Jun 6, 1986 - 3 mGy for linear tomography of the target joint ipsilateral to the beam, 1.9 mGy for the GE. 9800 slow ScoutView,. 1.8 mGy for xeroradiography,.
107
Radiation Dose in Radiography, CT, and Arthrography of the Temporomandibular Joint
E. L. Chnstiansen1
Thermoluminescent
R.J.Moore2 J. R. Thompson#{176}
A. N. Hasso3 D. B. Hinshaw,
Jr.4
dosimetry
studies
were
to compare radiation dosages
phantom
performed
on
a Rando
in temporomandibular
used
Humanoid joint
head
examinations.
transaxial and direct sagittal high-resolution CT, reduced milliamperage CT, tomoarthrography, pluridirectional and linear tomography, pantomography, transcranial plain films, and fluoroscopy. Radiation doses were determined for the brain, lens, pituitary gland, condylar marrow, and thyroid gland. Condylar marrow received doses of 64 and 52 mGy, respectively, for the GE 9800 and 8800 high-resolution scans; 21 and 17 mGy, respectively, for the dynamically sequenced scans; and 26 mGy for the GE 9800 direct sagfttal sections. Tomoarthrography yielded 31 mGy and fluoroscopy 12 mGy. Other lower doses showed 5 mGy for polytomography, 3 mGy for ipsilateral joint linear tomography, 1.9 mGy for the GE 9800 slow ScoutView, 1.8 mGy for xeroradiography, 0.9 mGy for contralateral joint linear tomography, 0.3-0.4 mGy for transcranial plain films and pantomography, and 0.2 mGy for the GE 8800 ScoutView. The estimated error in this study was calculated to be ±15%. On a relative scale, the radiatiOn doses from high-resolution CT and tomoarthrography are high, dynamic CT yields a medium dose, and all other tomographic and plain-film techniques yield low doses. Studies
included
dynamic
The demand for temporomandibular because of greater awareness among dysfunction. accuracy
While of the
emphasis
various
(TMJ)
be given
should
techniques,
joint
physicians
radiography
and dentists
has
to the sensitivity
a knowledge
of the
increased
of TMJ
resulting
pain
and
and diagnostic radiation
doses
is important
in the selection of the appropriate TMJ study. A review of the recent literature disclosed interest in TMJ dosimetry dating back to 1 964 [1]. Two artides dealt with radiation dose from mandibular radiography [2,
3]. Another
Received June 6, 1986; accepted after revision August 27, 1986. I Department of Endodontics, Section of TMJ/ Orofacial Pain, School of Dentistry, Loma Unda Lhiiversity, Loma Unda, CA 92350. Address reprint requests to E. L. Christiansen. 2 Department of RadiatiOn Sciences, School of Medicine,
Loma
Unda
lkiiversity,
Loma
Unda,
CA
discussed
TMJ
microfocai
spot
magnification
radiography
in which
dosimetry was also discussed [4]. Two recent articles compared X-ray doses to the TMJ (among other sites) from various plain-film and tomographic procedures, but CT was not induded [5, 6]. This investigation was designed to compare the radiation doses from the complete spectrum of X-ray examinations used for the TMJ, including tomoarthrography and CT. We believe that information on X-ray dose is important in considering which examination to use for a particular patient. Our purpose was also to discover how CT and tomoarthrography doses compare with more conventional plain-film and tomographic studies.
92350.
of Radiation Sciences, Section of School of Medicine, Loma Unda Loma Unda, CA 92350.
3 Department Neuroradiology,
University,
4 Department of Radiation Sciences, Section of Magnetic Resonance Imaging, School of Medicine, Loma Unda 1kuversity, Loma Unda, CA 92350.
AJR 148:107-109, January 1987 0361-803X/87/1481-0107 C American Roentgen Ray Society
Materials
and
Methods
Lithium fluoride (LJF-1 00) thermoluminescent radiation exposure in a Rando Humanoid estimated 280 mA (72 ,C/kg) for calibration. the
on an Eberline from the mean. sample.
dosimeter
(TLD)
The
mean
TLR-5 reader, after which the chips were Those chips varying more than 5% from
chips
were
value
TLD chips were
used
to measure
to an for the chips was determined binned according to ±1% variations the mean were discarded from the
skull phantom.
exposed
CHRISTIANSEN
108
Triplets marrow
of TLD chips were placed spaces,
and
over
used for readings thyroid
taken Readings
gland.
the
lens
of
in the sella turcica, the
eyes.
Single
condylar
chips
AJR:148,January
3500 V.
in the cortex of the frontal lobes and in the from the three chips at any given site were
3000
to give
location
identical
Whenever
the beam
hardness
changed
significantly,
to CT, TLD chips were calibrated
tomography
decreases
with
increasing
beam
hardness.
as from
plane
because chip sensitivity Sensitivity
averaged
3.4
200O 1
> 0
The minimum TLD chip reading (usually in a chip from the superiormost level of the head phantom) was chosen as the background level unless the reading exceeded 10 counts, in which case 10 was chosen to be the background level. Each “raw” TLD reading was then converted into an exposure reading according to the formula, exposure reading (raw TLD reading - background) /sensitivity. =
estimated
sources
of error
in the
surface
TLD
chips
are
2
3
1500
0
a
w 1000
1000
500
500
counts/mR.
The
1987
were
a single value. The same chips were assigned the for each study to minimize variation in sensitivities. Kodak Lanex regular intensifying screens were loaded with Kodak OG-1 X-ray film (system speed of 400). Film images of the phantom’s TMJs were made for all examinations to verify proper exposure and positioning.
averaged
ET AL.
/ 2
3
4
5
6
7
8
9
10
11
12
13
14
Us 15
IS
17
a 0ut ii
19
20
21
22
23
24
of Exposures
Numb.r
Fig. 1.-Thermoluminescent-dosimeter (TLD) linearity tested with sayeral exposures with same TLD chips in same locations for Siemens Multiplanagraph
II and Quint
Sectograph
(inset)
over 6-month
period.
±10%
chamber calibration, ±3% from orientation effect [7], and ±2% inherent in the chips. The estimated sources of error from the internal chips are ±10% from chamber calibration, ±3% beam hardening, and ±2% inherent in the chips. For both external and internal chips the total estimated error is ±1 5%. For soft tissue (including marrow), exposure readings were converted to dose readings by multiplying by a Roentgen-to-rad factor of 0.90. The results are expressed in milliGrays (1 mGy 100 mrad).
from
=
Linearity
of the TLD chips
was also investigated.
Exposures
made of the target condyle with a Siemens Multiplanagraph Quint Sectograph over a period of 6 months. The number sures ranged from one to 24.
were II and a
of expo-
Results
Linearity of the TLD chips is within acceptable limits for the two tomographic methods tested, and there is no evidence to suggest significant drift in chip sensitivity during the study (Fig. 1). The target condylar marrow received doses of 64 and 52 mGy, respectively, for the General Electric 9800 and 8800 series
through
scanners
thejoint;
with
high-resolution
overlapping
21 and 1 7 mGy, respectively,
axial images for the dynam-
ically sequenced axial overlapping projections; and 26 mGy for the GE 9800 overlapping direct sagittal scans. Tomoarthrography yielded 31 mGy and flyoroscopy 1 2 mGy for a total of 43 mGy. All other studies showed lower doses, with 5 mGy for polytomography, 3 mGy for linear tomography of the target joint ipsilateral to the beam, 1 .9 mGy for the GE 9800 slow ScoutView, 1 .8 mGy for xeroradiography, 0.9 mGy for linear tomography of the target joint contralateral to the beam, 0.3-0.4 mGy for transcranial plain films and pantomography, and 0.2 mGy for the GE 8800 ScoutView.
Discussion The
radiation
tissue, fell into high-resolution
niques studied.
dose relative
to the categories
condylar of high,
marrow, medium,
the and
target low;
CT was highest relative to the other techThe high-resolution CT dose was also greater
in all locations other to radiation scatter.
CT techniques
than the condyle, and we attributed this Some investigators use high-resolution
in direct
sagittal
scanning
of the TMJ [8, 9].
We find that usually fewer sections are used in direct sagittal imaging than in axial plane scanning: in the range of six or seven
as compared
sections
with 20 overlapping
transaxial
sections. nificantly
We found that direct sagittal scanning did not sigincrease the dose to the lens and thyroid when compared with high-resolution axial CT. Section for section, high-resolution CT exposes the patients to about three times the dose than does lower-milliamperage dynamic CT. Of interest, the GE 9800 dose was higher than the GE 8800 in both the high-resolution and dynamic scanning modes. This is probably because of the continuous rather than pulsed output of the X-ray tube of the GE 9800 scanner. Unilateral TMJ tomoarthrography, a relatively high-dose study, involves fluoroscopic guidance with videofluoroscopic and tomographic records of the dual compartment injections. The dose from the 24 linear tomographic sections (30.8 mGy) must be added to the 2-mm dose from fluoroscopy (11.6 mGy) for a total dose of 42.4 mGy. Unquestionably, plain films rather than tomography and/or single-compartment arthrographic studies would yield reduced radiation doses. Polytomography, linear tomography, pantomography, and all transcranial raphy)
The
plain-film techniques (with rank as relatively low-dose
radiation
risk
from
the exception of xeroradiogstudies in this investigation.
examinations of the The threshold dose for the induction of a vision-impainng cataract is in the thousands of mGy range [1 0]. The greatest eye dose in this study was 4.6 mGy for high-resolution CT, indicating a minute risk for this somatic effect. With respect to carcinogenesis, of the tissues exposed for
TMJ with the techniques
radiographic
discussed
which risk factors exist (marrow, and skin),
the thyroid
The probabilities straight-line
gland
thyroid,
curve
brain, salivary gland,
has the highest
for radiation-induced
dose-effect
is minute.
radiosensitivity.
cancer,
with no threshold,
based
on a
are 0.1 5 and
MR:148,January
TEMPOROMANDIBULAR
1987
0.05 chances per million and males, respectively
[1 1]. The risk factor
three
for adults
times
theoretical
greater
per year per mGy for adult females for children is
than
[1 1]. Assuming
risk for high-resolution-CT-based
cancer
the
worst
induction
0.45 chances per million per year. probability of spontaneous occurcancers per million per year yields a theoretical worst-case increase in the chance of getting thyrod cancer of no more than 0.1% [12]. This small added risk could be further reduced through thyroid shielding during TMJ radiographic studies, especially in children. gives
a maximum
risk
Comparing this with rence of 400 thyroid
of
the
The absolute radiation dose values of this study are only valid for our institution since radiation dose is a complex function of a number of variables. The radiographic technique may vary from one institution to another, but it is reasonable to expect that the relative grouping of these studies as high-, medium-, or low-dose would be maintained.
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doses
during
roentgenography
of the
JOINT
DOSIMETRY
109
2. White sc. Acee TC. Absorbed bone marrow dose m certain dental radiographic techniques. J Am Dent Assoc 1979;98(4):553-558 3. Schwartz HC, Wollin M, Leake DL, Kagan AR. Interface radiation dosimetry in mandibular reconstruction. Arch Otolaryngo! 1979;105(5):293-295 4. Murphy WA, Adams RJ, Gilula LA, Barber JY. MagnifiCatiOn radiography of the temporomandibular pnt: technical considerations. Radiology 1979;133:424-440 5. Borglin K, Petersson A, Rohlin M, mapper K. Radiation dosimetry in radiology of the temporomandibular joint. Br J Radio! 1984;57:997-1007 6. Brooks SL, Lanzetta ML Absorbed doses from temporomandibular joint radiography. Oral Surg Oral Med Oral Patho! 1985;59:647-652 7. Archer BR, Bushong SC, Thomby JI. Muftivariant analysis of TLD oriontation effects. Med Phys 1980;5(4):352-354 8. Manzione JV, Seftzer SE, Katzberg RW, HammerSchlag SB, Chiango BF. Direct sagittal computed tomography of the temporomandibular joint. A/NA 1982;3:677-679 9. Manzione JV, Katzberg RW, Brodsky GL, Seltzer SE, Melkns HZ. Internal derangements of the ternporomandibular joint: diagnosis by direct sagittal computed tomography. Radiology 1984;150: 111-115 10. Hall EJ. RadiatiOn cataractogenesis. In: Radiobioiogy for the radiologist. New York: Harper & Row, 1978:349-356 1 1 . Committee on Radiological Lhiits, Standards and Protection. Medical radiation: a guide to goodpractice. Chicago: American College of Radiology, 1985 12. Gregg EC. RadiatiOn risks with diagnostic x-rays. Radiology 1977;
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