Absorbed and effective doses from cone beam volumetric imaging for implant planning

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Absorbed and effective doses from cone beam volumetric imaging for implant planning

  1. 1. Dentomaxillofacial Radiology (2009) 38, 79–85 ’ 2009 The British Institute of Radiology http://dmfr.birjournals.orgRESEARCHAbsorbed and effective doses from cone beam volumetric imagingfor implant planningT Okano*,1, Y Harata1, Y Sugihara2, R Sakaino1, R Tsuchida1, K Iwai3, K Seki1 and K Araki11Department of Radiology, Showa University School of Dentistry, Tokyo, Japan; 2J Morita Manufacturing Corporation, Kyoto,Japan; 3Department of Radiology, Nihon University School of Dentistry, Tokyo, Japan Objectives: Volumetric CT using a cone beam has been developed by several manufacturers for dentomaxillofacial imaging. The purpose of this study was to measure doses for implant planning with cone beam volumetric imaging (CBVI) in comparison with conventional multidetector CT (MDCT). Methods: The two CBVI systems used were a 3D AccuitomoH (J. Morita), including an image-intensifier type (II) and a flat-panel type (FPD), and a CB MercuRayH (Hitachi). The 3D AccuitomoH operated at 80 kV, 5 mA and 18 s. The CB MercuRayH operated at 120 kV, 15 mA, 9.8 s. The MDCT used was a HiSpeed QX/iH (GE), operated at 120 kV, 100 mA and 0.7 s, and its scan length was 77 mm for both jaws. Measurement of the absorbed tissue and organ doses was performed with an Alderson phantom, embedding the radiophotoluminescence glass dosemeter into the organs/tissues. The values obtained were converted into the absorbed dose. The effective dose as defined by the International Commission on Radiological Protection was then calculated. Results: The absorbed doses of the 3D AccuitomoH of the organs in the primary beam ranged from 1–5 mGy, and were several to ten times lower than other doses. The effective dose of the 3D AccuitomoH ranged from 18 mSv to 66 mSv, and was an order of magnitude smaller than the others. In conclusion, these results show that the dose in the 3D AccuitomoH is lower than the CB MercuRayH and much less than MDCT. Dentomaxillofacial Radiology (2009) 38, 79–85. doi: 10.1259/dmfr/14769929 Keywords: tomography, X-ray computed; radiation dosage; dental implantsIntroductionVolumetric CT using a cone beam technique dedicated planning in cases of extensive tooth loss. The 3Dto dentomaxillofacial imaging has been introduced1–4 AccuitomoH (J Morita Mfg. Corp., Kyoto, Japan), onand its clinical use for a variety of dental diagnostic the other hand, can only visualize a localized area suchpurposes5–18 has been described. The terminology used as the lower molar region, due to a smaller imagingfor this method is variable, including cone beam CT volume. This means that the 3D AccuitomoH can either(CBCT) or cone beam volumetric imaging (CBVI). Of be used as a complement to panoramic radiography orthe CBVI systems, NewTomH (QR; Quantitative as an adjunct to intraoral radiography in cases such asRadiology srl, Verona, Italy), CB MercuRayH dental caries and periodontal/periapical diseases when(Hitachi Medical Corp., Tokyo, Japan) and i-CAT more detailed three-dimensional (3D) information is(Imaging Sciences International, Hatfield, PA) were required. It can also be used as a substitute fordesigned to obtain data of the dentomaxillofacial conventional CT, e.g. to visualize a localized arearegion, similar to conventional CT, by one 360 ˚ including not only the implant site but also therotation around the head. The information obtained temporomandibular joint. A prototype of the 3Dcan be used for orthodontics analyses and implant AccuitomoH was introduced by Arai and his colleagues in 19992 and some of its clinical applications were described later.7 The regional imaging volume, cylind-*Correspondence to: Dr Tomohiro Okano, Department of Radiology, ShowaUniversity School of Dentistry, 2-1-1 Kitasenzoku, Ota-ku, Tokyo 145-8515, rical in shape, is limited to 30 mm in height and 40 mmJapan; E-mail: tokano@senzoku.showa-u.ac.jp in diameter. A small cone-shaped X-ray beam irradiatesReceived 9 October 2007; revised 29 February 2008; accepted 4 March 2008 an image intensifier (II) connected to a charge-coupled
  2. 2. Effective doses from CBVI80 T Okano et al device (CCD) receptor for approximately 18 s, while tube current is also selectable. In this experiment, the the C-arm makes a 360 ˚ rotation with the longitudinal maximum combination of 120 kV and 15 mA was axis of the volume of interest as its centre. The organs selected using the implant mode, 102.4 mm in spherical and tissues exposed by the primary beam are thus diameter covering the upper and lower jaws. The limited. As a result, the effective dose may be equivalent effective energy was also estimated to be 50 keV. The to that of panoramic radiography and lower than MDCT system used was a HiSpeed QX/iH (GE conventional CT or large area CBVI. Iwai19 made Yokogawa, Tokyo, Japan), operated at 120 kV and radiation dose measurements using the prototype of 100 mA as in routine conditions. The slice thickness this machine and found effective doses that were was 0.625 mm and the pitch was 1. The scan length was somewhat lower than that of panoramic radiography. 77 mm for the upper and lower jaws. The effective On the other hand, a new 3D AccuitomoH using a flat energy was estimated to be 50 keV. panel detector (FPD) for imaging volume, either The same phantom as described above was used for 40 mm in height and 40 mm in diameter or 60 mm in measurements of the dose absorbed in organs and height and 60 mm in diameter, has been introduced. tissues. The phantom was transversely cut into 34 slices This may give higher doses to the patients because of from the top of the head to the pelvis. The thickness of the larger volume. each slice was 2.5 cm. Photoluminescence glass (GD- Another CBVI system, CB MercuRayH, is equipped 352M; DoseAceH dosemeter system, Asahi with a 12 inch image intensifier and three modes in a Technoglass, Tokyo, Japan) was used as detector spherical field-of-view (FOV): facial (192.5 mm in material for our dosemeter system.21 This silver- diameter), panoramic (150 mm in diameter) and activated phosphate glass gives off radiophotolumines- implant (102.4 mm in diameter) modes.4 The mode cence when exposed to ionizing radiation. The amount can be chosen according to the diagnostic purpose. The of luminescence emitted as UV light is proportional to effective dose of the system has been reported to be the radiation dose exposed to the glass. The dosemeter several to ten times higher than other CBVI systems system consisted of small rod-shaped glass chip such as NewTom and i-CAT.20 On the other hand, detectors, 12 mm in length and 1.5 mm in diameter, conventional CT has been widely used and accepted as enveloped by a holder, 14.5-mm long and 4.3 mm in a standard for pre-surgical assessment, in spite of the diameter, capable of being embedded in the phantom. relatively higher dose to the patients. The readings obtained by the glass dosemeter were Since it can be assumed that an increasing number of compared with the ‘‘exposure’’ (air kerma in free air) radiographic examinations will be performed with estimated by an ionization chamber, TN30009, coupled CBVI in near future, it is important to know the doses with a readout device, Ramtec 1000 (Toyo Medic, of radiation that result from these procedures. The Tokyo, Japan), calibrated by the Japan Quality purpose of this study was, therefore, to measure doses Assurance Organization (Tokyo, Japan). The values in implant planning with CBVI including the 3D obtained were converted into the absorbed dose in air AccuitomoH and CB MercuRayH in comparison with by the use of a correction factor of 1.59 for 3D conventional MDCT. AccuitomoH and 2.00 for both CB MercuRayH and MDCT. From the air dose, the dose absorbed by tissues and organs was then calculated by multiplying by a Materials and methods factor of 4.97 for the bone surface and 1.06 for the other tissues and organs for 3D AccuitomoH, and 4.15 The exposure conditions in each modality, as shown in for bone and 1.066 for tissues/organs, respectively, for Table 1, were routinely used in our institute. Such CB MercuRayH and MDCT. The factor was estimated exposure conditions were determined visually by the as the ratio of the mass energy absorption coefficients authors using a RANDOH Woman phantom (Alderson of air to compact bone or muscle, as shown in the Research Laboratories, Stamford, CT) which included International Commission on Radiation Units and human bone and teeth. For instance, in a 3D Measurements Report 17.22 The variation of the AccuitomoH, the selectable tube voltage ranges from dosemeter was assessed using 1 mGy of exposure to 137 60–80 kV and the tube current from 1–10 mA, and a Cs c-rays, and the results showed that the standard routinely used combination of 80 kV and 5 mA was deviation of readings was ,4.5% between dosemeters selected for both the II and the FPD types. The effective and ,2% within the same dosemeter. energy was estimated to be 37 keV from measurement A total of 155 dosemeters were used to estimate doses of a half-value layer at 80 kV. The region of interest to the tissues and organs, including those recommended was the lower molar area including the body of the by the International Commission on Radiological mandible; the imaging volumes used were 30 mm in Protection’s (ICRP) Publication 60 (1990)23 to calculate height and 40 mm in diameter for the II type, and effective dose. The tissues and organs were gonads, 40 mm in height and 40 mm in diameter and 60 mm in bone marrow (red), colon, lung, stomach, bladder, height and 60 mm in diameter for the FPD type. On the breast, liver, oesophagus, thyroid, bone surface, eye other hand, in the CB MercuRayH, the selectable tube lens and the three major salivary glands. Brain, adrenal voltages are 60 kV, 80 kV, 100 kV and 120 kV, and the gland, upper large intestine, small intestine, kidney,Dentomaxillofacial Radiology
  3. 3. Effective doses from CBVI T Okano et al 81Table 1 Exposure conditions for each modality Cone beam volumetric imaging MDCT 3D AccuitomoH CB MercuRayH FPD type (large) FPD type (small) II type Implant mode HiSpeed QX/iHExposure voltage (kV) 80 120 120Exposure current (mA) 5 15 100Shape of FOV cylinder Sphere CylinderImaging volume 60 mm diameter/ 40 mm diameter/ 40 mm diameter/ 102 mm dimeter 77 mm scan length 60 mm height 40 mm height 30 mm heightFOV, field-of-view; FPD, flat-panel detector; II, image-intensifier detector; MDCT, multidetector CTpancreas, spleen, thymus, and uterus/cervix were also absorbed by the parotid gland, included in the primaryincluded. 1–13 dosemeters for each organ were placed in beam, ranged from 0.67–27.8 mGy depending on theholes shaped as dosemeter holders and embedded in slices modality. Similar results were attained in the otherof the phantom. For example, 6 dosemeters were used for salivary glands. The mandible was also included in thethe left and right parotid glands (3 each) in the same slice primary beam, and the dose ranged from 2.47–of the phantom, and 13 were used in 6 slices for the lung. 23.52 mGy. On the other hand, the dose to the thyroid Each exposure was repeated 100 times for 3D was low because it was outside of the primary beam.AccuitomoH, 50 times for CB MercuRayH and 20 times Table 4 shows the equivalent doses converted fromfor MDCT, and the results were averaged. The absorbed mean absorbed doses of tissues and organs using thedose was obtained by averaging the values for all radiation weighting factor of one. The doses to thedosemeters embedded in the organ. The averaged bone bone marrow, bone surface, and skin were the averagemarrow dose was estimated as follows. 49 dosemeters doses to the total body. The effective dose was thenwere placed in the bone marrow of cranial bone, calculated using the tissue weighting factors and finallymandible, vertebra, clavicle, ribs, pelvic bones and others, estimated to be about 18–66 mSv for 3D AccuitomoH,and the average absorbed dose for each bone was depending on the imaging volume, 452 mSv for CBmultiplied by the weight of each bone marrow. The MercuRayH and 596 mSv for MDCT, based on the 1990sum of these was divided by the total weight of the bone ICRP recommendation. The effective doses approvedmarrow, 765 g. The distribution of marrow has already in the 2007 ICRP recommendation were usually higherbeen reported for the average Japanese person.24 because of the inclusion of the salivary gland and brainFurthermore, the average dose absorbed by the bone doses to the calculations, as shown in Table 5.surface was also estimated in a similar way. On theassumption that mineral content is proportional to therisk of bone tumour, the dose absorbed by each bone wasmultiplied by the weight of each bone mineral. The sum Discussionwas then divided by the total weight of bone mineral,3700 g. The distribution of bone mineral for the average Cone beam volumetric imaging has been widelyJapanese person was obtained from a previous employed not only for the pre-surgical planning of dentalreport.25 The skin dose was separately measured by implants but also for orthodontic purposes. It is also usedmeans of 24 dosemeters placed around the surface of the to visualize the details of tooth structures and period-face and head, where the primary beam entered. ontal/periapical bone changes. The increasing utilizationExposure was performed ten times to gain enough doses of these modalities inevitably induces an increase into ensure proper measurement, and a mean exposure was radiation exposure to the general population. The patientthen obtained. The ratio of the skin surface irradiated,approximately 0.04 m2 to the total body surface of Table 2 Tissue weighting factors as defined by the International1.5 m2 for Japanese people,20 was estimated to be 0.025. Commission on Radiation Protection (ICRP) 1990 and 2007The average skin dose was calculated by multiplying this recommendationsfactor by the mean absorbed skin dose at the irradiated Tissue WT SWTarea. The effective dose as defined by the ICRP23 was ICRP 1990then calculated. In addition, based on the new ICRP Gonads 0.20 0.20recommendations,26 the effective dose was calculated. Bone marrow, colon, lung, stomach 0.12 0.48The tissue weighting factors defined by the ICRP in 1990 Breast, bladder, oesophagus, liver, thyroid 0.05 0.25 Bone surface, skin 0.01 0.02and 2007 are shown in Table 2. Remainder tissues (10 in total) 0.05 0.05 ICRP 2007 Bone marrow, colon, lung, stomach, breast, 0.12 0.72 remainder tissues (14 in total)Results Gonads 0.08 0.08 Bladder, oesophagus, liver, thyroid 0.04 0.16The average doses absorbed by the organs in the head, Bone surface, brain, salivary glands, skin 0.01 0.04neck and breast are shown in Table 3. The dose WT, tissue weighting factor; SWT, sum of tissue weighting factors Dentomaxillofacial Radiology
  4. 4. Effective doses from CBVI82 T Okano et al Table 3 Absorbed dose (mGy) in organs of the head/neck and in some other organs Cone beam volumetric imaging MDCT 3D AccuitomoH CB MercuRayH FPD type (large) FPD type (small) II type Implant mode HiSpeed QX/iH Brain 0.19 0.07 0.04 3.67 4.42 Eye lens 0.25 0.09 0.06 5.76 2.45 Parotid gland 3.81 1.86 0.67 13.69 27.81 Submandibular gland 4.13 2.09 1.78 14.24 25.77 Sublingual gland 4.93 3.60 2.42 12.81 22.79 Thyroid 0.62 0.30 0.12 3.72 4.63 Bone marrow (mandible) 5.00 2.74 2.47 13.64 23.52 Facial skin 5.95 3.68 3.56 12.93 14.75 Breast 0.03 0.01 0.01 0.16 0.24 FPD, flat-panel detector; II, image-intensifier detector; MDCT, multidetector CT should be notified of the absorbed dose before the study lens and thyroid, which may have been outside the and appropriate consideration should be given to reduce irradiated area in our study. On the other hand, the dose for each individual patient. reducing the tube potential and tube current from Several studies concerning absorbed doses and 120 kV and 15 mA to 100 kV and 10 mA, respectively, effective doses have been published.19,20,27,28 The induced a substantial reduction of the absorbed dose to absorbed doses of organs in the primary beam of the 50%. The effective dose estimated in this study, NewTomH 9000, operated at 110 kV and 3.4 mA, 451.81 mSv, was more than twice that of the case that reported by Tsiklakis et al,28 were similar to our results used a lower tube potential and tube current in the same from the 3D AccuitomoH. This study showed that the implant mode, 168.4 mSv,20 and a little more than half absorbed dose from CBVI increased with irradiated of that of the case that used a larger FOV, such as the volume (as shown in Table 3), resulting in an increase facial mode, 846.9 mSv.20 Although the two studies of the effective dose as well (as shown in Table 5). were performed with different exposure parameters Ludlow et al20 showed similar results, as shown in including geometry, FOV, and dosemeters used, the Table 6. The absorbed doses involved in the primary doses estimated in both studies corresponded reason- beam from CB MercuRayH using the same tube ably well. This means that the results obtained in our potential and tube current were very close to our study can be used in comparison with Ludlow’s results, except in several tissues such as the brain, eye results.20 In this study, the absorbed doses were Table 4 Equivalent dose (mSv) in tissues/organs measured in this study Cone beam volumetric imaging MDCT 3D Accuitomo CB MercuRay Tissue/Organ FPD type (large) FPD type (small) II type Implant mode HiSpeed QX/i Gonads Ovarium 0.17 0.05 0.06 1.48 2.62 Testis 0.32 0.12 0.10 2.71 3.58 Bone marrow (red) 69.37 31.81 22.26 639.49 859.63 Colon 0.30 0.10 0.11 2.49 4.75 Lung 11.08 4.70 3.07 70.84 173.44 Stomach 1.58 0.68 0.51 14.09 26.29 Bladder 0.21 0.07 0.07 1.96 2.74 Breast 32.25 10.19 9.10 145.91 244.67 Liver 2.22 0.96 0.68 16.64 33.64 Oesophagus 11.38 4.77 2.91 85.82 201.55 Thyroid 616.52 298.52 115.17 3723.62 4625.83 Skin 297.33 121.58 89.03 973.28 943.86 Bone surface 1512.41 781.21 662.87 6241.33 8941.00 Brain 189.34 69.05 43.36 3675.88 4424.61 Salivary glands 4162.67 2197.27 1248.64 13726.81 26294.72 Kidney 0.57 0.23 0.22 6.65 15.71 Adrenal gland 0.79 0.33 0.24 8.40 16.85 Upper large intestine 0.54 0.22 0.19 6.28 10.61 Small intestine 0.25 0.09 0.08 2.38 3.81 Pancreas 0.88 0.38 0.28 9.11 19.49 Spleen 0.80 0.32 0.24 9.16 20.91 Thymus 53.70 22.24 12.93 381.40 642.34 Uterus/cervix 0.16 0.05 0.05 1.46 2.74 FPD, flat-panel detector; II, image-intensifier detector; MDCT, multidetector CTDentomaxillofacial Radiology
  5. 5. Effective doses from CBVI T Okano et al 83Table 5 Effective doses (mSv) estimated by the International Commission on Radiation Protection’s (ICRP) 1990 and 2007 recommendations Cone beam volumetric imaging MDCT 3D AccuitomoH CB MercuRayHEffective dose FPD type (large) FPD type (small) II type Implant mode HiSpeed QX/iHICRP 1990 66.08 31.05 18.18 451.81 595.65ICRP 2007 101.46 49.92 29.62 510.57 768.88FPD, flat-panel detector; II, image-intensifier detector; MDCT, multidetector CTTable 6 Comparison of absorbed dose (mGy) and effective dose (mSv) of the CB MercuRayH and Ludlow’s results20 Present study Ludlow, 200620 Ludlow, 200620Exposure conditions (kV/mA) 120/15 120/15 100/10Mode (diameter) Implant (10 cm) Facial (20 cm) Facial (20 cm)Absorbed dose (mGy) Brain 3.67 9.20 3.97 Eye lens 5.76 16.29 6.21 Parotid gland 13.69 14.15 5.47 Submandibular gland 14.24 11.28 Sublingual gland 12.81 10.07 Thyroid 3.72 11.40 6.33 Bone marrow (mandible) 13.64 10.03 NA Effective dose (mSv) 451.81 846.9 476.6NA, not availablemeasured using a photoluminescence glass dosemeter. In comparison with panoramic radiography, asAlthough this type of dosemeter was reported to be shown in Table 7, the absorbed dose in CBVI wasuseful in measuring the absorbed dose from radio- much higher even when using the 3D AccuitomoH withtherapy units,29,30 measurements of the absorbed dose a smaller exposure volume. The effective dose from 3Dresulting from an energy range of diagnostic X-rays AccuitomoH was also two to eight times higher thanhave not yet been reported. It has been reported that from panoramic radiography, where the effective dosewhen the dosemeter is equipped with a tin (Sn) filter to ranged between 4–10 mSv depending on the system usedaccommodate a diagnostic X-ray energy range, it can and the method employed.27,31,32 In comparison withbe applied down to an energy level of 15 keV.29 The CT, as shown in Tables 3 and 5, the absorbed dose invalues obtained are then corrected by using the the tissues of the head, neck and breast was severalmeasured factor for the specific energy of the X-ray times higher in CT than in 3D AccuitomoH, and thesystem used. In this study, 1.59 was used as resulting effective dose was almost 10 times greater inthe correction factor to convert the values obtained CT. This is a reason why CBVI systems such as 3Dby the dosemeter to the absorbed dose. A photolumi- AccuitomoH are usually evaluated using limited irradia-nescence glass dosemeter in diagnostic radiology could tion volume. However, if a larger area is used, thebe utilized, although studies to assure its effectiveness effective doses approach the doses of CT, as shown byshould be performed in the future. Ludlow20 and this study. In the use of large area CBVITable 7 Comparison of absorbed dose (mGy) and effective doses (mSv) of the 3D AccuitomoH flat-panel detector (FPD) model (smaller areamode) and those of panoramic radiography.Type CBVI Panoramic radiography 3D Accuitomo FPD typeApparatus (small) Orthophos Proline OrthophosExposure conditions 80/5 60/16 60/4 62/16 (kV/mA)References Present study Ref. 28, Table 2 Ref. 31, Table 1 Ref. 32, Table 4Brain 0.07 0.35 NA 0.03Eye lens 0.09 NA 0.00 0.01Parotid gland 1.86 0.74 0.29 0.61Submandibular gland 2.09 0.63 0.18 0.08Sublingual gland 3.60 0.54 0.10 0.21Thyroid 0.30 0.05 0.04 0.05Bone marrow (mandible) 2.74 0.58 0.31 NAFacial skin 3.68 NA NA NABreast 0.01 NA NA 0.00Effective dose (mSv) 31.05 6.2 3.85 9NA, not available Dentomaxillofacial Radiology
  6. 6. Effective doses from CBVI84 T Okano et al systems, such as CB MercuRayH, Ludlow suggested glands was defined as the mean of doses of the parotid, that the lower tube voltage and tube current setting can submandibular and sublingual glands in the study. As a produce subjectively equivalent image quality and it result the effective dose increased by 15% to 60%, as shown may provide substantial dose reduction to less than in Table 5. Some other tissues and organs mentioned in the 50%. In our CT study, 120 kV and 100 mA were used draft were not measured in this study, but they would not for a scan length of 77 mm including the maxilla and significantly affect the effective dose because most of them mandible. The bone window setting was used to would be irradiated by very low doses. observe the original axial and reformatted images. In In conclusion, these results show that the dose in the this case, the tube current can reduce substantially to 3D AccuitomoH is lower than CB MercuRayH, and 100 mA or maybe less than the head and neck soft much less than MDCT, and suggest that lower tube tissue study. Such a reduction may be possible in dental current settings should be used to reduce the dose in the implant studies as well as in paranasal sinus studies,33,34 CB MercuRayH and MDCT. in which the resulting effective dose might be much less than 1 mSv. The results showed that such dose Acknowledgments reduction can be accomplished in the study. The effective dose, as described in a new recommen- This work was supported by a Grant-in-Aid for Scientific dation from ICRP in 2007,26 can also be calculated. In Research by the Japan Society for the Promotion of Science the new recommendation, the brain and salivary gland (no. 17390503). 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