- Email: [email protected]
Influence of Dental Radiographic Cones on Radiation Exposure
Influence of dental radiographie cones on radiation exposure
R. D. Ice, PhD, Ann Arbor, Mich W. J. Updegrave, DDS, Philadelphia E. I. Bogucki, MS, St. Louis
Skin exposures from 65 kvp and 90 kvp dental radiographic units from use of long cones, long lead-lined cones, short cones, short lead-lined cones, and short pointed cones were evaluated. Comparisons were made on 100 patients who had each received a full mouth series of radiographs (20 films). Radiation measurements were made with thermoluminescent dosimeters positioned on the patient’s body. The anatomic regions mea sured were: parotid gland, thyroid gland, gonadal (lap dose), premolar, occipital, subcorneal, and central forehead. The exposure of the operator also was measured. Analysis of variance indicated a significant dif ference in radiation exposure at both 65 kvp and 90 kvp as well as significant differences between cones. Comparisons were made between 65 kvp and 90 kvp with respect to the total radiation ex posure. Results indicated that lead-lined cones are the most effective in reducing skin exposure from scatter radiation in clinical dental radiography.
Radiation exposure in patients in clinical dental radiographic examination has been investigated repeatedly in the past ten years. 1-2 Comparable evaluation of the results has not been possible be cause of an absence of reported statistical accur acy and precision. The reporting of reduced ra diation exposure by percent leads to confusion as no standard basis has been established by which the percent reduction from one author can be correlated with that of another author. Is there a significant difference in radiation output by use of various dental cones other than a sim ple reduction of the region of exposure by col limation? A linear response between the number of germ cell mutations and radiation exposure is acknowl edged.3 Extrapolation of this response to low radiation exposures indicated zero effect only at zero radiation dose.4 This has produced the no threshold theory that all radiation is harmful and cumulative, and that even low doses of radiation can induce potential mutations. The Council on Dental Materials and Devices and the Council on Dental Research , 5 therefore, have established guidelines for minimizing ra diation exposure of patients in dental radiography. As part of the guidelines, the Councils recom mended that open-ended cones be used to re duce the scatter radiation produced by pointed plastic cones. Shielded open-ended cones are considered beneficial because they collimate the useful radiation beam to the desired size, elimi nate scatter radiation from pointed cones, and absorb the low energy radiation that contributes to film fogging. The objective of this investigation was to eval uate clinically patient radiation exposure associ ated with a full mouth radiological examination using long lead-lined cones (LL), short leadlined cones (SL), long open-ended cones (LU), short open-ended cones (SU) and standard point JADA, Vol. 83, December 1971 ■ 1297
ed cones (SP) at two different radiation qualities, 90 kilovolt (peak) (kvp) and 65 kvp. The patient radiation exposure at the skin has been reported under many experimental condi tions. Maisky, Reid, and Maddalone 6 reported 15 milliroentgen (mr) to 125 mr to the eyes from a single exposure. Kitabatake and others7 estimated radiation doses of 0.5 to 3 mr exposure in male gonads, 0.03 to 1 mr in female gonads, and 10 to 1,0 0 0 mr to the eyes. Bjarngard and others8 reviewed literature of oral radiographic dosimetry through 1958 and assessed organ doses for a full mouth examination requiring 14 films. On the basis of 30 patients, the eye received 1.5 rads, the thyroid 0.5 rads, and the submandibular glands 2 rads. The maximal skin dose was 26 rads and the calculated integral absorbed dose to the head and neck was 2,800 gm rads. On a target phantom, the testes re ceived 0.9 mrads, and the ovaries 0.4 mrads. Bjarngard and others 9 also reported that the go nadal dose and, in all probability, the integral dose increased with HVL and that further re duction of other skin doses becomes smaller at HVL above 3 mm aluminum. Thus, the filter contributes to the gonadal dose and the best HVL implies a balancing of gonadal dose and integral dose with primarily the skin dose. However, Wainwright10 reported that the gonadal dose was unaffected by increased filtration or kilovoltage. Wuehrmann 11 enumerated the results of collimation which are the same as those observed with lead-lined open-ended cones. Richards 12 measured the gonadal dose rates to a phantom during periapical examinations con sisting of 14 exposures. The observed gonadal dose was about 1 mr per 14 exposures. Richards concluded that the short open-ended shielded cone, operated at 65 kvp, was the technique of choice. Menczer, 13»14 using an open-ended metal cone, indicated a reduced gonadal exposure when com pared with that of short, pointed cones. Calvert and Carmichael15 used film density measurements to illustrate decreased scatter radiation when vari ous types of dental X-ray cones were lined with lead foil. Lubenau and Gerusky, 16 using the re sults of 5,252 dental X-ray surveys, estimated an individual gonadal exposure of 0.06 to 0 .6 mr per year. With use of eight combinations of cones, filters, and collimators, O’Shaughnessy and Mitchell17 measured 0.05 to 0.5 mr/R of exposure at the testes. They concluded that, of the cones exam 1298 ■ JADA, Vol. 83, December 1971
ined, the long cone should be used. Medwedeff, Knox, and Latimer 18 built a device that simply reduces the area usually exposed to the beam by 26% . This device has been evaluated by Winkler. 19 Howley and co-workers20 used thermolumi nescent dosimetry (TLD) to evaluate dental X-ray exposures. Glass encapsulated lithium fluorine dosimeters were placed in a Rando phantom to compare absorbed doses between a standard dental radiographic and a panoramic dental Xray unit. Weissman and Sobkowski21 used TLD to examine absorbed radiation during intraoral periapical radiography. They concluded that a shielded cone was preferred in dental radiography.
Methods and materials
■ Thermoluminescent dosimetry: Calcium sulfate with manganese as an impurity, when exposed to ionizing radiation, attains an excited energy state proportional to the amount of absorbed radia tion. After radiation exposure, the CaS04:Mn is heated to cause a deexcitation to occur with the release of a light photon. The light produced is quantitated with a photomultiplier tube. The light output is proportional to the amount of absorbed radiation. CaS04:Mn dispersed in Teflon disks (12 mm in diameter and 0.4 mm thick) were heated for one hour at 300 C and allowed to cool to room temperature in the oven over 23 hours to empty out all possible excited orbital states. The dosim eters then were placed in a black, light-proof, polyethylene pouch. A Con-Rad Model TLD 5A was calibrated to 1 mr per digit with use of light sources of the manufacturers. The dosimeter re sponse was corrected for 60 kev energy, 2.79 mm HVL A1 with a 25 R Victoreen r chamber (Model 7-5) previously calibrated by the Nation al Bureau of Standards. All readouts were within 30 minutes of exposure, and under con stant nitrogen flush. All dosimeters were correct ed for background radiation, weight of sample, and the results averaged. ■ Radiographic technique: A General Electric Model 90 dental X-ray unit was used. The HVL at 90 kvp and 65 kvp was 3.4 mm A1 and 2.5 mm Al, respectively. The output at 16-inch target skin distance (TSD), 90 and 65 kvp, was 1.73 and 0.87 R per milliampere-minute, respectively. One hundred adult patients were each given a full
mouth series of 20 exposures (16 periapical and four bitewing) with speed D film (Kodak US or Rinn SF). The technique was standardized by use of Rinn right-angle and bisecting-angle instru ments.22 The exposure factors were 90 kvp, 15 ma at 0.25 second average; and 65 kvp, 10 ma at 1.0 0 second average. Five types of cones were used: pointed plas tic, 8 inches (SP); open-ended plastic, 8 inches (SU); open-ended plastic, lead-lined, 8 inches (SL); open-ended plastic, 16 inches (LU); openended plastic, lead-lined, 16 inches (LL). All cones were collimated to 2.75 inches di ameter at their extremities. An attempt was made to use a sixth cone with a rectangular collimator positioned at the facial surface as part of a filmholding device. 19 However, the number of retakes necessary because of cone cutting negated any intercone comparison. ■ Dosimeter locations: Each dosimeter was fas tened with adhesive tape to these positions on the patient: gonadal (centered on a board placed horizontally in the patient’s lap), occipital (cen tered on the head rest of the dental chair), forehead (centered horizontally 1.5 cm above the upper edge of the eyebrows), corneal ( 1.0 cm at the center of lower left eye margin), premolar (1.5 cm distal to left commissure on occlusal level), thyroid (in the hollow at the base of the neck), parotid (2.5 cm anterior to tragus of ear). Radiation exposure to the dentist was deter mined by a dosimeter placed on the left waist pocket of the dental gown. The rings of the Rinn instruments were placed
adjacent to the skin and the open cone surface was placed within 0.5 cm of the ring (illustration). The pointed cones were positioned 0.5 cm from the patient’s skin.
Results The total radiation exposure at each anatomic location, after a full-mouth series of radiographs (20 films, 65 kvp), is shown in Table 1. The data represent the average exposure of ten patients with each cone. The standard deviation, (SD) for each measurement is the range of the indi vidual measurement that would encompass 6 8 % of the patients examined. The corresponding ex posures for a high voltage technique (90 kvp) are given in Table 2. The sensitivity of the measuring system was limited to 0.04 mr. At 90 kvp, the radiation exposure to the dentist was below the 0.04 mr limit of sensitivity for each cone. The data in Tables 1 and 2 indicate that lined cones can substantially reduce radiation exposure to the patient without any significant loss in ra diographic visualization. So that the relative merits of each type of cone could be considered, the radiation exposure for each location was summed per patient (Table 3). The results indicate that long lead-lined cones give the least amount of scattered radiation to the patient’s skin. The amount of scatter radiation was less in all patients with the 90 kvp technique. This would be expect ed as the higher kvp is more penetrating at the skin surface. It was hypothesized that there was no signifi-
Mandibular anterior technique with use of Rinn X-C-P instrument and lead-lined 16-inch cone.
Ice—Updegrave-Bogucki: RADIATION EXPOSURE ■ 1299
Table 1 ■ Average* dental radiation exposuref per full mouth exam ination (milliroentgens). Anatomical region
Type of dental cone Short, pointed
Gonadal Occipital Forehead Corneal Premolar Thyroid Parotid Exposure of dentist
Short, unlined
Short, lined
Long, unlined
X-
SD
X.
SD
X
SD
X
1.72 1.64 22.25 827.77 922.32 30.42 265.21
0.16 0.36 1.53 73.64 63.48 3.62 130.78
1.95 1.70 27.06 1233.46 1135.93 36.73 390.33
0.22 0.26 3.93 191.72 57.73 132.38
1.42 1.28 7.97 935.64 1069.10 18.39 446.32
0.10 0.42 0.76 51.24 74.54 40.19 233.23
1.66 1.83 16.36 870.45 1018.46 63.70 193.37
0.09
0.09
0.11
0.06
0.04
0.04
0.08
2 .8 6
Long, lined
SD
X
SD
142.14 64.89 40.19 89.22
0.94 0.78 4.92 720.49 856.25 20.03 124.34
0.13 0.10 0.92 50.16 55.18 3.52 38.77
0.05
0.06
0.05
0.20 0.37 2 .2 0
*n = 10. fExposure factors: 65 kvp, 10 ma, 20 film examination, average exposure time of 1.00 second, and Al HVL at 2.5 mm Al.
Table 2 ■ Average* dental radiation exposuref per full mouth exam ination (m illiroentgens). Anatomical region
Type of dental cone Short, pointed
Gonadal Occipital Forehead Corneal Premolar Thyroid
Short, uniined
Short, lined
Long, unlined
Long, lined
X
SD
X
SD
X
SD
X
SD
X
SD
1.23 1.13 21.44 663.77 827.58 31.33
0.12 0.25 4.50 44.34 65.22 3.80
1.60 2.06 19.84 776.69 956.05 44.99
0.15 0.29 1.76 36.11 42.75 4.74
1.01 1.93 13.41 812.39 880.73 24.60
0.20 0.52 2.63 50.37 69.34 3.43
0.88 1.65 19.62 732.48 775.91 36.76
0.18 0.23 1.64 71.53 50.69 5.87
0.74 1.62 7.22 541.80 561.88 22.16
0.19 0.52 0.89 30.96 54.23 5.00
Exposure of dentist_________________ Below sensitivity limits of 0.04 mr________________________________________________ *n = 10. tExposure factors: 90 kvp, 15 ma, 20 film examination, average exposure film time 0.25 seconds, and HVL at 3.4 mm Al.
Table 3 ■ Average radiation exposure per dosimeter per patient.* Cone
Long, lined Short, pointed Long, unlined Short, lined Short, unlined *x= 2
90
65 k v p f
Û.
1300 ■ JADA, Vol. 83, December 1971
sured on the dentist was below the sensitivity limits (Table 4) and the fact that a lower radia-
>
cant difference in the amount of exposed radia tion at each anatomical location as produced by the different dental cones. The hypothesis was tested by an analysis of variance .23 If the results of the tests indicated an F value less than 2.6, the hypothesis would be correct; results greater than 2.6 proved the hypothesis false. Thus, there is a significant difference among dental cones in the amount of scatter radiation produced. (The hy pothesis was tested at the 0.95 (1-a) confidence level. This states that the results are valid 95% of the time.) The F values calculated from the analysis of variance tests are shown in Table 4. At 65 kvp, a significant difference between dental cones existed when exposed radiation was measured in the gonadal, premolar, comeal, and forehead regions. No significant difference be tween dental cones was found when exposed ra diation was measured in the parotid, thyroid, or occipital regions, or on the dentist. At 90 kvp, there was a significant difference between dental cones when exposed radiation was measured at all anatomical locations except the occipital regions. The increased quantity of sig nificance for 90 kvp over the results of 65 kvp indicates the increased need for concern about the type of dental cone used with the high kvp tech nique. The fact that the amount of radiation mea
X
SD
~x
SD
253.1 292.4 309.4 354.3 391.9
42.3 51.0 37.0 62.8 69.0
184.3 239.0 228.4 287.4 286.4
31.5 39.1 41.2 47.0 45.7
all dosimeters with one cone type.
(7 dosimeters/patient) {10 patients). t10 ma, 20 film exposures, average exposure time of 1.00 second. $15 ma, 20 film exposures, average exposure time of 0.25 second.
Table 4 ■ F test* for significant difference
between
cones in different anatom ical regions. Anatomical region
Parotid Thyroid Gonadal Premolar Occipital Corneal Forehead
65 kvp Degrees of freedomf (4,46) (4,45) (4,44) (4,46) (4,46) (4,44) (4,46)
90 kvp F
Degrees of freedom f
F
0.96 1.01 5.09$ 3.21$ 1.83 2.76$ 18.95$
(4,46) (4,46) (4,46) (4,44) (4,46) (4,46) (4,46)
6.34$ 3.94$ 3.82$ 6.36$ 0.93$ 4.76$ 4.78$
Exposure of dentist_______________ (4,43)______ 1.92_____ Below sensitivity limits “Confidence level: 1 - or = 95% (4,46 = 2.60). tDegrees of freedom used for statistical purposes. ^Significant difference indicated between cones.
tion exposure to the skin was observed (Table 3) indicate that the high voltage technique is the technique of choice in dental radiography. This is substantiated by the fact that the dosimeter located in the occipital region, which would mea sure predominantly scatter radiation, indicated no significant difference between the 90 kvp and 65 kvp technique. A significant difference between dental cones, indicated by the analysis of variance test, was probed by the Neuman-Keuls24 method. Calcu lated for each value was the q statistic
VMS error/n where r is the number of steps the two means are apart on an ordered scale; n is the number of ob servations in each mean; Tj is the mean of j obser vations; and Tjj is the mean of a second set of ob servations. qr was analyzed at the 95% confidence level with 4 and 46 degrees of freedom. The results for the 65 kvp, low voltage tech nique are shown in Table 5. A line under the particular cone type and extending under another cone type indicates no significant difference. Cones not underlined by the same line do differ with respect to the amount of radiation exposure to the patient. No significant difference by any cone style was evident when the radiation was mea sured at the parotid, thyroid, and occipital po sitions on the patient or with respect to exposure by the dentist. Of the seven regions measured for radiation and the measurement of exposure to the dentist, the lowest values were given four times each by short lead-lined and long lead-lined cones. No significant difference between lead-lined cones was observed except at the premolar region where the short lead-lined cone gave the lowest amount of measured radiation. In the gonadal region, whereas there was no significant difference be tween short lead-lined cones and any other cone, there was a significant difference between the long lead-lined cone and the long unlined, short point ed, and short unlined cones. The results indicate that either the long or short lead-lined cone is preferred over the short pointed cone, and the long or short unlined cones when the low voltage (65 kvp) technique is used. The results for the 90 kvp high voltage tech nique are in Table 6 . As in Table 5, a common line under the particular cone types indicates no significant difference in radiation exposure to
Table 5
■ Schematic* Neum an-Keuls resultsf: 65 kvp, 10 ma, 20 exposures. Cones
Anatomic regions Parotid
LL
SL
LU
SP
SU
Thyroid
LL
SL
LU
SP
SU
Gonadal
LL
SL
LU
SP
SU
Premolar
SL
SP
LU
LU
SU
Occipital
SL
LL
SP
SU
LU
Corneal
SL
SP
LU
LL
SU
Forehead
SL
LL
LU
SP
SU
Exposure of dentist
LL
SL
LU
SP
SU
'Common line: no significant difference. tSignificance: q {1,40). LL: long, lined. SP: short, pointed. lined. SU: short, unlined.
long , unlined.
LU:
SL: short,
Table 6
■ Schematic* Neum an-Keuls resultsf: 90 kvp, 10 ma, 20 exposures. Cones
Anatomic regions Parotid
LL
LU
SP
SL
SU
Thyroid
LL
SL
SP
LU
SU
Gonadal
LL
LU
SL
SP
SU
Premolar
LL
LU
SP
SL
SU
Occipital
SP
LL
LU
SP
SU
Corneal
LL
SP
LU
SU
SL
Forehead
LL
SL
LU
SU
SP
unlined.
SL: short,
'Common line: no significant difference. tSignificance q.95 (1,40). LL: long, lined. SP: short, pointed. lined. SU: short, unlined.
LU:
long,
the patient at the dosimeter site. Cones not un derlined by the same line do differ with respect to the amount o f radiation exposure received by the patient. No significant difference in radiation exposure by any cone type was evident when mea sured at the occipital region. Long lead-lined cones, in all instances but one, produced the lowest radiation exposure to the patient. The long lead-lined cone is preferred when the high vol tage (90 kvp) technique is used.
Summary
Radiation exposure was reduced significantly at 65 kvp with both the 8 -inch or 16-inch openended lead-lined cones compared with that of Ice—Updegrave— Bogucki: RADIATION EXPOSURE ■ 1301
open-ended nonlead-lined or short, pointed cones. At high kvp techniques (90 kvp), the radiation exposure was reduced significantly with the 16inch open-ended lead-lined cone compared with that of the 8-inch open-ended lead-lined, the openended nonlead-lined cone, or the short, pointed cones. A significant reduction in the skin exposures at entry was obtained at 90 kvp technique over that of the 65 kvp technique. Because of the significant reduced radiation ex posure indicated in this investigation, open-ended lead-lined cones should be included as standard dental procedure. Doctor Ice is director of radiopharmaceutical services and associate professor of pharmacy, nuclear medicine sec tion, University Hospital, University of Michigan, Ann Arbor, 48104. Doctor Updegrave is professor of dental radiology, Temple University, School of Dentistry. Mr. Bogucki is in the St. Louis School of Medicine, St. Louis. 1. Bureau of Radiological Health, Public Health Service. Population exposure to X-Rays, US 1964. Washington, D.C., Govt Print Off, p 148. 2. Bureau of Radiological Health, Public Health Service. Population dose from X-Rays, U S 1964. Washington, D.C., Govt Print Off, 1969, p 133. 3. Morgan, K.Z. and Turner, J.E. eds. Principles of radi ation protection. New York, John Wiley and Sons, 1967, p 415. 4. Russell, W.L.; Russell, L.B.; and Kelley, E.M. Sym posium on the intermediate and low level effects of ionizing radiation. London, Taylor and Francis, 1960. 5. Council on Dental Materials and Devices, Council on Dental Research. Radiation hygiene and practice in dentistry III. JADA 76:115 Jan 1968. 6. Maisky, S.J.; Reid, C.B.; and Maddalone, L. Filter and collimating system for protection in dental radiography.
1302 ■ JADA, Vol. 83, December 1971
Oral Surg 10:627 June 1957. 7. Kitabatake, T., and others. Radiation dose in dental roentgenography, with special reference to enlargement dental radiography. Nagoya J Med Sci 24:234 March 1962. 8. Bj'arngard, B., and others. Radiation doses in oral ra diography. Odont Rev 11:100, 1960. 9. Bj'arngard, B., and others. Radiation dose in oral ra diography. Odont Rev 10:355, 1959. 10. Wainwright, W.W. Filtration for lowest patient dose in dental radiography. Oral Surg 16:561 May 1963. 11. Wuehrmann, A.H. Radiation protection and dentistry. St. Louis, C. V. Mosby Co., 1960, p 136. 12. Rictiards, A.G. New method for reduction of gonadal irradiation of dental patients. JADA 65:1 July 1962. 13. Menczer, L.F. The open-ended metal column for the dental X-ray machine. JADA 73:1083 Nov 1966. 14. Menczer, L.F. Study of radiation exposure to gonads of preschool boys from diagnostic dental roentgenograms. JADA 66:30 Jan 1963. 15. Calvert, K., and Carmichael, C. Open-end lead-lined dental X-ray cones. Oral Surg 23:328 March 1967. 16. Lubenau, J., and Gerusky, T.M. Results of the Penn sylvania Department of Health dental x-ray survey program. Health Phys 14:151 Feb 1968. 17. O’Shaughnessy, P.E., and Mitchell, D.F. Effect of altering physical roentgenographic factors on patient radi ation dose levels. JADA 69:335 Sept 1964. 18. Medwedeff, F.M.; Knox, W.H.; and Latimer, P. A new device to reduce patient irradiation and improve dental film quality. Oral Surg 15:1079 Sept 1962. 19. Winkler, K.G. Influence of rectangular collimation and intraoral shielding on radiation dose in dental radiog raphy. JADA 77:95 July 1968. 20. Howley, J.R.; Robbins, C.; and Dickinson, M. Thermo luminescent dosimetry applied to dental X-Ray exposures. Radiol Health Data Rep 9:397 Aug 1968. 21. Weissman, D.D., and Sobkowski, F.J. Comparative thermoluminescent dosimetry of intraoral periapical radi ography. Oral Surg 29:376 March 1970. 22. Updegrave, W.J. Right-angle dental radiography. Dent Clin N Amer 571 Nov 1968. 23. Winer, BJ. Statistical principles in experimental de sign. New York, McGraw-Hill, 1962, p 100. 24. Winer, BJ. Statistical principles in experimental de sign. New York, McGraw-Hill, 1962, p 101.
R. D. Ice, PhD, Ann Arbor, Mich W. J. Updegrave, DDS, Philadelphia E. I. Bogucki, MS, St. Louis
Skin exposures from 65 kvp and 90 kvp dental radiographic units from use of long cones, long lead-lined cones, short cones, short lead-lined cones, and short pointed cones were evaluated. Comparisons were made on 100 patients who had each received a full mouth series of radiographs (20 films). Radiation measurements were made with thermoluminescent dosimeters positioned on the patient’s body. The anatomic regions mea sured were: parotid gland, thyroid gland, gonadal (lap dose), premolar, occipital, subcorneal, and central forehead. The exposure of the operator also was measured. Analysis of variance indicated a significant dif ference in radiation exposure at both 65 kvp and 90 kvp as well as significant differences between cones. Comparisons were made between 65 kvp and 90 kvp with respect to the total radiation ex posure. Results indicated that lead-lined cones are the most effective in reducing skin exposure from scatter radiation in clinical dental radiography.
Radiation exposure in patients in clinical dental radiographic examination has been investigated repeatedly in the past ten years. 1-2 Comparable evaluation of the results has not been possible be cause of an absence of reported statistical accur acy and precision. The reporting of reduced ra diation exposure by percent leads to confusion as no standard basis has been established by which the percent reduction from one author can be correlated with that of another author. Is there a significant difference in radiation output by use of various dental cones other than a sim ple reduction of the region of exposure by col limation? A linear response between the number of germ cell mutations and radiation exposure is acknowl edged.3 Extrapolation of this response to low radiation exposures indicated zero effect only at zero radiation dose.4 This has produced the no threshold theory that all radiation is harmful and cumulative, and that even low doses of radiation can induce potential mutations. The Council on Dental Materials and Devices and the Council on Dental Research , 5 therefore, have established guidelines for minimizing ra diation exposure of patients in dental radiography. As part of the guidelines, the Councils recom mended that open-ended cones be used to re duce the scatter radiation produced by pointed plastic cones. Shielded open-ended cones are considered beneficial because they collimate the useful radiation beam to the desired size, elimi nate scatter radiation from pointed cones, and absorb the low energy radiation that contributes to film fogging. The objective of this investigation was to eval uate clinically patient radiation exposure associ ated with a full mouth radiological examination using long lead-lined cones (LL), short leadlined cones (SL), long open-ended cones (LU), short open-ended cones (SU) and standard point JADA, Vol. 83, December 1971 ■ 1297
ed cones (SP) at two different radiation qualities, 90 kilovolt (peak) (kvp) and 65 kvp. The patient radiation exposure at the skin has been reported under many experimental condi tions. Maisky, Reid, and Maddalone 6 reported 15 milliroentgen (mr) to 125 mr to the eyes from a single exposure. Kitabatake and others7 estimated radiation doses of 0.5 to 3 mr exposure in male gonads, 0.03 to 1 mr in female gonads, and 10 to 1,0 0 0 mr to the eyes. Bjarngard and others8 reviewed literature of oral radiographic dosimetry through 1958 and assessed organ doses for a full mouth examination requiring 14 films. On the basis of 30 patients, the eye received 1.5 rads, the thyroid 0.5 rads, and the submandibular glands 2 rads. The maximal skin dose was 26 rads and the calculated integral absorbed dose to the head and neck was 2,800 gm rads. On a target phantom, the testes re ceived 0.9 mrads, and the ovaries 0.4 mrads. Bjarngard and others 9 also reported that the go nadal dose and, in all probability, the integral dose increased with HVL and that further re duction of other skin doses becomes smaller at HVL above 3 mm aluminum. Thus, the filter contributes to the gonadal dose and the best HVL implies a balancing of gonadal dose and integral dose with primarily the skin dose. However, Wainwright10 reported that the gonadal dose was unaffected by increased filtration or kilovoltage. Wuehrmann 11 enumerated the results of collimation which are the same as those observed with lead-lined open-ended cones. Richards 12 measured the gonadal dose rates to a phantom during periapical examinations con sisting of 14 exposures. The observed gonadal dose was about 1 mr per 14 exposures. Richards concluded that the short open-ended shielded cone, operated at 65 kvp, was the technique of choice. Menczer, 13»14 using an open-ended metal cone, indicated a reduced gonadal exposure when com pared with that of short, pointed cones. Calvert and Carmichael15 used film density measurements to illustrate decreased scatter radiation when vari ous types of dental X-ray cones were lined with lead foil. Lubenau and Gerusky, 16 using the re sults of 5,252 dental X-ray surveys, estimated an individual gonadal exposure of 0.06 to 0 .6 mr per year. With use of eight combinations of cones, filters, and collimators, O’Shaughnessy and Mitchell17 measured 0.05 to 0.5 mr/R of exposure at the testes. They concluded that, of the cones exam 1298 ■ JADA, Vol. 83, December 1971
ined, the long cone should be used. Medwedeff, Knox, and Latimer 18 built a device that simply reduces the area usually exposed to the beam by 26% . This device has been evaluated by Winkler. 19 Howley and co-workers20 used thermolumi nescent dosimetry (TLD) to evaluate dental X-ray exposures. Glass encapsulated lithium fluorine dosimeters were placed in a Rando phantom to compare absorbed doses between a standard dental radiographic and a panoramic dental Xray unit. Weissman and Sobkowski21 used TLD to examine absorbed radiation during intraoral periapical radiography. They concluded that a shielded cone was preferred in dental radiography.
Methods and materials
■ Thermoluminescent dosimetry: Calcium sulfate with manganese as an impurity, when exposed to ionizing radiation, attains an excited energy state proportional to the amount of absorbed radia tion. After radiation exposure, the CaS04:Mn is heated to cause a deexcitation to occur with the release of a light photon. The light produced is quantitated with a photomultiplier tube. The light output is proportional to the amount of absorbed radiation. CaS04:Mn dispersed in Teflon disks (12 mm in diameter and 0.4 mm thick) were heated for one hour at 300 C and allowed to cool to room temperature in the oven over 23 hours to empty out all possible excited orbital states. The dosim eters then were placed in a black, light-proof, polyethylene pouch. A Con-Rad Model TLD 5A was calibrated to 1 mr per digit with use of light sources of the manufacturers. The dosimeter re sponse was corrected for 60 kev energy, 2.79 mm HVL A1 with a 25 R Victoreen r chamber (Model 7-5) previously calibrated by the Nation al Bureau of Standards. All readouts were within 30 minutes of exposure, and under con stant nitrogen flush. All dosimeters were correct ed for background radiation, weight of sample, and the results averaged. ■ Radiographic technique: A General Electric Model 90 dental X-ray unit was used. The HVL at 90 kvp and 65 kvp was 3.4 mm A1 and 2.5 mm Al, respectively. The output at 16-inch target skin distance (TSD), 90 and 65 kvp, was 1.73 and 0.87 R per milliampere-minute, respectively. One hundred adult patients were each given a full
mouth series of 20 exposures (16 periapical and four bitewing) with speed D film (Kodak US or Rinn SF). The technique was standardized by use of Rinn right-angle and bisecting-angle instru ments.22 The exposure factors were 90 kvp, 15 ma at 0.25 second average; and 65 kvp, 10 ma at 1.0 0 second average. Five types of cones were used: pointed plas tic, 8 inches (SP); open-ended plastic, 8 inches (SU); open-ended plastic, lead-lined, 8 inches (SL); open-ended plastic, 16 inches (LU); openended plastic, lead-lined, 16 inches (LL). All cones were collimated to 2.75 inches di ameter at their extremities. An attempt was made to use a sixth cone with a rectangular collimator positioned at the facial surface as part of a filmholding device. 19 However, the number of retakes necessary because of cone cutting negated any intercone comparison. ■ Dosimeter locations: Each dosimeter was fas tened with adhesive tape to these positions on the patient: gonadal (centered on a board placed horizontally in the patient’s lap), occipital (cen tered on the head rest of the dental chair), forehead (centered horizontally 1.5 cm above the upper edge of the eyebrows), corneal ( 1.0 cm at the center of lower left eye margin), premolar (1.5 cm distal to left commissure on occlusal level), thyroid (in the hollow at the base of the neck), parotid (2.5 cm anterior to tragus of ear). Radiation exposure to the dentist was deter mined by a dosimeter placed on the left waist pocket of the dental gown. The rings of the Rinn instruments were placed
adjacent to the skin and the open cone surface was placed within 0.5 cm of the ring (illustration). The pointed cones were positioned 0.5 cm from the patient’s skin.
Results The total radiation exposure at each anatomic location, after a full-mouth series of radiographs (20 films, 65 kvp), is shown in Table 1. The data represent the average exposure of ten patients with each cone. The standard deviation, (SD) for each measurement is the range of the indi vidual measurement that would encompass 6 8 % of the patients examined. The corresponding ex posures for a high voltage technique (90 kvp) are given in Table 2. The sensitivity of the measuring system was limited to 0.04 mr. At 90 kvp, the radiation exposure to the dentist was below the 0.04 mr limit of sensitivity for each cone. The data in Tables 1 and 2 indicate that lined cones can substantially reduce radiation exposure to the patient without any significant loss in ra diographic visualization. So that the relative merits of each type of cone could be considered, the radiation exposure for each location was summed per patient (Table 3). The results indicate that long lead-lined cones give the least amount of scattered radiation to the patient’s skin. The amount of scatter radiation was less in all patients with the 90 kvp technique. This would be expect ed as the higher kvp is more penetrating at the skin surface. It was hypothesized that there was no signifi-
Mandibular anterior technique with use of Rinn X-C-P instrument and lead-lined 16-inch cone.
Ice—Updegrave-Bogucki: RADIATION EXPOSURE ■ 1299
Table 1 ■ Average* dental radiation exposuref per full mouth exam ination (milliroentgens). Anatomical region
Type of dental cone Short, pointed
Gonadal Occipital Forehead Corneal Premolar Thyroid Parotid Exposure of dentist
Short, unlined
Short, lined
Long, unlined
X-
SD
X.
SD
X
SD
X
1.72 1.64 22.25 827.77 922.32 30.42 265.21
0.16 0.36 1.53 73.64 63.48 3.62 130.78
1.95 1.70 27.06 1233.46 1135.93 36.73 390.33
0.22 0.26 3.93 191.72 57.73 132.38
1.42 1.28 7.97 935.64 1069.10 18.39 446.32
0.10 0.42 0.76 51.24 74.54 40.19 233.23
1.66 1.83 16.36 870.45 1018.46 63.70 193.37
0.09
0.09
0.11
0.06
0.04
0.04
0.08
2 .8 6
Long, lined
SD
X
SD
142.14 64.89 40.19 89.22
0.94 0.78 4.92 720.49 856.25 20.03 124.34
0.13 0.10 0.92 50.16 55.18 3.52 38.77
0.05
0.06
0.05
0.20 0.37 2 .2 0
*n = 10. fExposure factors: 65 kvp, 10 ma, 20 film examination, average exposure time of 1.00 second, and Al HVL at 2.5 mm Al.
Table 2 ■ Average* dental radiation exposuref per full mouth exam ination (m illiroentgens). Anatomical region
Type of dental cone Short, pointed
Gonadal Occipital Forehead Corneal Premolar Thyroid
Short, uniined
Short, lined
Long, unlined
Long, lined
X
SD
X
SD
X
SD
X
SD
X
SD
1.23 1.13 21.44 663.77 827.58 31.33
0.12 0.25 4.50 44.34 65.22 3.80
1.60 2.06 19.84 776.69 956.05 44.99
0.15 0.29 1.76 36.11 42.75 4.74
1.01 1.93 13.41 812.39 880.73 24.60
0.20 0.52 2.63 50.37 69.34 3.43
0.88 1.65 19.62 732.48 775.91 36.76
0.18 0.23 1.64 71.53 50.69 5.87
0.74 1.62 7.22 541.80 561.88 22.16
0.19 0.52 0.89 30.96 54.23 5.00
Exposure of dentist_________________ Below sensitivity limits of 0.04 mr________________________________________________ *n = 10. tExposure factors: 90 kvp, 15 ma, 20 film examination, average exposure film time 0.25 seconds, and HVL at 3.4 mm Al.
Table 3 ■ Average radiation exposure per dosimeter per patient.* Cone
Long, lined Short, pointed Long, unlined Short, lined Short, unlined *x= 2
90
65 k v p f
Û.
1300 ■ JADA, Vol. 83, December 1971
sured on the dentist was below the sensitivity limits (Table 4) and the fact that a lower radia-
>
cant difference in the amount of exposed radia tion at each anatomical location as produced by the different dental cones. The hypothesis was tested by an analysis of variance .23 If the results of the tests indicated an F value less than 2.6, the hypothesis would be correct; results greater than 2.6 proved the hypothesis false. Thus, there is a significant difference among dental cones in the amount of scatter radiation produced. (The hy pothesis was tested at the 0.95 (1-a) confidence level. This states that the results are valid 95% of the time.) The F values calculated from the analysis of variance tests are shown in Table 4. At 65 kvp, a significant difference between dental cones existed when exposed radiation was measured in the gonadal, premolar, comeal, and forehead regions. No significant difference be tween dental cones was found when exposed ra diation was measured in the parotid, thyroid, or occipital regions, or on the dentist. At 90 kvp, there was a significant difference between dental cones when exposed radiation was measured at all anatomical locations except the occipital regions. The increased quantity of sig nificance for 90 kvp over the results of 65 kvp indicates the increased need for concern about the type of dental cone used with the high kvp tech nique. The fact that the amount of radiation mea
X
SD
~x
SD
253.1 292.4 309.4 354.3 391.9
42.3 51.0 37.0 62.8 69.0
184.3 239.0 228.4 287.4 286.4
31.5 39.1 41.2 47.0 45.7
all dosimeters with one cone type.
(7 dosimeters/patient) {10 patients). t10 ma, 20 film exposures, average exposure time of 1.00 second. $15 ma, 20 film exposures, average exposure time of 0.25 second.
Table 4 ■ F test* for significant difference
between
cones in different anatom ical regions. Anatomical region
Parotid Thyroid Gonadal Premolar Occipital Corneal Forehead
65 kvp Degrees of freedomf (4,46) (4,45) (4,44) (4,46) (4,46) (4,44) (4,46)
90 kvp F
Degrees of freedom f
F
0.96 1.01 5.09$ 3.21$ 1.83 2.76$ 18.95$
(4,46) (4,46) (4,46) (4,44) (4,46) (4,46) (4,46)
6.34$ 3.94$ 3.82$ 6.36$ 0.93$ 4.76$ 4.78$
Exposure of dentist_______________ (4,43)______ 1.92_____ Below sensitivity limits “Confidence level: 1 - or = 95% (4,46 = 2.60). tDegrees of freedom used for statistical purposes. ^Significant difference indicated between cones.
tion exposure to the skin was observed (Table 3) indicate that the high voltage technique is the technique of choice in dental radiography. This is substantiated by the fact that the dosimeter located in the occipital region, which would mea sure predominantly scatter radiation, indicated no significant difference between the 90 kvp and 65 kvp technique. A significant difference between dental cones, indicated by the analysis of variance test, was probed by the Neuman-Keuls24 method. Calcu lated for each value was the q statistic
VMS error/n where r is the number of steps the two means are apart on an ordered scale; n is the number of ob servations in each mean; Tj is the mean of j obser vations; and Tjj is the mean of a second set of ob servations. qr was analyzed at the 95% confidence level with 4 and 46 degrees of freedom. The results for the 65 kvp, low voltage tech nique are shown in Table 5. A line under the particular cone type and extending under another cone type indicates no significant difference. Cones not underlined by the same line do differ with respect to the amount of radiation exposure to the patient. No significant difference by any cone style was evident when the radiation was mea sured at the parotid, thyroid, and occipital po sitions on the patient or with respect to exposure by the dentist. Of the seven regions measured for radiation and the measurement of exposure to the dentist, the lowest values were given four times each by short lead-lined and long lead-lined cones. No significant difference between lead-lined cones was observed except at the premolar region where the short lead-lined cone gave the lowest amount of measured radiation. In the gonadal region, whereas there was no significant difference be tween short lead-lined cones and any other cone, there was a significant difference between the long lead-lined cone and the long unlined, short point ed, and short unlined cones. The results indicate that either the long or short lead-lined cone is preferred over the short pointed cone, and the long or short unlined cones when the low voltage (65 kvp) technique is used. The results for the 90 kvp high voltage tech nique are in Table 6 . As in Table 5, a common line under the particular cone types indicates no significant difference in radiation exposure to
Table 5
■ Schematic* Neum an-Keuls resultsf: 65 kvp, 10 ma, 20 exposures. Cones
Anatomic regions Parotid
LL
SL
LU
SP
SU
Thyroid
LL
SL
LU
SP
SU
Gonadal
LL
SL
LU
SP
SU
Premolar
SL
SP
LU
LU
SU
Occipital
SL
LL
SP
SU
LU
Corneal
SL
SP
LU
LL
SU
Forehead
SL
LL
LU
SP
SU
Exposure of dentist
LL
SL
LU
SP
SU
'Common line: no significant difference. tSignificance: q {1,40). LL: long, lined. SP: short, pointed. lined. SU: short, unlined.
long , unlined.
LU:
SL: short,
Table 6
■ Schematic* Neum an-Keuls resultsf: 90 kvp, 10 ma, 20 exposures. Cones
Anatomic regions Parotid
LL
LU
SP
SL
SU
Thyroid
LL
SL
SP
LU
SU
Gonadal
LL
LU
SL
SP
SU
Premolar
LL
LU
SP
SL
SU
Occipital
SP
LL
LU
SP
SU
Corneal
LL
SP
LU
SU
SL
Forehead
LL
SL
LU
SU
SP
unlined.
SL: short,
'Common line: no significant difference. tSignificance q.95 (1,40). LL: long, lined. SP: short, pointed. lined. SU: short, unlined.
LU:
long,
the patient at the dosimeter site. Cones not un derlined by the same line do differ with respect to the amount o f radiation exposure received by the patient. No significant difference in radiation exposure by any cone type was evident when mea sured at the occipital region. Long lead-lined cones, in all instances but one, produced the lowest radiation exposure to the patient. The long lead-lined cone is preferred when the high vol tage (90 kvp) technique is used.
Summary
Radiation exposure was reduced significantly at 65 kvp with both the 8 -inch or 16-inch openended lead-lined cones compared with that of Ice—Updegrave— Bogucki: RADIATION EXPOSURE ■ 1301
open-ended nonlead-lined or short, pointed cones. At high kvp techniques (90 kvp), the radiation exposure was reduced significantly with the 16inch open-ended lead-lined cone compared with that of the 8-inch open-ended lead-lined, the openended nonlead-lined cone, or the short, pointed cones. A significant reduction in the skin exposures at entry was obtained at 90 kvp technique over that of the 65 kvp technique. Because of the significant reduced radiation ex posure indicated in this investigation, open-ended lead-lined cones should be included as standard dental procedure. Doctor Ice is director of radiopharmaceutical services and associate professor of pharmacy, nuclear medicine sec tion, University Hospital, University of Michigan, Ann Arbor, 48104. Doctor Updegrave is professor of dental radiology, Temple University, School of Dentistry. Mr. Bogucki is in the St. Louis School of Medicine, St. Louis. 1. Bureau of Radiological Health, Public Health Service. Population exposure to X-Rays, US 1964. Washington, D.C., Govt Print Off, p 148. 2. Bureau of Radiological Health, Public Health Service. Population dose from X-Rays, U S 1964. Washington, D.C., Govt Print Off, 1969, p 133. 3. Morgan, K.Z. and Turner, J.E. eds. Principles of radi ation protection. New York, John Wiley and Sons, 1967, p 415. 4. Russell, W.L.; Russell, L.B.; and Kelley, E.M. Sym posium on the intermediate and low level effects of ionizing radiation. London, Taylor and Francis, 1960. 5. Council on Dental Materials and Devices, Council on Dental Research. Radiation hygiene and practice in dentistry III. JADA 76:115 Jan 1968. 6. Maisky, S.J.; Reid, C.B.; and Maddalone, L. Filter and collimating system for protection in dental radiography.
1302 ■ JADA, Vol. 83, December 1971
Oral Surg 10:627 June 1957. 7. Kitabatake, T., and others. Radiation dose in dental roentgenography, with special reference to enlargement dental radiography. Nagoya J Med Sci 24:234 March 1962. 8. Bj'arngard, B., and others. Radiation doses in oral ra diography. Odont Rev 11:100, 1960. 9. Bj'arngard, B., and others. Radiation dose in oral ra diography. Odont Rev 10:355, 1959. 10. Wainwright, W.W. Filtration for lowest patient dose in dental radiography. Oral Surg 16:561 May 1963. 11. Wuehrmann, A.H. Radiation protection and dentistry. St. Louis, C. V. Mosby Co., 1960, p 136. 12. Rictiards, A.G. New method for reduction of gonadal irradiation of dental patients. JADA 65:1 July 1962. 13. Menczer, L.F. The open-ended metal column for the dental X-ray machine. JADA 73:1083 Nov 1966. 14. Menczer, L.F. Study of radiation exposure to gonads of preschool boys from diagnostic dental roentgenograms. JADA 66:30 Jan 1963. 15. Calvert, K., and Carmichael, C. Open-end lead-lined dental X-ray cones. Oral Surg 23:328 March 1967. 16. Lubenau, J., and Gerusky, T.M. Results of the Penn sylvania Department of Health dental x-ray survey program. Health Phys 14:151 Feb 1968. 17. O’Shaughnessy, P.E., and Mitchell, D.F. Effect of altering physical roentgenographic factors on patient radi ation dose levels. JADA 69:335 Sept 1964. 18. Medwedeff, F.M.; Knox, W.H.; and Latimer, P. A new device to reduce patient irradiation and improve dental film quality. Oral Surg 15:1079 Sept 1962. 19. Winkler, K.G. Influence of rectangular collimation and intraoral shielding on radiation dose in dental radiog raphy. JADA 77:95 July 1968. 20. Howley, J.R.; Robbins, C.; and Dickinson, M. Thermo luminescent dosimetry applied to dental X-Ray exposures. Radiol Health Data Rep 9:397 Aug 1968. 21. Weissman, D.D., and Sobkowski, F.J. Comparative thermoluminescent dosimetry of intraoral periapical radi ography. Oral Surg 29:376 March 1970. 22. Updegrave, W.J. Right-angle dental radiography. Dent Clin N Amer 571 Nov 1968. 23. Winer, BJ. Statistical principles in experimental de sign. New York, McGraw-Hill, 1962, p 100. 24. Winer, BJ. Statistical principles in experimental de sign. New York, McGraw-Hill, 1962, p 101.