CONSIDERATIONS FOR CONTROL OF RADIATION
EXPOSURES TO PERSONNEL FROM SHIPMENTS
OF RADIOACTIVE MATERIALS ON
PASSENGER AIRCRAFT
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Radiation Prof rams
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CONSIDERATIONS FOR CONTROL OF RADIATION EXPOSURES TO PERSONNEL
FROM SHIPMENTS OF RADIOACTIVE MATERIALS ON PASSENGER AIRCRAFT
Office of Radiation Programs
Environmental Protection Agency
Washington, D.C. 20460
December 1974
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FOREWORD
The use of radioactive materials in nuclear medicine and other
areas has increased rapidly in the past several years with the result
that many shipments of these materials exist in general commerce every
day. Shipments of radioactive materials on passenger aircraft are
increasing at a rate of 15-25% annually. While most of these packages
contain either very small quantities of radioactive materials or materials
which exhibit little or no penetrating radiation, it has been estimated
that a significant number emit enough radiation that exposure to the
travelers aboard these aircraft could be a high percentage of the
current Federal radiation protection guidance. Additionally, because
of several incidents in recent years involving the shipment of such
materials, various Federal agencies have conducted studies to determine
the nature and extent of this problem.
Because of the responsibility vested in EPA (42 USC 2021h) for
radiation directly or indirectly affecting health, including guidance
to Federal agencies in the formulation of radiation standards, EPA
has examined the question of exposure of passengers aboard commercial
aircraft. The results of this examination are contained in this report,
along with a recommendation on exposure levels that should be incorporated
into the regulations of those Federal agencies charged to regulate
conditions under which radioactive materials can be transported. The
approach used in this instance, as well as any other circumstance
involving radiation exposure of the U.S. population, has been to carry
out EPA's basic responsibility to assure public health protection.
This responsibility is carried out within the broad precedents established
by the former Federal Radiation Council whose functions and respon-
sibilities were transferred to the Environmental Protection Agency
in 1970. This report was developed with information and comments
provided by the Department of Transportation, the Federal Aviation
Administration, the Atomic Energy Commission, and the Public Health
Service, all of which have responsibility and expertise relative to
transportation of radiation materials. We hope that the report will
serve to communicate to the public the basis for our recommendation
as to what constitutes reasonable protection of travelers on commercial
aircraft.
Comments on this analysis as well as any new information would be
welcomed; they may be sent to the Director, Technology Assessment
Division (AW-559), Office of Radiation Programs, U.S. Environmental
Protection Agency, Washington, D.C.
D. Rowe, Ph.D.
Deputy Assistant Administrator
for Radiation Programs
iii
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CONTENTS
Page
FOREWORD. Ill
I. INTRODUCTION AND BACKGROUND 1
II. APPLICABLE RADIATION PROTECTION PRINCIPLES 3
III. TECHNICAL ANALYSIS 6
A. Alternative Aproaches to Reduce Passenger Exposure....... 6
Additional Shielding of Packages 6
B. Effect of Package Placement on Passenger Exposure 19
1. Spacing of Individual Packages 19
2. Package Placement in the Cargo Compartment 21
3. Special Aircraft Compartments 26
4. Restricted Seating Areas on Aircraft 28
C. Effect of Shipping Procedures on Passenger Exposure 29
1. Modified Schedules for Mo-Tc Generators 29
2. More Frequent Shipments of Smaller Mo-Tc Generators.. 29
3. Tc-99m Shipments Instead of Mo-Tc Generators 32
4. Surface and Air Cargo Shipments Instead of Passenger
Aircraft Shipments 33
D. Annual Dose Estimates 34
E. Impact on Other Exposures 36
IV. SUMMARY AND RECOMMENDATION 37
REFERENCES 38
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I. INTRODUCTION AND BACKGROUND
The number of packages of radioactive material shipped on passenger
aircraft annually has increased rapidly over the past few years and is
estimated at about 800,000 (1) each year, a number that is expected to
increase even more. While most of these packages contain either very
small quantities of radioactive materials or materials which exhibit
little or no radiation external to the package, a certain fraction of
the packages contain radioactive materials which have significant external
radiation for which protection must be provided. It has been reported
that shipments of the radiopharmaceutical source, known as a
molybdenum-technetium (Mo-Tc) generator, currently make up the majority
of these shipments for which radiation protection is required (2).
The Society of Nuclear Medicine (2) estimated that about 80,000 of
these Mo-Tc generators were shipped in 1972. The shipment of radio-
active materials for all purposes has been growing at a rate of 15
to 25% annually (3). Because of the relatively high energy of Mo-99 gamma
rays and the number and frequency of shipments, Mo-Tc generators are
generally regarded as the most significiant radiopharmaceutical, in terms
of potential exposure to aircraft travelers, routinely shipped on passenger
aircraft. Other shipments which have a potential for external radiation
exposure include Ra-226, 1-131 and Sn-In-113 generators. However,
according to the AEC (7), almost all of the packages with a TI (exposure
rate in mrem per hour at 3 feet from the surface of the package) greater
than three which are transported on passenger aircraft are Mo-Tc generators.
Thus, shipments of these generators produce the greatest exposure to
aircraft travelers and control efforts should be directed to these shipments.
As a result of an incident involving leakage of a shipment of a
source quantity of Mo-Tc by passenger aircraft in 1971 (3), the Atomic
Energy Commission initiated investigations (4)(5)(6) to determine the
nature and extent of the potential problem of shipping radioactive
materials on passenger aircraft. The results of these investigations
indicated that while the majority of flights on which radioactive materials
were carried had no discernible radiation exposure to passengers, on
some flights passengers were exposed to rates ranging from 20 to 25
mR/hour. These high exposure rates were apparently due to noncompliance
with loading and spacing requirements on the aircraft. In a further
analysis (7) of the problem the AEC determined that population doses
(about 1,400 person rem per year) were comparable to other man-made
sources of exposure to the general public but that individual doses
to certain aircraft passengers who travel frequently could be as high
as 160 to 170 mrem per year. Thus, in assessing the exposure of
passengers, there is a need to examine both individual and selected
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population groups exposures. It is the purpose of this report to consider
radiation protection factors for shipment of such material on aircraft
and to provide recommendations for the radiological protection of
passengers. The analysis will consider costs and effectiveness of various
protection measures in order that the most efficiacious balance can
be gained between the medical benefits of these materials and exposure
of the air-traveling public.
Nearly all radioactive materials being shipped on commercial
aircraft are shipped from one installation licensed by the Atomic
Energy Commission to another with a similar license. The packages must
meet specific requirements prior to leaving a licensed installation and
must receive detailed inspection and satisfy other requirements during
unpackaging and use. In shipment between these two licensed installa-
tions, the current regulatory policy of the U.S. Department of Trans-
portation is that such materials be packaged in a way that they can move
in normal commerce. These requirements specify type and quantities of
radioactive materials (permitted for shipment in such normal commerce).
The DOT regulations also specify exposure rate limits for packages
submitted for shipment to provide protection from external radiation as
follows:
Exposure rate on acces- Exposure rate 3 feet
Package Label sible surface of from external surface
Category package (mR/hour) ' of package (TI)(mR/hour)
Radioactive - White I 0.5 0
Radioactive - Yellow II 10 . 0.5
Radioactive - Yellow III 200 10
Current DOT regulations permit all three categories to be shipped
on passenger carrying aircraft. The greatest reduction to individual
passenger exposure would be gained by eliminating shipments of Radioactive-
Yellow III packages. Elimination of the shipment of Radioactive-Yellow
II packages would provide a slight additional reduction to individual
passenger exposure and elimination of Radioactive-White I would have no
significant effect because of the negligible external rate limit. Most
of the Mo-Tc generators used by hospitals for radionuclide diagnostic
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examination are currently shipped on passenger aircraft as Yellow-Ill
packages. Prohibiting shipments of Yellow-III packages would complicate
procedures of the nuclear medicine industry unless options are available
such as additional package shielding, ground transport, cargo aircraft
shipments, or combinations of these to allow shipments of the required
material to be made. This report examines the degree to which these
actions can be reasonably applied to reduce dose to passengers during
shipment primarily of Yellow-III packages.
Reductions of dose to personnel on aircraft can also be gained by
prohibiting shipment of long-lived radioactive materials which could be
shipped by other transport systems such as truck or rail. It is unlikely
that an effective means of transport could be provided for long distance
shipments for radionuclides with half-lives of less than about one week.
Since Mo-Tc generators have a half life of 2.8 days, shipment of many
of these generators on aircraft is generally necessary. These sources
are the principal contributor of radiation exposure to individuals on
aircraft; thus this mechanism of solving the problem alone can hardly
be used. The approach is viable, however, for reducing needless radiation
exposure to aircraft passengers from the shipment of long-lived radio-
nuclides.
II. APPLICABLE RADIATION PROTECTION PRINCIPLES
The Federal Radiation Council (8), in May of 1960, promulgated
guidance to Federal agencies for protection of the public from ionizing
radiation. The recommendations of the National Council on Radiation
Protection and Measurements (NCRP) (9) are consistent with the FRC
guidance. The functions of the FRC were transferred to the Environmental
Protection Agency in 1970; therefore, the basis for control of radiation
exposure of the traveling public is the current Federal guidance which
contains numerical guides and other principles. The various principles
applicable to Federal agencies relevant to this problem area are as
follows:
1. "Under the working assumptions used, there can be no single
'permissible' or 'acceptable' level of exposure, without regard to the
reasons for permitting the exposure. The radiation dose to the population
which is appropriate to the benefits derived will vary widely depending
upon the importance of the reason for exposing the population to a
radiation dose."
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2. "Also, under the assumptions used, it is noted that all
exposures should be kept as far below any arbitrarily selected levels
as practicable. There should not be any man-made radiation exposure
without the expectation of benefit resulting from such exposure.
Activities resulting in man-made radiation exposure should be authorized
for useful applications provided the recommendations set forth in this
staff report are followed. Within this context, any numercial recom-
mendations should be considered as guides, and the need is for a series
of levels, each of which might be appropriate to a particular action
under certain circumstances."
3. The FRC expanded this concept as ". . . This report introduces
the use of the term Radiation Protection Guide (RPG). This term is
defined as, the radiation dose which should not be exceeded without
careful consideration of the reasons for doing so:, every effort should
be made to encourage the maintenance of radiation doses as far below
this guide as practicable." For individuals in the population the RPG
is 0.5 rem per year whole body dose; where the individual whole body
doses are not known the recommended whole body dose protection guide for
a suitable sample of the population is 0.17 rem i>er year.
4. "The Federal agencies should apply these Radiation Protection
Guides with judgment and discretion, to assure t.hat reasonable probability
is achieved in the attainment of the desired goal of protecting man from
the undesirable effects of radiation. The Guides may be exceeded only
after the Federal agency having jurisdication over the matter has care-
fully considered the reason for doing so in light of the recommendations
5. The Administrator is responsible for following the activities
of the Federal agencies in this area and promoting the necessary
coordination to achieve an effective Federal program.
In accordance with the above basic guides, the use in medicine
of many of the radionuclides shipped on aircraft is beneficial to
society. It is well known that patients benefit directly from such
procedures and improvements are continously being made to offer more
beneficial procedures using radiation and radioactive materials to the
public. The costs of producing, processing, shipping, and using medical
radioisotopes are included in the price charged the patient. Therefore,
the patient, who is the individual receiving the benefit, bears the
monetary cost involved and a clear mechanism exists for having incremental
costs of increased protection of all personnel involved passed on to
the beneficiary. Shipments of radioisotopes involve radiation exposure
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of the general public and transportation industry workers who receive
no offsetting benefit except the assurance that society has this medical
service available. In this instance it appears reasonable that an
examination of the shipment of radioactive materials used in medicine
contrast the risks that the general public must bear against a place-
ment of incremental costs for risk minimization on those who receive
the benefits. An additional factor that should be satisfied is that
methods of radiation dose reduction be both technically and economically
feasible.
When examining a component of a broader problem area, it is important
to assure that actions aimed at reducing doses within that component
do not produce the same or higher radiological impact elsewhere because
of adjustments that may result. This consideration is especially
important in transportation of radioactive materials where several other
modes of transport are available which may result in higher exposures
to selected groups such as cargo handlers, travelers, or to the population
because of longer times in transit, more frequent handling, etc.
To the degree possible, it is appropriate to consider established
procedures, regulations, and other protective measures in alternate
approaches to reduce radiation exposure in order to assure that any
resulting changes will be at the minimum possible to achieve the desired
goal. In this examination considerable recognition is given to the form
of regulations established over the years by the Department of Transpor-
tation for shipments of hazardous materials. These regulations for
radioactive materials are based on labeling, shielding, integrity, and
placement of packages; thus the alternatives examined include these
factors which have been proven to allow straightforward and effective
regulatory and compliance requirements.
As mentioned earlier it is also important to recognize that in
establishing exposure limits consideration must be given to population
groups as well as individuals. However, because of the limited
population being exposed at any given time from a shipment on an air-
craft, the problem of control for this mode of transportation appears
to require emphasis on protection of individuals. This possibility
was borne out by the AEC (7) analysis in which it was estimated that
the annual population dose was about 1,400 man rem and annual doses
to individual passengers were estimated to range as high 170 mrem/year.
Since the dose is normally due to external radiation fields, there is
no persistent dose commitment that needs to be considered. Therefore,
in this situation it is accepted that protection of individuals will
provide adequate protection for any population passenger groups.
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III. TECHNICAL ANALYSIS
A. Alternative Approaches to Reduce Passenger Exposure
Several alternatives are available to reduce the radiation exposure
to passengers on aircraft. While not all options are feasible, the
following are expected to be potential approaches for passenger
protection: (1) additional shielding of packages, (2) placement options
on aircraft, and (3) modified shipping procedures. The principal
alternative analyzed in detail is additional shielding. It is believed
that examination of this alternative brings out data on costs and
effectiveness of most common controls to allow a determination of a
means for reducing exposures to aircraft passengers to a range that can
be found acceptable. It is apparent that a combination of these alter-
natives could be developed and implemented to reduce the dose received
by aircraft passengers. Such a combination might be (1) ground trans-
portation for closeby shipments, (2) increased package shielding for
longer shipments necessitating air transport and (3) elimination of all
packages labelled radioactive-yellow III with half lives greater than
30 days (except radiopharmaceuticals) from passeager carrying aircraft.
Additional Shielding of Packages
By using additional shielding, the package TI will be reduced
and smaller radiation doses (corresponding to common practice, dose=
dose equivalent herein) will be received by passengers. In order to
evaluate additional packaging shielding cost as a function of dose rate
in the passenger compartment, our analysis was made making use of
data provided by the AEC (7). The AEC data were based principally
on data reported by Brownell (14).
The cost effective analysis for additional shielding was based
on lead shielding for a standard 500 mCi Mo-99-Tc-99m source which
is the largest generator currently shipped. Dose rates due to the
Mo-Tc generator were based on a source strength of 2485 mCi since the
unit is typically shipped on Saturday morning. Mo-Tc generators were
chosen for the analysis because they are probably the most dosimetrically
significant of the radiopharmaceuticals shipped on passenger aircraft.
Lead was chosen as the shielding material for the analysis since it
is currently employed in packaging shielding. Brownell (14) also
evaluated depleted uranium and tungsten shields and found these shields
comparable in cost if they were returned to the manufacturer with credit
given to the customer.
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Dose rates in mrem/hr-100 mCi at one meter from the surface of the
package containing the Mo-Tc generator as a function of lead thickness
were based on Brownell's data (14). Mallinckrodt and New England
Nuclear package size parameters were employed. Values of TI as a
function of lead thickness appropriate for a 2485 mCi Tc-99m generator
are presented in Figure 1.
The TI values in Figure 1 were converted to a dose rate at the
seat location using methods derived by the AEC (7) for a package located
on the floor of the cargo compartment directly below the seat. The
results are shown in Figure 2. A transmission factor "Fo" of 0.7 was
utilized for all packages in this analysis. The vertical height of
the generator package was assumed to be 35.6 cm consistent with the
container used by the New England Nuclear Corporation. The separation
distance from the top of the package to the floor of the passenger
compartment was obtained by subtracting the package height from the
distance between the floors of the cargo and passenger compartments.
Since the DC-9 cargo compartment configuration indicates higher seat
location dose rates for a given lead thickness, this passenger air-
craft was examined in detail in succeeding calculations as a limiting
case. Since the generator package was assumed to be on the floor of
the cargo compartment, the other passenger aircraft with larger distances
between the passenger and cargo floors had smaller estimated dose rates
at the seat location for any given shielding thickness.
The five aircraft considered here account for almost 90% of
shipments of radioactive materials which exhibit penetrating radiation (7)
In addition, these five aircraft also represent a size spectrum of air-
craft currently used for passenger transport. Thus, the cargo compart-
ment dimensions of the DC-9 (the limiting case here) would be expected
to be similar to those of other smaller aircraft, such as the B-737
and the BAC-111, and dose rates calculated using the dimensions of
dhe DC-9 would be approximately the same for these other aircraft.
Figures 1 and 2 were utilized to compute seat location dose rates
as a function of appropriate TI values for the DC-9. The results for
selected TI values are presented in Table 1. For example, a 5.35 cm lead
shield is required to reduce the TI to 1 for the evaluated 2485 mCi
source. At a TI of 1, the DC-9 seat location dose rate is approximately
0.49 mrem/hr; at a TI of 0.5 the dose rate is approximately 0.25 mrem/hr.
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100.0
10.0
1 "i
g.»
Ss
«-
-------
100.0
FIGURE 2. 99Mo - 99mTc (2485 mci) & A LEAD SHIELD
SEAT LOCATION DOSE RATES FOR INDICATED PASSENGER AIRCRAFT
NEW ENGLAND NUCLEAR AND MALLINCKRODT DESIGN PACKAGE
IS LOCATED ON THE FLOOR OF THE CARGO COMPARTMENT
DIRECTLY BELOW THE PASSENGER SEAT
SEAT LOCATION DOSE RATES FOR 2485 mci
DC-8
B-727
10.0
O
o
O
<
111
o
K
LU
K
oc
o
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l.o
.10
TECHNETIUM - 99m GENERATOR
DC-9 DOSE RATE=0.494T
B-707 DOSE RATE=0.419T
B-727 DOSE RATE=o.309T
B-747 DOSE RATE=0.197T
DC-8 DOSE RATE-=0.343T
.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0
LEAD THICKNESS (cm)
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Table 1. Seat Location Dose Rates for One Package in the DC-9 Cargo
Compartment*
Approximate Transport Index Values Seat Location Dose Rate
TI (mrem/hr at 1 meter) (mrem/hr)
0.5 0.25
1 0.49
2 0.99
3 1.48
.4 1.98
5 2.47
6 2.96
7 3.46
8 3.95
9 4.45
10 4.94
* 2485 mCi technetium-99m generator located on the floor of the cargo
compartment directly below the passenger seat location.
10
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Cost evaluations of additional shielding for one Mo-Tc generator
package include the disposable lead shield cost, ground delivery cost,
air freight (plus 5 per cent tax) cost and additional industrial plus
hospital handling costs for shields weighing more than 70 pounds.
Cost values were determined as a function of weight. The weight of
the lead shield as a function of lead thickness for the Mo-Tc generator
was determined by averaging the New England Nuclear and Mallinckrodt
values given by Brownell. The results are shown in Figure 3. The
use of New England Nuclear values would result in a lighter estimated
shield weight. The average cost of the shield (materials plus fabrication)
was determined to be $0.295 per pound. Delivery cost was determined
to be $7 per package up to 65 pounds and an additional 10 cents per
pound for amounts over 65 pounds. The package weight was assumed to
be equal to the lead shield weight. These data and a weighted average
air freight cost plus 5% tax (Boston rate) were based on Brownell's
report. Incremental costs were made relative to a 25 pound, 3.55 cm
thick lead shield, which appears to be the type most commonly used at
the present time. The total incremental cost was determined by adding
incremental costs as shown in Table 2. All simplifying assumptions made
here were the same as those made by the AEC and Brownell with the single
exception that no handling cost was added until the weight reached
70 pounds. The 70 pound limit is consistent with the maximum allowable
weight for baggage on the per-piece plan commonly used by major commercial
air carriers. Excess baggage charges are levied on single pieces of
luggage weighing more than 70 pounds under the per-piece plan.
Cost effective curves (total incremental cost per package versus
seat location dose rate) were developed from information in Table 2
and Figures 2 and 3. The cost effective curves for one Mo-Tc generator
on.the floor of the cargo compartment of various aircraft are presented
in Figure A. The inflection points in the cost effective curves are
the result of non-linear dose reduction with additional shield weight
and increased rate charges for ground and air delivery of the packages.
A step function change also occurs as the result of added handling
costs which were added for shields weighing more than 70 pounds.
Interpretation of the cost effective curve for the DC-9 aircraft
in Figure 4 indicates that the seat location dose rate could be reduced
to 0.5 mrem/hr for an additional cost of $11 per package relative
to a 25 pound package; for $30 the dose rate would be 0.25 mrem/hr.
The largest portion of the $30 cost is due to the additional $12.50
cost of handling which is added in one lump for shields weighing more
11
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1,000 i
FIGURE 3. WEIGHT OF LEAD SHIELD
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Table 2. Incremental Costs (Dollars) Relative to a 25 Pound Package
Incremental Costs(Dollars)
Weight (Ib)
25
30
34
35
40
50
60
70
80
90
100
Disposable
Shield
Cost
0
1.47
2.65
2.94
4.42
7.37
10.32
13.27
16.22
19.17
22.12
Ground
Delivery
Cost
0
0
0
0
0
0
0
.50
1
2
3
Air Freight
Plus 5% Tax
(Boston Rate)
0
0
0
0
0
1
2
4
5
5
5
Industrial
Plus Hospital
Handling Cost
0
0
0
0
0
0
0
12.50
12.50
12.50
12.50
Total
0
1.47
2.65
2.94
4.42
8.37
12.32
30.27
34.72
38.67
42.62
13
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50
40
FIGURE 4. COST EFFECTIVE CURVES FOR ONE PACKAGE FOR
DIFFERENT TYPE PASSENGER AIRCRAFT
2485 mci99Mo - """Tc SOURCE SHIELDED BY LEAD.COST
INCREMENTAL IS MADE RELATIVE TO A 25lb. LEAD SHIELD
FOR AN AVERAGE NEW ENGLAND NUCLEAR AND MALLINCKRODT
SOURCE DESIGN. THE INCREMENTAL COST INCLUDES COSTS FOR
DISPOSABLE LEAD SHIELDS, GROUND DELIVERY, AIR FREIGHT
+5% TAX (BOSTON RATE) AND ADDED INDUSTRIAL PLUS
HOSPITAL HANDLING COST FOR THE HEAVIER SHIELDS.
o
o
E
UJ
Q.
V)
30 _
5
UJ
E
U
20 -
10 -
i'l
0.5 1 1.5 2 2.5 3
DOSE RATE TO SEAT LOCATION FROM ONE PACKAGE DIRECTLY
BELOW SEAT ON FLOOR OF CARGO COMPARTMENT (mrem/hr)
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than 70 pounds. If this handling cost were for shields above 85 pounds,
the lower dose rate of 0.25 rarem/hr could be achieved at roughly twice
the cost of the 0.5 mrem/hr rate. For any given package, the seat
location dose rates would be lower for the other aircraft analyzed.
If more than one package is stored in the cargo compartment, the seat
location dose rate will obviously increase above those values presented
in Figure 4 unless additional shielding is added or spacing is used.
Cost effective curves such as shown in Figure 4 are useful for
displaying decision-making data in that they show the degree of
efficiency of a control mechanism relative to the parameter being
considered, in this case the cost. For example, the data in Figure
4 show that spending money on shielding to reduce the external dose
rate becomes inefficient for exposure rates below 0.5 mrem/hr for the
DC-9 aircraft. Such data do not, however, provide the criterion for a
control decision, but by indicating the degree of efficiency in reducing
the dose rate through expenditures for additional shielding, they become
important to such a judgment. Other elements that should also be
satisfied are the importance of the overall activity, who receives the
benefits, who bears the risks, the distribution of risks and control
costs, and whether controls would disrupt obtaining the benefits of
the activity. If these factors are considered at the level of 0.5
mrem/hr, which is shown in Figure 4 to be the level below which controls
based on shielding become inefficient, it is found that the beneficial
activity will certainly continue, the costs will be minimal and will be
borne by patients who receive the benefit, and the dose to passengers
who are bearing the risk for essentially no direct benefit is cost
effectively reduced. On the basis of these factors this control level
is both technically and economically feasible.
The $11 cost increment represents an increase of about 4% of the
$300 cost for a large Mo-Tc generator (400 to 500 mCi). The influence
of incremental costs on diagnostic examinations can be based on
information presented by the Society of Nuclear Medicine (2) that
about 80,000 generators are used each year to perform 2.9 x 10
diagnostic procedures. At an incremental cost of $11 per shipment,
each procedure will cost about $0.30 more; at a cost of about $30 the
added cost would be about $0.90. These incremental costs are insig-
nificant when compared to the typical costs of these diagnostic
procedures which typically range between $100 and $150.
It is also possible to construct similar cost effective curves for
reduction of population dose impact as a function of cost. For a given
15
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population size and number of packages such curves would have the same
shape as those in Figure A. Such information is important to control
decisions if benefits and risks are generally distributed over a given
population and a criterion is available to decide between risks and costs.
The AEC determined that approximately 1,400 man-rems per year could be
expected for a seat level dose rate equivalent of 2 mrem/hr maximum and
1 mrem/hr average from air shipments, and that reduction of this population
impact would cost in the range of $1,000 per man-rem. Two important
factors are involved that make it difficult to base control decisions
on this projected population impact. First, risks are borne unknowingly
by passengers for others who are clearly defined to receive the benefit
of having the shipment occur. The passenger obtains no direct benefit;
he may indirectly benefit by the fact that such procedures are available
and he may one day need one. Second, when a suitable sample of
individuals are likely to receive radiation doses approaching current
exposure guides, the exposure of these individuals becomes the principal
consideration in control decisions. Control of radiation exposure
of passengers on commercial aircraft Is, therefore, one of protecting
the exposure of individuals and not the population.
A direct correlation exists between the seat location dose rate
and TI's per package and TI's per flight. This relationship, which
would be of importance to shippers and regulatory agencies in
developing procedures is shown in Figures 5 and 10 for the DC-9 cargo
compartment configuration. If more than one package is considered
for a given seat location dose rate, the maximum tl per package would
need to be reduced to meet any given dose rate criteria, however, the
maximum TI per flight can be increased if spacing between the packages
is utilized. The multiple package and spacing alternative is examined
in a separate section of this paper.
A cost effective curve for the approximate maximum TI per package
on a DC-9 is presented in Figure 6. The total incremental cost per
package relative to a 25 pound package is shown to be $11 per package
for a maximum TI per package of 1. Brownell determined an incremental
cost relative to a 34 pound package of $17 per package to reduce the
TI to 1. The cost of a large Mo-Tc generator (400 to 500 mCi) is about
$300.
16
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10
c
UJ
€
E
2.5
0
<
b 1.5
.4
.2
FIGURE 5. APPROXIMATE MAXIMUM Tl PER PACKAGE FOR THE
2485 mci 99Mo - 99mTc SOURCE PER PACKAGE
IN A LEAD SHIELD
I II
1 I I
.2
.3
.4 .5 .6 .8 1.0
1.5
2.5
6
10
DOSE RATE TO SEAT LOCATION DIRECTLY ABOVE THE PACKAGE LOCATED ON THE
FLOOR OF THE C*RGO COMPARTMENT (mrem/hr)
17
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100
80
60
_ 40
&
ui
o
o
oc
UJ
0.
fe
o
u
z
UJ
5
u
25
15
10
9
8
7
6
3
2.5
2
1.5
FIGURE 6. COST EFFECTIVE CURVE FOR APPROXIATE
MAXIMUM Tl PER PACKAGE
2485mci 99Mo -• 99mTc SOURCE PER PACKAGE
INCREMENTAL COST ARE RELATIVE TO A 25lb. LEAD
SHIELD
l\l III
.15 .2 .25 .3 .4 .5 .6 .7 .8.9.1.0 1.5 2 2.5 3 4 5 6 7 8 9 10
APPROXIMATE MAXIMUM Tl PER PACKAGE (mrem/hr at 1 meter)
JS
-------
B. Effect of Package Placement on Passenger Exposure
1. Spacing of Individual Packages
Although package shielding directly influences seat location dose
rate, the seat location dose rate is also influenced by the number and
placement of additional packages in the cargo compartments of passenger
aircraft. These factors are especially important relative to the
maximum TI per package and the maximum TI per flight that would be
allowed to meet any selected seat dose rate criteria. The dose rate
from multiple packages is dependent on the spacing between packages.
The DC-9 has the smallest separation distance (of the evaluated
passenger aircraft) between the floors of the passenger and cargo
compartments so the placement option evaluation will be based on the
limiting geometry of the DC-9. In the evaluation of spacing of multiple
packages, the dose rate from three packages in the passenger compartment
was considered. Three packages were chosen consistent with the AEC's
conclusion that three packages contribute essentially all of the
radiation dose at the seat location with the maximum radiation dose
rate. The dose rate to the seat location when three packages of
equal TI are loaded with one package directly below the seat and two
packages loaded symmetrically at a spacing out distance (SOD) on either
side of the center package were computed using the AEC model. All
packages were assumed to be located on the floor of the cargo
compartment. Assumptions for the parameters used in the analysis were
the same as those used previously in the cost effective evaluation of
additional packaging shielding. A vertical transmission factor of
0.7 and a generator package vertical height of 35.6 centimeters were
assumed. TI values were taken from Figure 1 of this paper. The maximum
seat location dose rates for three 2485 mCi Mo-Tc generator packages
in the DC-9 cargo compartment are presented in Figure 7. Curves were
drawn.1 for SOD's of 0 cm, 70 cm, and 210 cm. A SOD of zero centimeters
represents the worst case for three packages on the floor of the cargo
compartment. A SOD of 210 cm was evaluated since this SOD was
evaluated by the AEC (7). A SOD of 70 cm was evaluated as an
intermediate case. Relative to the worst case of a SOD of zero,
SOD's of 70 cm and 210 cm result in dose rate reduction factors for
the maximum seat location of 1.39 and 2.26 respectively. It should
be pointed out that these dose reduction factors may be difficult to
realize in current cargo compartment loading practices. The difficulty
in achieving compliance with spacing out distances is a strong argu-
ment against strong dependence on this alternative for achieving dose
reductions to the maximum seat location in the passenger compartment.
19
-------
100.0
FIGURE 7.
SOD=70CM
ui
m
o
s
z
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5
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Z
v>
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I
o
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ff
THREE "Mo-99"1^ (2485mci) SOURCE PACKAGES EACH
WITH A LEAD SHIELD - SEAT LOCATION DOSE RATES
DC 9 CARGO COMPARTMENT^ NEW ENGLAND NUCLEAR
AND MALLINCKRODT DESIGN (ONE PACKAGE IS LOCATED
DIRECTLY BELOW THE SEAT AND TWO PACKAGES ARE
LOADED SYMMETRICALLY AT A SOD (SPACING OUT
DISTANCE) CM ON EITHER SIDE. OF THE CENTER
PACKAGE.
10.0
MAXIMUM SEAT LOCATON DOSE
RATE FOR THREE 2485 mci
TECHNETIUM—99m GENERATOR
o
u
o
UJ
V)
UI
<
UJ
8
Q
I.O
SOD=210CM
J L
_L
J I I '
J L
.5
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0
20
LEAD THICKNESS(cm)
-------
Deviations from the SOD during loading will significantly increase
the maximum individual dose rate.
In order to cost effectively evaluate the spacing option on the
DC-9 for three technetium-99m generator packages, the curves (total
incremental cost per package versus seat location dose rate) shown in
Figure 8 were developed for SOD's of 0, 70, and 210 centimeters. For
an added cost of $11 per package (corresponds to incremental cost for
a 57 pound shield plus freight) and a spacing out distance of 210 cm
between packages, the maximum DC-9 seat location dose rate can be reduced
to 0.6 mrem/hr. Without spacing between the packages, the maximum seat
location dose rate is 1.6 mrem/hr for an added cost of $11.
In order to meet a given seat location dose rate criteria,
maximum TI's per package and TI's per flight were determined for the
DC-9 cargo configuration and the results are presented in Figures
9 and 10. Utilizing a maximum seat location dose rate of 0.5 mrem/hr
and Figure 9 for evaluation purposes, the maximum TI per package for
a DC-9 is 1 if only one package is stored in the cargo compartment.
The maximum TI per package is reduced to 0.8 for three packages and
a spacing out distance of 210 cm between packages. If spacing is not
utilized, the maximum TI per package would have to be reduced to 0.35
in order for three packages to be carried on the DC-9 at a maximum
seat location dose rate of 0.5 mrem/hr. Figure 10 shows that the total
TI per flight for the DC-9 is reduced to one unless spacing is employed.
If the Tl/package is reduced to 0.8 and spacing between packages is
utilized, the maximum TI per flight for the DC-9 can be increased
to approximately 2.5. An analysis similar to that conducted for the
DC-9 can be done for other types of passenger aircraft.
/'2. Package Placement in the Cargo Compartment
/The dose rate to the seat location from one package in the cargo
compartment is strongly dependent on where the package is located in
the cargo compartment and slightly dependent on the package size. In
order to evaluate the effect of package size, a sensitivity analysis
was conducted for a package located on the floor of the DC-9 cargo com-
partment and a package located at the top of the DC-9 cargo compartment.
The results of the sensitivity analyses are shown in Tables 3 and 4.
21
-------
35
FIGURE 8. COST EFFECTIVE CURVES FOR THREE PACKAGES
2485mci "MO - M'mTc SOURCE PER PACKAGE SHIELDED BY LEAD-DC-9 CARGO
COMPARTMENT
TOTAL COST INCREMENT IS MADE RELATIVE TO A 25lb LEAD SHIELD-ONE PACKAGE
IS LOCATED DIRECTLY BELOW THE SEAT ON THE FLOOR OF THE CARGO COMPARTMENT
AND TWO PACKAGES ARE LOADED SYMMETRICALLY AT A SOD (SPACING OUT DISTANCE)
CM ON EITHER SIDE OF THE CENTER PACKAGE.
1 2 3 4 5 6 7 8 9 10
DOSE RATE AT THE SEAT LOCATION ABOVE THE THREE PACKAGES WITH THE GIVEN SOD BETWEEN PACKAGES (mrem/hr)
-------
10
u
.2 3
tt
UI
o.
.4
.2
FIGURE 9. DETERMINATION OF APPROXIMATE MAXIMUM
Tl PER PACKAGE UTILIZING DOSE RATE CRITERIA,
1 Package Directly Under Seat
3 Packages SOD=210cm
248Smci "MO - 99mTc SOURCE PER PACKAGE
DC-9 CARGO CONFIGURATION
3 Packages SOD=70cm
3 Packages SOD=Ocm
I
J I
.2
.3
1 2346 10
DOSE RATE TO SEAT LOCATION (mrem/hr)
20
30 40 50
100
NJ
-------
10
FIGURE 10. APPROXIMATE MAXIMUM Tl PER FLIGHT
cc
LU
O.
I
X
O
4
3.5
3
A. 5
2.
1,5
1.0
2485 mci 99Mo - 99mTc SOURCE PER
PACKAGE-DC-9 CARGO COMPARTMENT
I I I
I
III til
.15 .2 .25
1.0 1.5 2 2.5 3 4 56
10
MAXIMUM DOSE RATE TO SEAT LOCATION (mrem/hr)
-------
Table 3. Floor. Location Package Size Sensitivity Analysis for
the DC-9
Approximate Maximum Seat Location
Dose Rate Normalized to 1 for 40 cm
(vertical height) package located
Package Vertical Height (cm) on the DC-9 cargo compartment floor
15
20
25
30
35
40
50
Table 4. Top of Cargo Compartment
Analysis
Package Vertical Height (cm)
15
20
25
30
35
40
50
55
0.84
0.87
0.90
0.93
0.97
1.0
1.1
Location Package Size
Approximate Maximum
Dose Rate Normalized
cm (vertical height)
at top of the cargo
1.6
,1.4
1.3
1.2
1.1
1.0
.85
.79
Sensitivity
Seat Location
to 1 for a 40
package located
compartment
25
-------
The floor location package size sensitivity analyses (Table 3)
assumed that the package was on the floor of the cargo compartment and
that the spacing between the floors of the cargo and passenger compart-
ments was 118 cm. The seat location was assumed to be 40 cm above the
floor of the passenger compartment. The maximum seat location dose
rate was assumed to be proportional to I/(40 + 118 + d/2) . Since
d/2 was much less than 40 + 118, package size "d" changes did not
greatly change the seat location dose rate.
The package loading location which will result in the maximum
seat location dose rate is the case where the package is located at
the top of the cargo compartment directly under the floor of the
passenger compartment;. For this package location, the maximum seat
location dose rate was assumed to be proportional to 1/(40 + d/2) .
The results in Table 4 indicate that the maximum seat location dose
rate is more dependent on package size for a package located at the
top of the cargo compartment than for a package located on the floor
of the cargo compartment.
Utilizing the data in Tables 3 and 4, a comparison was made of
the maximum seat location dose rate for a package on the floor and at
the top of the DC-9 cargo compartment. The comparison results presented
in Table 5 indicate that the maximum seat location dose rate increases
significantly when the package is placed at the top rather than on
the floor of the cargo compartment. If the package is loaded at the top
rather than on the floor of the cargo compartment * the maximum seat
location dose rates would be even greater for other types of passenger
aircraft that have a greater separation distance between the floors of
the passenger and cargo compartments. Passenger seat location dose,.rates
will be greatly increased for packages located at the top of the cargo
compartment above those loaded on the floor of the cargo compartment.
3. Special Aircraft Compartments
Radioactive materials could be shipped in passenger aircraft with
low exposure to passengers if the material was placed in compartments
designed specifically to provide protection. Two basic design philo-
sophies are available for this alternative; first, the distance factor
philosophy which would place the radioactive material at a sufficient
distance from normally occupied compartments to maintain low exposure
levels to occupants; and second, the shielding philosophy which would
provide sufficient mass between the radioactive material and aircraft
26
-------
Table 5. Maximum Seat Location Dose Rate Comparison For Different
Cargo Compartment Loading Locations
Approximate DC-9 Seat Location
Dose Rate Ratio
[Package at Top of Cargo Compartment
Package Vertical Height (cm) Package on Floor of Cargo Compartment]
15 10
20 8.8
25 7.8
30 6.7
35 6.0
40 5.3
50 4.2
Table 6. Weighted Exposure Time for Select Groups
Select Groups Weighted Exposure Time Per Year (Hours)
Average Maximum
Most frequent travellers 17 50
Weekday commuters 13* 125*
Weekend commuters 23 130
*The weighted exposure time includes a time reduction factor of 1/2 to
account for the fact that the number of TI's on flights carrying radio-
active material on weekdays is less than half the number on weekends.
Table 7. Weighted Exposure Time* for Passenger Who Sits in the Seat
Location Having the Maximum Dose Rate
Trips/yr in Seat Location
Having the Maximum Dose Rate Weighted Exposure Time (Hours)
Maximum Dose Rate Time Average Dose Rate Time
T 5
2 10 (see table 6)
3 15
4 20
* Assumes 5 hours per trip 27
-------
passengers to maintain a low exposure level to passengers. An example
of the first case is a wingtip compartment which would provide a
maximum spacing distance to passengers. The second case could be achieved
through the use of a permanent lead shield in the cargo compartment in
which all radioactive material packages would be placed for shipment.
Both of these cases would require a detailed analysis by aircraft
designers to insure that the additional weight and/or structural
requirements would not reduce or interfere with flight safety. The
costs would also require close scrutiny since modification of essentially
all aircraft currently in service would be required. In addition,
this option introduces the regulatory issue of placing more of the
protection requirements on the carrier rather than the shipper. However,
this alternative could provide the additional protection indirectly
and thus could be investigated thoroughly to determine its acceptability.
4. Restricted Seating Areas on Aircraft
The AEC has recommended that predesignated areas within the
cargo compartment for all passenger aircraft be identified and used
for storage of radioactive materials during shipiient. An adjunct to
this recommendation would be the identification jf those seats at which
the higher exposure rates would exist when radioactive materials were
on board. The use of these seats could then be restricted on any or
all flights in which radioactive materials are carried. This alter-
native appears feasible for those flights which have partial occupancy.
However, when occupancy is at or near capacity, the cost of restricting
the use of a group of seats could be high depending on the flight time.
However, even if use of the restricted seats were permitted for
under capacity or near capacity conditions, there would be some
reduction in overall exposure because not all flights are at capacity.
An estimate of the exposure reduction which could be attained if
restricted seats were not used during flights of less than full
capacity can be made by assessing data on flight occupancy factors
in conjunction with data on the fraction of flights carrying radio-
active material. This option may be worthy of investigation since
the dose reduction would be achieved with no additional cost.
For either of the above cases a significant reduction in the dose
to the embryo and the fetus could be accomplished by prohibiting the
seating of fertile women in the restricted seats. This is due primarily
28
-------
to the higher radiosensitivity of the embryo and the fetus as discussed t
by the NCRP (9).
C. Effect of Shipping Procedures on Passenger Exposure
1. Modified Schedules for Mo-Tc Generators
It appears feasible to modify shipping schedules of the Mo-Tc
generators to reduce the exposure rate to passengers. The first
modification considered is the shipment of one Mo-Tc generator (500
mCi quantity) at 8 a.m. on Sunday rather than 8 a.m. on Saturday (14).
In order to have 500 mCi remaining at 8 a.m. on Friday, 1930 mCi
should be shipped at 8 a.m. on Sunday. This includes a correction factor
for radiological decay and 10% overage for elution efficiency and other
factors. The attached Figure 11 presents cost effective curves for
both the 1930 and 2485 mCi source strengths. If sufficient lead
shielding is added to limit the maximum passenger seat dose rate (from
one package) to .5 mrem/hr, a cost saving of $1.50 per package will
result if the weekly shipment is made at 8 a.m. on Sunday rather than
8 a.m. on Saturday. If sufficient lead shielding is added to limit the
maximum passenger seat dose rate (from one package) to .2 mrem/hr, a
cost savings of $3 per package will result if the weekly shipment is made
at 8 a.m. on Sunday rather than 8 a.m. on Saturday. The cost savings
for other dose rate criteria can be determined from an analysis of
Figure 11.
2. More Frequent Shipments of Smaller Mo-Tc Generators
A second alternative for shipment of Mo-Tc generators is to ship
two sources per week instead of one. Such a change would reduce doses
to the maximum Individual but would not significantly reduce population
dose.
This option requires twice as many shipments per week than the
shipment of a single "500 mCi" source. In order to have 500 inCi at
8 a.m. on Wednesday and 500 mCi at 8 a.m. on Friday, 1520 mCi can be
shipped at 8 a.m. on Saturday and 294 mCi can be shipped at 8 a.m.
on Wednesday. If both the 294 mCi and 1,520 mCi shipments are made in
25 pound lead shields the dose rate to the seat location directly above
the packages will not exceed 1.8 mrem/hour. These results are shown
in Figure 12. The dose rate to the seat location from a 2485 mCi package
29
-------
50
45
FIGURE 11. COST EFFECTIVE CURVES FOR ONE PACKAGE FOR DIFFERENT
SHIPMENT DATES
40
99Mo - 99mTc SOURCE SHIELDED BY LEAD-DC-9 CARGO
CONFIGURATION-COST INCREMENT IS MADE RELATIVE
TO A 25lb LEAD SHIELD
35
2
1
UJ
u
<
x
u
oc
UJ
a.
8
_i
<
ff
U
30
25
20
15
10
8 a.m. Saturday Shipment — 2485mci
"8 a.m. Sunday Shipment—1930mci
1.0
1.5
2.0
30
DOSE RATE TO SEAT LOCATION FROM PACKAGE DIRECTLY BELOW SEAT ON
THE FLOOR OF THE CARGO COMPARTMENT (mrem/hr)
-------
<
cc
UJ
Q.
UJ
LU
CC
U
FIGURE 12. COST EFFECTIVE CURVE FOR ONE PACKAGE ( OPTION ANALYSIS OF BREAKING THE
2485 mci PACKAGE UP INTO 2 PACKAGES 1520mci AND 294mci
"Mo - 99mTc SOURCE SHIELDED BY LEAD-DC-9 CARGO
COMPARTMENT CONFIGURATION-COST INCREMENT
10 -
.04 .06 .08 .1 .2 .3 .4 .5 1 2
DOSK RATE TO SEAT LOCATION FROM. PACKAGE DIRECTLY BELOW SEAT (mrem/hr)
-------
in a 25 pound shield is 2.9 mrem/hr. By breaking up the 2485 mCi source
into two packages and maintaining the same shielding, the dose rate is
lowered from 2.9 to 1.8 mrem/hour at the expense of doubling the shipping
costs since two packages rather than one had to be shipped per week.
The general conclusion from this analysis is that it does not
appear cost effective to break the shipment up into several packages
weighing 25 pounds or less. It costs less dollars for greater mrem/hr
reduction to add shielding to one package. The reason it costs more
to break the large shipment up into smaller shipments is that ground
delivery and air freight charges are the same up to some minimum
weight (40 Ib. for air freight and 65 Ibs. for ground delivery). The
delivery charge is the same for both a five pound and a forty pound
package. In addition, there is the cost of two shields instead of one.
3. Tc-99m Shipments Instead of Mo-Tc Generators
Shipments of Tc-99m could be made instead of the Mo-Tc generators.
Because of the half-life of Tc-99m it would be necessary to ship on
a daily basis and thus there would be five shipments per week instead
of one. However, the Tc-99m has a much lower photon energy and this
can be shielded with a much smaller quantity of materials to bring
the external dose rate down to well within 0.5 mrem/hour at one meter
for a 2,500 mCi shipment.
The cost per package shipped is estimated at $3 for a lead shield,
$7 for ground delivery and $10 for air freight for a total of $20 per
shipment or $100 per week. This cost can be compared to the weekly
costs for Mo-Tc generator shipments of $27.50 for a 25 pound shield and
$39.82 for a 60 pound shield neither of which would include the cost of
preparing the Tc-99m sources at the producer's facility as compared to
the cost of preparing the Mo-Tc generator.
It appears the greatest problem associated with this alternative
is assurance of daily delivery of the Tc-99m to the user. While a
system for rapid delivery probably exists in many areas, routine rapid
delivery services undoubtedly are not available for many areas or are
prohibitively expensive. In addition, areas which suffer frequent
disruption in transportation services because of inclement weather or
other causes could be ill served.
32
-------
Shipments of Tc-99m could supplement Mo-Tc generators and thus
potentially reduce the quantity of material shipped via the generators
while still assuring a supply of Tc-99m for medical use. This alter-
native may offer the industry an economic means of meeting passenger
exposure criteria for selected situations especially when combined with
other procedures. Its actual use would probably need to be established
over time by the various industry segments weighing timing, costs,
convenience, and other factors.
4. Surface and Air Cargo Shipments Instead of Passenger
Aircraft Shipments
Mo-Tc generators could be shipped by surface (truck) or air cargo
flights only or a combination of these two options. Several scenarios
could be developed as to what methods or combinations of methods would
provide adequate service and what the costs would be. This alternative
appears to offer the greatest risk reduction since the major source of
passenger dose is the shipment of Mo-Tc generators (7) and these
passenger exposures would be reduced to practically zero.
The AEC estimated that the cost of shipping via truck was
approximately $10 per package more than the cost via passenger air-
craft and that the cost on cargo aircraft was the same. This higher
cost for truck shipment is probably a significant reason why it is not
used more and air shipment is chosen in the largest number of cases.
Certainly for distances of a few hundred miles, trucks would assure 48
hour delivery of shipments. The incremental cost of shipping by surface
would-be only about 3% of the current cost of generators ($300) and
would be only $0.28 per patient examination (2).
"While the shipment of Mo-Tc generators via surface or cargo aircraft
would undoubtedly complicate the delivery of this radiopharmaceutical
in some areas of the country, it is not immediately evident that the
practice of nuclear medicine would be significantly affected. Since
the principal producers of Mo-Tc generators are geographically
distributed, it appears quite feasible that they would be able to
adequately serve by truck most users in their vicinity within the two
to three day period currently used in shipping by passenger aircraft.
It is also reasonable to assume that maximum exposures to individuals
would be less since these individuals would be located at much greater
distances and, in most cases, their exposure times would be less. It
is concluded that this alternative appears feasible and should be
investigated in much more detail.
33
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D. Annual Dose Estimates
Although any given limitation on a seat location dose rate serves to
limit passenger exposure for a given trip, it is important to consider the
implications of such practices on annual dose. Number of trips, seating
choice, frequency of shipment, and hours flown are large determinants of
annual passenger dose. The AEC devised a model relating these factors
to convert dose rate to an annual dose. Weighted exposure times in hours
per year based on this model are presented in Table 6 for select groups.
The indicated weighted exposure times reflect select group flying habits
and representative radioactive traffic factors. These times are based on
500 hours flown each year, reduced by assumed probabilities of what chance
a flight will have radioactive material on it and what chance a selected
traveler will select the seat with the maximum dose rate. Probabilities
were assumed for maximum probable conditions and average conditions.
Both maximum and average weighted exposure times are presented in
Table 6. The average seat location dose rate which is assumed as 1/2 the
maximum dose rate consistent with the AEC recommendation was utilized
to compute the dose rate for those situations where an individual does
not sit in the seat having the maximum seat dosa rate. The average dose
rate was multiplied by the appropriate weighted exposure time in Table
6 to obtain an annual dose. It should be recognized that the computed
dose may be somewhat conservative in that it in basically the surface
entrance dose rather than an average whole bod/ or gonadal dose. All
packages are assumed to be placed on the floor of the cargo compartment.
The annual dose to the passenger who sits in the seat location having
the maximum dose rate can be computed based on the number of trips per year
the passenger sits in the seat having the maximum dose rate. Using the
assumptions of the AEC model, the weighted exposure time for this passenger
for 1, 2, 3, and 4 trips per year in the seat location having the maximum
dose rate is presented in Table 7.
In order to illustrate the use of the exposure time data in Table 6
and 7, the annual dose for select groups was computed, as shown in Table 8,
for maximum seat location dose rates of 0.5 mrem/hr and 0.25 mrem/hr. The
average dose rate in the aircraft was assumed to be half these rates. It
must be recognized that the data in Table 8 are based on the assumptions
that all aircraft on which radioactive materials are shipped will have the
same maximum seat location dose rate when material is shipped and that the
traveler will occupy the seat for 5 hours when he randomly selects it.
34
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Table 8. Annual Doses to Select Grouos Based on Indicated Maximum Seat Location Dose Rates
Trips per Year
Sitting in Seat
Having Maximum
Dose Rate
Annual Dose (mrem)*
OJ
Select Group
Most frequent traveller
Most frequent traveller
Most frequent traveller
Most frequent traveller
Most frequent traveller
Weekend commuter
Weekend commuter
Weekday commuter
Weekday commuter
* Assumes that maximum seat dose rate is the same on all passenger aircraft which transports
radioactive material that traveller could select and that when he selects seat with
maximum dose rate, he would occupy it 5 hours.
for 0.5 mrem/ hour
Average Maximum
0
1
2
3
4
0
4
0
4
4.2
6.8
9.2
12
14
5.8
16
3.2
13
12
14
17
20
22
32
42
31
41
for .25 mrem/hour
Average Maximum
2.1
3.4
4.6
5.9
7.1
2.9
8
1.6
6.5
6.2
7.4
8.7
9.9
11
16
21
16
21
-------
With such circumstances Table 8 indicates that a weekend commuter may
receive, for a seat dose rate of 0.5 mrem/hr, an annual dose of up to 42
millirem, of which 10 millirem comes from occupying the seat for 5 hours on
4 different trips. If industrial shippers were to choose, as could
reasonably be expected, to meet a dose rate criterion of, say, 0.5
mrem/hr by standardizing to a shield that would meet the criterion for the
limiting aircraft (in this case the DC-9), then shipments on other aircraft
could be expected, as shown in Figure 4, to have seat dose rates less than
0.5 mrem/hr. Since only about 16% of shipments are on DC-9 aircraft, but a
large fraction (about 50%) are on B-727 aircraft where dose rates for
packages with the same shielding would be less, it is unlikely that this
annual dose of 42 millirem would occur. Also, since the limiting case is
based on a DC-9 aircraft which is generally used for relatively short
trips (usually one to two hours) the assumption of seat occupancy is
quite conservative. When account is given, therefore, for lower maximum
seat dose rates on other aircraft on which the largest fraction of
shipments occur and realistic seat occupancy times, it is reasonable
to expect, for packages shielded and placed to limit the maximum seat
dose rate of 0.5 mrem/hr, that the dose per trip would be about one
millirem and the largest annual dose to selected frequent travelers
would be less than 25 millirem. These doses are believed to be
protective of sensitive groups in the population such as children and
pregnant females who travel infrequently, and are comparable to other
well controlled sources which expose the public to radiation.
The health risk to an individual from cancer is minimal at exposure
levels that would result in doses to indivudals of less than 25 mrem/yr.
Based on U.S. vital statistics, the probability that an individual will
die of cancer is about 0.19. After a lifetime irradiation at 0.025
rem per year (in excess of background radiation) this probability is
increased by about 0.0002, which is the best estimate based on the
geometric mean of absolute risk (.0001) and relative risk (.0004). This
represents an increase of about one tenth of one percent. This is not the
total impact from lifetime total body exposure; the NAS-BEIR Committee (10)
estimates the total of both fatal and non-fatal radiation induced cancers
would be a factor of 2 larger. Genetic effects are more difficult
to estimate; but their total increase, expressed over several generations,
would be comparable to the increased cancer incidence.
E. Impact on Other Exposures
Since it appears that the most efficacious approach to reduce
exposures to personnel aboard passenger aircraft is to increase packaging
shielding, it is expected that exposures to all personnel involved in
36
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handling packages and many of those using sources would be reduced to
an extent similar to that for personnel aboard aircraft. The impact
of an attempt to reduce exposure aboard aircraft is not expected to
result in a transference of radiation dose to other personnel in other
parts of the transportation industry since procedures, storage awaiting
shipment, schedules, and number of times handled would not be expected
to change from the current situation. The possible exception to this is
diversion of the majority of shipments to surface transport in lieu
of developing increased package shielding and placement requirements. In
this instance, the general public will still quite likely receive less
exposure since the demand for most of the materials precludes their
being in transit for long periods and the fact that the alternative modes
of transport (trucks principally) do not also transport passengers.
IV. SUMMARY AND RECOMMENDATION
This analysis indicates that a number of technically and economically
feasible actions can be taken to reduce the radiation doses received
by personnel on passenger aircraft from radioactive materials which,
because of short half lives or urgent medical nseds, are required to
be shipped by air. These actions allow the public to derive the full
benefits of nuclear medicine, are not expected to produce additional
radiation impact on other members of the population, and are consistent
with current air transport regulations based ou package labeling,
quantities, and placement requirements. The actions to obtain such
radiation dose reductions will result in additional monetary costs;
however, there are cost-effective levels available which result in
minimal increases in the total costs to patients for nuclear medicine
procedures. A cost-effective level of dose rate reduction based on
case corresponds to an increased cost of about $0.30 to a patient who
normally pays'$100 to $150 for the procedure. Such a dose rate reduction
can be gained for the limiting aircraft by increasing package shielding
from the 25 pounds currently used to about 58 pounds, an action that
corresponds to a TI of 1.0 for Mo-Tc generators and a maximum seat level
dose rate of 0.5 mrem/hr on the limiting aircraft. Shipment of such
packages on the types of passenger aircraft available are expected to
result, whith appropriate credit given to occupancy and travel time,
in doses to the travelling public of about one millirem per trip and
less than 25 millirem to those who travel frequently. Achievement
of such exposures is protective of public health and is in accord with
principles contained in current Federal radiation guidance.
On the basis of the foregoing analysis, it is recommended that
necessary transportation of radioactive materials on commercial aircraft
be conducted in such a manner that the dose equivalent rate at seat
level to any occupant of an aircraft does not exceed 0.5 mrem/hr.
37
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REFERENCES
1. Burns, W. J., Testimony before a Subcommittee of the Committee
on Government Operations, U.S. House of Representatives, March
14, 15, and April 5, 1973.
2. Goodrich, J. K., ibid.
3. National Transportation Safety Board, Special Study of the Carriage
of Radioactive Materials by Air, NTSB-AAS-72-4, April 1972.
4. Shapiro, J., et al., Determination of Exposure Rates to Occupants
of Passenger Aircraft Used to Transport Radioactive Materials,
AEC Contract No. AT (11-1) 2356, June 1973.
5. Shapiro, J., et al., Determination of Exposure Rates to Occupants
of Passenger Aircraft Used to Transport Radioactive Materials,
AEC Contract No. AT (11-1) 2405, April 1974.
6. Johnson, R. M., and E. R. Hermann, "Survey to Establish Radiation
Dose Rates Received by Airline Passengers and Crew," July 1973,
7. U.S. Atomic Energy Commission, Recommendations for Revising
Regulations Governing the Transportation of Radioactive Material
in Passenger Aircraft, submitted to the Federal Aviation Adminis-
tration, July 1974.
8. Federal Radiation Council, Background Material for the Develop-
ment of Radiation Protection Standards, FRC Report No. 1, May 1960.
9. National Council on Radiation Protection and Measurements, Basic
Radiation Protection Criteria, NCRP Report No.. 39, January 1971.
10. National Academy of Sciences, National Research Council, The Effects
on Populations of Exposure to Low Levels of Ionizing Radiation,
Report of the Advisory Committee on the Biological Effects of
Ionizing Radiation, November 1972.
11. International Commission on Radiological Protection, Implications
of Commission Recommendations that Doses be kept as Low as Readily
Achievable, ICRP Publication 22, April 1973.
12. Rowe, W. D. and A. C. B. Richardson, Basic Concepts for Environ-
mental Radiation Standards, IAEA-SM-184/20.
13. Senate of the United States, Committee on Commerce, Working Paper,
Hazardous Materials Transportation Act, August 1974.
14. Brownell, Gordon L. and John A. Correia, Impact on the Cost of
Shipping Radiopharmaceuticals of Varying the Package External
Radiation Levels, A Report to the U.S. Atomic Energy Commission,
July 8 (1974).
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