Radiation Protection
Robert L. Metzger, Ph.D.
1. Sources of Exposure to Ionizing Radiation
Naturally 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.
2
1. Sources of Exposure to Ionizing Radiation
Naturally 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.
3
1. Sources of Exposure to Ionizing Radiation
Naturally 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)
4
1. Sources of Exposure to Ionizing Radiation
Naturally 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.
5
1. Sources of Exposure to Ionizing Radiation
Naturally 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.
6
1. 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.
7
1. Sources of Exposure to Ionizing Radiation
Naturally 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.
8
1. Sources of Exposure to Ionizing Radiation
Naturally Occurring Radiation Sources

Cosmic Radiation
 Air travel can add to individual’s
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.
9
Annual Dose Equivalent
360 mrem
1% 3%
4%
11%
11%
8%
8%
54%
X-Rays
Radon
Internal
Other
Terrestrial
Consumer
Cosmic
Nuc Med
10
Annual Dose - Other 1%





Occupational Dose – 0.3%
Fallout - <0.3%
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.
11
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.
12
Cancer Mortality in the US
13
Legend for Mortality Data
14
1. Sources of Exposure to Ionizing Radiation
Technology 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.
15
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.
16
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.
17
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
18
1. Genetically Significant Dose (GSD)




c.f. Bushberg, et al. The Essential Physics of Medical
Imaging, 2nd ed., p. 747.
19
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.
20
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
21
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




22
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



23
2. 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 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
24
2. Personnel Dosimetry
Film 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
25
2. 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 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
26
2. Personnel Dosimetry
Thermoluminescent (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
27
2. Personnel Dosimetry
Optically 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 (Al2O3:C) is commonly
used
Broad dose response range like TLDs
They can be reread several times
28
2. Personnel Dosimetry
Pocket 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.
29
2. Summary
c.f. Bushberg, et al. The Essential Physics of Medical
Imaging, 2nd ed., p. 753.
30
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.



31
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
32
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
33
4. 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-ray
tube housing, limited to 100 mR/hr at 1 m from housing) radiation
34
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.
35
4. Radiation Protection and Exposure Control
Shielding

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
36
4. 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 = 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
37
4. Radiation Protection and Exposure Control
Shielding

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)
38
4. Radiation Protection and Exposure Control
Shielding




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
39
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.
40
4. Radiation Protection and Exposure Control
Protection 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
41
4. Radiation Protection and Exposure Control
Protection 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 lowenergy 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
42
Depth Dose




Recall Dose = Energy absorbed per gram.
For soft radiations, the dose decreases dramatically with depth as the
patient’s 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.
43
Depth Dose
Percent Depth Dose
Depth Dose for Medium Energy X-Ray
100
90
80
70
60
50
40
30
20
10
0
0
5
10
15
20
Depth (cm)
44
4. Radiation Protection and Exposure Control
Protection 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
45
4. Radiation Protection and Exposure Control
Protection 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
46
4. Radiation Protection and Exposure Control
Protection 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
47
4. Radiation Protection and Exposure Control
Protection 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.
48
4. Radiation Protection and Exposure Control
Protection 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
49
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
50
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.




51
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.
52
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 selfregulate 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
53
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
54
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
55
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)
56
5. Dose Limits
c.f. Bushberg, et al. The Essential Physics of Medical
Imaging, 2nd ed., p. 791.
57
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
58
5. Summary



Regulatory agencies, advisory bodies and their functions
Dose limits
 Occupational and public dose limits
 Organ limits
ALARA principle
59
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)




60
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 "highradiation area."
61
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




62