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Cone-beamcomputedtomographyforroutine
orthodontictreatmentplanning:Aradiation
doseevaluation
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Cone-beam computed tomography for routine
orthodontic treatment planning: A radiation
dose evaluation
Maria Alves Garcia Silva,a Ulrich Wolf,b Frank Heinicke,c Axel Bumann,d Heiko Visser,e and Edgar Hirschf
Goiás, Brazil, and Leipzig, Berlin, and Oldenburg, Germany
Introduction: Because of the advantages and possibilities of cone-beam computed tomography (CBCT),
orthodontists use this method routinely for patient assessment. The aim of this study was to compare the
radiation doses for conventional panoramic and cephalometric imaging with the doses for 2 different CBCT
units and a multi-slice CT unit in orthodontic practice. Methods: The absorbed organ doses were measured
by using an anthropomorphic phantom loaded with thermoluminescent dosimeters at 16 sites related to
sensitive organs. The 4 devices (Sirona DS Plus [Sirona Dental Systems, Bernsheim, Germany], i-CAT
[Imaging Sciences International, Hatfield, Pa], NewTom DVT 9000 [QR, Verona, Italy], and Somatom
Sensation [Siemens Medical Solutions, Erlangen, Germany]) were used with standard protocols and, when
possible, in the auto-exposure mode. Equivalent and effective doses were calculated. The calculation of the
effective doses was based on the International Commission on Radiological Protection’s 2005
recommendations. Results: The lowest organ dose (13.1 ␮Sv) was received by the thyroid gland during
conventional panoramic and lateral cephalometric imaging. The highest mean organ dose (15,837.2 ␮Sv)
was received by the neck skin from the multi-slice CT. The effective dose was also lower for the panoramic
and lateral cephalometric device (10.4 ␮Sv), and highest for the multi-slice CT (429.7 ␮Sv). Conclusions:
From a radiation-protection point of view, conventional images still deliver the lowest doses to patients.
When 3-dimensional imaging is required in orthodontic practice, a CBCT should be preferred over a CT
image. Further studies are necessary to justify the routine use of CBCT in orthodontic treatment planning.
(Am J Orthod Dentofacial Orthop 2008;133:640.e1-640.e5)
T
hree-dimensional (3D) craniofacial imaging
techniques have changed how professionals approach diagnoses in dentistry and orthodontics.
Although computed tomography (CT) is still used in
many clinical situations when 3D information is
needed, its use has been limited in dentistry due to its
high cost, low vertical resolution, and high dose of
radiation. The cone-beam CT (CBCT) scanner is intrinsically 3D in its acquisition of images and provides
a
Associate professor, Department of Stomatologic Sciences, School of Dentistry, Federal University of Goiás, Goiás, Brazil.
b
Professor, Centre for Radiotherapy and Radio Oncology, University of
Leipzig, Leipzig, Germany.
c
Assistant professor, Centre for Radiotherapy and Radio Oncology, University
of Leipzig, Leipzig, Germany.
d
Private practice, Berlin, Germany; assistant clinical professor, Department of
Craniofacial Sciences and Therapy, University of Southern California, Los
Angeles.
e
Professor, Private practice, Oldenburg, Germany.
f
Assistant professor, Department of DentoMaxilloFacial Radiology, Dental
School, University of Leipzig, Leipzig, Germany.
Supported by CAPES Brazilian Foundation.
Reprint requsts to: Maria Alves Garcia Silva, Rua 13, No. 778, Setor Marista,
74150-140 Goiania, Goiás, Brazil; e-mail, [email protected].
Submitted, April 2007; revised and accepted, November 2007.
0889-5406/$34.00
Copyright © 2008 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2007.11.019
usable images from equipment that is compact and
affordable for small diagnostic centers.1,2
CBCT has been considered the examination of choice
in many instances, since it provides high-resolution imaging, diagnostic reliability, and risk-benefit assessment.3,4
Its use is recommended in orthodontic practice for impacted teeth,5 temporomandibular joint evaluations,6,7 3D
views of the upper airways,8 assessment of maxillofacial
growth and development, and dental age estimation.9
CBCT has also demonstrated validity for biomechanical
simulations, models of bone remodeling, simulations for
orthodontic surgical planning,10 and measurements taken
by digitizing points in 3D coordinates.11 Because of these
advantages and possibilities in orthodontic assessment,
treatment, and follow-up, and its relatively low cost, many
orthodontists use CBCT routinely for all patients.
The radiation dose to the patient with CBCT is
markedly lower than that of multi-slice CT5,12; doses
are 3 to 7 times more than panoramic doses and 40%
less than conventional CT.13,14 However, orthodontic
assessment with CBCT should follow the “as low as
reasonably achievable” (ALARA) principle. Other
studies have shown a dose reduction of 50% in orthodontic practice with digital direct15 or indirect16 ceph640.e1
640.e2 Silva et al
American Journal of Orthodontics and Dentofacial Orthopedics
May 2008
Table I. Sites in which TLD 100H chips were placed
(all TLDs were in the primary radiation beam)
Organ
Bone marrow
Spine
Brain
Eye
Thyroid gland
Salivary glands
Skin
Table II.
Technical parameters and FOV exposure of
the phantom
TLD location
Third cervical vertebra
Mandibular ramus
Cervical
Hypophysis
Lens
Maxillary and mandibular premolars
Maxillary sinus floor
Thyroid
Submandibular
Parotid
Thyroid
Neck (back)
Philtrum
Parotid
Nasion
alometric radiography or the collimated lateral beam
for cephalometric images.17 Radiation doses between
conventional and CBCT images for orthodontic practices have not been compared. The aim of this study
was to compare the absorbed radiation and effective
doses for conventional panoramic and cephalometric
imaging, 2 CBCT units, and a multi-slice CT unit in
orthodontic practice.
MATERIAL AND METHODS
Dose measurements were carried out on an anthropomorphic phantom, especially designed for dosimetry
studies in dental radiography. The phantom was developed and built at the University of Göttingen (Germany)18 and consisted of 48 transverse sections, each 6
mm thick with small holes positioned perpendicular to
the axial axis of the phantom. Lithium fluoride thermoluminescent dosimeter chips (Harshaw TLD-100H,
Thermo Electron, Oakwood Village, Ohio) were used.
One advantage of lithium fluoride-based thermoluminescent materials is their tissue-equivalent properties.
The absorbed dose from selected locations, corresponding to the radiosensitive organs of interest, was measured by using a set of 48 TLD chips, which were
individually packed in thin polyethylene bags to prevent contamination by dirt and humidity. The TLD
chips were placed in each phantom site inside and on
the surface of the phantom, as shown in Table I. Three
dosimeters were placed in each anatomic site to calculate the mean value of each location, while retaining the
same dosimeters in the same positions for each exposure. Before the study, all dosimeters were calibrated
using the same type and range of radiation that would
NewTom 9000
i-CAT
Orthophos DS
Orthophos DS
Somaton Sensation
FOV
Tube
energy
(kV)
Tube
current
(mA)
23 cm
13 cm
Program 1
Lateral cephalometric
10 cm
110
120
70
76
120
5.4
23.87
10 per 14 s
9 per 0.64 s
90
be used during the experiments. Prior to every exposure, the dosimeters were annealed at 240°C for 10
minutes and cooled to 35°C. All TLDs were read
immediately after each exposure, using a Harshaw
5500 Series Automatic TLD Reader (Harshaw/Bicron,
Solon, Ohio).
The devices used in this study were the NewTom
9000 (QR, Verona, Italy), the i-CAT (Imaging Sciences
International, Hatfield, Pa), the Panoramic Orthophos
Plus DS (Sirona Dental Systems, Bernsheim, Germany), and the multi-slice CT (Somatom Sensation 64;
Siemens Medical Solutions, Erlangen, Germany). Table II shows the technical parameters and the field of
view (FOV) for each unit. Considering the small
amount of radiation and the exposure latitude of the
TLDs, the phantom, after loading with the TLD, was
exposed 5 times, to provide a reliable measure of
radiation in the dosimeters. Later, the values were
divided by 5 to obtain a value for each region. Thyroid
shields were not used during the exposures. To compare the data, we used a large FOV to obtain images
from the whole maxilla and mandible parts. The x-ray
parameters were for a young male adult. Automatic
parameters were used for the NewTom and the i-CAT.
Since the phantom is composed of multiple slabs,
several tapes were used to align them and maintain their
positions when the phantom was irradiated. The phantom was positioned according to the manufacturer’s
specifications for each machine, following the reference lines and head rests. The dosimetry was performed
3 times for each technique to ensure reliability.
After reading, a sensitivity value was applied for
each TLD. The exposure doses were recorded in
nanocoulombs (nC), and, after applying energy calibration factors (reader calibration factor and element
correction coefficient), the dosimetry data were converted into milligrays (mGy) and recorded. The standard deviation of readings from TLD-100H was less
than ⫾ 5%. Doses from the 3 TLDs, located in the same
tissue or organ, were averaged, representing the organ
dose. The weighted dose for bone marrow was calcu-
Silva et al 640.e3
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 133, Number 5
lated by using the sum of the radiation from the third
cervical vertebra and the mandibular ramus, as previously described.19 The submandibular and parotid
salivary gland doses were used for calculating the
weighted dose for the salivary glands. The thyroid
gland was individually calculated considering its specific weighted factor. For the skin surface area, 5 points
were measured: thyroid skin, neck (back), philtrum,
parotid, and nasion skin. These values were used to
calculate the equivalent dose (HT) with the equation
HT ⫽ ⌺ WR ⫻ DT, where the HT for a tissue or an
organ is the product of the radiation-weighting factor
(WR) and the average absorbed dose (DT) measured for
that organ.20 The equivalent dose was used to compare
the effects of different types of radiation on tissues or
organs in sieverts (Sv).
The effective dose (E) is a calculation proposed by
the International Commission on Radiological Protection (ICRP).20 It is calculated by multiplying actual
organ doses by risk-weighting factors (related to an
organ’s sensitivity) and represents the dose that the
total body can receive and that would provide the same
cancer risk as different doses to various organs.20 This
effective dose was calculated as follows: E ⫽ ⌺ WT ⫻ HT,
where E is the product of the ICRP’s tissue-weighting
factor (WT) for the type or tissue or body and the
human-equivalent dose for tissue (HT). The tissueweighting factor represents the contribution of each
tissue or organ to the overall risk. This dose was
expressed in ␮Sv. In this study, we used the weighting
factors proposed by the ICRP in 2005 and approved by
the Main Commission of ICRP at its meeting in March
2007; they include the salivary tissue in the risk
estimation.21
RESULTS
The average doses absorbed by the organs are
shown in Table III. The mean value was obtained from
9 measurements from each technique and each site (3
dosimeters in each site, performed 3 times). The lowest
organ dose and equivalent dose (13.1 ␮Sv) was received by the thyroid gland, during the panoramic and
lateral cephalometric examination. The highest mean
organ dose (15,837.2 ␮Sv) was obtained for the neck
skin with the multi-slice CT. Table IV gives the
equivalent and effective doses. Again, the highest value
was associated with the multi-slice CT (429.7 ␮Sv)
during brain exposure. The highest effective doses were
observed, in decreasing order, for multi-slice CT, iCAT, NewTom 9000, and panoramic and lateral cephalometric images.
Table III.
Mean absorbed doses (␮Gy) to various tissues
for each unit
Panoramic/
NewTom
lateral
Multi-slice
9000
i-CAT cephalometric
CT
Bone marrow
Third cervical
vertebra
Mandibular ramus
Brain
Hypophysis
Eye
Lens
Thyroid gland
Thyroid
Salivary glands
Submandibular
Parotid
Skin
Thyroid
Neck (back)
Philtrum
Parotid
Nasion
648.9
1244.7
731.3
1282.9
62.8
360.4
7525.6
9930.4
316.1
745.0
30.2
1488.9
472.8
1229.2
45.8
892.8
232.4
124.3
13.1
1417.7
1426.7
1678.7
1364.1
1502.2
566.8
324.4
11815.0
14204.4
663.8
1257.1
3273.6
1489.4
451.2
157.5
651.1
1434.9
1510.9
1060.9
25.9
270.8
25.3
608.7
19.9
1889.0
15837.2
12791.8
14734.4
1008.2
Table IV.
Mean equivalent dose (␮Sv) and effective
dose (␮Sv) for each unit
Bone marrow*
Brain
Eye
Thyroid gland
Salivary glands†
Skin‡
Effective dose
NewTom
9000
i-CAT
946.8
316.1
472.8
232.4
1552.7
1427.0
56.2
1007.1
745.0
1229.2
124.3
1433.15
963.0
61.1
Panoramic/
lateral
Multi-slice
cephalometric
CT
211.6
30.2
45.8
13.1
445.5
190.1
10.4
872.8
1488.9
892.8
1417.7
13009.7
9252.1
429.7
*Mean of mandibular ramus and cervical spine.
†
Mean of submandibular and parotid glands.
‡
Mean of thyroid skin, neck, philtrum, parotid, and nasion skin.
DISCUSSION
Most orthodontic patients are children in active
growth, who are more sensitive to the effects of
radiation. Images are usually required for planning,
treatment evaluation, and follow-up. Many questions in
orthodontic practice can be answered by conventional
radiographic images alone, although a 3D view is often
required.6-11 However, the selection criteria for an
image at any treatment phase should follow the
ALARA principle. We found a higher effective dose
related to the CBCT, compared with the conventional
images usually required for orthodontic treatment. The
choice of CBCT should be related to the patient’s
640.e4 Silva et al
clinical needs. We measured the doses associated with
conventional panoramic and cephalometric images. By
using digital images, the dose could be half as much.15
These doses were calculated for a young man. Due to
differences in size and susceptibility, the actual values
for children would be greater.
Among the CBCT units evaluated, the highest dose
was related to the i-CAT (61 ␮Sv). Ludlow et al,14
comparing CBCTs with a larger FOV, showed higher
doses for CB Mercuray and i-CAT, and lower dose for
the NewTom, as also seen in this study.
Considering only the radiation dose, the use of a
CBCT image is not recommended routinely in orthodontic practice. Therefore, the decision making in oral
radiology is a balance between the risk assessment and
the diagnostic information needed. When additional
information is necessary, such as for patients with
impacted teeth, dental resorption, ankylosis, temporomandibular joint evaluation, or surgical planning,
CBCT should be the method of choice, since the CT
delivers a much higher dose, as shown in this study and
by others.12,22,23 Farman and Scarfe24 showed that 3D
cephalometric assessments can be made from existing
database projections. They suggested using a CBCT
scanner to provide a very low dose traditional cephalometric image and then 3D images from specific
regions. This could lead to a 3D assessment when
needed, without unnecessary patient exposure. However, European guidelines indicate no lateral cephalogram for Class I malocclusions. In these situations, the
increased radiation with CBCT scans at the end of
treatment is not justifiable. Three-dimensional images
are probably unnecessary for all patients in orthodontic
practices, but clinical studies should confirm this. The
ALARA principle can also be followed by using skull
caps, eye covers, and thyroid shields during conventional lateral cephalogram to reduce radiation exposure.
Now, there is a tendency to use 3D imaging for
orthodontic planning and for finding unexpected anatomic variations that can expand and change the treatment plan. However, a question remains. Are we really
missing some aspects in 2-dimensional (2D) images,
even without clear clinical reasons for 3D images? The
limitations of 2D images have been well studied in the
literature. According to McKee et al,25 mesiodistal
tooth angulations in both jaws when measuring panoramic radiographs are not accurate. Adams et al26
showed the limitations of standard 2D cephalometry.
Evaluating distances in 3D space with 2D images
exaggerates the true measure and gives a distorted view
of craniofacial growth.
We intended to compare CBCT images with conventional panoramic and lateral cephalometric exami-
American Journal of Orthodontics and Dentofacial Orthopedics
May 2008
nations. However, some orthodontic patients also
require a temporomandibular series, posteroanterior
cephalograms, periapical views of the anterior teeth,
occlusal, or bite-wing radiographs. Sometimes, a complete-mouth survey is needed.27 Taking into account
that the effective doses related to a full-mouth radiographic survey, as reported by Gibbs,28 are 13 to 14
␮Sv (with rectangular collimation), 64 to 73 ␮Sv (with
round collimation), and 83 to 100 ␮Sv (with short-cone
bisecting), the sum of the effective doses for panoramic
and lateral cephalometric and periapical images would
be in the same range or even higher than that of CBCT,
and still without 3D evaluation. Other studies should
address the clinical diagnostic value of 3D imaging to
evaluate the risk-benefit balance in using CBCT routinely for orthodontic patients.
Comparing imaging quality, Holberg et al29 found
better visualization for the periodontal ligament space
using CT compared to CBCT, although no statistical
tests were applied to their results. Swennen and Schutyser12 highlighted the limitations of CBCT for orthodontic purposes, such as scanning volume and restricted FOV, when compared with multi-slice CT.
However, Hashimoto et al30 demonstrated that CBCT
imaging performance was better than 4-row multidetector helical CT. It is also expected that CBCT
manufacturers will improve reconstruction algorithms
and postprocessing imaging, providing higher resolution to the images, while keeping the radiation exposure
to the patient as low as possible. Personal clinical
experience should also be considered when evaluating
these relatively new images. Practitioners should be
aware that 3D data present new challenges and a
different approach from traditional viewing of static
images. For this, some training is necessary to prescribe
the image properly and interpret the 3D images. Nevertheless, CT (not CBCT) for orthodontic purposes
should be restricted to patients who have a real necessity for larger FOV visualization (greater than 30 cm)
or soft-tissue assessment.
CONCLUSIONS
From the dose to the patient point of view, the
routine use of CBCT is not recommended in orthodontic procedures, because conventional images deliver
lower doses to patients. However, when 3D imaging is
required in orthodontic practice, CBCT should be
preferred over multi-slice CT. Further studies should
address whether the diagnostic value of CBCT imaging
justifies the higher dose.
American Journal of Orthodontics and Dentofacial Orthopedics
Volume 133, Number 5
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