NATIONAL BUREAU OF STANDARDS REPORT

3956

Progress Report

on

USE OP IONIZATION CHAMBERS IN OBTAINING

DATA ON RADIATION AT POINTS WITHIN THE

HEAD DURING DENTAL X-RAY EXPOSURE

byDonald C. Hudson

John W. Kumpula

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

0708-20-3857 December 31, 1954 3956

Progress Report

USE OF IONIZATION CHAMBERS IN OBTAINING

DATA ON RADIATION AT POINTS WITHIN THE

HEAD DURING DENTAL X-RAY EXPOSURE

by

Donald C . Hudson*

and

John W. Kumpula**

* Guest Worker,, Colonel U. S. Air Force Dental Service;

Dental Research Section, National Bureau of Standards.

** Laboratory Mechanic, Dental Research Section, National

Bureau of Standards

.

This work is a part of the dental research program conducted

at the National Bureau of Standards in cooperation with the

Council on Dental Research of the American Dental Association,

the Army Dental Corps, the Air Force Dental Service, the Navy

Dental Corps and the Veterans Administration.

(Task 7756-41 BV No. 55-14)

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

TL L1 , „ Approved for public release by the

The publication, r r '

unless permission Director of the National Institute of

25 , d.c. Such pc Standards and Technology (NIST)

cal ly prepared If On October 9, 2015

r In part, Is prohibited

tandards, Washington

eport has been specifi-

•eport for Its own use.

USE OF IONIZATION CHAMBERS IN OBTAINING

DATA ON RADIATION AT POINTS WITHIN THE

HEAD DURING DENTAL X-RAY EXPOSURE

Abstract

A study to determine levels of ionizing radiation at various points in and about the human head

during dental radiography was undertaken. A phantom

of tissue-equivalent wax was built around an adult

human skull, and measurements were made using small

Sievert ionization chambers placed at the skin and

within the skull at ten different locations.

Radiation absorbed during full- mouth intra-oral

dental radiography using conventional 8" skin -target

distance, 65 KV and. 10 ma with 1.5 mm of aluminum

filtration, and exposing 14 films, was measured.

Dosage at the skin of the cheek amounted to 20-25R

and various lower values were obtained at other points

within the head

.

A comparison of these radiation levels was made

with measurements taken at the same points in the head

when using a panoramic extra-oral radiographic technic.

Maximum dosage in this technic occurred in the lymphatic

region of the neck and a reading of .A2R was recorded

there during full-mouth exposure. Levels within the

skull ranged downward from this value.

2

1 . INTRODUCTION

A project at the Dental Research Laboratory, National Bureau

of Standards, sponsored by the U. S. Air Force Dental Service, is

concerned with the development of a device for making extra-oral

full-mouth panoramic dental X-ray exposures. In connection with

this project, it was desired to determine levels of radiation

produced at various points in and about the head using the panoramic device. For purposes of comparison, measurements were also

desired that would indicate radiation levels existing during fullmouth exposure using conventional dental X-ray technic.

2. APPARATUS EMPLOYED

Since the panoramic method employs a narrow beam of X-rays

in making exposure, an ionization chamber of small volume was required. Such a device was found in the Sievert ionization chamber

[1,2], which has an air volume slightly in excess of 30 mm, and a

physical size which was easily accommodated in the specimens to be

irradiated. The Sievert chamber (Fig. 1 and 2), is a condenser-type

R meter, having a wide range of sensitivity dependent upon the charge

applied, and can be relied upon to produce measurements accurate to

within ± 10% at the energies used in this experiment. All voltage

measurements after charging and after exposure to radiation were

made using the Kiethley Electrometer. Using calibration curves previously prepared for each chamber, and corrections for atmospheric

pressure and humidity, radiation levels to which the chambers had

been exposed were calculated.

The X-ray source was a standard radiographic unit, operated

at 6 l XV and 10 ma, having \ mm A1 . equivalent inherent filtration.
.

.

'
- 3

-

to which was added 1 mm A1 . The quality of the radiation was 18-20

KEV, calculated from its absorption coefficient.

A wax phantom head was constructed about an adult human skull.

The wax was of tissue -equivalent density to X-rays and consisted

of a mixture of 50$ paraffin and 50$ beeswax by weight to which was

added .5$ by weight of rosin [3]- The phantom was constructed to

permit access to points within the head for the placement of the

ionization chambers (Pig. 3 and 4)

.

3. EXPERIMENTAL METHOD

Ten points were chosen at which to measure radiation levels.

Several of these were chosen because they are located in areas rich

in lymphoid or glandular tissue. Points at which overlap or intersecting planes of radiation might be expected were also included.

These points were: (l) at the skin of the neck when using the panoramic exposure and at the skin of the cheek when using conventional

exposure; (2) in the region of the sella tursica; (3) in the region

of the parotid gland; (4) in the sublingual region; (5) in the center

of the base of the tongue; (6) in the cornea of the eye; (7) in the

region of the thyroid gland; (8) in the deep cervical lymphatic region;

(9) in a lower bicuspid tooth socket; and (10) at a point just posterior

and medial to the lower third molar tooth. The last-mentioned location was included since the axis about which the beam of X-rays was

rotated during panoramic exposure passed through this point. It was

desired to determine if any excessive concentration of radiation

occurred at this center of rotation.

Rate of delivery from the filtered X-ray source was approximately

558 mr/sec in air at 12" from the target when using the slit or narrow

- 4 -

beam in the panoramic technic * and about 647 mr/sec in the air at

the same distance when using a round cone of rays for the conventional intra-oral technic. Delivery rates were measured using the

Sievert chambers

.

Skin-target distance was 8" when employing the standard intraoral 14 film radiographic method and varied from 8" to 12.5" depending on the position of the X-ray source at any given time in its

cycle of motion about the head during radiography by the panoramic

method. Total exposure time was 25 sec. with the panoramic technic

and 40.5 sec. with the intra-oral method.

In each full-mouth exposure included in this experiment, the

conditions that would exist during actual clinical practice were

adhered to. Standard lead-backed dental films (Eastman Radiatized)

were positioned in the phantom for each single exposure by the conventional technic. One series of 14 exposures was found to be sufficient to produce radiation levels at all measuring points falling

within the range of the ionization chambers. It was necessary to

repeat the exposure ten times when using the panoramic method in

order to obtain levels of radiation that could be reliably measured,

using the same chambers

.

Total skin- surface area exposed to radiation at any point in

the exposure cycle using the panoramic method, amounted to less than

one square inch. During exposure by conventional methods, approximately 12 square inches of skin area were irradiated during each

individual film exposure and overlapping of Irradiated areas is

unavoidable during a series of films required for full-mouth radiography .

- 5

-

4 . RESULTS

Levels of radiation measured at the points selected are graphically displayed In Figure 5* It will be noted that under the conditions of this experiment, the highest level of ionizing radiation

during full-mouth radiographic exposure using the panoramic technic

existed in the cervical lymphatic region of the neck and amounted

to .42R. The highest levels of radiation when using conventional

intra-oral radiographic technic, existed at the skin of the cheek

and in the region of the thyroid gland, where 23 and 27 R, respectively, were recorded.

5 . SUMMARY

Levels of ionizing radiation produced at points in and about

a wax phantom of the human head, were measured during full -mouth

dental radiography by a panoramic method and by a conventional 14-

film intra-oral technic . The panoramic method was found to produce

radiation levels approximately l/50th as intense as those recorded

at comparable points when using conventional dental radiographic

technic

.

6

.

ACKNOWLEDGEMENT

The authors wish to express their appreciation to the personnel

of the Naval Medical Research Institute, Bethesda, Maryland, for

their cooperation in furnishing the ionization chambers and in charging and measuring voltages on the chambers during this experiment.

Lt . James W. Duckworth and Lt . (JG) Robert Sharp rendered most valuable service in performing the above mentioned technical procedures.

6

BIBLIOGRAPHY

1. Wilson, C. R., Radium Therapy - Physical Aspects, Second

Edition. Chapman and Hall, Ltd., London, England, 97 (19^8).

2. Sievert, R. M., Acta Radiologica, Supplementum XVI, (1932).

3. Hasterlik, R. J., Argonne Cancer Research Hospital,

Chicago, Illinois, (Personal communication)

.

Figure 1. Sievert ionization chamber, showing small size

Figure

2.

Sievert

ionization

chamber.

(c)

Dielectric.

(a)

Outer

shell.

(dj

Thin-walled

cap.

(b)

Inner

condenser

element

(e)

Air

chamber,

with

antenna.

Figure 3. Wax phantom showing placement of ionization

chamber at skin of cheek and recessed location

for measurements in region of neck lymphatics.

Figure

4

.

Wax

phantom

disarticulated

for

placement

of

•

ionization

chambers

at

internal

points.

FULL

MOUTH

14

FILMS

8'

S.T.D.

FULL

MOUTH

PANORAMIC

65

KV

lOmo.

1.5

mm

Al.

65

KV

SOmo,

1.5

mm

A3

Q> Inoc

O o z H<

uiz X oH oH

-J

-1 111 z 0.

UJ

HO 1 • OX

UJ >• 5 UJ o UJ <

0) 111 cn

a o CL

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Q

HO

<r 5 1 6

CD > Z ^ I UJ

cn

h o o C -H •H S

cti

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Figure

5.

Chart

showing

levels

of

radiation

measured

at

10

selected

and

about

the

human

head

phantom,

using a

conventional

an

full-mouth

radiographic

technic.

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