Radiation Protection

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Radiation Protection

• Robert L. Metzger, Ph.D.

2
1. Sources of Exposure to Ionizing
RadiationNaturally Occurring Radiation Sources

• 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)
• 3 mSv or 300 mrem (80) is from naturally
  occurring sources
• Radon
• Internal radiation
• Terrestrial radioactivity
• Cosmic radiation

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 748.
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1. Sources of Exposure to Ionizing
RadiationNaturally Occurring Radiation Sources

• Radon
• Biggest contributor to natural background (2 mSv
  or 200 mrem/year)
• Radon (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 half-life of 1620 years
• Radon is an alpha emitter with a half-life of
  approx. 4 days

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 748.
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1. Sources of Exposure to Ionizing
RadiationNaturally Occurring Radiation Sources

• 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 4-8
  Bq/m3 (0.2-0.4 pCi/L)
• Indoors is 40 Bq/m3 (1 pCi/L)
• EPA Remedial action recommended in excess of 160
  Bq/m3 (4 pCi/L)

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1. Sources of Exposure to Ionizing
RadiationNaturally Occurring Radiation Sources

• Internal Radiation
• Second largest source of natural background
  radiation (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

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 748.
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1. Sources of Exposure to Ionizing
RadiationNaturally Occurring Radiation Sources

• 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.
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1. Sources of Exposure to Ionizing
RadiationNaturally 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.
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1. Sources of Exposure to Ionizing
RadiationNaturally Occurring Radiation Sources

• 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

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 748.
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1. Sources of Exposure to Ionizing
RadiationNaturally Occurring Radiation Sources

• Cosmic Radiation
• Air travel can add to individuals cosmic
  exposure
• Airline crews and frequent fliers receive an
  additional ?1 mSv
• 5 hour transcontinental flight will result in an
  equivalent dose of ?25 mSv or 2.5 mrem
• Apollo astronauts 2.75 mSv or 275 mrem during a
  lunar mission

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 748.
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Annual Dose Equivalent360 mrem
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Annual Dose - Other 1

• Occupational Dose 0.3
• Fallout - lt0.3
• Nuclear Fuel Cycle 0.1
• Miscellaneous 0.1
• Natural Sources Account for 82 of total annual
  dose with only 18 coming from man made sources.

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Natural Sources of Radiation

• The variation of dose from the cosmic and
  terrestrial radiation is large depending on the
  area of the country (see handout).
• High altitude areas have higher cosmic radiation
  levels (e.g. Denver, Flagstaff)
• Areas that are heavily mineralized have higher
  terrestrial radiation levels.
• Radon levels also vary significantly, but vary
  from home to home rather than whole geographic
  areas (e.g. Watras house)
• The overall variation in cosmic and terrestrial
  radiations exceed 100 mrem per year and affect
  everyone in a city/area (e.g. Denver)
• Cancer incidence does not follow the background
  radiation levels at all.

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Cancer Mortality in the US
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Legend for Mortality Data
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Sources of Exposure to Ionizing
RadiationTechnology Based Radiation Sources

• 60 mrem or 0.6 mSv
• 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.
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1. Occupational Exposures
?

• 1 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.
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1. Collective Effective Dose Equivalent

• The product of the average effective dose
  equivalent and the size of the exposed population
  is the collective effective dose equivalent
• Expressed in person-sieverts (person-Sv or
  person-rem) not used much anymore

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 746.
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1. 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 do 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 for a
  person of that age and sex

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1. Genetically Significant Dose (GSD)
?
?
?
?
c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 747.
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1. Summary

• The average annual effective dose equivalent to
  the US population from all radiation sources is
  3.6 mSv/year or 360 mrem/year
• 3 mSv/year naturally occurring sources
• Radon 2 mSv
• 0.6 mSv/year technologically enhanced sources
• Medical x-rays 0.39 mSv or 39 mrem,
• Nuclear Medicine 0.14 mSv or 14 mrem
• Data is from mid 80s. Current estimates are
  higher due to the increased use of CT. Recent
  estimates are 385 mrem with 85 mrem due to
  medical.

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1. Summary

• Collective effective dose equivalent (person-Sv
  or person-rem)
• Product of the average effective dose equivalent
  and the size of the exposed population (No longer
  used commonly)
• GSD (mSv or mrem)
• Used to express genetic risk to the whole
  population from a source of radiation exposure
• GSD from diagnostic x-rays is 0.2 mSv or 20 mrem
  
• GSD from nuclear medicine is 0.02 mSv or 2 mrem

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Raphex 2002 General 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

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Question

• 1. The Genetically significant dose (GSD) for
  diagnostic x-rays and nuclear medicine in the US
  is
• A. 2 mSv and 0.20 mSv
• B. 0.20 mSv and 2 mSv
• C. 0.02 mSv and 0.20 mSv
• D. 0.20 mSv and 0.02 mSv

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2. Personnel DosimetryFilm 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 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 high-energy beta radiation

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2. Personnel DosimetryFilm Badges

• Most film badges can record doses from about 100
  mGy to 15 Gy (10 mrad to 1500 rad) for photons
  and from 500 mGy to 10 Gy (50 mrad to 1,000 rad)
  for beta radiation
• The dosimetry report lists the shallow
  equivalent dose, corresponding to the skin dose,
  and the deep equivalent dose, corresponding to
  penetrating radiation
• Generally placed at waist level or shirt-pocket
  level
• For fluoroscopy, placed at collar level outside
  the lead apron to measure radiation dose to
  thyroid and lens of eye
• Pregnant radiation workers typically wear a
  second badge at waist level (behind the lead
  apron, if used) to assess the fetal dose
• Excessive moisture or heat will damage film
  inside badge

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2. Personnel DosimetryThermoluminescent (TLD)
Dosimeters

• TLD is a dosimeter in which consists of a
  scintillator in which electrons become trapped in
  excited states after interactions with 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 of energy absorbed by
  the TLD
• After TLD has been read, it may be baked in an
  oven and reused

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2. Personnel DosimetryThermoluminescent (TLD)
Dosimeters

• Lithium Fluoride (LiF) is one of the most useful
  TLD materials
• LiF TLDs have a wide dose response range of 10
  mSv to 103 mSv (1 mrem to 105 rem)
• Used in nuclear medicine to record extremity
  exposures

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2. Personnel DosimetryOptically Stimulated
Luminescent (OSL) Dosimeters

• The principle of OSL is similar to TLDs except
  that the light emission is stimulated by a laser
  light instead of heat
• Crystalline aluminum oxide activated with carbon
  (Al2O3C) is commonly used
• Broad dose response range like TLDs
• They can be reread several times

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2. Personnel DosimetryPocket Dosimeters

• 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 0 to 200 mR or 0 to 5
  R
• Analog or digital

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 752.
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2. Summary
c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 753.
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Raphex 2002 General Questions

• G95. Film badges
• A. Can measure only the total dose of radiation,
  but cannot distinguish between low and high
  energy x-rays.
• B. Can measure exposures of 1 mR.
• C. Are insensitive to heat.
• D. Use the optical density of the film to measure
  dose.

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3. Radiation Detection Equipment In Radiation
Safety

• Geiger-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 energy to penetrate
  the survey meter window
• Are relatively insensitive to x- and gamma
  radiations
• Portable Ionization Chambers
• Used when accurate measurements of radiation
  exposure are required, measurement of x-ray
  machine outputs
• Measure 1 mR/hr to 500 R/hr

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4. Radiation Protection and Exposure Control

• There are four principal methods by which
  radiation exposures to persons can be minimized
  time, distance, shielding and contamination
  control
• Time
• reducing time spend near a radiation source
• Distance
• inverse square law
• For diagnostic x-rays, a good rule of thumb is
  that at 1 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 2 m from the x-ray tube and the patient
  and behind a shielded barrier or out of the room,
  whenever possible

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4. Radiation Protection and Exposure
ControlShielding

• Shielding is used to reduce exposure to patients,
  staff and the public
• Shielding against primary (focal spot), scattered
  (patient) and leakage (x-ray tube housing,
  limited to 100 mR/hr at 1 m from housing)
  radiation

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Shielding NCRP 49 vs. 147

• The Bushberg X-Ray shielding section is based on
  NCRP 49 which is obsolete and out of print.
  Bushberg notes that it is badly out of date.
• NCRP 147 replaced NCRP 49 in 2005. It should be
  used for all shielding calculations.
• NCRP 147 uses a different methodology to
  calculate the shielding values and uses much more
  realistic values for occupancy, tube kVps, weekly
  mAs, and film/screen speeds.
• It eliminates the gross overshielding resulting
  from the use of NCRP 49 with the lowered
  non-occupational dose limits.
• NCRP 147 also provides shielding methodologies
  for CT and othr modalities.

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4. Radiation Protection and Exposure
ControlShielding

• Shielding calculations depend on
• radiation exposure level (mR/week) depends on
  techniques and patient load
• workload (amount of x-rays produced per week), W
  (mA.min/week)
• use factor, 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 and is assigned a use factor
  according to typical room use
• U ranges between 0 and 1, secondary barriers have
  a use factor of 1

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4. Radiation Protection and Exposure
ControlShielding

• 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 1 for full occupancy (work areas, offices
  etc.)
• T 1/5 for partial occupancy (corridors, rest
  rooms etc.)
• T 1/16 for occasional occupancy (waiting rooms,
  toilets, etc.)
• T 1/40th for landscaping, etc.
• Distance, d, measured from source of radiation to
  the area to be protected

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4. Radiation Protection and Exposure
ControlShielding

• Shielding calculations determine the thickness of
  an attenuating material required to reduce
  radiation exposure to acceptable levels
• 1 mSv/year or 100 mrem/year (2 mR/week) for
  non-occupational personnel (members of public and
  non-radiation workers)
• 0.1 or 10 mR/week for controlled areas (pregnant
  worker limit)

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4. Radiation Protection and Exposure
ControlShielding

• Lead usually used for shielding and specified as
  weight per square foot (lb/ft2). Typically 2
  lb/ft2 (0.8 mm or 1/32th inch) or 4 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
• Shielding material used from base of floor to a
  height of 7 feet
• Acrylic, leaded glass, gypsum drywall, steel are
  other materials used besides lead for shielding

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4. Radiation Protection and Exposure Control

• CT scanner shielding (Use NCRP 147 with web based
  scatter values)
• Personnel protection in Dx Radiology (lead
  aprons, thyroid shields etc., pg. 771 of
  Bushberg)
• Shielding in nuclear medicine
• Shielding in PET (Beware!) Undershielding in some
  clinics have led to high technologist and
  non-occupational doses. PET shielding guide from
  AAPM is not published as yet.

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4. Radiation Protection and Exposure
ControlProtection of the Patient in Medical
X-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
• Increasing kVp increases transmission (less
  absorption) of x-rays through the patient
• Even though mR/mAs increases as kVp increases, an
  accompanying reduction in mAs will decrease the
  incident exposure to the patient
• Contrast will decrease due to higher effective
  energy of the x-ray beam

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4. Radiation Protection and Exposure
ControlProtection of the Patient in Medical
X-ray Imaging

• Tube Voltage and Beam Filtration
• Filtration of the polychromatic x-ray energy
  spectrum can significantly reduce exposure by
  selectively attenuating the low-energy x-rays in
  the beam
• As the tube filtration increases, the beam
  becomes hardened (effective energy increases) and
  dose to patient decreases because fewer
  low-energy photons are in the incident beam
• The amount of filtration that can be added is
  limited by the increased demands on tube loading
  to offset reduction in tube output, and the
  decreased contrast due to excessive beam
  hardening
• Quality of x-ray beam is assessed by measuring
  the HVL

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Depth Dose

• Recall Dose Energy absorbed per gram.
• For soft radiations, the dose decreases
  dramatically with depth as the patients body
  attenuates the beam.
• The radiation dose at a given depth is the depth
  dose (rad).
• The exposure at skin entrance (ESE) is the
  Roentgen exposure at the point where the
  radiation enters the body.

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Depth Dose
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4. Radiation Protection and Exposure
ControlProtection of the Patient in Medical
X-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
  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 source-to-object distance (SOD) and
  source-to-image distance (SID) helps reduce dose
  (patient volume exposed decreased due to reduced
  beam divergence)
• For fixed SID (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

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4. Radiation Protection and Exposure
ControlProtection of the Patient in Medical
X-ray Imaging

• X-Ray Image Receptors
• The speed of the image receptor determines the
  number of x-ray photons and thus the patient dose
  necessary to achieve an 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 (increased quantum
  mottle) will reduce the incident exposure to the
  patient

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4. Radiation Protection and Exposure
ControlProtection of the Patient in Medical
X-ray Imaging

• X-Ray Image Receptors
• Computed Radiography (CR) devices have a wide
  dynamic range so they compensate to some degree
  for under- and overexposure and can reduce
  retakes
• CR roughly equivalent to 200 speed screen-film
  systems
• Techniques for extremities with CR devices should
  be used at higher exposure levels while exposures
  for pediatric patients should be used at
  increased speed (e.g. 400 speed) to reduce dose

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4. Radiation Protection and Exposure
ControlProtection of the Patient in Medical
X-ray Imaging

• Computed Tomography (CT)
• Reduce mAs and perhaps kVp for thinner and
  pediatric patients
• Pediatric protocols required in AZ.
• 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.
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4. Radiation Protection and Exposure
ControlProtection of the Patient in Medical
X-ray Imaging

• 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 problems

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4. Summary

• Time, distance and shielding used to protect
  persons from radiation exposure
• Shielding calculations depend on mR/week,
  workload, use factor, occupancy factor and
  distance from x-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 and using organ
  shielding, using faster film-screen systems,
  eliminate screening chest and yearly dental exams

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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 1.
• C. Assign all areas adjacent to the installation
  an occupancy factor (T) of 1.
• 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 2
  mR/hr.

52
Raphex 2000 General Questions

• G93. The occupancy factor (T) is changed from
  1/16 to 1/2 and the 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
• The occupancy factor (T) is the fraction of time
  that the area is occupied. Since T is increased
  by a factor of 8 and the activity (A) is doubled,
  the exposure is increased by a factor of 16.
  Thus, 4 HVLs (24 16) of lead are required to
  maintain the same radiation level. 0.3 mm x 4
  1.2 mm Pb.

53
5. Regulatory Agencies and Radiation Exposure
Limits

• U.S. Nuclear Regulatory Commission (NRC)
  regulates special nuclear material, source
  material, by-product material of nuclear fission,
  regulates the maximum permissible dose equivalent
  limits
• Some states known as agreement states arrange
  with the NRC to self-regulate medically related
  licensing and inspection requirements of
  radioactive materials
• Food and Drug Administration (FDA) regulates
  radiopharmaceutical development, manufacturing,
  performance and radiation safety requirements
  associated with the production of commercial
  x-ray equipment
• U.S. Department of Transportation (DOT) regulates
  the transportation of radioactive materials

54
5. Advisory Bodies

• National Council on Radiation Protection and
  Measurements (NCRP)
• Collect, analyze, develop and disseminate, in the
  public interest, information and recommendations
  about radiation protection, radiation
  measurements, quantities and units
• International Commission on Radiological
  Protection (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 serve as
  the reference documents from which many
  regulations are crafted

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5. Summing internal and external doses

• Dose from an internal exposure continues after
  the period of 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
• The committed effective dose equivalent (CEDE) is
  a weighted average of the committed dose
  equivalents to the various tissues and organs of
  the body
• CEDE ?wT H50,T

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5. Summing internal and external doses

• 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)

57
5. Dose Limits
c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 791.
58
5. As Low As Reasonably Achievable (ALARA)
Principle

• Dose limits to workers and the public are
  regarded as upper limits rather than as
  acceptable doses or thresholds of safety
• In addition to the dose limits, all licenses are
  required to employ good health physics practices
  and implement radiation safety programs to ensure
  that radiation exposures are kept as low as
  reasonably achievable (ALARA), taking societal
  and economic factors into consideration
• The ALARA doctrine is the driving force for many
  of the policies, procedures, and practices in
  radiation laboratories, and represents a
  commitment by both employee and employer to
  minimize radiation exposure to staff, the public,
  and the environment to the greatest extent
  possible

59
5. Summary

• Regulatory agencies, advisory bodies and their
  functions
• Dose limits
• Occupational and public dose limits
• Organ limits
• ALARA principle

60
Raphex 2001 General Questions

• 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. 5 mSv (500 mrem)
• E. 1 mSv (100 mrem)

61
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., cleaning staff).
• 2. Anyone who could receive a measurable
  exposure, but on an irregular basis (e.g., nurses
  who work in areas where "portable" films are
  taken).
• 3. Workers who are likely to receive an
  occupational dose of between 10 and 100 mrem per
  year.
• 4. Workers who are likely to receive an
  occupational dose of greater than 1,250 mrem per
  year.
• 5. Workers who have regular access to "high
  radiation areas.
• A. 1, 3
• B. 4, 5
• C. 1, 2
• D. 2, 3, 5
• E. 1, 2, 5

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 1 mSv (100 mrem) per hour at 30 cm
from the radioactive sources or adjacent to walls
shielding radiation producing equipment, i.e., a
"high-radiation area."
62
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