2. • Determining the quantity of radiation exposure or dose.
• Exposure – measure of radiation on the basis of its
ability to produce ionization in air under standard
conditions of temperature and pressure (STP).
3. Absorbed dose (DT)
• Energy absorbed by any type of ionizing radiation per
unit of mass of any type of matter.
4. Equivalent dose (HT)
• compare the biologic effects of different types of radiation on a
tissue or organ.
• HT = WR x DT
• Particulate radiations have a high LET & are more damaging to
tissue than x- rays – this biologic effectiveness of different types of
radiation – WR
• Photons – 1
• Neutrons & high-energy protons – 5
• α particles - 20
5. Effective dose (E)
• Estimate the risk in humans.
• E = Σ WT x HT
• Radiosensitivity of different tissues measured by WT.
• Red bone marrow, breast, colon, lung, & stomach - 0.12
• Gonads - 0.08
• Bladder, esophagus, liver, & thyroid - 0.04
• Bone surface, brain, salivary glands, & skin - 0.01
9. • NCRP recommends Diagnostic Reference Levels of 1.6 mSv
skin dose for IOPA & bitewing.
• Average weekly exposure for patient/ operator - 0.001 Sv.
• Maximum of 13 week exposure is 0.05 Sv.
• Dentist and staffs are allowed to receive 20 mSv/yr - 0.2-1%
of allowable exposure
How much is acceptable ???
10.
11. The principle:
• Physical & chemical effects produced by the radiation.
1. Ionization
2. Photographic effect
3. Luminescence
4. Scintillation
Radiation monitoring devices
16. Advantages:
• Most accurate method.
• Gives immediate information.
Disadvantages:
• No permanent record of exposure.
• No indication of the type of energy of the radiation.
• Not sensitive to low energy radiation.
• Fragile & easily damaged.
17. Principle:
• The ability of radiation to blacken the photographic film.
Application:
• Film badges.
2. Photographic effect
18. Principle:
• The property of certain materials that emit light when stimulated
by - chemical/ electrical/ heat.
Application:
• TLD badges
3. Luminescence
22. • Monitor the individuals who are exposed to radiation during the
course of their work.
• Must for all occupationally exposed individuals.
• Mandatory to wear personnel dosimeter if the annual dose is
greater than 1 mSv.
• Pocket dosimeter, the film badge or the thermoluminescent
dosimeter.
Personnel Dosimeter
23. • Radiation measurement by time-integrated dose, i.e. the
dose summed over a period of time, usually about 3 months.
• The dose is consequently 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 (10–20 mrem).
24. Pocket dosimeter
1. Minometer/ Condensor type/ indirect reading type
• Principle: ‘air wall’ ionization
• Working:
• Insertion into a charger - voltage potential.
• Radiation penetrating the chamber causes the current to leak
in proportion to the radiation exposure.
• Reinsert into the charge reader - voltage drop is calibrated.
• 2 dosimeters are worn at a time.
• Lower of the two readings taken as more accurate.
25. 2. Direct Reading Dosimeter
• Principle: Gold Leaf Electroscope.
• Working:
• Charging to 200V - quartz fiber is displaced electro statically.
• Fiber is viewed through a lens & focused on a scale.
• Exposure to radiation discharges the fiber, allowing it to
return to the original position.
• Can measure radiation up to 50 C/kg (200 mR).
26.
27. Film badge monitoring
• Has small X-ray films sandwiched between several filters that
detects radiation.
• Inexpensive, simple mode of functioning.
• Detects radiation at or above 0.1 mSv.
28.
29. Wearing of the badge:
• Monitored every 2 weeks/ 4 weeks.
• If accidental high exposure be suspected - should be immediately
processed.
30. Advantages:
1. Good for measuring any type and energy of radiation. e.g. X-
rays, gamma radiations.
2. Continuous assessment is possible.
3. Provides a permanent record of dose received.
4. Simple, robust & relatively inexpensive.
31. Disadvantages:
1. They are insensitive to radiation below 0.1 mSv.
2. They cannot be worn longer than 4 weeks duration at a stretch
due to fogging.
3. Accuracy is only 10 to 50%.
4. The results are dependent on processing, strength, type of
developer used & speed of the film used.
5. No immediate indication of exposure- all information is
retrospective.
34. Working:
Few electrons
become trapped in
higher energy levels Light is collected
& measured by
photomultiplier
tube
Energy is released in
the form of light
by heating 250C
Amount of light
is proportional to
the radiation dose
(Sv)
37. Advantages:
1. Can measure exposures to individuals as low as 1.3 C/kg (5 mR).
2. Can withstand certain degree of heat, humidity, & pressure.
3. Crystals are reusable.
4. Instantaneous readings are possible if the department has a TLD
analyzer.
5. Read out simple and quick.
6. Can store dose over long period of time.
38. Disadvantages:
1. Not cost effective.
2. Read out is destructive, giving no permanent record.
3. Results cannot be checked or reassessed.
deposition of 1 Gy of high-energy protons causes five times as much damage as 1 Gy of x-ray photons
for instance, the jaws, the it measures the equivalent whole-body dose.
allows the risk from exposure to one region of the body to be compared with the risk from exposure to another region
In diagnostic radiology : 1R = 1 r = 1 rem
For diagnostic radiology 1 Sv equals 1 Gy.
Increased risk of tumor if exposed to > 100 mGy.
The process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or ions is termed as ionization.
electrode positioned in the middle of a cylinder that contains gas.
Strength of the current is proportional to the radiation intensity.
Lithium fluoride will emit light when stimulated by heat.
on luminescence property is (TLD)
Lithium fluoride will emit light when stimulated by heat.
on luminescence property is (TLD)
Radiation on scintillating crystals - absorbs it and emit light - photomultiplier tube converts into an electrical pulse & measured
The values obtained are valid only when properly worn & irradiated only during occupational exposure & are returned on time.
recharge the Indirect Reading Pocket Dosimeters after every reading.
can measure radiation up to 50 C/kg (200 mR)
In India, film badges have been recently replaced by TLD badges.
1, as many low energy photons may not penetrate the film.
2. as an outcome of high temperature & light.
4. as many low energy photons may not penetrate the film.
In India, film badges have been recently replaced by TLD badges.
collar level - outside the lead apron - estimate dose to the unprotected regions H & N.
trunk level - underneath the lead apron - estimate of radiation to protected organs.
If only one is worn - must be at the collar outside the lead apron, because, the neck receives 10–20 times more radiation
Application: Radiotherapy- for measuring doses received
by patients while actually undergoing the treatment exposures.
