- Email: [email protected]
New method for reduction of gonadal irradiation of dental patients
the Journal of the American Dental Association
New method for reduction of gonadal irradiation of dental patients
Albert G. R ich a rd s* M .S ., A nn A rbor, M ich .
A pinhole camera on the lap of a phantom body was used to disclose the sources of x-radiation that expose the gonadal region of the dental patient. A short, open-ended, shielded x-ray cone, used with a dental x-ray machine oper ated with 65 kvp, reduces by almost one half, gonadal exposure. O pen-ended shielded cones easily may be substituted fo r the pointed plastic cones that are standard equipment on existing dental x-ray units.
T h e purpose o f this report is to illustrate how the use o f a suitable x-ray cone can reduce by approximately one half the gonadal irradiation o f the dental patient. SOURCES OF GONADAL IRRADIATION
T h e proper starting point in reducing the gonadal exposure to x-rays o f the dental
patient is to learn first the origin of the offending radiation and then to take the necessary measures to control or elimi nate the sources. T h e sources can be iden tified readily by placing a lead-walled pinhole camera in a position comparable to the lap o f the subject with the camera directed upward toward his face and the head of the x-ray apparatus. Figure 1, above left, indicates the loca tion o f the pinhole camera in relation to the head o f the., phantom and the x-ray apparatus while the region o f the maxil lary central incisor is examined roentgenographically. I n this example, the pin hole camera has been moved from the position comparable to the subject’s lap to a position closer both to the face of the subject and the x-ray apparatus so that the scattered radiation w ill be more intense and the time of exposure that is necessary to produce an image within the pinhole camera will be considerably re duced. In spite of the closer proximity of the pinhole camera to the sources of the scattered radiation, the exposure that is
Fig. 1 • A b o v e left: Ph otograph dep ictin g position of pinhole cam era relative to phantom head and x-ray apparatus e q u ip p e d with pointed plastic cone. A b o v e right: Photograph m ade with pinhole cam era portraying the nose and lower half o f phantom 's face and the head and pointed plastic cone of the x-ray apparatus. A light fixture, h an gin g from the ceiling of the laboratory, is also visible. Below left: Roentgenogram m ade with pinhole cam era of the sources of radiation which expose the reproductive organs of the dental patient. These sources are: ( I ) leakage radiation from the focal spot o f the x-ray tube; (2) scattered radiation from the aluminum filter and other strongly irradiated metallic parts of the ap paratus which are located behind the lead dia phragm ; (3) the irradiated portion of the pointed plastic cone; and (4) the subject's chin, oral region and nose. Below right: C o m p o site print of B and C, relating the location o f the sources of the invisible x-rays to the visible details of the ph o to gra ph
RICHARDS . . . VOLUME 65, JULY 1962 • 17/3
necessary to produce pictures with the pinhole camera is so great that phantom heads must be substituted for living patients. Usable pictures made w ith the pinhole camera require exposures 100,000 or more times as great as are used rou tinely with living subjects. T h e pinhole camera is designed to contain both photographic and roentgenographic films and thus produce, simulta neously, photographic and roentgenographic images o f the same subject. T h e photographic film in the camera is very sensitive to light and relatively insensitive to roentgen rays and therefore is exposed almost exclusively by the light that re flects from the surface o f the subject in the proper directions to enter the camera through its pinhole opening. Th e roentgenographic film is located in the camera behind the photographic film and is sepa rated from it by a thin opaque barrier. T h e roentgenographic film is held firm ly between two intensifying screens that w ill produce images in fluorescent light when they are excited by x-radiation. T h e roentgenographic emulsion is far more sensitive to exposure by this fluores cent light than to direct exposure to x-radiation. Any material that is exposed to the primary beam from a dental x-ray ap paratus w ill both transmit and absorb some o f the radiation and in addition w ill produce secondary radiation which scat ters in all directions— very much as light from an automobile headlamp is scat tered by fog. T h e operation of the pin hole camera depends on that minute frac tion o f the secondary radiation which scatters in the proper direction to pass through the pinhole opening o f the camera. It is this radiation which excites the intensifying screens and exposes the roentgenographic film. A detailed ac count o f the construction and operation o f the pinhole camera has been presented elsewhere.1 Figure 1, above right and below left, are the photograph and roentgenogram
respectively that were produced simulta neously by the pinhole camera when the region of the maxillary central incisor of the subject was examined with roentgen rays by a technic which utilized a short, pointed, plastic cone. T h e photograph portrays the phantom’s face, the head and pointed cone o f the x-ray apparatus, and even a light fixture hanging from the ceiling of the laboratory. T h e roent genogram clearly identifies as the sources of the radiation that irradiate the gonadal region, the subject’ s chin, oral region and nose, the irradiated portion o f the pointed cone, the aluminum filter and other strongly irradiated metallic parts o f the apparatus which are located behind the lead diaphragm, and the focal spot of the x-ray tube. T h e image of the focal spot was produced by leakage radiation whereas the other three images were pro duced by scattered radiation. Figure 1, below right, was produced by superimposing the photograph and roent genogram (Fig. 1, above right and below left) and printing them as a unit. This illustration provides a visible plane of ref erence (the photograph) on which the sources of the invisible x-radiation can be visualized. Figure 2 indicates, when the remainder o f the maxillary teeth are examined by roentgen rays, that the same sources of ra diation are serving to expose the gonadal region as were acting when the maxillary central incisors were examined in Figure 1, below left. When the mandibular teeth are examined roentgenographically, the contribution to the exposure o f the gon adal region from the filter and other metallic parts located behind the lead diaphragm is greatly reduced or totally absent depending on the extent of up ward direction of the x-ray beam. T h e phantom used in this study, unlike the phantom reported in an earlier inves tigation,2 contained no skull, hence no calcified structures appear in these roent genograms. This phantom was cast of equal parts o f paraffin and beeswax, to
18/4 • THE JO U R NAL OF THE AMERICAN DENTAL ASSOCIATION
Fig. 2 • R oe n tge n o gram s m ade with pinhole cam era of the sources of radiation which expose the reproductive o rg an s of the dental patient while the follow ing maxillary areas are examined with x-rays: Left: Lateral incisor and cuspid. A b o v e right: Bicuspids and first molar. Below right: Second and third molars
which was added approximately 2 per cent of rosin by weight.3 T h e region o f the maxillary central in cisor of the subject again was examined roentgenographically, but by a technic which substituted a short open-ended plastic cone o f the same length for the short pointed plastic cone. A n aperture in the lead diaphragm o f the same size was used in each cone, therefore the size of the beam remained constant. T h e inner diameter of the open-ended cone selected was large enough so that none o f the ma terial o f the cone would be irradiated by the primary x-ray beam and, hence, no scattered radiation could come from this source. T h e elimination of the scattered radia tion from the pointed cone by the use of the open-ended cone proved entirely suc
cessful as indicated in Figure 3. Th e arrangement o f the equipment that was used in making Figure 3, above right, below left and right, is pictured in Figure 3, above left. Figure 4 demonstrates that almost complete elimination o f the focal spot of the x-ray tube and o f the aluminum filter and other strongly irradiated metallic parts o f the apparatus as sources of gonadal irradiation can be accomplished by placing a lead-foil lining (0.0125 inch thick) within the open-ended cone. A l though the actual thickness o f the lead foil is small, its effective thickness is much greater because of the oblique path the radiation follows in passing through the lead barrier. When the lead-lined, openended, plastic cone is used, the face o f the subject remains as the only source o f scat-
RICHARDS . . . VOLUME 65, JULY 1962 • 19/5
Fig. 3 • A b o v e left: Ph otograph de p ictin g position of pinhole camera relative to phantom head and x-ray apparatus equipped with open-ended plastic cone. A b o v e right: Ph otograph m ade with pinhole cam era of face of phantom and the head and open-ended plastic cone of the x-ray apparatus. Below left: Roentgenogram m ade with pinhole cam era which indicates the absence o f scattered radiation from the open-ended cone. Below right: C o m p o site print of B and C
Fig. 4 • A b o v e left: Ph otograph dep ictin g position of pinhole cam era relative to phantom head and x-ray apparatus equip ped with an open-ended plastic cone into which has been placed a cylindrical lead sleeve or shield, 0.0125 inch thick. A b o v e right: Photograph made with pinhole cam era of face of phantom and the head and open-ended, shielded, plastic cone of the x-ray apparatus. Below left: Roentgenogram m ade with pinhole cam era which indicates the almost com plete elimination of the leakage radiation from the focal spot of the x-ray tube and the scattered radiation from the aluminum filter and other strongly irradiated metallic parts of the apparatus which are located between the lead diaphragm and the x-ray tube. Below right: C o m p o site print of B and C reveals the face of the subject remains as the only source of scattered radiation which can expose his reproductive organs
RICHARDS . . . VOLUME 65, JULY 1962 • 21/7
T a b le 1 • Vertical angulation values Region
M a x illa ry
M an d ib ular
45° d ow nw ard
15° upw ard
Lateral and cuspid incisors
45° d ow nw ard
20° upw ard
Bicuspids and first molar
35° dow nw ard
10° upward
Secon d and third molars
25° d ow nw ard
C entral incisors
0°
tered radiation which can expose his re productive organs.
was used as the subject and the gonadal dose rate was measured with a Victoreen Ratemeter. T h e Ratemeter was calibrated against a suitable secondary standard chamber. T h e ionization chamber of the Ratemeter was located horizontally, 26 inches below the occlusal plane of the subject, and in a frontal plane directly beneath the nasal spine. Periapical ex aminations, consisting o f 14 exposures, were made of the subject with 65 and 90 kvp and 10 ma. and with the follow ing types o f cones: 1. Short, pointed, plastic cone.
M EASU REM EN T OF G O N A D A L IR R A D IA T IO N
T h e quantitative influence o f various types o f dental x-ray cones on gonadal irradiation was investigated next. Th e head o f a cadaver, preserved in Formalin,
2. Short, cylindrical, open-ended, plas tic cone, plus an added aluminum filter o f 0.5 mm. in thickness. 3. Short, cylindrical, open-ended, shielded, plastic cone, plus an added alu minum filter of 0.5 mm. in thickness.
kvp. H e a d of a cadaver was used as the subject from which these data were obtained
2 X 0.20
2 X 0.25
2 X 0.375
0.20
2 X 0.20
2 X 0.20
2 X 0.25
M a x . cu sp id *
M a x. b icu spid f
M a x. m o ia rf
M an d . central incisors
M a n d . cu sp id *
M a n d . b icuspid f
M a n d . m o la rj
Reduction in d ose
T otal fo r 14 ex posures
0.25 sec.
Recommended times of exposure
60 = 0.20
= 0.17
= 0.16
60 X — 60
X
X — 60
—
1.04 mr
= 0.12
= 0.10
= 0.12
X I ™ = 0.06 60
X — 60
X
X 2 4 60
27.0 mr/min n ,. X ---------- ------ = 0.11 mr 60 sec/min
Pointed cone plus no a d d ed filter
= 0.13
60
60
60
= o.o8
0.04
= 0.13
2 7 .9 %
0.75 mr
X — = 0.08 60
X — = 0.08 60
x
X
X Ü 2 = 0.13 60
X — 60
v 20.0 n no X ----- --- 0.08 mr 60
Short open-ended co n e plus 0.5 mm. A l filter
= 0.09
= 0.06 mr
4 7 .1 %
0.55 mr
1 7 .3 %
' 0.86 mr
X 3.5 X — = 0.13 60
X 3.5 X — = 0.11 60
X 1 2 ^ = 0.07 60 X — = 0.07 60
X 3.5 X — = 0.07 60
X 3.5 X — = 0.04 60
X 3.5 X — = 0.17 60
X 3.5 X — = 0.13 60
X 3.5 X — = 0.13 60
X 3.5 X — = 0.08 mr 60
Long o p e n-e nd e d cone plus 0.5 mm. A l filter
X — = 0.05 60
X — = 0.03 60
X — = 0.09 60
X 1 1 2 = 0.09 60
X — 60
X — 60
Short op e n-e nd e d shielded co ne plus 0.5 mm. A l filter
• THE JO URNAL OF THE AM ERICAN
M a x . central incisors
Regions
65 kvp and 10 ma.
T ab le 2 • C alculated go n a d a l d o se s (In air). Periapical examinations made with recom mended times o f expo su re for ultra-speed films
22/8 DENTAL A S S O C IA T IO N
= 0.18
X
X
X
X
X — 60
2 X 0.15
0.1
2 X 0.1
2 X 0.1
2 X 0.1
M a x . m o la r i
M an d . central incisors
M a n d . cuspid§
M a n d . bicuspid |{
M a n d . m o la r !
•Region of lateral and cuspid, f Region of bicuspids and first molar. ^Region of second and third molars. §Region of lateral and cuspid. (| Region of bicuspids and first molar. {[Region of second and third molars.
Reduction in d o se
Total for 14 exposures
= 0.15
X — 60
2 X 0.1
M a x . bicuspid ||
60
60
60
60
—
1.09 mr
= 0.12
= 0.13
= 0.13
= 0.06
= 0.17
2 X 0.Ì
M a x . cuspid§ 60
0.15 sec.
M a x . centra! incisors
v 61.0 mr/min n -r X ---------- L— = 0.15 mr 60 sec/min
= 0.09
= 0.10
= 0.04
= 0.12
= 0.13
= 0.15
= 0.12 mr
60
2 3 .8 %
0.83 mr
x 2i = = 0.08
60
x 2 ^
60
60
X 26J
x ?M 60
60
X 3M
x ^ ° 60
60
90 kvp and Ì0 ma.
60
60 = 0.09
= 0.11
60 = 0.07
= 0.04
X 60
= 0.12 mr
= 0.06
= 0.12
0.94 mr 1 3 .8 %
4 1 .3 %
90 X 3 . 5 X — = 0.11 60
X 3.5 X — 60
X 3.5 X — = 0.10 60
X 3.5 X — 60
X 3.5 X — = 0.15 60
11 2 X 3.5 X — = 0.13 60
132 X 3.5 X — = 0.15 60
X 3.5 X — 60
0.64 mr
= 0.07
X — = 0.08 60
X — 60
X
17 9 X — = 0.09 60
X
X
v 36.0 n no X ----- = 0.09 mr 60
RICHARDS . .. VOLUME 65, JULY 1962 « 23/9
24/10 • THE JOURNAL OF THE AMERICAN DENTAL ASSOCIATION
4. Long, cylindrical, open-ended, plas tic cone, plus an added aluminum filter o f 0.5 mm. in thickness. Th e inherent filtration o f the x-ray apparatus was equivalent to 1.5 mm. of aluminum and the filtration o f the pointed plastic cone was almost equal to 0.5 mm. o f aluminum. Therefore, when the openended cones, which offer no filtration, were substituted for the pointed cone in these tests, an added filter o f 0.5 mm. of aluminum was used. T h e diameter o f the x-ray beam at the end o f each cone was 2.7 inches. T h e focal-cone tip distance for the short cones was 8.2 inches, and for the long cone was 16.3 inches. Th e center o f the x-ray beam always was directed at the center o f the film packet for each examination. T h e values of the vertical angulation used in making these examinations are listed in Table 1. Figure 5 indicates the values of the gonadal dose rates for the various regions by the two voltages, and also provides a graphic comparison o f the reduction of the gonadal dose rates by the use of the various cones. I t is important to realize that the values listed in Figure 5 are dose rates, and not doses. Although the gon adal dose rates for the long cone are the lowest, the times o f exposure are 3.5 times longer than those for the similarly filtered short cones. (Because o f the thickness of the cheek and teeth, it is estimated that the film packet lies one inch beyond the end of the x-ray cone. Therefore, the focal-film distance for the short cones is 8.2 + 1.0 or 9.2 inches, and 16.3 + 1.0 or 17.3 inches for the long cone. Th e factor for converting exposure times o f the short cone to exposure times o f the long cone is (1 7 .3 )2/ (9 .2 )2 or 3.5.) Gonadal dose rates are higher with 90 kvp than with 65 kvp, as shown in Figure 5. These dose rates can be converted to gonadal doses (in air) by multiplying the dose rate by the time o f exposure that is appropriate for each region when films of a given speed are used.
Table 2 was prepared by multiplying
these experimentally determined gonadal dose rates, for the various regions and types o f cones, by the manufacturer’s rec ommended times o f exposure for ultra speed films exposed with 65 and 90 kvp, and 10 ma. o f current. T h e recommended times o f exposure for all regions except those of the regions o f the central incisors are doubled, because these regions occur bilaterally in the mouth. T h e data in Table 2 indicate that the total gonadal exposures to radiation, re sulting from periapical examinations of 14 exposures made with the short pointed cone and no added filter and with both 65 and 90 kvp, are 1.04 mr and 1.09 mr respectively; with the 90 kvp technic, the contribution was larger by 4.8 per cent. A ll of the sources o f radiation shown in Figure 1, below left, were contributing to the exposure o f the gonadal region in these first two tests. T h e elimination of the scattered radiation from the pointed cone, as shown in Figure 3, below left, reduces further the total gonadal ex posure to radiation at 65 and 90 kvp to 0.75 and 0.83 mr, respectively. Again the exposure, using 90 kvp, was larger by 10.7 per cent. T h e elimination o f the radiation from the focal spot and the scattered radiation that escapes through the aperture in the lead diaphragm, as shown in Figure 4, below left, for the short, open-ended, shielded cone, reduces the total gonadal exposure to radiation at 65 and 90 kvp to 0.55 and 0.64 mr, respectively, and again the exposure from 90 kvp is the larger by 16.4 per cent. T h e use o f the long cone, with its inherent lower dose rates and prolonged times o f exposure, reduces the total gonadal exposure to radiation at 65 and 90 kvp to 0.86 and 0.94 mr, respectively; the exposure from 90 kvp is the larger by 9.3 per cent. T h e use o f the long, openended, plastic cone did not reduce the gonadal exposure as effectively as did the short, open-ended, plastic cone when either voltage was used.
With each type of cone, the total
RICHARDS . . . VOLUME 65, JULY 1962 • 25/11
gonadal exposure was greater with 90 kvp than with 65 kvp. In preparing Table 2, the film-manufacturer’ s recom mended minimum times o f exposure for 90 kvp were used. I f the recommended maximum times of exposure had been used, the gonadal exposures for 90 kvp for the various cones would have been about 20 per cent higher than those listed. T h e smallest gonadal exposure, 0.55 mr, was achieved with a short, openended, shielded, plastic cone used with x-radiation generated with 65 kvp. This amount o f exposure is exceedingly small and can be appreciated better when one recalls that every day o f a person’s life his gonadal region and entire body are exposed to approximately 0.30 mr from sources o f natural background radiation in his environment. SUM M ARY \
A pinhole camera has been used to dis close the sources o f x-radiation that ex pose the gonadal region of the dental patient. A short, open-ended, shielded x-ray cone, used with a dental x-ray apparatus operated with 65 kvp, was found to be very effective in reducing, by almost one half, the exposure o f the patient’s gonadal region to these sources of radiation. C O N C L U S IO N S
1. T h e sources o f x-radiation that expose the reproductive organs o f the dental patient now may be listed: (a ) T h e irra
diated portion o f his face and oral cavity; (b ) the irradiated portion of the pointed plastic cone o f the x-ray apparatus; (c ) the aluminum filter and other strongly ir radiated metallic parts o f the apparatus which are located behind the lead dia phragm; (d ) the focal spot o f the x-ray tube. 2. Th e use o f a short, open-ended, shielded cone can reduce, by almost one half, the gonadal exposure of the dental patient, and it reduces the exposure of the remainder o f the patient’s body and the operator’s body to x-radiation. 3. Th e gonadal exposure to x-radiation is smaller when the x-ray apparatus is operated with 65 kvp than with 90 kvp if the recommended times o f exposure of the film’s manufacturer are utilized. 4. Open-ended, shielded cones easily may be substituted fo r the pointed plastic cones that are standard equipment on existing dental x-ray equipment and it appears desirable that x-ray equipment be furnished with open-ended, shielded cones.
This investigation was supported by Research Grant No. D -III6 from the National Institute of Dental Re* search, National Institutes of Health, U.S. Public Health Service. ^Professor of dentistry, School of Dentistry, University of Michigan. 1. Richards, A . G. Pinhole camera for radiation re* search ¡n dentistry. J. D. Res. 41:29 Jan.-Feb. 1962. 2. Richards, A . G. Radiation protection via the pin hole camera. O ral Surg., O ra l Med. & O ral Path. 13:953 A ug. I960. 3. Hudson, D. C., and Kumpula, J. W . Ionization chambers for radiation data during dental x-ray ex posure. Arm ed Forces M . J. 6:1131 Aug. 1955.
Clearness and Simplicity • T he clear and simple words of common usage are always better than those of erudition. T he jargon of the philosophers not seldom conceals an absence of thought. Andre Maurois. T he W riter’s Craft.
New method for reduction of gonadal irradiation of dental patients
Albert G. R ich a rd s* M .S ., A nn A rbor, M ich .
A pinhole camera on the lap of a phantom body was used to disclose the sources of x-radiation that expose the gonadal region of the dental patient. A short, open-ended, shielded x-ray cone, used with a dental x-ray machine oper ated with 65 kvp, reduces by almost one half, gonadal exposure. O pen-ended shielded cones easily may be substituted fo r the pointed plastic cones that are standard equipment on existing dental x-ray units.
T h e purpose o f this report is to illustrate how the use o f a suitable x-ray cone can reduce by approximately one half the gonadal irradiation o f the dental patient. SOURCES OF GONADAL IRRADIATION
T h e proper starting point in reducing the gonadal exposure to x-rays o f the dental
patient is to learn first the origin of the offending radiation and then to take the necessary measures to control or elimi nate the sources. T h e sources can be iden tified readily by placing a lead-walled pinhole camera in a position comparable to the lap o f the subject with the camera directed upward toward his face and the head of the x-ray apparatus. Figure 1, above left, indicates the loca tion o f the pinhole camera in relation to the head o f the., phantom and the x-ray apparatus while the region o f the maxil lary central incisor is examined roentgenographically. I n this example, the pin hole camera has been moved from the position comparable to the subject’s lap to a position closer both to the face of the subject and the x-ray apparatus so that the scattered radiation w ill be more intense and the time of exposure that is necessary to produce an image within the pinhole camera will be considerably re duced. In spite of the closer proximity of the pinhole camera to the sources of the scattered radiation, the exposure that is
Fig. 1 • A b o v e left: Ph otograph dep ictin g position of pinhole cam era relative to phantom head and x-ray apparatus e q u ip p e d with pointed plastic cone. A b o v e right: Photograph m ade with pinhole cam era portraying the nose and lower half o f phantom 's face and the head and pointed plastic cone of the x-ray apparatus. A light fixture, h an gin g from the ceiling of the laboratory, is also visible. Below left: Roentgenogram m ade with pinhole cam era of the sources of radiation which expose the reproductive organs of the dental patient. These sources are: ( I ) leakage radiation from the focal spot o f the x-ray tube; (2) scattered radiation from the aluminum filter and other strongly irradiated metallic parts of the ap paratus which are located behind the lead dia phragm ; (3) the irradiated portion of the pointed plastic cone; and (4) the subject's chin, oral region and nose. Below right: C o m p o site print of B and C, relating the location o f the sources of the invisible x-rays to the visible details of the ph o to gra ph
RICHARDS . . . VOLUME 65, JULY 1962 • 17/3
necessary to produce pictures with the pinhole camera is so great that phantom heads must be substituted for living patients. Usable pictures made w ith the pinhole camera require exposures 100,000 or more times as great as are used rou tinely with living subjects. T h e pinhole camera is designed to contain both photographic and roentgenographic films and thus produce, simulta neously, photographic and roentgenographic images o f the same subject. T h e photographic film in the camera is very sensitive to light and relatively insensitive to roentgen rays and therefore is exposed almost exclusively by the light that re flects from the surface o f the subject in the proper directions to enter the camera through its pinhole opening. Th e roentgenographic film is located in the camera behind the photographic film and is sepa rated from it by a thin opaque barrier. T h e roentgenographic film is held firm ly between two intensifying screens that w ill produce images in fluorescent light when they are excited by x-radiation. T h e roentgenographic emulsion is far more sensitive to exposure by this fluores cent light than to direct exposure to x-radiation. Any material that is exposed to the primary beam from a dental x-ray ap paratus w ill both transmit and absorb some o f the radiation and in addition w ill produce secondary radiation which scat ters in all directions— very much as light from an automobile headlamp is scat tered by fog. T h e operation of the pin hole camera depends on that minute frac tion o f the secondary radiation which scatters in the proper direction to pass through the pinhole opening o f the camera. It is this radiation which excites the intensifying screens and exposes the roentgenographic film. A detailed ac count o f the construction and operation o f the pinhole camera has been presented elsewhere.1 Figure 1, above right and below left, are the photograph and roentgenogram
respectively that were produced simulta neously by the pinhole camera when the region of the maxillary central incisor of the subject was examined with roentgen rays by a technic which utilized a short, pointed, plastic cone. T h e photograph portrays the phantom’s face, the head and pointed cone o f the x-ray apparatus, and even a light fixture hanging from the ceiling of the laboratory. T h e roent genogram clearly identifies as the sources of the radiation that irradiate the gonadal region, the subject’ s chin, oral region and nose, the irradiated portion o f the pointed cone, the aluminum filter and other strongly irradiated metallic parts o f the apparatus which are located behind the lead diaphragm, and the focal spot of the x-ray tube. T h e image of the focal spot was produced by leakage radiation whereas the other three images were pro duced by scattered radiation. Figure 1, below right, was produced by superimposing the photograph and roent genogram (Fig. 1, above right and below left) and printing them as a unit. This illustration provides a visible plane of ref erence (the photograph) on which the sources of the invisible x-radiation can be visualized. Figure 2 indicates, when the remainder o f the maxillary teeth are examined by roentgen rays, that the same sources of ra diation are serving to expose the gonadal region as were acting when the maxillary central incisors were examined in Figure 1, below left. When the mandibular teeth are examined roentgenographically, the contribution to the exposure o f the gon adal region from the filter and other metallic parts located behind the lead diaphragm is greatly reduced or totally absent depending on the extent of up ward direction of the x-ray beam. T h e phantom used in this study, unlike the phantom reported in an earlier inves tigation,2 contained no skull, hence no calcified structures appear in these roent genograms. This phantom was cast of equal parts o f paraffin and beeswax, to
18/4 • THE JO U R NAL OF THE AMERICAN DENTAL ASSOCIATION
Fig. 2 • R oe n tge n o gram s m ade with pinhole cam era of the sources of radiation which expose the reproductive o rg an s of the dental patient while the follow ing maxillary areas are examined with x-rays: Left: Lateral incisor and cuspid. A b o v e right: Bicuspids and first molar. Below right: Second and third molars
which was added approximately 2 per cent of rosin by weight.3 T h e region o f the maxillary central in cisor of the subject again was examined roentgenographically, but by a technic which substituted a short open-ended plastic cone o f the same length for the short pointed plastic cone. A n aperture in the lead diaphragm o f the same size was used in each cone, therefore the size of the beam remained constant. T h e inner diameter of the open-ended cone selected was large enough so that none o f the ma terial o f the cone would be irradiated by the primary x-ray beam and, hence, no scattered radiation could come from this source. T h e elimination of the scattered radia tion from the pointed cone by the use of the open-ended cone proved entirely suc
cessful as indicated in Figure 3. Th e arrangement o f the equipment that was used in making Figure 3, above right, below left and right, is pictured in Figure 3, above left. Figure 4 demonstrates that almost complete elimination o f the focal spot of the x-ray tube and o f the aluminum filter and other strongly irradiated metallic parts o f the apparatus as sources of gonadal irradiation can be accomplished by placing a lead-foil lining (0.0125 inch thick) within the open-ended cone. A l though the actual thickness o f the lead foil is small, its effective thickness is much greater because of the oblique path the radiation follows in passing through the lead barrier. When the lead-lined, openended, plastic cone is used, the face o f the subject remains as the only source o f scat-
RICHARDS . . . VOLUME 65, JULY 1962 • 19/5
Fig. 3 • A b o v e left: Ph otograph de p ictin g position of pinhole camera relative to phantom head and x-ray apparatus equipped with open-ended plastic cone. A b o v e right: Ph otograph m ade with pinhole cam era of face of phantom and the head and open-ended plastic cone of the x-ray apparatus. Below left: Roentgenogram m ade with pinhole cam era which indicates the absence o f scattered radiation from the open-ended cone. Below right: C o m p o site print of B and C
Fig. 4 • A b o v e left: Ph otograph dep ictin g position of pinhole cam era relative to phantom head and x-ray apparatus equip ped with an open-ended plastic cone into which has been placed a cylindrical lead sleeve or shield, 0.0125 inch thick. A b o v e right: Photograph made with pinhole cam era of face of phantom and the head and open-ended, shielded, plastic cone of the x-ray apparatus. Below left: Roentgenogram m ade with pinhole cam era which indicates the almost com plete elimination of the leakage radiation from the focal spot of the x-ray tube and the scattered radiation from the aluminum filter and other strongly irradiated metallic parts of the apparatus which are located between the lead diaphragm and the x-ray tube. Below right: C o m p o site print of B and C reveals the face of the subject remains as the only source of scattered radiation which can expose his reproductive organs
RICHARDS . . . VOLUME 65, JULY 1962 • 21/7
T a b le 1 • Vertical angulation values Region
M a x illa ry
M an d ib ular
45° d ow nw ard
15° upw ard
Lateral and cuspid incisors
45° d ow nw ard
20° upw ard
Bicuspids and first molar
35° dow nw ard
10° upward
Secon d and third molars
25° d ow nw ard
C entral incisors
0°
tered radiation which can expose his re productive organs.
was used as the subject and the gonadal dose rate was measured with a Victoreen Ratemeter. T h e Ratemeter was calibrated against a suitable secondary standard chamber. T h e ionization chamber of the Ratemeter was located horizontally, 26 inches below the occlusal plane of the subject, and in a frontal plane directly beneath the nasal spine. Periapical ex aminations, consisting o f 14 exposures, were made of the subject with 65 and 90 kvp and 10 ma. and with the follow ing types o f cones: 1. Short, pointed, plastic cone.
M EASU REM EN T OF G O N A D A L IR R A D IA T IO N
T h e quantitative influence o f various types o f dental x-ray cones on gonadal irradiation was investigated next. Th e head o f a cadaver, preserved in Formalin,
2. Short, cylindrical, open-ended, plas tic cone, plus an added aluminum filter o f 0.5 mm. in thickness. 3. Short, cylindrical, open-ended, shielded, plastic cone, plus an added alu minum filter of 0.5 mm. in thickness.
kvp. H e a d of a cadaver was used as the subject from which these data were obtained
2 X 0.20
2 X 0.25
2 X 0.375
0.20
2 X 0.20
2 X 0.20
2 X 0.25
M a x . cu sp id *
M a x. b icu spid f
M a x. m o ia rf
M an d . central incisors
M a n d . cu sp id *
M a n d . b icuspid f
M a n d . m o la rj
Reduction in d ose
T otal fo r 14 ex posures
0.25 sec.
Recommended times of exposure
60 = 0.20
= 0.17
= 0.16
60 X — 60
X
X — 60
—
1.04 mr
= 0.12
= 0.10
= 0.12
X I ™ = 0.06 60
X — 60
X
X 2 4 60
27.0 mr/min n ,. X ---------- ------ = 0.11 mr 60 sec/min
Pointed cone plus no a d d ed filter
= 0.13
60
60
60
= o.o8
0.04
= 0.13
2 7 .9 %
0.75 mr
X — = 0.08 60
X — = 0.08 60
x
X
X Ü 2 = 0.13 60
X — 60
v 20.0 n no X ----- --- 0.08 mr 60
Short open-ended co n e plus 0.5 mm. A l filter
= 0.09
= 0.06 mr
4 7 .1 %
0.55 mr
1 7 .3 %
' 0.86 mr
X 3.5 X — = 0.13 60
X 3.5 X — = 0.11 60
X 1 2 ^ = 0.07 60 X — = 0.07 60
X 3.5 X — = 0.07 60
X 3.5 X — = 0.04 60
X 3.5 X — = 0.17 60
X 3.5 X — = 0.13 60
X 3.5 X — = 0.13 60
X 3.5 X — = 0.08 mr 60
Long o p e n-e nd e d cone plus 0.5 mm. A l filter
X — = 0.05 60
X — = 0.03 60
X — = 0.09 60
X 1 1 2 = 0.09 60
X — 60
X — 60
Short op e n-e nd e d shielded co ne plus 0.5 mm. A l filter
• THE JO URNAL OF THE AM ERICAN
M a x . central incisors
Regions
65 kvp and 10 ma.
T ab le 2 • C alculated go n a d a l d o se s (In air). Periapical examinations made with recom mended times o f expo su re for ultra-speed films
22/8 DENTAL A S S O C IA T IO N
= 0.18
X
X
X
X
X — 60
2 X 0.15
0.1
2 X 0.1
2 X 0.1
2 X 0.1
M a x . m o la r i
M an d . central incisors
M a n d . cuspid§
M a n d . bicuspid |{
M a n d . m o la r !
•Region of lateral and cuspid, f Region of bicuspids and first molar. ^Region of second and third molars. §Region of lateral and cuspid. (| Region of bicuspids and first molar. {[Region of second and third molars.
Reduction in d o se
Total for 14 exposures
= 0.15
X — 60
2 X 0.1
M a x . bicuspid ||
60
60
60
60
—
1.09 mr
= 0.12
= 0.13
= 0.13
= 0.06
= 0.17
2 X 0.Ì
M a x . cuspid§ 60
0.15 sec.
M a x . centra! incisors
v 61.0 mr/min n -r X ---------- L— = 0.15 mr 60 sec/min
= 0.09
= 0.10
= 0.04
= 0.12
= 0.13
= 0.15
= 0.12 mr
60
2 3 .8 %
0.83 mr
x 2i = = 0.08
60
x 2 ^
60
60
X 26J
x ?M 60
60
X 3M
x ^ ° 60
60
90 kvp and Ì0 ma.
60
60 = 0.09
= 0.11
60 = 0.07
= 0.04
X 60
= 0.12 mr
= 0.06
= 0.12
0.94 mr 1 3 .8 %
4 1 .3 %
90 X 3 . 5 X — = 0.11 60
X 3.5 X — 60
X 3.5 X — = 0.10 60
X 3.5 X — 60
X 3.5 X — = 0.15 60
11 2 X 3.5 X — = 0.13 60
132 X 3.5 X — = 0.15 60
X 3.5 X — 60
0.64 mr
= 0.07
X — = 0.08 60
X — 60
X
17 9 X — = 0.09 60
X
X
v 36.0 n no X ----- = 0.09 mr 60
RICHARDS . .. VOLUME 65, JULY 1962 « 23/9
24/10 • THE JOURNAL OF THE AMERICAN DENTAL ASSOCIATION
4. Long, cylindrical, open-ended, plas tic cone, plus an added aluminum filter o f 0.5 mm. in thickness. Th e inherent filtration o f the x-ray apparatus was equivalent to 1.5 mm. of aluminum and the filtration o f the pointed plastic cone was almost equal to 0.5 mm. o f aluminum. Therefore, when the openended cones, which offer no filtration, were substituted for the pointed cone in these tests, an added filter o f 0.5 mm. of aluminum was used. T h e diameter o f the x-ray beam at the end o f each cone was 2.7 inches. T h e focal-cone tip distance for the short cones was 8.2 inches, and for the long cone was 16.3 inches. Th e center o f the x-ray beam always was directed at the center o f the film packet for each examination. T h e values of the vertical angulation used in making these examinations are listed in Table 1. Figure 5 indicates the values of the gonadal dose rates for the various regions by the two voltages, and also provides a graphic comparison o f the reduction of the gonadal dose rates by the use of the various cones. I t is important to realize that the values listed in Figure 5 are dose rates, and not doses. Although the gon adal dose rates for the long cone are the lowest, the times o f exposure are 3.5 times longer than those for the similarly filtered short cones. (Because o f the thickness of the cheek and teeth, it is estimated that the film packet lies one inch beyond the end of the x-ray cone. Therefore, the focal-film distance for the short cones is 8.2 + 1.0 or 9.2 inches, and 16.3 + 1.0 or 17.3 inches for the long cone. Th e factor for converting exposure times o f the short cone to exposure times o f the long cone is (1 7 .3 )2/ (9 .2 )2 or 3.5.) Gonadal dose rates are higher with 90 kvp than with 65 kvp, as shown in Figure 5. These dose rates can be converted to gonadal doses (in air) by multiplying the dose rate by the time o f exposure that is appropriate for each region when films of a given speed are used.
Table 2 was prepared by multiplying
these experimentally determined gonadal dose rates, for the various regions and types o f cones, by the manufacturer’s rec ommended times o f exposure for ultra speed films exposed with 65 and 90 kvp, and 10 ma. o f current. T h e recommended times o f exposure for all regions except those of the regions o f the central incisors are doubled, because these regions occur bilaterally in the mouth. T h e data in Table 2 indicate that the total gonadal exposures to radiation, re sulting from periapical examinations of 14 exposures made with the short pointed cone and no added filter and with both 65 and 90 kvp, are 1.04 mr and 1.09 mr respectively; with the 90 kvp technic, the contribution was larger by 4.8 per cent. A ll of the sources o f radiation shown in Figure 1, below left, were contributing to the exposure o f the gonadal region in these first two tests. T h e elimination of the scattered radiation from the pointed cone, as shown in Figure 3, below left, reduces further the total gonadal ex posure to radiation at 65 and 90 kvp to 0.75 and 0.83 mr, respectively. Again the exposure, using 90 kvp, was larger by 10.7 per cent. T h e elimination o f the radiation from the focal spot and the scattered radiation that escapes through the aperture in the lead diaphragm, as shown in Figure 4, below left, for the short, open-ended, shielded cone, reduces the total gonadal exposure to radiation at 65 and 90 kvp to 0.55 and 0.64 mr, respectively, and again the exposure from 90 kvp is the larger by 16.4 per cent. T h e use o f the long cone, with its inherent lower dose rates and prolonged times o f exposure, reduces the total gonadal exposure to radiation at 65 and 90 kvp to 0.86 and 0.94 mr, respectively; the exposure from 90 kvp is the larger by 9.3 per cent. T h e use o f the long, openended, plastic cone did not reduce the gonadal exposure as effectively as did the short, open-ended, plastic cone when either voltage was used.
With each type of cone, the total
RICHARDS . . . VOLUME 65, JULY 1962 • 25/11
gonadal exposure was greater with 90 kvp than with 65 kvp. In preparing Table 2, the film-manufacturer’ s recom mended minimum times o f exposure for 90 kvp were used. I f the recommended maximum times of exposure had been used, the gonadal exposures for 90 kvp for the various cones would have been about 20 per cent higher than those listed. T h e smallest gonadal exposure, 0.55 mr, was achieved with a short, openended, shielded, plastic cone used with x-radiation generated with 65 kvp. This amount o f exposure is exceedingly small and can be appreciated better when one recalls that every day o f a person’s life his gonadal region and entire body are exposed to approximately 0.30 mr from sources o f natural background radiation in his environment. SUM M ARY \
A pinhole camera has been used to dis close the sources o f x-radiation that ex pose the gonadal region of the dental patient. A short, open-ended, shielded x-ray cone, used with a dental x-ray apparatus operated with 65 kvp, was found to be very effective in reducing, by almost one half, the exposure o f the patient’s gonadal region to these sources of radiation. C O N C L U S IO N S
1. T h e sources o f x-radiation that expose the reproductive organs o f the dental patient now may be listed: (a ) T h e irra
diated portion o f his face and oral cavity; (b ) the irradiated portion of the pointed plastic cone o f the x-ray apparatus; (c ) the aluminum filter and other strongly ir radiated metallic parts o f the apparatus which are located behind the lead dia phragm; (d ) the focal spot o f the x-ray tube. 2. Th e use o f a short, open-ended, shielded cone can reduce, by almost one half, the gonadal exposure of the dental patient, and it reduces the exposure of the remainder o f the patient’s body and the operator’s body to x-radiation. 3. Th e gonadal exposure to x-radiation is smaller when the x-ray apparatus is operated with 65 kvp than with 90 kvp if the recommended times o f exposure of the film’s manufacturer are utilized. 4. Open-ended, shielded cones easily may be substituted fo r the pointed plastic cones that are standard equipment on existing dental x-ray equipment and it appears desirable that x-ray equipment be furnished with open-ended, shielded cones.
This investigation was supported by Research Grant No. D -III6 from the National Institute of Dental Re* search, National Institutes of Health, U.S. Public Health Service. ^Professor of dentistry, School of Dentistry, University of Michigan. 1. Richards, A . G. Pinhole camera for radiation re* search ¡n dentistry. J. D. Res. 41:29 Jan.-Feb. 1962. 2. Richards, A . G. Radiation protection via the pin hole camera. O ral Surg., O ra l Med. & O ral Path. 13:953 A ug. I960. 3. Hudson, D. C., and Kumpula, J. W . Ionization chambers for radiation data during dental x-ray ex posure. Arm ed Forces M . J. 6:1131 Aug. 1955.
Clearness and Simplicity • T he clear and simple words of common usage are always better than those of erudition. T he jargon of the philosophers not seldom conceals an absence of thought. Andre Maurois. T he W riter’s Craft.