J Forensic Sci, July 2008, Vol. 53, No. 4
doi: 10.1111/j.1556-4029.2008.00766.x
Available online at: www.blackwell-synergy.com
TECHNICAL NOTE
Kenneth P. Hermsen,1 D.D.S., M.S.; Stanley S. Jaeger,2 M.S.; and Mackenzie A. Jaeger2
Radiation Safety for the NOMADTM Portable
X-Ray System in a Temporary Morgue Setting*
ABSTRACT: The purpose of this study was to determine the radiation levels resulting from leakage and scatter encountered by the forensic dental personnel using the NomadTM at St. Gabriel, LA, following Hurricane Katrina. Using a Keithley Radiation Survey Meter and Lucite head phantom, radiation levels were measured at various distances and angles from the NomadTM corresponding to the positions occupied by the dental
personnel at St. Gabriel. The measurements were used to approximate the maximum total radiation dose from the Nomad to each team member for
a 2- and a 4-week deployment. The results show that the maximum scatter radiation dose to any team member was 4.4 lR per X-ray or 0.253 millisieverts (mSv) for a 2-week deployment and 0.506 mSv for a 4-week deployment. Therefore, the leakage and scatter radiation dose from the
NomadTM was insignificant compared with established radiation safety guidelines of 50 mSv per year for all team members.
KEYWORDS: forensic science, forensic odontology, NomadTM, radiation safety
The forensic odontologists who responded to the need for identification of the victims of Hurricane Katrina from New Orleans
were pleased to find a new tool available to them at the temporary
morgue site at St. Gabriel, LA. The new tool was a battery-powered, portable, hand-held X-ray unit called the NomadTM (Fig. 1).
Sold and distributed by Aribex, Inc., Orem, Utah, the units performed exceptionally well. They proved to be a very valuable piece
of equipment that had the portability and versatility required in the
somewhat austere conditions that typically exist in a temporary
morgue environment. The objective of this study was to determine
the exposure output and scatter characteristics of the NomadTM
Portable X-ray Unit for a given period of time and the prospective
radiation dose to the operator, assistant, and computer operator at
various body locations and angles from the beam, as encountered
in the morgue at St. Gabriel, LA, following Hurricane Katrina.
The radiation safety characteristics of the NomadTM, reported by
D. Clark Turner, Donald K. Kloos, and Robert Morten (1) for the
operator and the patient, were provided by Aribex in their promotional material. Their findings confirm that radiation levels for the
patient and operator are well within established radiation safety
guidelines. However, their report did not consider radiation levels
for additional personnel that were required to be in close proximity
to the NomadTM in a temporary morgue setting. In the morgue, the
patient cannot hold an X-ray film or computer sensor in position,
requiring a second team member, the assistant, to perform that function. The morgue operation in St. Gabriel also made use of digital
X-rays requiring a third person be present to operate the computer.
Early in the operation at St. Gabriel, there were as many as three
dental stations, each with three-person forensic dental teams operating simultaneously within the dental section. As professionals who
1
Creighton University Medical Center School of Dentistry, Omaha, NE
68178.
2
Creighton University Medical Center, Omaha, NE 68178.
*An oral presentation of this work was presented to the Odontology Section of the American Academy of Forensic Sciences at their Annual Meeting in San Antonio, Texas, February 2007.
Received 9 Sep. 2007; and in revised form 18 Nov. 2007; accepted 24
Nov. 2007.
2008 American Academy of Forensic Sciences
frequently deal with radiation, the issue of radiation safety was a
concern to the team leaders because of the close proximity of the
dental teams. There were no dosimeter badges available to measure
the amount of radiation to which the team members may be
exposed. To address the issue, it was decided that a coin would be
taped to a dental periapical X-ray film. Each member was provided
a film with a coin attached and wore the film for a period of 7 days
under the Tyvek suit whenever they were in the morgue. At the end
of 7 days, the films were developed. None of the films showed the
image of the coin, indicating that none of the team members was
exposed to enough radiation to expose the film. However, considering the number of X-rays taken at St. Gabriel, there was a need to
quantify the radiation levels more precisely at various distances and
locations to confirm that radiation dose levels to all personnel in the
morgue were within the recommended radiation safety levels.
Methods
A polymethyl methacrylate (Lucite) head phantom (Fig. 2)
(Dupont, Inc., Wilmington, DE) was used to approximate a human
head for measurements from 0 to 90, and two Lucite rectangular
blocks were used for readings from 105 to 180 to approximate
the mandible and maxilla. The head phantom (Fig. 2) has a diameter of 16 cm and the blocks have a thickness of 5.1 cm each,
10.2 cm in total. Both have a density of 1.19 (€0.01 g ⁄ cm3), so
multiplying the density to each thickness equals about 19.0- and
12.1-cm equivalent tissue thickness for the head phantom and
Lucite blocks, respectively. All exposures were carried out with the
removable external lead ring in place at the end of the NomadTM
cone (Fig. 3). Exposures were taken through the Lucite phantom
and measured using the Keithley Radiation Survey Meter (Keithley
Instruments, Inc., Cleveland, OH) (Fig. 4) in the integrate mode on
a scale of 0–200 micro-Roentgens (lR). The NomadTM was set to
0.12 sec, 60 kVp, and 2.3 mA for each X-ray exposure, the same
settings that were typically used at St. Gabriel. Readings were
taken in a horizontal plane at angles of 0 to 180 in 15-increments (Fig. 5). 0 was directly behind the NomadTM and 180 was
directly in front of the cone in direct line with the radiation beam.
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TM
FIG. 4—Keithley Integrating Radiation Survey Meter, Model 36150
(Keithley Instruments, Inc., Cleveland, OH).
FIG. 1—The Nomad is a hand-held, portable X-ray unit that is powered
by rechargeable batteries. It proved to be a very valuable tool in the operation at St. Gabriel.
FIG. 2—Polymethyl methacrylate (Lucite) phantom (Dupont, Inc., Wilmington, DE).
FIG. 5—Horizontal measurements were taken in 15 increments from 0
to 180 at a distance of 0.46 and 1 m at three different vertical positions
corresponding to the height of the head, chest, and waist of the assistant
and operator.
at a horizontal distance of 0.46 m away from the phantom at the
0 angle. Additionally, the operator’s hand dosage measurements
were taken at points ‘‘A’’ and ‘‘B’’ (Fig. 3), front and back respectively, of the NomadTM handle to check for radiation leakage. For
the assistant, measurements were taken at a horizontal distance of
1 m (Fig. 7) corresponding to the exposure to the assistant’s head,
chest, and waist. A vertical distance of 1.5 m from the floor was
used as the head height, 1.33 m from the floor as the chest height,
and 0.93 m from the floor as the waist height. Measurements were
taken at 45 and 90 for the computer operator at a horizontal distance of 1.5 m away from the phantom and a height of 0.93 m. A
reading at the waist height was the only height measurement
required due to the computer operator being seated at the computer
while the exposure is taking place.
FIG. 3—The lead ring proved to be very important for shielding from
scatter radiation. Operation without the lead ring in place resulted in radiation measurements as much as 10 times higher.
The operator occupied what the NomadTM promotional material
called the ‘‘zone of significant occupancy’’ (Fig. 6) from 0 to
c. 35. Readings were taken at the operator’s head, chest, and waist
Results
The radiation levels as detected by the Keithley Radiation Survey Meter are tabulated in Table 1. These measurements represent
the amount of radiation in micro-Roentgens per exposure at the
various locations. Using these measurements, the dose to the
HERMSEN ET AL. • RADIATION SAFETY FOR THE NOMAD
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FIG. 7—Measurements were taken at a horizontal distance of 1 m for the
assistant’s head, chest, and waist.
FIG. 6—‘‘Zone of Significant Occupancy,’’ Aribex, Inc. Used by
permission.
operator, assistant, and computer operator deployed to St. Gabriel
was calculated based on operation of the NomadTM unit for one
12-day period (Table 2) and two 12-day periods (Table 3). The
number of exposures was calculated based on each dental team
averaging 30 examinations per shift, 16 exposures per victim, and
working 12 complete 12-h shifts during a 2-week deployment. The
results show that the maximum radiation dose as a result of scatter
radiation was to the assistant’s chest when the assistant occupied
the position at 60 to the NomadTM or 30 behind the plane of the
lead ring. At this location, the assistant’s chest was exposed to
4.4 lR of radiation per X-ray (Table 1) or 0.253 millisieverts
(mSv) per 5760 X-rays for a 2-week deployment (Table 2). The
radiation measurements for all angles and locations can be found in
Tables 1, 2, and 3. It should be noted that in our study, we found
that having the lead ring properly positioned on the end of the
NomadTM cone was essential. Removing the lead ring resulted in
TABLE 1—Radiation dose per exposure.
Dose in lR for Given Angle
Person
Location Distance (m)
Assistant
Operator (body)
(hand)
Computer
Waist
Chest
Head
Waist
Chest
Head
A
B
Waist
1
1
1
0.46
0.46
0.46
0
15
30
45
60
75
90
105
120
135
150
165
180
0.3
0.5
0.7
1.5
2.1
3.4
2.3
1.0
0.7
1.1
0.9
0.9
1.0
1.8
2.1
2.9
3.0
3.0
4.4
4.0
2.7
3.3
2.9
2.4
2.9
2.3
0.6
1.1
1.1
1.1
1.2
1.2
1.5
2.2
2.0
2.3
2.8
2.2
3.2
3.3
2.7
3.9
33.5
3.6
1.5
0.3
0.4
Exposure conditions: 60 kVp, 2.3 mA, 0.12 sec (0.276 mAs).
Waist height from floor, 0.93 m; chest height from floor, 1.33 m; head height from floor, 1.5 m.
TABLE 2—Radiation dose for 2-week deployment.
Dose in mSv for Given Angle
Distance
Location
(m)
Person
Assistant
Operator (body)
(hand)
Computer
Waist
Chest
Head
Waist
Chest
Head
A
B
Waist
1
1
1
0.46
0.46
0.46
1.5
0
15
30
45
60
75
90
105
120
135
150
165
180
0.016
0.026
0.037
0.079
0.111
0.180
0.122
0.053
0.037
0.058
0.048
0.048
0.053
0.095
0.111
0.154
0.159
0.159
0.253
0.212
0.143
0.175
0.154
0.127
0.154
0.122
0.032
0.058
0.058
0.058
0.064
0.064
0.079
0.117
0.106
0.122
0.148
0.117
0.170
0.175
0.143
0.207
1.775
0.191
0.016
0.021
Exposure conditions: 60 kVp, 2.3 mA, 0.12 sec (0.276 mAs).
Waist height from floor, 0.93 m; chest height from floor, 1.33 m; head height from floor, 1.5 m.
16 exposures ⁄ patient · 30 patients ⁄ day · 12 day period = 5760 exposures.
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TABLE 3—Radiation dose for 4-week deployment.
Dose in mSv for Given Angle
Person
Location Distance (m)
Assistant
Operator (body)
(hand)
Computer
Waist
Chest
Head
Waist
Chest
Head
A
B
Waist
1
1
1
0.46
0.46
0.46
1.5
0
15
30
45
60
75
90
105
120
135
150
165
180
0.032
0.052
0.074
0.158
0.222
0.360
0.244
0.106
0.074
0.116
0.096
0.096
0.106
0.190
0.222
0.308
0.318
0.318
0.506
0.424
0.286
0.350
0.308
0.254
0.308
0.244
0.064
0.116
0.116
0.116
0.128
0.128
0.158
0.234
0.212
0.244
0.296
0.234
0.340
0.350
0.286
0.414
3.55
0.382
0.032
0.042
Exposure conditions: 60 kVp, 2.3 mA, 0.12 sec (0.276 mAs).
Waist height from floor, 0.93 m; chest height from floor, 1.33 m; head height from floor, 1.5 m.
16 exposures ⁄ patient · 30 patients ⁄ day · 12 day period · 2 periods = 11,520 exposures.
radiation readings almost 10 times higher than measurements with
the ring in place.
Discussion
The risks and benefits of ionizing radiation have been well established over the past several decades. The National Council on Radiation Protection and Measurements (NCRP), established by
Congress in the mid-1960s, is responsible for collecting and analyzing worldwide data regarding radiation safety. Based on their analysis, the NCRP develops safety guidelines that establish annual
maximum permissible dose (mpd) levels. According to the NCRP,
every day in the United States, we are exposed to c. 3.65 mSv of
naturally occurring radiation from our environment. The maximum
permissible dose for occupational exposure established by the
NCRP is currently 50 mSv (2). This means that the NCRP has
determined that an individual who works with ionizing radiation
can be exposed to up to 50 mSv of radiation annually in performing their occupation without increasing the risk for developing radiation-related illnesses. This exposure is in addition to the 3.65 mSv
from the environment. The annual dose limit for a radiation worker’s hand cannot exceed 500 mSv.
In our study, it was estimated that c. 5760 exposures would be
the maximum number of radiographs that could have been taken by
any dental team while on a 2-week deployment at St. Gabriel. This
number was attained by assuming an average of 16 exposures per
patient, 30 patients per day over a 12-day period and used as the
standard for all calculations. It was noted that the measurements
obtained in our study for the operator were similar to the exposure
values quoted in the NOMADTM literature of 1 mR of operator dose
for 138 mAs exposure. From phantom measurements, the maximum
dosage reading overall was recorded at the assistant’s chest 1 m
away and directly in front of the beam (180), a position that no
one on the dental team occupied while the digital sensors were
being exposed to radiation. The next highest reading outside the primary beam was for the assistant’s chest 1 m away and 60 from the
beam. Even if one member of the dental team remained as the assistant for their entire deployment and positioned at 60 for every
exposure, the 4.4 lR per exposure (Table 1) would accumulate to
only 0.253 mSv (Table 2) for the entire deployment. Therefore,
0.253 mSv is the maximum radiation dose that any member of the
dental team could have received in a 2-week deployment. Compared
with the annual occupational dose limit of 50 mSv, the radiation
exposure to the assistant was insignificant. The radiation dose to the
operator and computer operator was even less.
Even though the risk to the dental personnel was extremely low
at St. Gabriel and posed no health risk, radiation safety should
never be taken for granted. Every precaution should be taken to
limit exposure to the operator, assistant, and computer operator by
utilizing proper radiation safety procedures whenever and to whatever extent possible (3–5). As Low As Reasonably Achievable
(ALARA) is the approach that radiation safety experts take to provide the safest possible radiation environment. One way to ensure
ALARA is to follow appropriate Time-Distance-Shielding methods.
Set exposure time to the smallest value that will still provide accurate results, increase the distance between teams working simultaneously as much as possible, and shield oneself whenever the
equipment is provided and plausible. Also, if available, radiation
badges are a valuable tool to monitor each team member’s accumulated exposure over time.
Conclusion
As Forensic Odontologists, circumstances in a morgue setting
like St. Gabriel often require that dental personnel remain in relatively close proximity to the radiation source to obtain postmortem
radiographs. ALARA can be achieved when using the NomadTM
by never operating the NomadTM without the lead ring in place,
keeping the exposure time as short as possible, using digital radiography or conventional ‘‘E’’ speed film, having the assistant share
the ‘‘zone of significant occupancy’’ with the operator as much as
possible, and rotate duties during long deployments. St. Gabriel
was the first large-scale domestic use of the NomadTM and the
amount of scatter radiation associated with its use was largely
unknown to the dental personnel. However, the NomadTM proved
to be very valuable in accomplishing the task at hand and very
safe, posing no significant health risk to any of the dental personnel
at St. Gabriel.
Acknowledgments
The authors would like to thank Dr. Richard Weems and Dr.
Tarnjit Saini for their information and advice on dental radiology and Karen Farias for her assistance in the preparation of
this manuscript.
References
1. Turner C, Kloos D, Morton R. Radiation safety characteristics of
the NomadTM portable x-ray system [promotional material]. Orem, UT:
Aribex, Inc. Copyright, 2005–2006.
HERMSEN ET AL. • RADIATION SAFETY FOR THE NOMAD
2. National Council on Radiation Protection and Measurements. Radiation
protection in dentistry [report #145]. Bethesda, MD: NCRP, 2003.
3. Wall B, Kendall G, Edwards A, Bouffler S, Muirhead C, Meara J. What
are the risks from medical x-rays and other low dose radiation? Br J
Radiol 2006;79:285–94.
4. Mupparapu M. Radiation protection guidelines for the practicing orthodontist. Am J Orthod Dentofacial Orthop 2005;128(2):168–72.
5. White S, Pharoah M. Oral radiology; principles and interpretation, 5th ed.
St. Louis, MO: Moseby, 2004:47–67.
Additional information and reprint requests:
Kenneth P. Hermsen, D.D.S., M.S.
Creighton University Medical Center School of Dentistry
2500 California Plaza
Omaha, NE 68178
E-mail: kennethhermsen@creighton.edu
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