The integration of the Lixiscope into dental procedures was studied and compared with conventional dental radiographic techniques. It was found that through the use of intraoral sealed sources in conjunction with microchannel plate technology, the Lixiscope gives increased diagnostic information with decreased radiation dosage

Goble, J. C.

English

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DOSlMETRlG CONSIDERATIONS IN DENTAL APPLlCATiONS 
John 6. Goble, Sc.M. 
National Institute of Health 
Department of Health, Education, and Welfare 
The use of intraoral sealed sources in conjunction 
with the micro-channel plate technology may provide 
increased diagnostic information with decreased 
radiation dose compared to conventional dental 
radiographic techniques. These reductions in radia- 
tion dose are a result of several factors, some specific 
to the prototype NIH device, and others more 
generally applicable. These advantages include: 
1 ) Reduced depth dose 
2) Reduced volume of irradiated tissue 
3) Real-time operator feedback 
In addition to these specific advantages, the in- 
tegration of the Lixiscope into dental procedures may 
reduce the total number of normal radiographic ex- 
posures required. 
Reduced Depth Dose 
Due to the spectral distribution of energies pro- 
duced by bremsstrahlung in the target of an X-ray 
machine, some of the photons emitted from the tube 
head approach the applied accelerating potential. In 
general, dental radiographic exposures are made at 
80-90 kVp. Since these high energy photons 
penetrate both bone and soft tissue quite readily, they 
provide little radiographic contrast yet penetrate 
deeply into the irradiated tissue. 
In using isotopic sources of photons, the problem of 
high energy contamination of the beam iseliminated. 
Since the photons are emitted at discrete energies, 
beam energy may be optimized for a particular 
application by selection of the appropriate 
radionuclide. 
Reduced Volume of Irradiated Tissue 
Acollimated intraoral source provides many advan- 
tages with respect to volume of irradiated tissue 
(whether the image receptor is a microchannel plate 
device or not). In the normal dental techniques, at 
least two factors contribute to the large volume of 
tissue irradiated. 
Since there is considerable uncertainty in the 
positioning of the film within the patient's mouth, the 
beam must be wide enough to ensure that the struc- 
tures of interest will be imaged. In a more narrowly 
defined beam, the incidence of retakes will be much 
higher. This geometry produces irradiation of tissues 
that are not of interest to the dentist, and which are 
outside of the image receptor. By rigidly coupling the 
image receptor to the source, and collimating the 
beam size to the diameter of the input phosphor, 
needless irradiation of tissue is reduced. The effects 
of depth dose and of limited beam geometry are 
compared for the NIH prototype device and an 80 kVp 
unit commonly used for endodontic procedures. 
Doses are normalized to 1.0 rad at 1 cm on the beam 
centerline (Figures 1 and 2). 
A second major advantage stems from the fact that 
radiation dose to the tissue beyond the film is 
eliminated. The volume of tissue irradiated during the 
normal radiographic exposure includes not only those 
structures between the source and the film, but those 
tissues in the "shadow" of the film as well. In the 
intraoral geometry, only the tissues of interest are 
irradiated. 
Real-time Operator Feedback 
The real-time imaging technique permits the den- 
tist to examine the structures of interest at an angle 
that optimizes their visibility. In the normal 
radiograph, patient movement, poor film plqcement, 
improper techniques, and many other factors may 
contribute to the necessity of a retake. By receiving 
real-time feedback, thedentist optimizes the informa- 
tion available from the minimum number of ex- 
posures. 
Specific Design Considerations 
in the NIH Prototype Device 
With the practical nature of this conference in 
mind, a few comments on design considerations in 
DEPTH IN TISSUE 
Figure 1. Effects of Depth Dose using 80 kVp 
X-rays 
https://ntrs.nasa.gov/search.jsp?R=19800004142 2020-03-21T20:43:43+00:00Z
design goals of the device include: 
1) Maximum Exposure Rate: 1.0 R/min 
2) Maximum Leakage Radiation: .1 mR/hr at 1 
meter 
3) Beam Collimation: Rate at edge of input 
phosphor to be less than 10% of center-line rate 
4) Shielding of Operator: Less than .1 mR/hr to 
eyes 
Although these considerations are quite conser- 
vative and are specific to the NIH device, they are at 
least a starting point in making the Lixiscope a prac- 
tical clinical tool. Many of the advantagesseen in this 
1 .O 5.0 10.0 design follow from the intraoral geometry and from 
DEPTH IN TISSUE the rigid coupling of source and image receptor. 
Figure 2. Effects of Depth Dose using 1-1 25 Similar improvements in radiation dosimetry might 
well be made in  devices not using the microchannel Lixiscope Source 
plate technology. Because of the unique advantages 
the NIH device are probably appropriate. Although no of this particular configuration, however, it seems 
specific standards for the device exist, the NIH likely that the Lixiscope can provide adequate 
Prototype was designed to meet or exceed re- diagnostic information for a great many tasks with 
quirements for diagnostic type units. Some specific decreased radiation dose to the patient. 


Dosimetric considerations in dental applications

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