7/27/2019 145.full

1/5

RESEARCH

Dosimetry of digital panoramic imaging. Part I: patientexposure

F Gijbels 1 , R Jacobs* ,1 , R Bogaerts 2, D Debaveye 1, S Verlinden 2 and G Sanderink 3

1 Oral Imaging Centre, Katholieke Universiteit Leuven, Belgium; 2 Unit of Personal Dosimetry, Radiation Therapy, KatholiekeUniversiteit Leuven, Belgium; 3 Oral Radiology, ACTA, Amsterdam, The Netherlands

Objectives: To measure patient radiation dose during panoramic exposure with variouspanoramic units for digital panoramic imaging.Methods: An anthropomorphic phantom was lled with thermoluminescent dosemeters (TLD100 w ) and exposed with ve different digital panoramic units during ten consecutive exposures.Four machines were equipped with a direct digital CCD (charge coupled device) system, whereasone of the units used storage phosphor plates (indirect digital technique). The exposure settingsrecommended by the different manufacturers for the particular image and patient size were used:tube potential settings ranged between 64 kV and 74 kV, exposure times between 8.2 s and 19.0 s, atfuse current values between 4 mA and 7 mA. The effective radiation dose was calculated withinclusion of the salivary glands.Results: Effective radiation doses ranged between 4.7 m Sv and 14.9 m Sv for one exposure.Salivary glands absorbed the most radiation for all panoramic units. When indirect and direct digitalpanoramic systems were compared, the effective dose of the indirect digital unit (8.1 m Sv) could befound within the range of the effective doses for the direct digital units (4.714.9 m Sv).Conclusions: A rather wide range of patient radiation doses can be found for digital panoramicunits. There is a tendency for lower effective doses for digital compared with analogue panoramicunits, reported in previous studies. Dentomaxillofacial Radiology (2005) 34, 145149. doi: 10.1259/dmfr/28107460

Keywords: dental radiography, panoramic radiography, digital imaging, radiation dose

Introduction

A growing number of dental practitioners opt for digitalradiography instead of conventional lm radiography. 1 6

Although digital radiography was rst introduced forintraoral exposures and has been widely implemented, thepossible advantages of digital extraoral radiography arenow being recognized. According to a recent survey inBelgium, 7 panoramic units are available in 57% of privatedental ofces, 12% of which are digital (compared with30% digital for intraoral radiographs).

One of the main advantages of digital radiographycompared with analogue radiography is the possibility tosave radiation dose. The magnitude of dose savings for

digital extraoral radiography can be expected to be smallerthan for intraoral radiography because of the general use of intensifying screens for extraoral analogue exposures,which limit the amount of radiation required considerably.Nevertheless, reductions of radiation dose of 4070% havebeen reported in the literature. 810 However, most studiesdo not compare radiation doses of digital with analogueunits in similar settings. 812 Currently, to our knowledge,no studies have been published about the difference inradiation dose between direct digital (charge coupleddevice (CCD)) and indirect digital (storage phosphor plate)exposures.

Image quality of digital panoramic radiographs has beenstudied more extensively. The overall conclusion is thatdigital panoramic radiographs (both CCD- and phosphorplate-based) are of satisfactory diagnostic value. 810,1316

The aim of the current study was to compare patientradiation doses generated by ve different types of digital

*Correspondence to: Reinhilde Jacobs, Oral Imaging Centre, School of Dentistry,Oral Pathology and Maxillofacial Surgery, Katholieke Universiteit Leuven,Kapucijnenvoer 7, 3000 Leuven, Belgium;E-mail: reinhilde.jacobs@med.kuleuven.ac.beReceived 15 September 2004; revised 13 January 2005; accepted 16 January 2005

Dentomaxillofacial Radiology (2005) 34,Dentomaxillofacial Radiology (2005) 34,145149q 2005 The British Institute of Radiology

http://dmfr.birjournals. org

7/27/2019 145.full

2/5

panoramic units. In a second part of this study, reported inanother paper, occupational radiation doses are recordedand compared. 17

Material and methods

An anthropomorphic phantom representing an averageman (Rando w ; Alderson Research Laboratories, NY) waslled with thermoluminescent dosemeters (TLD-100 w

(LiF:Mg,Ti); Harshaw, Bicron NE, Solon, OH). Thedosemeters were distributed over the 13 most coronalslices of the phantom. They were placed in the bone(n 16), red bone marrow ( n 16), oesophagus ( n 3),lungs ( n 4), thyroid ( n 9), brain ( n 13), thymus(n 2), salivary glands ( n 8), skin ( n 10) and eyes(n 2). The position of the dosemeters was chosen bycomparing the phantom slices with the position of therespective organs in a cross-sectional anatomical atlas. 18

A number of dosemeters were kept separately to record thebackground radiation. After the dosemeters were exposedten times, they were read out in a Harshaw Model 6600Automated TLD Card Reader Workstation w (Bicron NE,Solon, OH). The calibration, processing and reading of thedosemeters was performed by the Unit of PersonalDosimetry of the university hospital. The absorbed organdoses were calculated by taking the average of the differentdosemeters per organ and dividing it by ten (ten exposuresper radiation unit). The whole body radiation dose for theskin, bone and red bone marrow was calculated using themethod described by Huda and Sandison. 19 Effective

radiation doses were calculated using the formula:

Deff S Dorg W T 1

with D eff being the effective dose expressed in m Sv, D orgthe absorbed organ dose and W T the tissue weightingfactor. 20 For calculation of the effective dose, the salivaryglands were included as part of the remainder organs, assuggested by Lecomber et al. 21

The phantom was positioned in ve digital panoramicunits: the Cranex Tome w (Soredex, Helsinki, Finland),Cranex Excel w (Soredex, Helsinki, Finland), Veraviewe-pocs 5D w (Morita, Osaka, Japan) (Figure 1), EC Proline w

(Planmeca, Helsinki, Finland) and the Orthoralix 9200DDE w (Gendex, Des Plaines, IL). Except for the CranexTome w , all panoramic units were equipped with CCD-based technology. With the Cranex Tome w , storagephosphor plates (MD10XHQ w ; Agfa, Mortsel, Belgium)were exposed and read out in an ADC Solo w (Agfa)phosphor plate scanner. Exposure parameters wereinstalled as suggested by the manufacturer (Table 1).Each exposure was repeated ten times and the results wereaveraged.

Results

The dosimetric results can be found in Table 2. Theabsorbed organ doses are expressed in m Gy, the effectivedoses in m Sv. Highest absorbed doses are found in thesalivary glands (109.9 410.1 m Gy). Therefore, theseorgans were assigned an individual weighting factor of 0.025 (instead of 0.05 to the average of all remainder

Figure 1 The phantom was positioned in ve digital panoramic units. The positioning in the Veraviewepocs 5D w is illustrated here

Dosimetry of digital panoramic imagingDosimetry of digital panoramic imagingF Gijbelset al

ntomaxillofacial Radiology

7/27/2019 145.full

3/5

organs). 21 Effective radiation doses range between 4.7 m Svand 14.9 m Sv. The panoramic machines with the highesteffective dose are the EC Proline w and the Cranex Excel w ,the machine with the lowest effective dose is theOrthoralix w . There is no clear difference between theunits operating with CCD or storage phosphor plate.A comparison of the different panoramic units is difcultbecause of the different exposure settings. When the resultsare analysed per unit of exposure (mA s or mAsproduct), a variation of 0.100.17 m Sv per mAs can befound, with the lowest dose for the Orthoralix w and thehighest dose for the Veraviewepocs w .

Discussion

The effective radiation dose data derived from this studyrange between 4.7 m Sv and 14.9 m Sv for the various digitalpanoramic units. This is a rather broad range, when takinginto account the fact that all tested panoramic equipmentwas recent and was equipped with a digital image receptor.

Because certain panoramic units ( e.g. Cranex Excel w )did not allow adjustment of exposure parameters, it wasdecided to install the parameters advised by the manu-facturers. This would, in the end, be the fairest comparison,

as it can be assumed that most practitioners use theseadvised parameter settings. The EC Proline w and CranexExcel w yield the highest effective dose, the Orthoralix w thelowest. When the exposure settings are considered, themachines with the highest dose work at the lowestkilovoltage (64 kV and 65 kV) and highest tube current(6 mA and 7 mA) and longest exposure time. TheOrthoralix w , yielding the lowest dose, operates at thehighest kilovoltage.

When doses are calculated per mAs, the results aredifferent. The Orthoralix w still yields the lowest dose per

mAs (0.10 m Sv mAs2 1), but the Veraviewepocs w the

highest (0.17 m Sv mAs2 1). The inuence of the tube

potential is less clear when data are considered per unitof exposure, because both machines operating at high tubepotential (Orthoralix 74 kV) and at low tube potential(Cranex Excel 65 kV) give low effective doses(0.10 m Sv mAs 2 1 and 0.11 m Sv mAs 2 1 , respectively).Because the dosimetric outcome cannot be explained byvarying exposure settings only, technical aspects of theradiation units, such as the size of the radiation eld andshape of the focal trough appear to play a signicant role.

In the present study design, no attempt was made to usethe lowest exposure settings possible. The latter wouldimply a more elaborate study protocol in which evaluationand preservation of diagnostic image quality would play amajor role.

When the data of the four CCD-based panoramic unitsare averaged and compared with the only storagephosphor-based unit of our study, comparable results arefound (8.1 m Sv for storage phosphor, 9.35 m Sv for CCD),especially when taking the variation in results for the CCDunits into account. Also the effective doses per mAs arecomparable for CCD and storage phosphor plate-basedunits (average of 0.13 m Sv mAs

2 1 compared with0.14 m Sv mAs

2 1).As in other dosimetric studies on panoramic

machines, 12,20 22 highest radiation doses were found inthe salivary gland tissue. The effective doses in the currentstudy were calculated with inclusion of the salivary glands,although this is not advised by the ICRP60. 20 Based ongrowing evidence on the sensitivity of salivary tissuetowards radiation, 2326 it was decided to apply the methodof Lecomber et al 21 to include the salivary tissue in the

effective dose calculations. Besides, in the draft version of the ICRP 2005 recommendations, a weighting factor isattributed to the salivary gland tissue for calculation of theeffective radiation dose. 27 When salivary glands would nothave been included in the effective dose calculations, thedoses would have been about three times (2.80 to 3.24)lower.

To allow comparison of the current data with previousstudies, both on analogue and digital panoramic machines,the effective ICRP60 dose was also calculated and listed inTable 3. When comparing our data with another dosimetric

Table 2 Absorbed organ doses ( m Gy) and effective doses ( m Sv) for the ve digital panoramic units. Effective doses are also calculated per unit of exposure (mAs) in the last row

Cranex Tome w Cranex Excel w Veraviewepocs 5D w EC Proline w Orthoralix 9200 DDE w

Bone 5.3 7.7 4.0 11.5 6.0Red bone marrow 5.7 8.2 4.6 12.1 6.2Oesophagus 3.8 1.4 2.6 1.4 3.1Lungs 0.4 0.3 1.1 0.5 0.4Thyroid 29.4 52.2 25.0 35.9 10.4Brain 32.9 23.3 10.1 85.7 34.4Thymus 0.5 3.1 6.6 3.1 0.6Salivary glands 206.6 327.7 126.1 410.1 109.9Skin 2.5 4.1 1.6 0.1Eye lens 7.4 4.0 2.0 5.2 5.9Effective dose 8.1 12.3 5.5 14.9 4.7Effective dose per mAs 0.14 0.11 0.17 0.12 0.10

Table 1 Exposure parameters for the panoramic machines

kV mA s

Cranex Tome w 70 4 15.0Cranex Excel w 65 6 19.0Veraviewepocs 5D w 70 4 8.2EC Proline w 64 7 18.3

Orthoralix 9200 DDEw

74 4 12.0

Dosimetry of digital panoramic imagingDosimetry of digital panoramic imagingF Gijbelset al 147

Dentomaxillofacial Radiolog

7/27/2019 145.full

4/5

study on a digital panoramic machine,12

the data arecomparable. The machine used in the previous study was,however, not investigated in our study. Other studies ondigital panoramic units mentioning effective radiationdoses could not be found. When the current data arecompared with previous studies on analogue panoramicunits, there is a tendency for lower radiation doses with thedigital machines (average effective ICRP60 dose of 4.1 m Sv compared with 6.8 m Sv on average for analogueunits). When the data (except for the data from Whiteet al 28 ), are analysed per unit of exposure (mAs), however,a range of 0.040 0.047 m Sv mAs

2 1 is found for theanalogue units and a range of 0.027 0.076 m Sv mAs

2 1

for the digital systems. The broader dose range of the

digital systems means that the benet of digital radiogra-phy in terms of dose savings is not always straightforward

and needs further optimization studies, where dosimetricdata are analysed in combination with image quality.In the second part of this study, the occupational

radiation dose is reported in the abovementioned settings. 17

Conclusion

The dosimetric data obtained in this study indicate thatvarious digital panoramic machines can provide a ratherbroad range of effective radiation doses for the patient(4.714.9 m Sv). In general, it appears that this implies aradiation dose saving compared with analogue panoramicradiography. Further optimization studies should try to

reduce doses further while preserving a good diagnosticimage quality.

References

1. Whaites E, Brown J. An update on dental imaging. Br Dent J 1998;185: 166172.

2. Hildebolt CF, Couture RA, Whiting BR. Dental photostimulablephosphor radiography. Dent Clin North Am 2000; 44: 273297.

3. Macdonald R. Digital imaging for dentists. Aust Dent J 2001; 46:301305.

4. Mauriello SM, Platin E. Dental digital radiographic imaging. J Dent Hyg 2001; 75: 323331.

5. Brennan J. An introduction to digital radiography in dentistry. J Orthod 2002; 29: 6669.

6. Parks ET, Williamson GF. Digital radiography: an overview. J Contemp Dent Pract 2002; 3: 2339.

7. Gijbels F, Jacobs R. Orale beeldvorming in de Belgische tandarts-praktijk. 4th Flemish Dental Congress of the VVT 2001; Poster R8.

8. Farman TT, Farman AG, Kelly MS, Firriolo FJ, Yancey JM, StewartAV. Charge-coupled device panoramic radiography: effect of beamenergy on radiation exposure. Dentomaxillofac Radiol 1998; 27:3640.

9. Dula K, Sanderink G, van der Stelt PF, Mini R, Buser D. Effects of dose reduction on the detectability of standardized radiolucent lesionsin digital panoramic radiography. Oral Surg Oral Med Oral PatholOral Radiol Endod 1998; 86: 227233.

10. Dannewitz B, Hassfeld S, Eickholz P, Muhling J. Effect of dosereduction in digital dental panoramic radiography on image quality. Dentomaxillofac Radiol 2002; 31: 5055.

11. Cohnen M, Kemper J, Mo bes O, Pawelzik J, Mo dder U. Radiationdose in dental radiology. Eur Radiol 2002; 12: 634637.

12. Ludlow JB, Davies-Ludlow LE, Brooks SL. Dosimetry of twoextraoral direct digital imaging devices: NewTom cone beam CT andOrthophos Plus DS panoramic unit. Dentomaxillofac Radiol 2003;32: 229234.

13. Schulze R, Krummenauer F, Schalldach F, dHoedt B. Precision andaccuracy of measurements in digital panoramic radiography. Dentomaxillofac Radiol 2000; 29: 5256.

14. Ramesh A, Tyndall DA, Ludlow JB. Evaluation of a new digitalpanoramic system: a comparison with lm. Dentomaxillofac Radiol2001; 30: 98100.

15. Benediktsdottir IS, Hintze H, Petersen JK, Wenzel A. Accuracy of digital and lm panoramic radiographs for assessment of position andmorphology of mandibular third molars and prevalence of dentalanomalies and pathologies. Dentomaxillofac Radiol 2003; 32:109115.

16. Molander B, Gro ndahl HG, Ekestubbe A. Quality of lm-based anddigital panoramic radiography. Dentomaxillofac Radiol 2004; 33:3236.

17. Gijbels F, Jacobs R, Debaveye D, Bogaerts R, Verlinden S, Sanderink G. Dosimetry of digital panoramic imaging. Part II: occupationalexposure. Dentomaxillofac Radiol 2005; 34: 150153.

18. Cahill DR. Atlas of human cross-sectional anatomy . Philadelphia,PA: Lea and Febiger, 1984.

Table 3 Literature overview of effective radiation doses (in m Sv) for various types of panoramic units

Exposure settings

First author (year) Equipment kV mA s Effective dose (ICRP) Effective dose (salivary glands)

AnalogueWhite (1992) 28 different units NS NS NS 6.7

Williams (2000)29

6 different units 6074 516 11.320 7.0a

Lecomber (2000) 21 Orthophos Siemens 62 16 14.1 9.0 16.4Danforth (2000) 30 PM 2002 CC Proline Planmeca 6870 67 18 3.9 Lecomber (2001) 22 PM 2002 CC Proline Planmeca 64 6 15 4.0 9.0Cohnen (2002) 11 Orthophos Siemens 73 15 14.1 10.0

DigitalLudlow (2003) 12 Orthophos Plus DS Sirona 66 16 14.1 6.2 22.0Current study Cranex Tome Soredex 70 4 15 3.3 8.1Current study Cranex Excel Soredex 65 6 19 4.5 12.3Current study Veraviewepocs 5D Morita 70 4 8.2 2.5 5.5Current study Proline EC Planmeca 64 7 18.3 5.7 14.9Current study Orthoralix 9200 DDE 74 4 12 2.4 4.7

NS, not specieda Re-calculated based on dosearea product and conversion factor suggested in paper

Dosimetry of digital panoramic imagingDosimetry of digital panoramic imagingF Gijbelset al

ntomaxillofacial Radiology

7/27/2019 145.full

5/5

19. Huda W, Sandison GA. Estimation of mean organ doses in diagnosticradiology from Rando phantom measurements. Health Phys 1984;47: 463467.

20. ICRP Publication 60. Radiation protection. 1990 recommendations of the International Commission on Radiological Protection. Ann ICRP1991; 21: paragraph 27.

21. Lecomber AR, Downes SL, Mokhtari M, Faulkner K. Optimisation of

patient doses in programmable dental panoramic radiography. Dentomaxillofac Radiol 2000; 29: 107112.22. Lecomber AR, Yoneyama Y, Lovelock DJ, Hosoi T, Adams AM.

Comparison of patient dose from imaging protocols for dental implantplanning using conventional radiography and computed tomography. Dentomaxillofac Radiol 2001; 30: 255259.

23. Preston-Martin S, Henderson BE, Bernstein L. Medical and dentalx-rays as risk factors for recently diagnosed tumors of the head. NatlCancer Inst Monogr 1985; 69: 175179.

24. Preston-Martin S, Thomas DC, White SC, Cohen D. Prior exposure tomedical and dental x-rays related to tumors of the parotid gland. J NatlCancer Inst 1998; 80: 943949.

25. Preston-Martin S, White SC. Brain and salivary gland tumors relatedto prior dental radiography: implications for dental practice. J Am Dent Assoc 1990; 120: 151158.

26. Horn-Ross PL, Ljung BM, Morrow M. Environmental factors and therisk of salivary gland cancer. Epidemiology 1997; 8: 414419.

27. 2005 recommendations of the International Commission on Radio-logical Protection. Draft for consultation. http://www.icrp.org/docs/

2005_recs_CONSULTATION_Draft.pdf [accessed 22 February2005].28. White SC. 1992 assessment of radiation risk from dental radiography.

Dentomaxillofac Radiol 1992; 21: 118126.29. Williams JR, Montgomery A. Measurements of dose in panoramic

dental radiology. Br J Radiol 2000; 73: 10021006.30. Danforth RA, Clark DE. Effective dose from radiation absorbed

during a panoramic examination with a new generation machine. OralSurg Oral Med Oral Pathol Oral Radiol Endod 2000; 89: 236243.

Dosimetry of digital panoramic imagingDosimetry of digital panoramic imagingF Gijbelset al 149

Dentomaxillofacial Radiolog