J. Edward DEPARTMENT DENTAL

Gilda, DDS, MS,“T and H. David Maillie, OF ORTHODONTICS,

RESEARCH

AND

EASTMAN

BIOPHYSICS,

SCHOOL

DENTAL

PhD,b Rochester, CENTER

OF MEDICINE

AND AND

THE

N.Y. DEPARTMENTS

DENTISTRY,

UNIVERSITY

OF OF

ROCHESTER

Absorbed radiation was measured in various craniofacial tissues on an adult phantom (Alderson Rando) when conventional cephalometric radiographic techniques were used. The views examined were lateral, 45” oblique, posteroanterior, lateral temporomandibular joint tomograph, and basilar (submental-vertex). Absorbed radiation was expressed in micrograys for the individual views and for combinations of views as customarily used in orthodontics and oral surgery. These data are compared with findings of contemporary investigators and the magnitude of the doses is compared with those in the literature for periapical and panoramic surveys. (ORAL SURC ORAL MED ORAL PATHOL

1992;73:638-43)

ontemporary orthodontics and orthognathic surgery rely heavily on radiologic examination at all stages of management: diagnosis, treatment planning, treatment progress, and evaluation after treatment. As a consequence, patients are subjected to low-level X-radiation and possible increased risk of carcinogenesis. Considerable attention has been directed to dose estimates and carcinogenic risk to radiosensitive tissues of the head and neck from dental intraoral and panoramic radiography.‘-* Doses delivered in conventional lateral and posteroanterior (P-A) cephalometric radiography have been reported by a number of investigators. 9-14 However, at least three other views are often used: 45” oblique, lateral temporomandibular joint (TMJ) tomograph, and basilar (submentalvertex). Data for those have not been reported systematically and, to the best of our knowledge, the risks from any of the cephalometric techniques have not been estimated. This study was designed to measure the absorbed dose in a number of tissues of the head and neck, including several known to be radiosensitive-particu-

“Assistant Chairman, Department of Orthodontics, Eastman Dental Center and Assistant Professor of Dental Research, School of Medicine and Dentistry, University of Rochester. bAssociate Professor of Biophysics, School of Medicine and Dentistry, University of Rochester. 7/16/35009

638

larly the thyroid and salivary glands-when routine diagnostic procedures are followed. The views exam.= ined were lateral, posteroanterior, 45” oblique, lateral TMJ tomograph, and basilar. Determinations were made for each of these views and for combinations of views often encountered in clinical situations. The data obtained provide a basis for examination of some of the problems inherent in such determinations. MATERIALS AND METHODS

Radiation absorbed by selected tissues was measured on a phantom, a dried adult skull and vertebral column embedded in anatomically formed tissueequivalent material (Alderson Rando). The phantom had been divided transversely into 2.5 cm thick slabs, numbered from 0 to 11 inclusive. Holes were drilled vertically in the slabs at appropriate locations to hold thermoluminescent dosimeters (TLD). These consisted of LiF powder sealed into plastic tubes (1 cm long X 2 mm diameter) that were placed vertically in the following regions: Pituitary gland: in the sella turcica and extended superiorly Mandibular condyles: through the condylar head and extended into the neck of the condyle Parotid gland: slightly posterior to and just lateral to the ramus, beginning about 1 cm inferior to the external auditory meatus Internal ramus: in ramal trabecular spaces between

Radiation

Volume Number

73 5

Table

I. Summary of protocol and materials used

Lateral Closure Rest Wide open “SSS” “000” 45” Oblique PosteroAnterior Closure Tomograph

Basilar

*“OOO”

in cephalometry

639

Wehmer cephalostat Model W105 GE-100 tube head

2.5

Kodak Lanex regular

Kodak Ortho-L T-Mat-L

90

15

5.25

25 X 20 cm

Wehmer cephalostat Model W105 GE-100 tube head Quint Sectagraph with Machlett rotating anode tube focal spot = 0.6

2.5

Kodak Lanex regular

Kodak Ortho-L

90

15

9.00

20 X 25 cm

Sandwich cassette with Kodak Lanex fine, medium, and regular

Kodak Ortho-G T-Mat-G

80

50

100

Pinpoint collimator plate giving 7 cm diameter field of TMJ area.

Kodak Lanex regular

Kodak Ortho-L

90

15

18.75

20 X 25 cm

Wzzer cephalostat Model wlO5 GE-100 tube head

Internal 0.75 External 2.00

2.5

tube tube

and “SSS” refer to positions on phonation.

the two cortical layers, distal to the third molar, and centered vertically at the level of the occlusal plane Submandibular gland: slightly lateral to the gonial angle. Sublingual gland: medial to the body of the mandible at the level of the second molar Thyroid gland: three ranks vertically beginning at the level of the Cs vertebra and continuing to the level of the T1 vertebra; right and left rows each three cm from midline No problems arose in positioning the phantom, except for the basilar technique. The phantom is not flexible, so rotation of the head on the occipital condyles with arching of the cervical vertebrae required for this view was not possible. Consequently, the head (slabs 0 to 8 inclusive) was first placed in the cephalostat with Frankfort horizontal plane oriented vertically and then exposed. Two stratagems were used to secure values for the thyroid, which lay below in the neck segment. The whole phantom was placed upright in the cephalostat, somewhat superior and anterior to the normal position, to simulate the position of the stretched cervical structures. Only slabs 8, 9, and 10 held TLDs. A second method used a skull with the adult vertebral column enclosed in a column of dried rice to simulate the neck region and into which the TLDs were positioned appropriately. Thermoluminescent dosimetry powder (LiF) was dispensed into polyethylene tubing (PE-90) at a weight of 5.5 mg. The powders were read on a Har-

s&w Model 2000 thermoluminesceiit detector. The accuracy of the readings was t 6%. The method has been described previously. l5 The LiF dosimeters were calibrated by exposure of representative dosimeters in an X-ray beam together with Victoreen R chambers. The chambers have a calibration traceable to the National Bureau of Standards. The X-ray generation used was a Picker Zephyr unit (Picker X-ray Corp., Cleveland, Ohio) operated at 100 kVp with a halfvalue layer (HVL) of 3.08 mm of aluminum. This corresponds to an effective energy of about 30 keV.16 The dosimeters were calibrated in terms of roentgens. The dose in Gy was obtained by multiplying the readings in roentgens by a conversion factor of 0.0091 Gy/R.17 The X-radiation sources, exposure factors, films, and other details are described in Table I. The right side of the phantom faced the anode for the lateral, the TMJ positions, and the oblique position. A radiograph was initially taken to confirm the correctness of positioning, followed by additional exposures, for a total of 20 for each series. Twenty exposures were required to produce a large enough dose for accurate measurements. Total absorbed dose divided by 20 prqvided dose per exposure in micrograys. The posteroanterior series were taken three times, whereas the TMJ tomograph with pin-hole collimator was only observed once. Other series were taken twice, except as noted in the footnote to Table II. Results were expressed as averages for each of the series. These experiments were conducted over a 5year

40

Gilda and Maillie

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Table

II. Absorbed radiation in micrograys Pituitary gland

Lateral Right Middle 24 Left Posteroanterior Right Average 21 Left 45” Oblique (left) Right Middle 8 Left TMJ Tomography (left) Right Middle 14 Left TMJ Tomography (left) Right Middle 306 Left Basilar Right Average 39 Left

Parotid gland

’ Internal ramus

j

Submandibular 1 gland

Sublingual gland

I

Thyroid

~ / Superior

Middle

Inferior

61

113

66

126

45

57

9

4

5

9

7

19

23

26

8

0

18 24 31

48 49 49

24 21 30

48 49 49

17 16 16

51 51 51

43 39 35

I 8 9

40

81

40

129

38

42

13

I

6

6

11

21

11

6

2

4

2

2

2

2

0

8 with collimator 26

without

I

1992

160

31 36 collimator 665 1130 15

II

42 41 40

168 142 115

11 4

0 1441

426

411

16

32

144

141

265

124

52

29

115

239 261 295

363 338 312

281 254 221

312 275 238

186 182 178

118

Values for posteroanterior view are averages of three determinations. Values for TMJ tomograph with collimation are single determinations. Values for other views are averages of two determinations, except for (a) right thyroid 45” oblique, which were taken three times and (b) basilar, in which adjusted phantom position was taken twice and rice cervical model exposed once, as described in text. Divide each number by 10 to obtain equivalent readings in millirads (mrad).

period so that minor differences in orientation of the phantom could be consideredrepresentative of everyday experience. Exposures were those customary for teenage/adult subjects and therefore are maximum values. Collimating deviceswere usedas noted in Table I. A thyroid collar was not placed. An aluminum wedge or dodger was placed between the subject and the film for the lateral view. A recent report14 suggests that our machine factors, films, and screensproduced quality radiographs with exposuresin the lower range of radiation delivered for views of this type. RESULTS

Mean values for the different areas in the several techniques are given in Table II. For the most part, tissuescloser to the central ray experienced higher dosesof radiation, with falling off as location was superior or inferior to it in the lateral, 45’ oblique, P-A, and tomograph. The basilar is a special case because the sagittal plane is parallel to the central ray and Frankfort horizontal plane is perpendicular. Here the structures above portion received lessand the thyroid and salivary glands, which are below, received much

larger doses. Left side (exit) structures, in general, received a widely varying percentage reduction from those on the right side (entry) in the lateral, 45” oblique, and TMJ tomograph, depending on location. Right and left structures in P-A and basilar technique received essentially the same amount of radiation The central ray radiation at entry and exit in one lateral view seriesmeasured 125 p.Gy and 1 pGy, respectively, but was not included in Table II. Finally, the absorbedradiation in thosetissue areas examined were summarized for combinations often used in routine practice. Although observations were made on one side only for the 45” oblique and TMJ tomograph, they were expressed as bilateral exposures in the combined values. These totals are given in Table III. DISCUSSION

The amount of radiation delivered to any tissuedependson many factors, among them the characteristics of the radiation, collimation, shielding, and dodging; film and intensifying screenspeed;head size and position; tissue mass,location, and distance from

Volume Number

Radiation

73 5

in cephalometry

641

III. Absorbed radiation in micrograys acc(ording to cephalometric technique and combinations of techniques Table

~ Condyle

Parotid ( gland

Internal ramus

24 27 51

61 24 85

113 49 162

66 27 93

126 49 175

115

255

475

271

567

163

377

701

403

819

28

58

196

11

14

612

740

1207

922

41

142

115

~ ‘z:F Lateral, closed Posteroanterior Lateral, closed Posteroanterior Lateral Closed Rest Open Posteroanterior 45” Oblique Left Right Lateral Closed Rest Open “SS.p* “OOO”Y Posteroanterior 45” Oblique Left Right TMJ Tomograph Left Right TMJ Tomograph Left Right Basilar

with

without

collimator

collimator

3’9

*“OOO”and “SSS” refer to positions on phonation. These doses are derived from those recorded in Table II. Divide each number by 10 to obtain equivalent readings in millirads

Submandibular gland

Sublingual gland 45 16 61

Superior

FEI

1Inferior

57 57 114

9 39 48

4 8 12

210

281

85

29

300

395

103

37

2

6

4

2

1594

691

595

128

61

261

338

254

275

182

(mrad).

the central ray. Correct anatomic placement of the TLDs in the phantom are of importance in the experimental setting. Our procedures were designedto reflect customary clinical practice. Characteristics of the X-radiation and of the. film-screen combinations were close to the optimum reported by Eliassonet all2 and Tyndall et a1.14Collimation was limited to the film’ area, a thyroid collar was not used, and when a dodger was used, it was placed between phantom and film. Attention to improvement of the latter two details would undoubtedly reduce exposures, especially to the thyroid. It should be pointed out, however, that the salivary glands and at least part. of the thyroid are always exposed to radiation. Considerable variation was noted in the literature for comparable measurements in lateral and P-A techniques, even among investigations that usedfaster screens, faster films, and other technical improvements. The most recent of these”, 12*14,l8 are listed in

Table IV. Our maximum dosesare lower except for submandibular salivary glands, where they are roughly equal and variable for the mandibular “marrow” and thyroid values. Precise comparison is not possible becauseof the many variables enumerated earlier. Location of the thyroid is usually described as extending from the fifth cervical vertebra down to the first thoracic vertebra. Most cephalometric radiographs usethe field immediately below the hyoid bone and consequently include at least the fifth cervical vertebra. In our phantom, this structure was contained in slab no. 8 and could be expected to include the upper part of the thyroid. Especially high doses were observed for the TMJ tomograph without the pin-hole collimator and for the basilar. In the latter view, the neck is directly presented to the X-ray beam and a considerable volume of thyroid consequently is exposeddirectly to the effective beam. The relatively high absorbed dose in both views suggestscaution in

42

Giida and Maillie

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&AL

itiED

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I'ATHOi

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Table IV. Recent reported doses to selected tissues for one lateral or posteroanterior micrograys unless otherwise noted) Pituitary

Lateral Present study Tyndall, ( 1989)18 Tyndall

24

j

I ’ Posteroanterior ~ 21

et al.

Condyle

~ ~

Lateral 61 107 59 15.9 mR

Parotid

1Posteroanterior 24

1 Lateral / 113

Submandibular

Posteroanterior

Lateral

49

126

’

Posteroanterior 49

1992

exposure: (In Mandible

Lateral

Posteroanterior

66 52

/ ( /

21

Thyroid

Lateral

Posternanterior

51 31 13 9.1 mR

10

8.7 mR

57

(1988)‘4

Eliasson et al. (1985)'2 Eliasson et al. (1984)"

52 59

180 55

189

115 153

99

135 69

133

‘*Doses were estimated from bar graphs in Fig. 1; upper and lower listed values were derived from Tech 2 and Tech 6 respectively, terials and apparatus to the present study. ‘ZDoses were estimated from curves shown in Figs. 8,6,7,9,5 and represented maximum reported radiation at 90 kVp. “Doses are maximum values for the specific tissues at 90 kVp for lateral and 55 kVp for postero-anterior. Values for lateral thyroid out shielding.

prescribing these techniques. Some reduction in risk for the basilar may be achieved by positioning the subject’s face towards the film rather than towards the anode, a suggestion offered by Remmelink.t9 Centrally placed collimation can substantially reduce radiation to the thyroid gland when the temporomandibular joint is the principal area of interest.20 Two considerations relative to these estimates, in general, are rarely emphasized. The Rando phantom was that of an adult, whereas orthodontic/surgical interests often center on children at an earlier age, especially in severe craniofacial anomalies. In addition, placement of the TLDs can be critical and may vary considerably, depending on the investigator’s judgement of anatomy. Consequently, even the best TLD-derived measurements can be expected to be imperfect estimates of true values. Our results should be considered as maximum estimates, with considerable variation especially in young subjects, in whom lesser amounts of radiation would have been used. TMJ laminagraphy may use adjustable rectangular collimators delivering full-field to almost pin-hole size, so that the range of exposure can vary greatly. Undoubtedly more precise collimation would have reduced the dose in many areas, as demonstrated by the use of pin-hole collimation in our experiment. Recent data on radiation, delivered to certain radiosensitive tissues in the head and neck by completemouth, interproximal, and panoramic surveys reported by Underhill et a1.,7 provide a basis for comparison with our findings. Such comparison has importance because the public and health care providers are increasingly concerned with the effects of radiation and patients/parents sometimes object stre-

5 88

172 which

exposure

were similar

was obtained

70 in ma-

with-

nously to the use of cephalometric radiographs. We have chosen to compare our lateral and posteroanterior cephalometric combination (row 3, Table III) with the Underhill et a1.7data, because it is this combination of cephalograms that is probably taken routinely, possibly to the exclusion of other views in many if not most facilities. The comparison with panoramic surveys is complicated by the wide range of radiation delivered, depending on the scan path of the different machines. Accordingly, the analysis is expressed in terms of the spread of values reported. Panoramic radiographs are more sparing of radiation to the pituitary and thyroid by one half to one fifth. However, doses to the salivary glands range from a two-thirds reduction to a 7.3-fold increase. Complete-mouth survey with round collimation delivers somewhat more than five times the radiation to the pituitary and thyroid, but 32, 5 1, and 128 times more radiation to the parotid, submandibular, and sublingual glands, respectively. Rectangular collimation reduces the dose of pituitary and thyroid by more than half, but still delivers 5, 14, and 57 times more to the parotid, submandibular, and sublingual glands. This pattern is repeated for the interproximal survey. Round collimation delivers the same exposure to the pituitary and twice the exposure to the thyroid, but 15, 21, and 43 times that of the lateral-posteroanterior cephalometric combination for the parotid, submandibular, and sublingual glands, respectively. Rectangular collimation reduces exposure to both the pituitary and thyroid by more than half. The parotid, submandibular, and sublingual receive 3.8, 1.3, and 7.9 times more radiation, respective1.y.

Radiation in cephalometry

Volume 73 Number 5

Such comparisons indicate that the lateral and posteroanterior combination generally used adds comparatively little to the radiation burden.

risk from interproximal radiography. ORAL SURG ORAL MED ORAL PATHOL

Our results agree, in general, with those reported in the contemporary literature and extend informa.tion relative to other techniques that have not been reported. This body of information indicates that the levels of radiation delivered by the most commonly used procedures (lateral and posteroanterior) are much lower than other standard procedures used in dentistry. Special procedures, such as TMJ imaging and basilar, may add much more to the radiation burden, but can be reduced substantially by proper collimation and shielding. The cautionary principle of limiting all radiologic exposure to an essential minimum applies with equal force to all of these procedures.

1

SURG ORAL MED 10.

11. 12.

13.

15. 16.

REFERENCES 1. Kuba RK, Beck JO. Radiation dosimetry in Panorex roentgenography. Part III. IRadiation dose measurements. ORAL SURG ORAL MED

ORAL PATHOL

1968;25:393-404.

2. Antoku S, Kihara T, Russell WJ, Beach DR. Doses of critical organs from dental radiography. ORAL SLJRG ORAL MED ORAL PATHOL

1976;41:251-60.

3. Bengtsson G. Maxillo-facial aspects of radiation protection, focused on recent research regarding critical organs. Dentomaxillofac Radio1 1978;7:5-14. 4. Wall BF, Fisher ES, Paynter R, Hudson A, Bird PD. Doses to patients from pantomographic and conventional dental radiography. Br J Radio1 1979;52:727-34. 5. Danforth RA, Gibbs SJ. Dental diagnostic radiation. What is the risk? J Calif Dent Assoc 1980;8:28-35. 6. Gibbs SJ, Pujol A, Chen TS, Malcolm AW, James AE. Patient

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8. Underhill TE, Kimura K, Chilvarquer I, et al. Radiobiologic risk estimation from dental radiology: Part II Cancer incidence and fatality. ORAL SURG ORAL MED ORAL PATHOL 1988; 66~261-27. 9. Bankvall G, Hakansson HAR. Radiation-absorbed doses and energy imparted from panoramic tomography, cephalometric radiography, and occlusal film radiography in children. ORAL

14.

We wishto thank Robert Graves,farmer AssistantProfessor,for his help, and Margaret A. Henzler, SeniorAssociate,Radiation Oncology,Schoolof Medicineand Dentistry, University of Rochester,whomadeavailableto usthe Department’sphantom.

1984;58:347-54.

7. Underhill TE. Chilvarauer I. Kimura K. et al. Radiobiologic risk estimation from dental radiology: Part I. Absorbed doses to critical organs. ORAL SURG ORAL MED ORAL PATHOL 1988;66:11

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Bankvall G, Enstrom H, Enstrijm C, Hollender L. Absorbed doses in the craniofacial region during various radiographic and radiotherapeutic procedures. Dentomaxillofac Radio1 1985;14:19-24. Eliasson S, Julin P, Richter S, Stenstriim B. Radiation absorbed doses in cephalography. Swed Dent J 1984;8:21-7. Eliasson S, Julin P, Philip A, Stenstrom B. Absorbed doses at varying tube voltage in lateral cephalography. Swed Dent J 1985;9:117-27. McNicol A, Stirrups DR. Radiation dose during the dental radiographic techniques most frequently used during orthodontic treatment. Eur J Orthod 1985;7:163-71. Tyndall DA, Matteson SR, Soltmann RE, Hamilton TL, Proffit WR. Exposure reduction in cephalometric radiology: a comprehensive approach. Am J Orthod Dentofac Orthop 1988; 93:400-12. Thomas WV, Maillie HD, Mermagen H. The whole and partial body dosimetry of the rat exposed to 250 KVP X-radiation. Health Physics 1968;14:365-71. Johns HS. The physics of radiology, 2nd ed. Springfield, Ill.: Charles C. Thomas, 1961:256-58. Physical aspects of irradiation: recommendations of the international commission on radiological units and measurements. (1964). Nat’d Bur Std (U.S.) Handbook 85. Tyndall DA. Order of magnitude absorbed dose reductions in cepbalometric radiography. Health Physics 1989;56:533-8. Remmelink HJ. Letter to the editor. Am J Orthod Dentofac Orthop 1986;90:84-5. Borglin K, Peterson A, Rohlin M, Thapper K. Radiation dosimetry in radiology of the temporomandibular joint. Br J Radiol 1984;57:997-1007.

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J. Edward Gilda, DDS Eastman Dental Center 625 Elmwood Ave. Rochester, NY 14620