An toàn bức xạ trong Xquang (Radiation protection)

Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Sources of Exposure to Ionizing Radiation Naturally Occurring Radiation Sources Radiation Protection – Chapter 23, Bushberg Kalpana Kanal, Ph.D., DABR Lecturer, Diagnostic Physics Dept of Radiology UWMC, HMC, SCCA ¬ Annual average total effective dose from exposure to ionizing radiation in USA is approximately 3.6 mSv or 360 mrem [National Council on Radiation Protection and Measurement (NCRP)] ¬ mSv or 300 mrem (80%) is from naturally occurring sources ¬ Radon ¬ Internal radiation ¬ Terrestrial radioactivity ¬ Cosmic radiation a copy of this lecture may be found at: http://courses.washington.edu/radxphys/PhysicsCourse04http://courses.washington.edu/radxphys/PhysicsCourse04-05.html c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 748 Kalpana M Kanal, Ph.D., DABR Sources of Exposure to Ionizing Radiation Naturally Occurring Radiation Sources Sources of Exposure to Ionizing Radiation Naturally Occurring Radiation Sources ¬ ¬ Radon ¬ Biggest contributor to natural background (2 (2 mSv or 200 mrem/year) mrem/year) ¬ Radon (Rn(Rn-222) is a radioactive gas formed during the decay of radium ¬ Radium is a decay product of uranium found in the soil and has a halfhalf-life of 1620 years ¬ Radon is an alpha emitter with a halfhalf-life of approx days Radon ¬ The progeny of radon are also radioactive, attach to aerosols and are deposited in the lungs ¬ Bronchial mucosa is irradiated inducing bronchogenic cancer ¬ ¬ Average concentration of radon outdoors is 44-8 Bq/m3 (0.1(0.1-0.2 pCi/L) Indoors is 40 Bq/m3 (1 pCi/L) ¬ Remedial action recommended in excess of 160 Bq/m3 (4 pCi/L) c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 748 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Sources of Exposure to Ionizing Radiation Naturally Occurring Radiation Sources ¬ Sources of Exposure to Ionizing Radiation Naturally Occurring Radiation Sources Internal Radiation ¬ Second largest source of natural background radiation (0.4 (0.4 mSv or 40 mrem/year) ¬ Ingestion of food and water containing primordial radionuclides ¬ K-40 is most significant ¬ Skeletal muscle has the highest concentration of potassium in the body ¬ Terrestrial or External Radiation ¬ Terrestrial radioactive materials that have been present on earth since its formation are called primordial radionuclides ¬ ¬ External radiation exposure, inhalation, ingestion 0.28 mSv or 28 mrem/year (∼ 0.3 mSv or 30 mrem/year) c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 748 c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 748 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR Sources of Exposure to Ionizing Radiation Naturally Occurring Radiation Sources ¬ Sources of Exposure to Ionizing Radiation Naturally Occurring Radiation Sources Cosmic Radiation ¬ Cosmic rays are energetic protons and alpha particles which originate in galaxies ¬ Most cosmic rays interact with the atmosphere, with fewer than 0.05% reaching sea level ¬ 0.27 mSv or 27 mrem/year (∼ 0.3 mSv or 30 mrem/year) ¬ c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 748 c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 748 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR Cosmic Radiation ¬ Exposures increase with altitude approx doubling every 1500 m as there is less atmosphere to attenuate the cosmic radiation ¬ Leadville, Colorado at 3200 m, 1.25 mSv/year ¬ More at poles than equator Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Sources of Exposure to Ionizing Radiation Technology Based Radiation Sources Sources of Exposure to Ionizing Radiation Naturally Occurring Radiation Sources ¬ 60 mrem or 0.6 mSv ¬ Cosmic Radiation ¬ Air travel can add to individual’s cosmic exposure ¬ Airline crews and frequent fliers receive an additional ∼1 mSv ¬ hour transcontinental flight will result in an equivalent dose of ∼25 µSv or 2.5 mrem ¬ Apollo astronauts – 2.75 mSv or 275 mrem during a lunar mission CT and fluoroscopy are highest contributors to medical x-rays ¬ → → → ← c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 744 c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 748 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 10 Occupational Exposures Collective Effective Dose Equivalent ¬ ¬ The product of the average effective dose equivalent and the size size of the exposed population is the collective effective dose equivalent Expressed in personperson-sieverts (person(person-Sv or personperson-rem) → mSv for diagnostic radiology is lower than expected because it includes personnel who receive very small occupational exposures ¬ 15 mSv or more are typical of special procedures utilizing fluoroscopy and cine ¬ c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 745 c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 746 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 11 Kalpana M Kanal, Ph.D., DABR 12 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Genetically Significant Dose (GSD) ¬ The genetically significant equivalent dose (GSD) is a dose parameter that is an index of potential genetic damage ¬ The GSD is defined as that equivalent dose that, if received by every member of the population, would be expected to produce the same genetic injury to the population as the actual doses received by the irradiated individuals ¬ GSD is determined by taking the equivalent dose to the gonads of each exposed individual and estimating the number of children expected expected for a person of that age and sex Genetically Significant Dose (GSD) ← → c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 747 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 13 14 Summary ¬ Summary The average annual effective dose equivalent to the US population population from all radiation sources is 3.6 mSv/year or 360 mrem/year ¬ mSv/year – naturally occurring sources ¬ Radon – mSv ¬ 0.6 mSv/year – technologically enhanced sources ¬ Medical xx-rays – 0.39 mSv or 39 mrem, ¬ Nuclear Medicine – 0.14 mSv or 14 mrem Kalpana M Kanal, Ph.D., DABR Collective effective dose equivalent (person(person-Sv or personperson-rem) ¬ Product of the average effective dose equivalent and the size of the exposed population ¬ GSD (mSv or mrem) ¬ Used to express genetic risk to the whole population from a source of radiation exposure ¬ GSD from diagnostic xx-rays is 0.2 mSv or 20 mrem ¬ GSD from nuclear medicine is 0.02 mSv or mrem Kalpana M Kanal, Ph.D., DABR 15 Kalpana M Kanal, Ph.D., DABR ¬ 16 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Raphex 2002 General Question Question ¬ G87 The annual average natural background radiation dose to members of the public in the United States, excluding radon, is approximately mrem ¬ A 10 B 50 C 100 D 200 E 400 ¬ ¬ ¬ ¬ ¬ The Genetically significant dose (GSD) for diagnostic xx-rays and nuclear medicine in the US is: ¬ A mSv and 0.20 mSv B 0.20 mSv and mSv C 0.02 mSv and 0.20 mSv D 0.20 mSv and 0.02 mSv ¬ ¬ ¬ Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 17 18 Personnel Dosimetry Film Badges Personnel Dosimetry Film Badges c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 749 ¬ ¬ ¬ ¬ ¬ ¬ A film pack (A) consists of a black envelope (B) containing film (C) placed inside a special plastic film holder (D) Using metal filters typically lead (G), copper (H) and aluminum (I), the relative optical densities of the film underneath the filters can be used to identify the general energy range of the radiation and allow for the conversion conversion of the film dose to tissue dose Open window (J) where film is not covered by a filter or plastic and is used to detect medium and highhigh-energy beta radiation ¬ ¬ ¬ Kalpana M Kanal, Ph.D., DABR Generally placed at waist level or shirtshirt-pocket level For fluoroscopy, placed at collar level outside the lead apron to to measure radiation dose to thyroid and lens of eye Pregnant radiation workers typically wear a second badge at waist waist level (behind the lead apron, if used) to assess the fetal dose Excessive moisture or heat will damage film inside badge Kalpana M Kanal, Ph.D., DABR 19 Kalpana M Kanal, Ph.D., DABR Most film badges can record doses from about 100 µGy to 15 Gy (10 mrad to 1500 rad) for photons and from 500 µGy to 10 Gy (50 mrad to 1,000 rad) for beta radiation The dosimetry report lists the “shallow” equivalent dose, corresponding corresponding to the skin dose, and the “deep” equivalent dose, corresponding to penetrating penetrating radiation 20 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Personnel Dosimetry Thermoluminescent (TLD) Dosimeters ¬ ¬ ¬ Personnel Dosimetry Thermoluminescent (TLD) Dosimeters TLD is a dosimeter in which consists of a scintillator in which electrons become trapped in excited states after interactions with ionizing ionizing radiation ¬ If the scintillator is later heated, the electrons can then fall to their ground state with the emission of light Thermoluminescent (TL) means emitting light when heated ¬ ¬ The amount of light emitted by the TLD is proportional to the amount amount of energy absorbed by the TLD ¬ After TLD has been read, it may be baked in an oven and reused ¬ Kalpana M Kanal, Ph.D., DABR Lithium Fluoride (LiF) is one of the most useful TLD materials LiF TLDs have a wide dose response range of 10 µSv to 103 mSv (1 mrem to 105 rem) Used in nuclear medicine to record extremity exposures Kalpana M Kanal, Ph.D., DABR 21 22 Personnel Dosimetry Pocket Dosimeters Personnel Dosimetry Optically Stimulated Luminescent (OSL) Dosimeters ¬ ¬ ¬ ¬ ¬ The principle of OSL is similar to TLDs except that the light emission emission is stimulated by a laser light instead of heat Crystalline aluminum oxide activated with carbon (Al2O3:C) is commonly commonly used Broad dose response range like TLDs They can be reread several times ¬ ¬ ¬ Major disadvantage to film and TLD dosimeters is that the accumulated exposure is not immediately indicated Pocket dosimeters measure radiation exposure, which can be read instantaneously Can measure exposures from to 200 mR or to R Analog or digital c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 752 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 23 Kalpana M Kanal, Ph.D., DABR 24 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Summary Raphex 2002 General Questions ¬ G95 Film badges: ¬ A Can measure only the total dose of radiation, but cannot distinguish between low and high energy xx-rays B Can measure exposures of mR C Are insensitive to heat D Use the optical density of the film to measure dose ¬ ¬ ¬ c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 753 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 25 26 Radiation Detection Equipment In Radiation Safety Radiation Protection and Exposure Control ¬ ¬ GeigerGeiger-Mueller Survey Instruments ¬ Measurements are in counts per minute (cpm) ¬ Surveys radioactive contamination in nuclear medicine ¬ Are extremely sensitive to charged particulate radiations with sufficient sufficient energy to penetrate the survey meter window ¬ Are relatively insensitive to xx- and gamma radiations ¬ Portable Ionization Chambers ¬ Used when accurate measurements of radiation exposure are required, required, measurement of xx-ray machine outputs ¬ Measure mR/hr to 500 R/hr Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 27 Kalpana M Kanal, Ph.D., DABR There are four principal methods by which radiation exposures to persons can be minimized: time, distance, shielding and contamination control control ¬ Time ¬ reducing time spend near a radiation source ¬ Distance ¬ inverse square law ¬ For diagnostic xx-rays, a good rule of thumb is that at m from a patient at 90 degrees to the incident beam, the radiation intensity is 0.1% to 0.15% (0.001 to 0.0015) of the intensity of the beam incident upon the patient for a 400 cm2 area field area ¬ The NCRP recommends that personnel should stand at least m from the xx-ray tube and the patient and behind a shielded barrier or out of the room, whenever possible 28 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Radiation Protection and Exposure Control Shielding ¬ ¬ Radiation Protection and Exposure Control Shielding Shielding is used to reduce exposure to patients, staff and the public Shielding against primary (focal spot), scattered (patient) and leakage (x (x-ray tube housing, limited to 100 mR/hr at m from housing) housing) radiation ¬ Shielding calculations depend on: ¬ radiation exposure level (mR/week) depends on techniques and patient load ¬ workload (amount of xx-rays produced per week), W (mA.min/week) ¬ Kalpana M Kanal, Ph.D., DABR use factor, U, U, indicates the fraction of time during which the radiation under consideration is directed at a particular barrier ¬ a wall that intercepts the primary beam is called a primary barrier barrier and is assigned a use factor according to typical room use ¬ U ranges between and 1, secondary barriers have a use factor of of Kalpana M Kanal, Ph.D., DABR 29 30 Radiation Protection and Exposure Control Shielding ¬ Radiation Protection and Exposure Control Shielding Shielding calculations depend on: ¬ occupancy factor, T, indicates the fraction of time during a week that a single individual might spend in an adjacent area ¬ T = for full occupancy (work areas, offices etc.) ¬ T = 1/4 for partial occupancy (corridors, rest rooms etc.) ¬ T = 1/16 for occasional occupancy (waiting rooms, toilets, etc.) ¬ Distance, d, d, measured from source of radiation to the area to be protected Kalpana M Kanal, Ph.D., DABR Shielding calculations determine the thickness of an attenuating material required to reduce radiation exposure to acceptable levels ¬ mSv/year or 100 mrem/year (2 mR/week) for nonnon-occupational personnel (members of public and nonnon-radiation workers) ¬ 0.1 or 10 mR/week for controlled areas Kalpana M Kanal, Ph.D., DABR 31 Kalpana M Kanal, Ph.D., DABR ¬ 32 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Radiation Protection and Exposure Control Shielding Radiation Protection and Exposure Control ¬ ¬ ¬ ¬ ¬ Lead usually used for shielding and specified as weight per square square foot (lb/ft2) Typically lb/ft2 (0.8 mm or 1/32th inch) or lb/ft2 (1.6 mm or 1/16th inch) is sufficient for diagnostic radiology Calculated using HVL and TVL of the material [(1/2)n – reduction in beam intensity, n is HVL] ¬ ¬ CT scanner shielding Personnel protection in Dx Radiology (lead aprons, thyroid shields shields etc., pg 771 of Bushberg) Shielding in nuclear medicine Shielding material used from base of floor to a height of feet Acrylic, leaded glass, gypsum drywall, steel are other materials used besides lead for shielding Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 33 Radiation Protection and Exposure Control Protection of the Patient in Medical XX-ray Imaging ¬ Radiation Protection and Exposure Control Protection of the Patient in Medical XX-ray Imaging Tube Voltage and Beam Filtration ¬ Achieve an optimal balance between image quality and dose to the patient ¬ Patient exposure can be reduced by using a higher kVp ad lower mAs mAs ¬ Increasing kVp increases transmission (less absorption) of xx-rays through the patient ¬ Even though mR/mAs increases as kVp increases, an accompanying reduction in mAs will decrease the incident exposure exposure to the patient ¬ Contrast will decrease due to higher effective energy of the xx-ray beam ¬ Kalpana M Kanal, Ph.D., DABR Tube Voltage and Beam Filtration ¬ Filtration of the polychromatic xx-ray energy spectrum can significantly reduce exposure by selectively attenuating the lowlow-energy xx-rays in the beam ¬ As the tube filtration increases, the beam becomes hardened (effective (effective energy increases) and dose to patient decreases because fewer low lowenergy photons are in the incident beam ¬ The amount of filtration that can be added is limited by the increased increased demands on tube loading to offset reduction in tube output, and the decreased contrast due to excessive beam hardening ¬ Quality of xx-ray beam is assessed by measuring the HVL Kalpana M Kanal, Ph.D., DABR 35 Kalpana M Kanal, Ph.D., DABR 34 36 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Radiation Protection and Exposure Control Protection of the Patient in Medical XX-ray Imaging ¬ Radiation Protection and Exposure Control Protection of the Patient in Medical XX-ray Imaging Field Area, Organ Shielding and Geometry ¬ Reducing field size limits the patient volume exposed to primary beam, reduces the amount of scatter and thus radiation dose to adjacent adjacent organs (scatter being reduced improves image contrast) ¬ Gonadal shielding can be used to protect the gonads from primary radiation when the shadow of the shield does not interfere with the anatomy under investigation ¬ Increasing sourcesource-toto-object distance (SOD) and sourcesource-toto-image distance (SID) helps reduce dose (patient volume exposed decreased decreased due to reduced beam divergence) ¬ For fixed SID (C(C-arm fluoro system), patient dose is reduced by increasing the SOD as much as possible ¬ A minimum patient to focal spot distance of 20 cm is required ¬ X-Ray Image Receptors ¬ The speed of the image receptor determines the number of xx-ray photons and thus the patient dose necessary to achieve an appropriate appropriate signal level ¬ Higher speed system requires less exposure to produce the same optical density and thus reduces dose to patient ¬ Either a faster screen (reduced spatial resolution) or faster film film (increased quantum mottle) will reduce the incident exposure to the patient Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 37 Radiation Protection and Exposure Control Protection of the Patient in Medical XX-ray Imaging ¬ 38 Radiation Protection and Exposure Control Protection of the Patient in Medical XX-ray Imaging X-Ray Image Receptors ¬ Computed Radiography (CR) devices have a wide dynamic range so they compensate to some degree for underunder- and overexposure and can reduce retakes ¬ CR roughly equivalent to 200 speed screenscreen-film systems ¬ Techniques for extremities with CR devices should be used at higher higher exposure levels while exposures for pediatric patients should be used at increased speed (e.g 400 speed) to reduce dose ¬ Computed Tomography (CT) ¬ Reduce mAs and perhaps kVp for thinner and pediatric patients ¬ Modern MSCT scanners – dose modulation, mA changes with patient size c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 779 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 39 Kalpana M Kanal, Ph.D., DABR 40 10 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Radiation Protection and Exposure Control Protection of the Patient in Medical XX-ray Imaging ¬ Summary Miscellaneous Considerations ¬ Careful identification of patients ¬ Determination of pregnancy status ¬ Eliminate screening exams that only rarely detect pathology ¬ “yearly” dental exams may not be appropriate for all patients ¬ Use of high speed dental film reduces dose ¬ “yearly” screening mammography exams not appropriate for women younger than 35 to 40 years old ¬ Technique errors and high repeat rates can be avoided by posting technique charts and using phototiming ¬ Good quality control program to eliminate equipment and processor processor problems ¬ ¬ ¬ ¬ ¬ Time, distance and shielding used to protect persons from radiation radiation exposure Shielding calculations depend on mR/week, workload, use factor, occupancy factor and distance from xx-ray source Typically or lb/ft2 lead is sufficient for shielding in diagnostic radiology Calculated using HVL and TVL of the material [(1/2)n – reduction in beam intensity, n is HVL] Protect patient by adjusting kVp, mAs, filtration, field size, geometry geometry and using organ shielding, using faster filmfilm-screen systems, eliminate screening chest and yearly dental exams Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 41 42 Raphex 2000 General Questions ¬ G92 A shielding design for a diagnostic or therapy installation, when there is no restriction on the beam direction, must: ¬ A Consider all walls as primary barriers B Assign all walls a use factor (U) of C Assign all areas adjacent to the installation an occupancy factor factor (T) of D Shield all areas to a radiation level of 0.1 rem per week E Shield such that adjacent areas will not receive instantaneous dose rates greater than mR/hr ¬ ¬ ¬ ¬ Raphex 2000 General Questions G93 The occupancy factor (T) is changed from 1/16 to 1/2 and the activity activity factor (A) is doubled for a radiation source whose HVL is 0.3 mm Pb In order to maintain the same level of protection, _ mm Pb must be added to the shielding ¬ A 0.3 B 0.6 C 0.9 D 1.2 E 1.5 ¬ ¬ ¬ ¬ ¬ Kalpana M Kanal, Ph.D., DABR The occupancy factor (T) is the fraction of time that the area is is occupied Since T is increased by a factor of and the activity (A) is doubled, doubled, the exposure is increased by a factor of 16 Thus, HVLs (24 = 16) of lead are required to maintain the same radiation level 0.3 mm x = 1.2 mm Pb Kalpana M Kanal, Ph.D., DABR 43 Kalpana M Kanal, Ph.D., DABR ¬ 44 11 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Regulatory Agencies and Radiation Exposure Limits ¬ ¬ ¬ Advisory Bodies U.S Nuclear Regulatory Commission (NRC (NRC)) regulates special nuclear material, source material, byby-product material of nuclear fission, regulates the maximum permissible dose equivalent limits ¬ Some states known as agreement states arrange with the NRC to self self-regulate medically related licensing and inspection requirements of radioactive materials Food and Drug Administration (FDA (FDA)) regulates radiopharmaceutical development, manufacturing, performance and radiation safety requirements associated with the production of commercial xx-ray equipment ¬ National Council on Radiation Protection and Measurements (NCRP (NCRP)) ¬ Collect, analyze, develop and disseminate, in the public interest, interest, information and recommendations about radiation protection, radiation radiation measurements, quantities and units ¬ International Commission on Radiological Protection (ICRP (ICRP)) ¬ Similar to NCRP, however its international membership brings to bear a variety of perspectives on radiation health issues ¬ The NCRP and ICRP have published over 200 monographs containing recommendations on a wide variety of radiation health issues that that serve as the reference documents from which many regulations are crafted U.S Department of Transportation (DOT (DOT)) regulates the transportation of radioactive materials Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 45 46 Summing internal and external doses ¬ ¬ ¬ Summing internal and external doses Dose from an internal exposure continues after the period of ingestion ingestion or inhalation, until the radioactivity is eliminated by radioactive decay or biologic removal The committed dose equivalent (H50,T) is the dose equivalent to a tissue or organ over the 50 years following the ingestion or inhalation of radioactivity ¬ To sum the internal and external doses to any individual tissue or organ, the deep dose equivalent (indicated by the dosimeter) and the committed dose equivalent to the organ are added ¬ The sum of the deep dose equivalent and the committed dose equivalent is called the total effective dose equivalent (TEDE (TEDE)) The committed effective dose equivalent (CEDE (CEDE)) is a weighted average of the committed dose equivalents to the various tissues and organs organs of the body ¬ CEDE = ∑wT H50,T Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 47 Kalpana M Kanal, Ph.D., DABR 48 12 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Dose Limits As Low As Reasonably Achievable (ALARA) Principle ¬ Dose limits to workers and the public are regarded as upper limits limits rather than as acceptable doses or thresholds of safety ¬ In addition to the dose limits, all licenses are required to employ employ good health physics practices and implement radiation safety programs to ensure ensure that radiation exposures are kept as low as reasonably achievable (ALARA), (ALARA), taking societal and economic factors into consideration ¬ The ALARA doctrine is the driving force for many of the policies, policies, procedures, and practices in radiation laboratories, and represents represents a commitment by both employee and employer to minimize radiation exposure to staff, the public, and the environment to the greatest greatest extent possible c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 791 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 49 50 Summary ¬ ¬ ¬ Raphex 2001 General Questions Regulatory agencies, advisory bodies and their functions Dose limits ¬ Occupational and public dose limits ¬ Organ limits ALARA principle ¬ G82 The annual recommended dose to the lens of the eye of a radiation worker is: ¬ A 500 mSv (50 rem) B 150 mSv (15 rem) C 50 mSv (5 rem) D mSv (500 mrem) E mSv (100 mrem) ¬ ¬ ¬ ¬ Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 51 Kalpana M Kanal, Ph.D., DABR 52 13 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Raphex 2000 General Questions ¬ G91 The NRC and state regulators require radiation monitoring of hospital staff in which categories? ¬ Anyone who regularly comes into the radiology department (e.g., (e.g., cleaning staff) Anyone who could receive a measurable exposure, but on an irregular basis (e.g., nurses who work in areas where "portable" films are taken) Workers who are likely to receive an occupational dose of between between 10 and 100 mrem per year Workers who are likely to receive an occupational dose of greater greater than 1,250 mrem per year Workers who have regular access to "high radiation areas.” areas.” ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ ¬ A 1, B 4, C 1, D 2, 3, E 1, 2, Raphex 2001 General Questions G83 The recommended weekly effective dose equivalent permitted for radiologists under current regulations is: ¬ A 10 mSv B 50 mSv C 100 mSv D 0.5 mSv E 1.0 mSv ¬ ¬ ¬ NRC requirements for monitoring call for a likelihood of the individual receiving more than 25% of the MPD and/or having access to areas where the radiation exposure rate could be greater than mSv (100 mrem) per hour at 30 cm from the radioactive sources or adjacent to walls shielding radiation producing equipment, i.e., a "highradiation area." ¬ Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 53 Kalpana M Kanal, Ph.D., DABR ¬ 54 14 [...]... tissues and organs organs of the body ¬ CEDE = ∑wT H50,T Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 47 Kalpana M Kanal, Ph.D., DABR 48 12 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg 5 Dose Limits 5 As Low As Reasonably Achievable (ALARA) Principle ¬ Dose limits to workers and the public are regarded as upper limits limits rather than as... the reference documents from which many regulations are crafted U.S Department of Transportation (DOT (DOT)) regulates the transportation of radioactive materials Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 45 46 5 Summing internal and external doses ¬ ¬ ¬ 5 Summing internal and external doses Dose from an internal exposure continues after the period of ingestion ingestion or inhalation,... younger than 35 to 40 years old ¬ Technique errors and high repeat rates can be avoided by posting technique charts and using phototiming ¬ Good quality control program to eliminate equipment and processor processor problems ¬ ¬ ¬ ¬ ¬ Time, distance and shielding used to protect persons from radiation radiation exposure Shielding calculations depend on mR/week, workload, use factor, occupancy factor and... public, and the environment to the greatest greatest extent possible c.f Bushberg, et al The Essential Physics of Medical Imaging, 2nd ed., p 791 Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 49 50 5 Summary ¬ ¬ ¬ Raphex 2001 General Questions Regulatory agencies, advisory bodies and their functions Dose limits ¬ Occupational and public dose limits ¬ Organ limits ALARA principle ¬ G82 The annual... Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 51 Kalpana M Kanal, Ph.D., DABR 52 13 Diagnostic Imaging Physics Course 10 February 2005 Radiation Protection – Chapter 23 Bushberg Raphex 2000 General Questions ¬ G91 The NRC and state regulators require radiation monitoring of hospital staff in which categories? ¬ 1 Anyone who regularly comes into the radiology department (e.g., (e.g., cleaning... of the individual receiving more than 25% of the MPD and/or having access to areas where the radiation exposure rate could be greater than 1 mSv (100 mrem) per hour at 30 cm from the radioactive sources or adjacent to walls shielding radiation producing equipment, i.e., a "highradiation area." ¬ Kalpana M Kanal, Ph.D., DABR Kalpana M Kanal, Ph.D., DABR 53 Kalpana M Kanal, Ph.D., DABR ¬ 54 14 ... radioactive materials Food and Drug Administration (FDA (FDA)) regulates radiopharmaceutical development, manufacturing, performance and radiation safety requirements associated with the production of commercial xx-ray equipment ¬ National Council on Radiation Protection and Measurements (NCRP (NCRP)) ¬ Collect, analyze, develop and disseminate, in the public interest, interest, information and recommendations... receive instantaneous dose rates greater than 2 mR/hr ¬ ¬ ¬ ¬ Raphex 2000 General Questions G93 The occupancy factor (T) is changed from 1/16 to 1/2 and the activity activity factor (A) is doubled for a radiation source whose HVL is 0.3 mm Pb In order to maintain the same level of protection, _ mm Pb must be added to the shielding ¬ A 0.3 B 0.6 C 0.9 D 1.2 E 1.5 ¬ ¬ ¬ ¬ ¬ Kalpana M Kanal, Ph.D.,... equivalent (H50,T) is the dose equivalent to a tissue or organ over the 50 years following the ingestion or inhalation of radioactivity ¬ To sum the internal and external doses to any individual tissue or organ, the deep dose equivalent (indicated by the dosimeter) and the committed dose equivalent to the organ are added ¬ The sum of the deep dose equivalent and the committed dose equivalent is called the total... distance from xx-ray source Typically 2 or 4 lb/ft2 lead is sufficient for shielding in diagnostic radiology Calculated using HVL and TVL of the material [(1/2)n – reduction in beam intensity, n is HVL] Protect patient by adjusting kVp, mAs, filtration, field size, geometry geometry and using organ shielding, using faster filmfilm-screen systems, eliminate screening chest and yearly dental exams Kalpana