Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency (IAEA) as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this". Exposure can be from a source of radiation external to the human body or due to internal irradiation caused by the ingestion of radioactive contamination. Ionizing radiation is widely used in industry and medicine, and can present a significant health hazard by causing microscopic damage to living tissue. There are two main categories of ionizing radiation health effects. At high exposures, it can cause "tissue" effects, also called "deterministic" effects due to the certainty of them happening, conventionally indicated by the unit gray and resulting in acute radiation syndrome. For low level exposures there can be statistically elevated risks of radiation-induced cancer, called "stochastic effects" due to the uncertainty of them happening, conventionally indicated by the unit sievert. Fundamental to radiation protection is the avoidance or reduction of dose using the simple protective measures of time, distance and shielding. The duration of exposure should be limited to that necessary, the distance from the source of radiation should be maxi mised, and the source shielded wherever possible. To measure personal dose uptake in occupational or emergency exposure, for external radiation personal dosimeters are used, and for internal dose to due to ingestion of radioactive contamination, bioassay techniques are applied.

1. RADIATION
PROTECTION
SUBRATA ROY
RTT HCG

2. AIM OF RADIATION PROTECTION
“To provide an appropriate
standard of protection for
man without unduly limiting
the beneficial practices
giving rise to radiation
exposure”.

3. Radiation protection can be defined as the protection
of people against exposure to ionizing radiation or radioactive
substances and the safety of radioactive sources,
including the means for achieving such protection and
safety. It encompasses the various procedures and devices
for keeping people’s doses and risks as low as can
be reasonably achieved and below prescribed dose
constraints,
as well as the means for preventing accidents
and for mitigating the consequences of accidents, should
they occur.

4. RADIATION QUANTITIES
 Dose Equivalent:- Factors affectinng the biological
effects of radiation.
 Dose.
 Types of radiation.
Dose Equivalent(H)
The dosemetric quality relevent to radiation.
H=D.Q
D= Absorbed dose.
Q= Quality Factor.
Units=sievert, 1 Sievert=1j/kg..[S.I

5. Quality Factor(Q)
Base on a range RBE related to the LET of the radiation
Independent of the organ or tissue
Recommended Quality Factors
Radiation Quality Factor
X-rays, γrays, and electrons 1
Thermal neutrons 5
Neutrons, heavy particles 20
Data are from NCRP. Recommendations on limits for exposure to ionizing radiation. Report No. 91

6. Effective Dose Equivalent

7. Weighting Factors
Recommended Values of the weighting Factors WT, for calculating Effective Dose Equivalent and the
Risk Coefficients from Which They Were Derived
Tissue (T) Risk Coefficient WT
Gonads 40 × 10-4 Sv-1 (40 × 10-6 rem-1) 0.25
Breast 25 × 10-4 Sv-1 (25 × 10-6 rem-1) 0.15
Red bone marrow 20 × 10-4 Sv-1 (20 × 10-6 rem-1) 0.12
Lung 20 × 10-4 Sv-1 (20 × 10-6 rem-1) 0.12
Thyroid 5 × 10-4 Sv-1 (5 × 10-6 rem-1) 0.03
Bone surface 5 × 10-4 Sv-1 (5 × 10-6 rem-1) 0.03
Remainder 50 × 10-4 Sv-1 (50 × 10-6 rem-1) 0.30
Total 165 × 10-4 Sv-1 (165 × 10-6 rem-1) 1.00
From NCRP. Recommended on limits for exposure to ionizing radiation. Report No. 91.

8. Background Radiation
 Low Level Radiation Effects.
 Effective Dose Equivalent limits.
 Structural Shielding Design.

9. Background Radiation
Radiation from the natural environment
Terrestrial radiation
e.g. elevation level of radon in many building
Emitted by naturally ocurring 238U in soil
Annual dose equivalent to bronchial epithelium = 24 mSv (2.4 rem)
Cosmic radiation
e.g. air travel
At 30,000 feet, the dose equivalent is about 0.5 mrem/h
Radiation element in our bodies
e.g. mainly from 40K
Emits β, γrays; T1/2 = 1.3 × 109 years

10. Estimated Total Dose Equivalent Rate for a Member of the Population in the United States and
Canada from Various Sources of Natural Background
Source
Dose Equivalent Rate (mSv/y)
Bronchial
Epithelium
Other Soft
Tissues
Bone Surfaces Bone Marrow
Cosmic 0.27 0.27 0.27 0.27
Cosmogenic 0.01 0.01 0.01 0.03
Terrestrial 0.28 0.28 0.28 0.28
Inhaled 24 － － －
In the body 0.35 0.35 1.1 0.50
Rounded totals 25 0.9 1.7 1.1
From NCRP. Exposure of the population in United States and Canada from national background radiation.

11. Radiation from various medical procedures
The average annual genetically significant dose equivalent in 1970 =
20 mrem/year
Occupational exposure excluded exposure from
Natural background
Medical procedures

12. Low-Level Radiation Effects
Effective Dose Equivalent limits
Structural Shielding Design
A.Primary Radiation Barrier
B.Secondary Barrier for Scattered Radiation
C.Secondary Barrier for Leakage Radiation
D.Door Shielding
E.Protection against Neotrons.

13. Low-Level Radiation Effect
Low level radiation
< Dose required to produce acute radiation syndrome
> Dose limits recommended by the standards

14. Low-Level Radiation Effects
Genetic effects
Radiation-induced gene mutation
Chromosome breaks and anomalies
Neoplastic disease
e.g. Leukemia, thyroid tumors, skin lesions
Effect on growth and development
Adverse effects on fetus and young children
Effect on life span
Diminishing of life span
Premature aging
Cataracts – opacification of the eye lens

15. Stochastic & Non Stochastic Effect
• Stochastic Effect:-Radiation effect which
has no threshold dose limits are called stochastic
effect
• Example:- incident of cancer due to radiation .

16. Non Stochastic/Deterministic Effect
• Non Stochastic Effect:-The harmful effect of
radiation Which has threshold dose limit for
occurence is called Diterministic effect.
• Example:-Formation Of Cataract in eye due to
Radiation.

18. Effective Dose Equivalent limits
Structural Shielding Design
A.Primary Radiation Barrier
B.Secondary Barrier for Scattered Radiation
C.Secondary Barrier for Leakage Radiation
D.Door Shielding
E.Protection Against Neutrons

19. Effective Dose Equivalent limits
The criteria for recommendations on exposure limits of
radiation workers
At low radiation levels, the nonstochastic effects are essentially
avoided
The predicted risk for stochastic effects should not be greater then
the average risk of accidental death among worker in “safe”
industries
ALARA principles should be followed
The risk are kept as low as reasonably achievable, taking into account,
social and economic factors

20. Occupational and Public Dose Limits
.
Summary of Recommendations
A. Occupation exposure (annual)
1. Effective dose equivalent limit (stochastic effects) 50 mSv 5 (rem)
2. Dose equivalent limits for tissues and organs
(nonstochastic effects)
a. Lens of eye 150 mSv (15 rem)
b. All others (e.g. red bone marrow, breast, lung,
gonads, skin and extremities) 500 mSv (50 rem)
3. Guidance: cumulative exposure 10 mSv × age (1 rem × age in
years)
B. Public exposures (annual)
1. Effective dose equivalent limit, continuous or
frequent exposure 1 mSv (0.1 rem)
2. Effective dose equivalent limit, infrequent exposure 5 mSv (0.5 rem)
3. Remedial action recommended when:
a. Effective dose equivalent > 5 mSv (>0.5 rem)
b. Exposure to radon and its decay products > 0.007 Jhm-3 (>2 WLM)
4. Dose equivalent limits for lens of eye, skin and
extremities 50 mSv (5 rem)
From NCRP. Recommendations on limits for exposure to ionizing radiation. Report. 91.

21. Occupational and Public Dose Limits
Summary of Recommendations
C. Education and training exposures (annual)
1. Effective dose equivalent 1 mSv (0.1 rem)
2. Dose equivalent limits for lens of eye, skin and
extremities 50 mSv (5 rem)
D. Embryo-fetus exposures
1. Total dose equivalent limit 5 mSv (0.5 rem)
2. Dose equivalent limit in a month 0.5 mSv (0.05 rem)
E. Negligible Individual Risk Level (annnual)
Effective dose equivalent per source or practice 0.01 mSv (0.001 rem)
From NCRP. Recommendations on limits for exposure to ionizing radiation. Report No 91.

22. Structural Shielding Design
A.Primary Radiation Barrier
B.Secondary Barrier for Scattered Radiation
C.Secondary Barrier for Leakage Radiation
D.Door Shielding
E.Protection Against Neutrons

23. Structural Shielding Design
Design of protective barriers
Ensure that the dose equivalent received by any individual dose
not exceed the applicable maximum permissible value
Dose equivalent limits of “controlled area” and
“uncontrolled area”
Controlled area: 0.1 rem/wk (5 rem/yr)
Uncontrolled area: 0.01 rem/wk (0.5 rem/yr)
Protection against 3 type of radiation
The primary radiation
The scattered radiation
The leakage radiation (from source housing)

24. Factors associated with the calculation of barrier thickness
 Workload (W)
 Use factor (U)
 Occupancy factor (T)
 Distance (d)

25. Workload (W)
For <500 kVp x-ray machine
W = Maximum mA × beam “on” time
= min/week
For MV machine
W = weekly dose delivered at 1 m from the source
= no. of patient treated/wk × dose delivered/p’t at 1 m
= rad/wk (at 1m)
Use Factor (U)
U = Fraction of operation time that radiation is directed toward
a
particular barrier
Depending on technique use

26. Typical Use Factor for Primary Protective Barriers
Location Use Factor
Floor 1
Walls ¼
Ceiling ¼ - ½ , depending on equipment and techniques

27. Occupancy Factor (T)
T = Fraction of operating time during which the area of interest
is occupied by the individualTable
Typical Occupancy Factors
Full occupancy (T = 1)
Work areas, offices, nurses’ stations
Partial occupancy (T = ¼ )
Corridors, rest rooms, elevators with operators
Occasional occupancy (T = 1/8 – 1/16)
Waiting rooms, toilets, stairways, unattended elevators,
outside areas used only for pedestrians or vehicular traffic

28. Distance
d = distance from the radiation source to the area to be protected
Applied inverse square law

29. A. Primary Radiation Barrier
Determine the thickness of the primary radiation barrier
P = Maximum permissible dose equivalent for the area to be
protected
Controlled area: 0.1 rad/wk
Non-controlled area: 0.01 rad/wk
B = transmission factor
Determining the barrier thickness by consulting broad beam
attenuation curves for the given beam energy
B
d
WUT
P  2
WUT
dP
B
2



30. B. Secondary Barrier for Scattered Radiation
Energy of the scatter
For orthovoltage radiation
Beam energy: Scatter = incident (assumed)
For MV beams
Beam energy at 90° scattered photon = 500 keV
Transmission of 500 kVp useful beam
Relatively lower energy in compare with the incident energy
Beam softening by Compton effect

31. C. Secondary Barrier for Leakage Radiation
The recommended leakage exposure rate for different
energy of the beams (< 500 kVp)
5-50 kVp
<0.1 R (in any h at any point 5 cm from the source)
> 50 kVp, < 500 kVp
< 1 R (in 1 h, at 1 m from the source)
< 30 R/h at 5 cm

32. C. Secondary Barrier for Leakage Radiation
The recommended absorbed dose rate for different
energy of the beam (> 500 kVp)
> 500 kVp
< 0.2% of the useful beam dose rate
(any point outside the max field size, within a circular plane of radius 2 m)
Cobalt teletherapy
Beam “off” position
< 2mrad/h (on average direction, 1m from the source)
< 10 mrad/h (in any direction, 1m from the source)
Beam “on” position
< 0.1% of the useful beam dose rate (1 m from the source)

33. D. Door Shielding
Advantages of the maze arrangement in treatment
room
Reduces the shielding requirement of the door
Expose mainly to multiply scattered radiation

34. E. Protection against Neutrons
Neutron contamination
High energy photon (> 10 MV) or electrons incident on the various
materials of target, flattening filter, collimators and other shielding
components
Increase rapidly in the range of 10 – 20 MV beam energy
The energy spectrum of emitted neutrons
Within the beam : range 1 MeV
Inside of the maze: few fast neutrons (> 0.1 MeV)