radiation protection...Koustav Majumder....


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radiation protection...Koustav Majumder....

  2. 2. INTRODUCTION •The protection of people and the environment from the harmful effects of ionizing radiation, which includes both particle radiation and high energy electromagnetic radiation •At the Second International Congress of Radiology in Stockholm in 1928, member of variuos countries were invited to send representatives to prepare x-ray protection recommendations •World War II was remodeled into two commissions that survive to this day: The International Commission on Radiological Protection (ICRP) The International Commission on Radiation Units and Measurements (ICRU) •U.S. Advisory Committee on X-Ray and Radium Protection (ACXRP) ,1929 which was renamed National Council on Radiation Protection and Measurements (NCRP), on 1964
  3. 3. DEFINITIONS Absorbed Dose: Energy per unit Dose Equivalent Dose: Absorbed dose × radiation weighting factor A radiation weighting factor (WR) is a dimensionless multiplier used to place biologic effects (risks) from exposure to different types of radiation on a common scale
  4. 4. CONTD…… Effective Dose Sum of equivalent doses to organs and tissues exposed, each multiplied by the appropriate tissue weighting factor (WT) Tissue Weighting Factor (W T), which represents the relative contribution of each tissue or organ to the total detriment resulting from uniform irradiation
  5. 5. CONTD….. Committed Equivalent Dose ICRP defined the committed equivalent dose as the integral over 50 years of the equivalent dose in a given tissue after intake of a radionuclide Committed Effective Dose If the committed equivalent doses to individual organs or tissues resulting from the intake of a radionuclide are multiplied by the appropriate tissue weighting factors and then summed, the result is the committed effective dose. Collective Equivalent Dose Product of the average equivalent dose to a population and the number of persons exposed Collective Committed Effective Dose The integral of the effective dose over the entire population out to a period of 50 years is called the collective committed effective dose.
  6. 6. Stochastic Effect •The probability of occurrence increases with increasing absorbed dose but the severity in affected individuals does not depend on the magnitude of the absorbed dose. • All-or-none phenomenon, •e.g cancer or genetic effect. •Probability of such effects occurring increases with dose, their severity does not. •There is no threshold, that is, no dose below which the probability of an effect is zero. • The dose-response relationship is therefore linear, or linear-quadratic, with no threshold.
  7. 7. Deterministic effects •Increases in severity with increasing absorbed dose in affected individuals, owing to damage to increasing number of cells and tissues.” • Examples : organ atrophy, fibrosis, lens opacification, blood changes, and decrease in sperm count. •The dose-response relationship is therefore sigmoid after a threshold
  8. 8. OBJECTIVE OF RADIATION PROTECTION (1) to prevent clinically significant radiation-induced deterministic effects by adhering to dose limits that are below the apparent or practical threshold, (2) to limit the risk of stochastic effects (cancer and hereditary effects) to a reasonable level in relation to societal needs, values, and benefits gained. The objectives of radiation protection can be achieved by reducing all exposure to as low as reasonably achievable (ALARA)
  9. 9. ALARA •The recommendation that standard-setting committees would like to make for personnel protection is zero exposure •Taking into account: Social, Technical, Economic, Practical, and Public policy considerations •NCRP 116 ALARA Guidance: Justification The need to justify radiation dose on the basis of benefit Optimization the need to ensure that the benefits are maximized Limitation the need to apply dose limits
  10. 10. Six fundamental principle should be considered  Eliminate or reduce the source of radiation,  Contain the source,  Minimize time in a radiation field,  Maximize distance from a radioactive source,  Use radiation shielding, and  Optimize resources. Hierarchy of Controls • Engineered Controls • Administrative controls • Personnel protective measures
  11. 11. NIRL (Negligible Individual Risk Level ) : •A level of average annual excess risk of fatal health effects attributable to irradiation, below which further effort to reduce radiation exposure to the individual is unwarranted •NIRL should not be thought of as an acceptable risk level, a level of significance, or a limit ,nor should it be the goal of ALARA, although it does provide a lower limit for application of the ALARA process.
  12. 12. Principle of radiation protection. Dose received by individuals depends on 1. Time : Dose = Dose Rate X Time 2. Distance : The Inverse Square Law i.e Dose ∞ 1/distance2 3. Shielding: Choice of shielding material and thickness depends on the energy and intensity of the beam Half Value Thickness (HVT): Thickness of a specified material which reduces the intensity of radiation to one half. I = I0e -µt, I0 (R/min) →Incident intensity I (R/min)→transmitted intensity, µ→attenuation coefficient
  13. 13. Tenth Value Thickness (TVT)  The thickness of the shielding material which reduces the intensity to one tenth of its original value is called TVT of the material for photon beam  TVT reduce intensity by a factor 1/10n  1 TVT = 3.3 HVT Thicknesses Of Some Materials, That Reduce Gamma Ray Intensity By 50% (1/2) Include Material Halving Thickness, [inches] Halving Thickness, [cm] Density, [g/cm³] Halving Mass, [g/cm²] Lead 0.4 1.0 11.3 12 Steel 0.99 2.5 7.86 20 Concrete 2.4 6.1 3.33 20 Packed soil 3.6 9.1 1.99 18 Water 7.2 18 1.00 18 Lumber or other wood 11 29 0.56 16 Air 6000 15 000 0.0012 18
  14. 14. Structural Shielding Design •For protection calculations, the dose-equivalent limit is assumed to be 0.1 rem/week for the controlled areas and 0.01 rem/week for the noncontrolled areas. These values approximately correspond to the annual limits of 5 rem/year and 0.5 rem/year, respectively. •Protection is required against three types of radiation: Primary Radiation, Scattered Radiation Leakage Radiation . •Primary Barrier : sufficient to attenuate the useful beam to the required degree. • Secondary Barrier : against stray radiation (leakage and scatter).
  15. 15. BARRIER THICKNESS DEPENDS ON: 1 . Workload (W): terms of weekly dose delivered at 1 m from the source 2. Use Factor (U): Fraction of the operating time during which the radiation under consideration is directed toward a particular barrier 3. Occupancy Factor (T): Fraction of the operating time during which the area of interest is occupied by the individual 4 .Distance (d): Distance in meters from the radiation source to the area to be protected. Inverse square law is assumed for both the primary and stray radiation.
  16. 16. A. Primary Radiation Barrier: P: maximum permissible dose equivalent for the area to be protected(e.g., 0.1 rad/week for controlled and 0.01 rad/week for non controlled area) B : Transmission factor for the barrier to reduce the primary beam dose to P in the area of interest For megavoltage x- and γ radiation, equivalent thickness of various materials can be calculated by comparing tenth value layers (TVLs) for the given beam energy
  17. 17. B. Secondary Barrier for Scattered Radiation: The amount of scattered radiation depends on: 1. the beam intensity incident on the scatterer 2. the quality of radiation 3. the area of the beam at the scatterer 4. the scattering angle α : fractional scatter at 1 m from the scatterer, for beam area of 400 cm2 incident at the scatterer Bs : Transmission factor for scattered radiation δ′ : The distance from the scatterer to the area of interest F : area of the beam incident at the scatterer
  18. 18. C. Secondary Barrier for Leakage Radiation •5 to 50 kVp: The leakage exposure rate4 shall not exceed 0.1 R in any 1 hour at any point 5 cm from the source assembly. •Greater than 50 kVp and less than 500 kVp.: The leakage exposure rate at a distance of 1 m from the source shall not exceed 1 R in any 1 hour •Greater than 500 kVp: The leakage dose rate from the source assembly at any point at a distance of 1 m from the electron path between the source and the target shall not exceed 0.5% •Cobalt teletherapy: Beam in the “off” position shall not exceed 2 mrad/h on the average and 10 mrad/h at a distance of 1 m from the source. Beam in the “on” position, the leakage dose rate from the source housing shall not exceed 0.1% at a distance of 1 m from the source.
  19. 19. D. Door Shielding • Require a motor drive as well as a means of manual operation in case of emergency •With a proper maze design, the door is exposed mainly to the multiply scattered radiation of significantly reduced intensity and energy •In most cases, the required shielding turns out to be less than 6 mm of lead.
  20. 20. Ionising Radiations Regulations(IRR99) Designation of areas Controlled areas Supervised Area Uncontrolled Area •For protection calculations, the dose-equivalent limit is assumed to be 0.1 rem/week for the controlled areas (5 rem/year )and 0.01 rem/week for the noncontrolled areas. (0.5 rem/year ).
  21. 21. Controlled areas  Areas where a person is likely to receive an effective whole      body dose of more than 6mSv per year or where there is significant risk of spreading contamination outside the work area. Must be physically demarcated Must have suitable signage Local rules should be drawn up Radiation Protection Supervisor appointed Environmental and personal monitoring should take place
  22. 22. Supervised areas  Any area where the conditions need to be kept under review  Any person is likely to receive an effective dose >1mSv/y or > than 1/10 of any other dose limit.  It does not automatically follow that outside every controlled area there will be a supervised area. Uncontrolled Areas •All other areas in the hospital or clinic and the surrounding environment • Uncontrolled areas are those occupied by individuals such as patients, visitors to the facility, and employees who do not work routinely with or around radiation sources. • Areas adjacent to but not part of the x-ray facility is also uncontrolled areas.
  23. 23. Instruments for detecting and measuring radiation  Level of radioactive contamination  Radiation dose rate in area  Identity and quantity of radioactive material  Accumulated dose to individuals in area Survey meters Laboratory counters Personnel dosimeters - 27
  24. 24. CONTD……  Survey meters • • • Geiger-Mueller (GM) instruments Ionization chamber instruments Scintilation instruments  Laboratory counters  Personnel dosimeters • Photographic film dosimeters (Film Badges) • Thermoluminescent dosimeters • Pocket dosimeters
  25. 25. Survey Meters Survey meters are used to determine the extend of possible contaminations. Most frequently used is the Geiger-Miller (GM) meter, which are based on the ionization effects of radiation in gas. The radiation is completely absorbed in the counter gas, creates a charged particles which are collected in the field of the applied voltage and converted to an electrical pulse. The number of pulses corresponds to the number of absorbed particles, but is independent from the applied collection voltage. Therefore the GM detector is used for measuring the rate of the radiation not the absorbed dose (energy).
  26. 26. CD V-715 Civil Defense High-Range Survey Meter 0-500 R/hr range 3.25 pounds, die cast aluminum and drawn steel case, watertight, will float. Powered with one D-sized battery, continuously for 150 hours, longer if on intermittent basis. Instrument accuracy on any of its four ranges is within +- 20% of true dose rate. Accuracy maintained throughout temperature ranges of 20 F to +125 F, relative humidities to 100% and altitudes up to 25,000'.
  27. 27. PERSONAL MONITORING DEVICES 1.Radiation film badges are composed of two pieces of film, covered by light tight paper in a compact plastic container. Various filters in the badge holder allow areas to be restricted to X-ray, -ray, -rays only. For -radiation the sensitivity is in the range of 10 - 1800 mrem. For -radiation the sensitivity is in the range of 50 - 1000 mrem. 2.Pocket dosimeter The pocket dosimeter or pen dosimeter is a common small sized ion chamber which measures the originated charge by direct collection on a quartz fiber electroscope.
  28. 28. THERMOLUMINESCENT DOSIMETER(TLD) TLD is the primary form of personnel radiation monitoring dosimeter.  Thermoluminescent dosimeters make use of the property of certain materials which absorb energy when exposed to X , Gamma or Beta radiation  On heating, the absorbed energy is released in the form of visible light. A plot of light intensity emitted against temperature is known as a glow curve.  For a given heating rate, the temperature at which the maximum light emission occurs, is called the glow-peak temperature and it is characteristic, of the individual TL material (also called phosphor)  The quantity of the visible light emitted (TL output) is found to be proportional to the energy absorbed by the TL material.  The estimation of radiation exposure may be based either on the height of the glow curve (differential method) or the area under the glow curve (integral method).
  29. 29. CONTD………… •The TLD personnel monitoring system essentially consists of two major parts: TLD badge and the TLD badge reader. •The TLD Badge Reader comprises of a plastic cassette containing three Teflon TLD discs (13.3mm and 0.8mm thick) that are mechanically clipped on to circular holes (12.0mm) punched in an aluminium card (52 x 30 x 1mm). •Materials : calcium fluoride, Lithium fluoride calcium sulfate lithium borate calcium borate, potassium bromide Feldspar
  30. 30. •Three CaSO4: Dy Teflon TLD discs are mechanically clipped on an Alluminium plate. An asymmetric “V” cut is provided in the card to ensure its loading in the plastic cassette TLD CARD Dimensions of A1 card: 52.5 mm X 30.0 mm X 1.0 mm Hole on A1 Plate : 12.0 mm dia Dimensions of TLD Disc : 13.3 mm dia Three well-defined regions in the plastic cassette / holder corresponding to three TLD discs of the TLD card. i. Disc D1- sandwiched between a pair of filter combination of 1.0mm thick Cu (Copper filter nearer to the disc). ii. Disc D2- sandwitched between a pair of 1.6mm thick (180mg/cm2) plastic filters and iii. Disc D3- under a circular open window.
  31. 31. TLD CASSETTE DIMENSIONS In this design of the TLD cassette, dimension of some of the filters was altered and crocodile clip was replaced by a smaller size clip. The cassette was made of ABS plastic (white) and filters were embedded into the plastic body. Dimensions : Main Body : Cu filter (rectangular) : 32 mm x 16 mm x 1mm A1 filter (circular) : 13.6 mm x thickness – 0.6 mm Plastic filter (rectangular) : 30.5 mm x 21 mm x 1.6 mm Open window : Dia – 14.5 mm Slider part : Cu filter (rectangular) : Dia – 15.6 mm, x thickness – 1 mm A1 filter (circular) : Dia – 12.6 mm, x thickness – 0.6 mm Plastic filter (rectangular) : Dia – 25 mm, x thickness – 1.5 mm Open window : Dia – 13.5 mm
  32. 32.  There are two types of TLD badges/ cassettes in use namely, 1. Chest Badge for whole body monitoring and 2. Wrist Badge  For extremity dosimetryAccuracy of measurement is about ± 20%.  TLD provides to us by BARC measures doses due to X-rays, gamma rays and beta rays.  It can be reused.  Disadvantage → it is not a permanent record, once heated for measurement, it lost all its data that recorded during radiation exposure.
  33. 33. Personal radiation monitoring device(prmd) http://www.epa.sa.gov.au/xstd_files/Radiation/Guideline/guide_prmd.pdf
  34. 34. Personal Protective Equipment (PPE) in Radiation Emergencies •In a radiation emergency, the choice of appropriate personal protective equipment (PPE) depends on •Response role and specific tasks •Risk of contamination •PPE can protect against •External contamination •Internal contamination via inhalation, ingestion, absorption through open wounds •Other physical hazards (e.g., debris, fire/heat, or chemicals) •PPE should include a personal radiation dosimeter whenever there is concern about exposure to penetrating ionizing radiation. •Direct-reading dosimeters should be worn so that a worker can easily see the read-out and/or hear warning alarms. •Recommended respiratory PPE includes a full-face piece air purifying respirator with a P-100 or High Efficiency Particulate Air (HEPA) filter3.
  35. 35. RADIATION SAFETY OFFICER (RSO) Responsibility : 1. Recommending or approving corrective actions, 2. Identifying radiation safety problems, 3. Initiating action, and ensuring compliance with regulation 4. Assisting the Radiation Safety Committee Duties : •Annual review of the radiation safety program for adherence to ALARA concepts. •Quarterly review of occupational exposures. •Quarterly review of records of radiation level surveys. •Educational Responsibility •Briefings and educational sessions to inform workers of ALARA programs. •The RSO will ensure that authorized users, workers, and ancillary personnel who may be exposed to radiation will be instructed in the ALARA philosophy •Establishment of investigational levels in order to monitor individual occupational external radiation exposures
  36. 36. Regulations that govern the use of cobalt-60 as teletherapy 1. Maintenance and repair 2. License amendments 3. Safety instructions 4. Safety precautions 5. Dosimetry equipment 6. Full calibration 7. Periodic spot checks 8. Radiation surveys 9. Five-year inspection
  37. 37. Protection for the Cobalt room  Treatment room must be equipped with a radiation monitor which should be clearly visible from the door  CCTV : Monitor the patient movement during treatment.  Interlock should be provided at the door  Emergency switches must be provided
  38. 38. In Case of radiation emergency: SOURCE DRAWER T-BAR  When yellow colored portion of the T – bar entirely inside the head cover, the source is in the fully shielded position.  If the amber colored portion of the T-bar is visible and the red colored portion is entirely inside the cover, radiation fields can be considered as safe.
  39. 39. RESPONSIBILITIES OF RADIATION SAFETY OFFICER IN CASE OF ACUTE EMERGENCY  To check radiation level in the maze area with Survey meter.  If the red tip of the source drawer position indicator rod is visible, high radiation fields will be present.  To take T-bar, from its location, enter room but avoid exposures to the treatment beam.  Insert the end of the T-bar over the red indicator rod through the head cover.  Apply firm pressure to the T-bar and push the source back into the fully shielded position. Insert the locking pin.
  40. 40. Radiation safety in HDR Remote after loading unit  Source safe (container) in HDR unit  Source movement and drive system  Manual retraction of sources  Emergency safe container  Source transfer container
  41. 41. In Treatment Room (HDR)  The radiation monitor( Zone monitor)  CCTV to monitor patient during treatment  Intercom system to communicate with the patient  Electrical interlocks at the entrance.  Portable shield / area monitor  Emergency stop motor / battery back up  Manual retraction hand crank  Posted emergency procedures
  42. 42. Summary of Atomic Energy Act 1962  Atomic Energy Act promulgated in 1962 by Central Government.  Power to control over radioactive substances or radiation generating plant in order to prevent radiation hazards and safety of radiation workers and public.  Power to inspect to ensure compliance of the act and rules made their under.  Power to appoint competent authority  Power to make rules. Under section 27 of the Atomic Energy Act. 1962, Atomic Energy Regulatory Board (AERB) was constituted on November 15, 1983 to carry out certain regulatory and safety functions envisaged under section 16, 17 and 23 of the Atomic Energy Act 1962.
  43. 43. Functions of AERB  Develop safety codes, guides, and standards  Review operational experience in the light of the radiological and other safety criteria recommended by International bodies and evolve major safety policies.  Prescribe acceptable limits of radiation exposure.  Review the emergency preparedness plans • • • Promote research and development. Prescribe the syllabi for training of personnel. Enforce rules and regulations promulgated under the Atomic Energy Act, 1962 for radiation safety in the country. • Maintain legislation with statutory bodies in the country as well as abroad regarding safety matters. • To keep the public informed on major issues of radiological safety significance.
  44. 44. THANK YOU