This document discusses radiation protection and the harmful effects of radiation. It covers background radiation sources, internal and external sources, stochastic and non-stochastic effects, acute and chronic radiation exposure risks. It provides guidelines for radiation monitoring with film badges and dosimeters. Protective measures for workers and patients are outlined including time, distance, barriers. Key terms like rad, rem, sievert and effective dose are defined. Risks of different exposures like medical imaging and pregnancy are addressed.
7. STOCHASTIC EFFECT
• Statistical Chance that a particular
effect will occur.
• Usually from a small absorbed dose.
• Does not have a threshold dose
e.g. cancer and genetic effect
8. NON-STOCHASTIC EFFECT
• Somatic effect that increases in severity
with increasing absorbed dose.
• Certainity effect.
• Threshold dose.
• E.g. cataracts,decrease in blood
count,decrease in sperm count.
9. Harmful effects of radiation
LOCAL EFFECTS
• Erythema- several hundreds of rem
needed
• Dry skin – due to low dose chronic
exposure
• Cataract –possible with a dose equivalent
of few hundred rem
10.
11.
12. GENERAL EFFECT
• Bone marrow and lymphatic tissue are
especially susceptible
• No threshold or lower limit demonstrated
• Dose as little as 5-25 rem to whole body can
cause chromosomal abnormality
• Chronic exposure – shortening of life span
13. GENETIC EFFECT
• Chromosomal aberration
• Gene mutations
• GONADAL EXPOSURE
RISK[Genetically Significant Dose]
• - Genetically significant dose defined as
ionising radiation to the gonads of
exposed individual which, if spread over
the entire population, would induce
same total genetic risk to their offspring
14. ACUTE WHOLE BODY IRRADIATION
• 1. ACUTE RADIATION SYNDROME – due to
exposure of 100-1000 rem, occur in atomic energy
center or in the Rx of leukemia
• 2. Supra lethal exposure- 600-1000 rem, leads to
GASTROINTESTINAL SYNDROME(die in 1 week)
• mid lethal- 450 rem, die in 1 month due to BONE
MARROW SYNDROME
• Sublethal exposure- 100-300 rem, nausea,
vomiting, cataract after 2-6 yrs, increase incidence
of leukemia
15. PREGNANCY
• from 1st to 10th day after fertilisation- 10 –15
rads dose –abortion / no congenital defect
• From 11th – 41st day of gestation(period of
organogenesis) – maximum sensitivity
• From 8th – 15th week- mental retardation
• -Recommended exposure limit 0.5 rem entire
pregnancy with no more than 0.05 rem in one
month
16. • LINEAR ENERGY TRANSFER- amount
of energy deposited per unit length of
travel, expressed in kev/ micron.
• Greater the LET ,the more severe the
biological effect.
17. • Relative biologic effectiveness:
• RBE =Dose of standard radiation
• ------------------------------------
• Dose of radiation in question
18. RADIATION UNITS
• ROENTGEN– unit of radiation exposure-
liberate a charge of 2.58x10-4c/kg of air.
• It is the approximate exposure to the body
surface for an AP film of the abdomen for
a patient of average thickness
19. • RAD: unit of absorbed dose
• It is equal to the radiation to deposit 100
ergs of energy to 1 gram of irradiated
tissue
• GRAY:SI unit of absorbed dose
• I GRAY= I jouleof energy in 1 kg of
tissue
• 1 GRAY = 100 RAD
• 1 RAD = 1 cGy
20. • ABSORBED DOSE- independent of
composition of irradiated material and
energy of the beam.
• Energy deposition in soft tissue = 95
erg/g in diagnostic energy range.
• Absorbed dose is proportional to the
degree of attenuation.
21. • REM: unit of absorbed dose equivalent
• It is a measure of biological
effectiveness of radiation
• SI unit:Sievert
• 1 Sievert = 100 rems
22. DOSE EQUIVALENT
• To express risk of radiation injury from all
kinds of ionizing radiation.
• H=ABSORBED DOSE X QUALITY
FACTOR
• REM=RADXQ
• cSv cGyXQ
23. Type of radiation Q factor
1. X rays 1
2. Gamma rays 1
3. Beta particle 1
4. Electrons 1
5. Thermal neutrons 5
6. Other neutrons 20
7. Protons 20
8. Alpha particle 20
24. • EFFECTIVE DOSE EQUIVALENT:
• Weighted dose equivalent to an organ
entailing the same risk as though the
same dose equivalent were given to the
whole body.
27. NEW RECOMMENDATION
Limit for Life
time exposure = age x 1 rem
----- An individual’s lifetime effective dose
equivalent should not exceed the value of
age in years
28. ALARA CONCEPTS
• NCRP report no.107 and ICRP publication 26
have addressed- As Low As Reasonably
Achievable concept.
• Reasonably Achievable aspect implies a
balancing of benefit (risk reduction) Vs
cost( financial and social)
• Approach:
• 1. Planning radiology dept.in advance of
construction.
• 2. Promoting awareness in the department
30. DEVICES FOR RADIATION MONITORING
• 1. Pocket dosimeter- resembles a
fountain pen, contains a thimble
ionisation chamber at one end.
• Exposure read by electrometer.
• DISADVANTAGES:
• Easily damaged
• Unreliable in unexperienced hands.
• Does not provide a permanent record.
31.
32. • . FILM BADGE:
• Consists of a dental film, cover by a plastic
and copper filter to show the quality of
radiation, backed by a lead foil.
• Worn over front of chest or hip.
• Usually worn for one month.
• Dosimetric comparison made with standard
films exposed to known amounts of radiation.
33. GUIDELINES FOR USING FILM
BADGE(BARC guidelines)
• 1. Used by persons directly working in
radiation
• 2. Name, personnel no., type of radiation,
period of use, location on the body- written on
front side.
• 3.Shouldn’t exchange between workers.
• 4.institution should keep one control film.
34. • 5.While leaving, workers should deposit
badge, & should be kept near control film
• 6.Shouldn’t leave badge in radiation area.
• 7.New worker form should be sent to BARC,
MUMBAI
• 8.All used and unused film packs should be
returned to BARC
• 9.Not to be worn for than one month.
38. • 3. Thermoluminescent dosimeter-
consists of crystals (LiF) which
store energy on exposure to ionising
radiation and lose energy on heating up in
the form of light.
measurement of light by
photomultiplier device
39.
40. ADVANTAGES OF TLD
• Small size (only milligram quantities of TL
material is needed).
• Particularly useful as extremity dosimeters
when some parts of the body are more
exposed than others .
• More sensitive and more accurate.
• Measures exposures as low as 5mrR.
• Excessive heat and humidity does not affect it.
• Ability to be reused.
41.
42. DISADVANTAGES
• Dose information is usually only given
once during heating and cannot be
repeated by subsequent heating.
• They are also subject to fading (i.e. the
loss of dose information due to
temperature or light effects).
• Cost
45. PROTECTIVE MEASURES
• 1. ExposureTime
• 2. Distance- Inverse Square Law
• 3. Barriers- usually lead or concrete
46. CALCULATION OF EXPOSURE
Step 1. WORKLOAD (W)- Xrays generated per
week:
Tube current [mA] x time in min of exp./ week
Step 2. Conversion of workload into roentgen
in terms of roentgens/ mA.min at a distance of 1
metre from xray source.
Step 3.Use factor- fraction of time that the beam is
directed at a particular barrier.
47. • Step 4- occupancy factor- is the fraction that
the workload should be decreased to correct
for the degree of occupancy of the area in
question, represents the amount of time that
the area will be occupied
• Step 5- Distance
48. • Weekly exposure E= E’WUT x 1/ d square
E’= Roentgen / mA.min at 1 meter
W= workload[mA.min/wk]
U= use factor
T= occupancy factor
D= distance
If total exposure[E] is less than 0.1R/wk for a
controlled area or 0.01/wk for an uncontrolled
area,no barrier is required.
49. LEAD BARRIER
• Half value layer (HVL)- thickness which
reduces exposure rate by one half.
50. Protective Barriers in Radiography and
Fluoroscopy
• 1. Radiation sources: the specification for x-ray
tube metal housing:leakage radiation shall not
exceed 0.1 R/Hour at a distance of 1 meter
• 2. Wall protection: to reduce the exposure to 10
mR/week, consistent with ALARA concept.
• The joint and holes must be covered by the
same protective barrier as the wall.
51. • 3. Controlled area: which is under the
supervision of the Radiation Safety Officer
and in which exposure limit is 1 rem / year
• 4. Uncontrolled area: not under supervision
and where the annual exposure limit to the
public prevail[0.5 rem for occaional
exposures].
52. • Four types of radiation
1. Useful beam
2. Leakage radiation
3. Scattered radiation
4. Stray radiation
53. TYPES OF WALL BARRIER
• 1. Primary protective barrier –
• To reduce the exposure rate of useful beam to
the occupational exposure limit.
• About 1/16 inch lead extending 7 feet up from
the floor, when xray beam is 5-7 feet from wall in
diagnostic energy range (upto 140 kv)
• Tales care of leakage radiation.
54. • 2. Secondary protective barrier-
• Scattered and leakage radiaition.
• 1/32 inch lead extends from top of the
primary barrier to the ceiling and should
overlap the primary barrier at least ½ inch at
the seam.
• 3. Control booth – should have the same
protection as wall and radiation should
scatter at least twice before reaching the
opening of the booth.
• Leaded glass portion should have same lead
equivalent as the adjacent wall.
55. WORKING CONDITIONS
• Never Expose a Human for
Demonstration Purposes.
• Never remain in a radiographic room
while exposure is in progress.
• Never hold a patient for therapy.
• Give yourself the same protection as a
loaded cassette.
56. • Fluoroscopy:
• Protective drape:at least 0.25 mm Pb
• Protective apron:0.5mmPb
• Lead shield:0.5mm Pb
• Lead protective gloves.
• Always wear a film badge or TLD monitor.
57.
58.
59. PROTECTION OF PATIENT
• WAYS TO MINIMISE PATIENT EXPOSURE
• 1. BEAM FILTRATION:
A.minimum total thickness in mm aluminium
equivalent including inherent filteration by glass
window of xray tube and cooling oil in tube
housing.
B .Half value layer of xray beam in mm Al.
60. • 2. Beam Limitation:
• Avoids unnecessary exposure of tissue
outside the area of interest.
• Reduced amount of scattered radiation.
• 3. Gonadal Shielding:
• Avoid direct exposure of gonads.
• Lead equivalent of shield is at least 0.5mm.
• 4.Modified Radiographic Techniques
61. • 5.High speed image receptors: use of highest
speed intensifying screens and films consistent
with satisfactory image quality.
6. Optimum film processing: automated film
processing avoids repeat examination
7. High kilovoltage:
8.Careful Technique
62. PATIENT PROTECTION IN
FLUOROSCOPY
• 1. By use of Intermittent fluoroscopy
• 2. Restriction of field size
• 3. Correct operating factors
Recommended factors—90-100 kvp, 2-
3 mAs, 2.5 mm aluminium filter
• 4.Filtration
• 5.Exposure limits
• 6.Primary Protective Barrier.
63. • Exposure limits:
• Not greater than 10R/min for equipment with
automatic exposure rate control.
• Not greater than 5R/min without automatic
exposure rate control.
• Timer to preset the on time of the
fluoroscopic tube for a cumulative total of no
more than five minutes.
64. • 4. Filtration
• 5. Exposure limits: exposure rate at the table top
must be no greater than 10 R/min. without
automatic exposure rate control.
• 6. A timer must be provided to preset the ontime of
the fluoroscopic tube not more than 5 min.
• 7. Primary protective barrier
66. PROTECTION IN MAMMOGRAPHY
• Compression must be used:
• 1.decreased exposure factors.
• 2.diminished amount of scattered radiation.
• 3.improved recorded detail.
67. CT SCANNING
• Tight collimation for each slice with
relatively small side scatter give the same
dose as the conventional examination.
• Noise can be reduced :
• A.increasing the exposure.
• B.periodic checking of the collimators.
