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Seediscussions,stats,andauthorprofilesforthispublicationat:http://www.researchgate.net/publication/5396999 Cone-beamcomputedtomographyforroutine orthodontictreatmentplanning:Aradiation doseevaluation ARTICLEinAMERICANJOURNALOFORTHODONTICSANDDENTOFACIALORTHOPEDICS:OFFICIAL PUBLICATIONOFTHEAMERICANASSOCIATIONOFORTHODONTISTS,ITSCONSTITUENTSOCIETIES,ANDTHE AMERICANBOARDOFORTHODONTICS·JUNE2008 ImpactFactor:1.38·DOI:10.1016/j.ajodo.2007.11.019·Source:PubMed CITATIONS READS 143 485 6AUTHORS,INCLUDING: MariaAGSilva UlrichWolf UniversidadeFederaldeGoiás/FederalU… UniversityofLeipzig 20PUBLICATIONS292CITATIONS 5PUBLICATIONS163CITATIONS SEEPROFILE SEEPROFILE AxelBumann HeikoVisser MESANTIS,Germany Georg-August-UniversitätGöttingen 16PUBLICATIONS551CITATIONS 38PUBLICATIONS244CITATIONS SEEPROFILE SEEPROFILE Availablefrom:AxelBumann Retrievedon:10October2015 ONLINE ONLY 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 REFERENCES 1. Arai Y, Tammisalo E, Hashimoto K, Shinoda K. Development of a computed tomographic apparatus for dental use. Dentomaxillofac Radiol 1999;28:245-8. 2. Sukovic P. Cone beam computed tomography in craniofacial imaging. 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