RADIATION PROTECTION

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 W T , for calculating Effective Dose Equivalent and the Risk Coefficients from Which They Were Derived Tissue (T) Risk Coefficient W T 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 ; T 1/2 = 1.3 × 10 9 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 Primary Radiation Barrier Secondary Barrier for Scattered Radiation Secondary Barrier for Leakage Radiation Door Shielding 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.

17. Effective Dose Equivalent limits Structural Shielding Design Primary Radiation Barrier Secondary Barrier for Scattered Radiation Secondary Barrier for Leakage Radiation Door Shielding Protection Against Neutrons

18. 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

19. 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.

20. 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.

21. Structural Shielding Design Primary Radiation Barrier Secondary Barrier for Scattered Radiation Secondary Barrier for Leakage Radiation Door Shielding Protection Against Neutrons

22. 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)

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

24. 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

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

26. Occupancy Factor (T) T = Fraction of operating time during which the area of interest is occupied by the individual Table 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

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

28. 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

29. 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

30. 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

31. 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)

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

33. 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)