed dose of X-rays owing to less
penetrating power of alpha particles
 By introducing a numerical value known as the radiation
weighting factor Wr which represents the biological effects of
different radiations, the unit of equivalent dose provides a
common unit allowing comparisons to be made between one
type of radiation with another.
 X rays gamma rays and beta particles Wr= 1
 Protons Wr = 10
 Alpha particles Wr= 20
Equivalent dose(H) = radiation-absorbed dose(D) x Wr
SI unit: sievert(Sv)
subunit: miilisievert, microsievert 1 sievert =
100 rems

50. Effective dose(E)
 This measure allows doses from different investigations of
different parts of the body to be compared, by converting all
doses to an equivalent whole body dose.
 This is necessary since some parts of the body are more
sensitive than others
 ICRP has allotted each tissue a numerical value known as
tissue weighting factor(Wt)based on its radiosensitivity.
 Sum of the individual tissue weighting factor represent the
weighting factor for the whole body.
 Effective dose(D) = equivalent dose (H) x tissue weighting
factor(Wt)
 SI unit: sievert

51. Dose rate
 This is a measure of the dose per unit
time for eg dose/hour and is a more
convenient measurable figure than
annual dose limit
 Si unit: microsievert/hour(uSvh-1)

52. Collective Dose
 To assess the overall effect of radiation dose on a large group
of people, the individual dose may be multiplied by the
population number exposed and it is collective dose.
 If N is the number of population recieving a mean organ
equivalent dose Ht, over a period of time t, then the collective
dose St is given by:
 St = Ht x N
 In a similar way, the collective effective dose (S) can be
defined as whole body exposure to a population group
exposed to radioactive materials in the environment and can
cover successive generations of the pouplation being studied;
 S = Et x N
 SI unit : man-sievert(man-Sv)

53. Committed dose
 If an individual is subjected to a radiation burden over a
period of time, then committed dose is the term is used.
 Absorbed dose the individual receives as a result of intake of
radioactive material.
 Committed dose equivalent: is the quantitative assessment
of the effect of a particular intake of radioactivity over the
whole of an individuals working life. Defined as the dose
accumulated over a period of 50 years following intake of
radioactive material.
 H(t)= H x t where t is the period of time in years
 if the committed dose equivalent is multiplied by a suitable
tissue weighting factor then the product is committed effective
dose(E(t))

54. Conclusion

55. References:
 Oral radiology; principles and
interpretation- White & Pharaoh.
 Principles of dental imaging-Langland &
Langlais
 Text book of dental and maxillofacial
radiology –Feny Karjodkar.
 Essentials of dental radiology and
radiography- Eric whaites
 Dental radiography principal and
techniques- Lannucci and Howerton
 Journal articles