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X-radiation in dental offices in Jefferson County, Alabama. I
ORAL ROENTGENOLOGY American
Academy
Arthur H. Wwhmuznn,
.
.
.
.
.
X-RADIATION
ALABAMA.
of Oral Roentgenology Editor
.
.
.
.
IN DENTAL
.
.
.
OFFICES
.
.
.
.
.
.
IN JEFFERSON
.
.
.
.
of
.
COUNTY,
I.
A. H. Jvuehrmann, LB., D.M.D.,’ I,. R. Munson-Hing, D.M.D., M.fi.,'* H. C. Jamison, B.A., D.D.S., M.P.H., Dr.P.H.,*” Birmingham, 4la. Dniz;ersity
.
Alabama
School
and
of Dentistry
INTRODUCTION
T
HE professions of medicine and dent,istry are said to contribute to the population’s whole-body radiation dose an amount exceeding that of background radiation. In view of the anticipated increased peace-time use of radiation and radioactive materials of all types, it is increasingly important that welldocumented information be obtained concerning the use of s-radiation in dental offices. On the basis of such data, it should be possible to decide whether or not it would be in the public interest to take any action toward modifying the present dental ofice procedures in so far as radiation usage is concerned. It was with this concept in mind that t,he administration of the Ncdical Center and the School of Dentistry of the University of Ala.bama agreed to participate in a survey of the dental offices of Jefferson County. This survey was performed during the summer of 1961 at the request of the Alabama State Health Department and in cooperation with the Jefferson County Department of Health. Financial arrangements were made between the State Health Department and the Division of R,adiological Health, United States Public Health Service, on the basis of a contract grantt which, at the request of t,hc State Health Department, was administered by the comptroller of the IJniversity of Alabama Medical Center. *Professor of Dentistry, University of Alabama School of Dentistry. **Associate Professor of Dentistry, University of Alabama School of Dentistry. tContract No. SAph 78332, Department of Health, Education, and Welfare, TJnited Public Health Service. Division of Radiological Health. 926
States
Volullle 16 Number 8
X-RADIATION
IN
DENTAL
OFFICES
927
The survey was carried out by means of a carefully designed questionnaire which was divided into three parts and used for the following three purposes: 1. Consultation with the dentist and, when necessary, with the dental assistant or hygienist. 2. Observation of the physical facilities related to the x-ray machine, x-radiation protection measures, and darkroom facilities and procedures. 3. Recording of physical measurements concerned with radiation characteristics and protection factors. The survey was conducted by dental students following an intensive period of training. Three teams of two members each participated. One of us accompanied each survey team during the initial ofice visits in order to be certain that all procedures were being followed faithfully and that there were no misunderstandings on the part of the team members. It was soon apparent that further surveillance was unnecessary. The completed questionnaires were returned to the Medical Center each day. They were checked by one of us for completeness; when necessary, the survey teams made subsequent visits to dental offlees and obtained missing information. The survey teams were instructed t,o code the information for transcription onto tabulating cards in accord with previously planned work codes. The coded information was key-punched and verified. Editing for inconsistent entries and computation of parametric statistics were accomplished by means of an IBM 1620 computer. Distributions for the preparation of tables were obtained by means of an IBM 082 sorter with counters for all possible numeric entries. OFFICE
PROCEDURES
The person interviewed in most offices was the dentist, but in a few oftices a dental hygienist or assistant supplied the information. After the interview was completed, the interviewer examined the darkroom while the other member of the team examined the x-ray machine and started radiat,ion survey procedures. Activation of the x-ray tube had to be done with care not to exceed tube capacity. The individual team member’s work schedule allowed for maximum tube cooling time. The survey was made with exposure factors that were less than 50 per cent of the duty cycle of the tube, thus minimizing the chances of damage to the x-ray tube. The duty cycles of the various tubes were obtained prior to the survey from the manufacturers of dental x-ray tubes. When the interview and the darkroom examination were completed, the two team members completed the radiation survey together ; some procedures called for one member to operate the machine while the other operated the monitoring instruments. Necessary x-ray machine modifications were made when feasible. X-ray psotection of the team members was obtained mainly by using distance. The rate meter used could be read at distances greater than 6 feet. However, to ensure the safety of the team members, leaded aprons were used during the monitoring procedures. Instruments necessary for monitoring the offices were obtained through purchase with funds allocated for this purpose
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The Inter&x<.-The intervicaw was carried out t,o obtain information about the operation of the x-ra,v installation. la the main, data were collected 1.0 determine ( 1) who owned the machinc~, (2) who was b&g interviewed, (3 1 the age, training, and type of practice of the doctor, (4) the age, type, and number of s-ray marhincs or radiation sources in the off&, (5) cvidtlnce of s-ray damage to persons taking roc~ntgenograms, (6) present or past radiation monitoring or survc’y activities and the result,s of such procedures, (7 j tlic type of roentgenographic surveys made on l)aticnts, (Si the type and numbers of’ films used, (!I) the sex, title, ago, and radiation csposurc of persons operating the s-ray machines, (10) the locations oi’ operators during film c:xposarc iilld their relationship to the primar’,v beam of radiation, ( 1 1 1 machine modifications and the reason for this change, ( 12) the: rorntgenographic technique or tcchniques used, (13) the work load of the s-ray machine, C14) thth use of shields, and (15) film-processing techniquc~s. When an office contained more than one machine, the rclcl-ant portions of additional questionnaires were filled out for each machine. In most instances, the information gathered in that intrrvie\v &ended into the past,. Changes in alld work load WVI’C noted by the interpersonnel, machines. technique, films, viewer, and a historical r~ord ot’ s-radiation use was accumulated whcncver possible. The Darkroont ~‘sanzinntion.-Tht: condition of the darkroom was graded subjectively on a three-point scale. In addition, the observer recorded his comments as to the adequacy of the room for processing films. The presence or absence of a thermometer and thermostatically controlled running water was noted. The room was observed from within for light leaks. The adequacy of the safelight was tested. This test was accomplished by ( 1) unwrapping an intraoral film with the safelight off, (2) placing the film with a coin upon it on the work bench for 10 minutes with the safelight on, and (3) t,urning off the safelight and processing the film in darkness. If an image of t,he coin was seen on the processed film, the safelight was judged to be inadequate, provided the darkroom was light tight. The X-ray Room Exan~incction.-A diagram of the s-ray room was drawn, and notations were made as to approximate dimensions, location of the machine, beam direction, occupancy of adjacent areas, and wall, floor, and ceiling construction. The s-ray loom was esamincd for accessory warning signals and shields for the operator. When shields were present, they mrre examined for ease of use during t,he t,aking of roentgenograms. 7%~ li,‘xamimtion of t/w d’i’-rtr~/ .llccchinr.-Thtl tJ-pc> of tnachinc~ in the dent,al office was recorded as h&g cithrr mohilt~ or fixed. The make, model, and serial number of bot,h the tube head and the console were noted. The type and stability of the tube head were ~rorded. The machine was examined for the kiloroltage and milliamperage ranges when these meters were present. The cone on t,he x-rav machine was removed, and the presence or absence and type and thickness of an; added filter material was recorded. The method of collimation
Volume Number
16 8
X-RADIATION
Ix
DEKTAL
929
OFFICES
of the x-ray beam was noted. The type of cone on the machine and the one usually used were observed. The timing mechanism was classified as being mechanical, electrical, electronic, or other. The timer cord was measured and the timer was examined to determine if it had a “dead-man” type of switch and if this switch terminated the exposure. When the machine had a voltmeter or a KVP meter, a 2 second exposure was made and fluctuations were classified as being less than 5, 5 to 10, or more than 10 KVP or volts. A voltmeter was placed in the electric line leading to the x-ray machine and observed for a period of 2 minutes with the x-ray machine turned off. Fluctuations in the line current were recorded. The machine was then activated for 2 seconds and fluctuations in the line voltage were noted. Machines with milliameters were activated and the milliamperage was read. Another reading was taken 2 minutes later, and any variation between the two readings was classified as being less than 1 Ma., 1 to 2 Ma., or more than 2 Ma. XONITORING
PROCEDURES
Measurements were made which would permit an evaluation radiation, scattered radiation, radiation leakage, timer accuracy, efficiency.
of primary and barrier
Primary Radiation.-A 14 by 17 inch fluorescent screen, separated from the observer by leaded glass and built into the side of a light-tight box, was used to examine the size of the primary x-ray beam.* The shape and position of the beam were observed through a small hole in the opposite side of the box. The diameter of the beam was measured on the screen at two different targetto-screen distances. The position of the tube target within the head of the x-ray machine was calculated from these measurements. To estimate the quality of the x-ray beam, the machine was set, when possible, at 65 KVP and 10 Ma. Machines possessing no variable KVP and/or milliampere meters were assumed to be set at 65 KVP and 10 Ma. Two Victoreen 25 R chambers, Model 70-5, were used to make “cap-on/cap-off” measurements. This technique will be described in a later publication. In addition to the routine survey, an exposure was made of’ a Surpak (a survey film package provided by the Division of Radiological Health) for the purpose of comparing the Surpak findings with the more extensive examination of the dental office. The Surpaks were exposed according to the directions supplied. The serial number of the Surpak was noted and the Surpaks were shipped to the Division of Radiological Health, United States Public Health Service, for evaluation. Scattered Ra.diation.-A Nucor Survey Meter, Model CS-40, was used to make measurements of scattered radiation while the x-ray machine irradiated a phantom. The phantom consisted of a skull embedded in a wax-paraffin mixture molded in the shape of the soft tissues of a human face. The wax-paraffin mixture had a density of one. The phantom head was placed in the patient’s head *This larger screen was used provided by the Division of Radiological to examine the areas immediately around the collimators.
by
the investigators Health. United the primary
outside
instead States beam
of the Slh Public Health of radiation
by 9 inch screen Service, in order for leaks in 0~
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hL4SSOK~IlI?;G,
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position, and the s-~;IJ- beam TTilS tlircvtcd ni the anl(~t~iol~, left, posterior, and right, postwior teeth of the phantom. Five second oxposnrcs were made with t hr beam directed at each of thcsc, posit ions. I)osr rate n~ras~tremenls i II nril liroentgcns per hour were made in the operator’s position, the assist,anl’s I)osition, and the position of any other persons usually present in the room during the making of S-IX\- cxposurc~~. ( Positions were tlet.crmined through thtx interview. ) 1~‘rom t,licse ill(‘ilsUi’clllelits, the milliroentgens per inilliartlpcrc-second and millirocntgens per I\-crk dose rates of the operator, assistant, iltld Othch?* personnel present in the s-raj- room were calculated. Similar Ill(~ilslII’~~Irlcllts and c~irlculations wcrc ills0 Inadr llndcr tllcW SNIlle conditions lvith the rat,e meter positionctl in the I\-ait,ing room, on the rcceptionist ‘s desk. and in other positions in the oficc \vhcrc~ pc~rsonncl might be SitUiltCd for prolonged periods of time. Hadiatio?~ Lcrrkn!/c.-Radiat,iorl leaking from the head of the s-rag machine was measured b\- scanning the tube housing with the rate meter at a distance of 25 cm. from the t,ubc housing. Before the machine was activated for these measurements, the primary beam VW blocked by removing the cone and placing a lead wafer r/4 inch thick in the diaphragm’s position. Maximum. leakage and its location were recordrd as the machine operated at 65 KVP and 10 Ma. Maximum lcakagc was corrected for distance (1 meter) and fract,ional operating time imposed by the duty cyclr of the x-ray tube. Where leakage was greater than 100 mr per hour, the excessive leakage was calculatjed. Timer Accuracy.-The accuracy of the timer was tested with a stop watch at 2 and 4 seconds. The accnracy of the timer at tither $$,I, j/s, and/or l/z second also was determined. A narrow strip of unexposed x-ray film was placed in a light-tight box. This box was placed within nnot,hcr box that was lead-lined in such a manner that the film box could be moved backward or forward smoothly. The x-ray beam was dircctcd at a small hole placed in the middle of the lead-lined box The film 110s was moved within the lead-lined box by means of ;I string attached to it, starting before and ending after the x-ray c~xposurc. The cycle of the electric current supplying the x-ray machine was recorded (60 cycles per second in all cases). The film strip was processed, and the number of black images of the hole in tlw Ired hs seen on tlw film was recorded. The accuracy of the timer was then calculated; for example, in l,G,, second an accurate timer will produce sis impulses of radiation or black images on the film when the machine uses a 60 cycle alternating current. Ba,rriej* E~ciency.--I2arricrs were classified as being (1) a protective apron ; (‘2) a primary barrier (for example, a wall shield, leaded glass, or ordinary wall) ; and (3) others, such as gonadal shields. When feasible, barriers were examined 1)~ directing the primary beam of radiation at the barrier with the machine set at 65 KVP and 10 Ma. The distance from the x-rag tube head to the barrier was that of the cone ordinarily used on t hc machine. Exit dose rates mere measured behind the barrichr with the rate mctcr .1 cm. from the barrier.
Volume Number MACHINE
16 8
X-RADIATION
Ilj
DEW’AL
OFFICES
931
MODIl?ICIC$TIONS
Machines that did not meet the specifications of Regulations Series 7, Radiological Health Service, Jefferson County Department of Health, Birmingham, Alabama, which are essentially identical with those included in Nntionnl Bureau of Standards Handboolc #76, were modified to meet the necessary requirements whenever possible. This was done only with the consent of the dentist responsible for the machine. The x-ray beam was collimated properly with lead diaphragms, and filtration requirements were met using commercially pure aluminum. Other needed modifications, such as adjustment of the head supports, were noted. Whenever a machine was modified, the beam diameter at the tip of the cone was re-examined using the fluorescent screen, and the output of the machine was remeasured at the tip of the cone in roentgens per second. A Surpak was also exposed after the machine had been modified. RESULTS
The results of this study were considered under the following general categories : ( 1) the population studied ; (2) attitudes toward ionizing radiation ; (3) pathologic changes thought to be related to x-radiation ; (4) equipment surveyed ; (5) darkroom facilities and developing techniques ; (6) roentgenographic surveys and techniques; (7) operators ; (8) roentgenographic work load; (9) exposure of personnel; (10) tube-housing leakage; (11) accuracy of timers ; (12) the primary x-ray beam; (13) x-ray machine modifications; and (14) correlations of estimates obtained using Surpaks and conventional measuring instruments. In the interest of brevity, this article will comment superficially on each of the above 14 categories. Publications to follow in this JOURNAL mill expand on most of these results. Th.e Population Studie&-All dental practitioners in Jefferson County, Alabama, participated in the survey. We surveyed 195 private offices and industrial clinics in which 206 dentists used 222 x-ray machines. An additional seventeen machines were surveyed in public dental clinics supervised by personnel with extreme interest in radiologic health. Because of the unusual interest of supervisors of public clinics, they were excluded from the analysis, except that some data about these machines were included in the correlation of results obtained from Surpaks and by the cap-on/cap-off met,hod. There were sixteen other dentists practicing in the county who did not use x-ray equipment. Except for six specialists whose roentgenographic examinations were done in other offices, the practitioners who did not use x-ray equipment mere past 50 years of age and had graduated from dental school at least 30 years before the survey. Half of the practitioners who used x-ray machines had graduated from dental school during the 10 year period preceding the survey. Attitudes Toward Ionizing Radiation.-Considerable educational efforts had been directed toward the dentists whose offices were surveyed. Apparently, these efforts had favorably influenced the attitudes toward ionizing radiation. Eightptwo per cent of the independent practitioners who were at liberty to take action
!l32
KUEHRMANS,
MASSON-HING,
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toward better conditions had either obtained a radiologic safety snrvcg, used some typo of personnel monitoring, modified their machines, arrangrd for t ht operator and assistant to be shielded, or sought positions at least 6 feet away from the machine when it was operated. Almost 53 per cent of the 178 dentists who practiced in the county in 1!)58, when t,he State Health I)epartment provided filters and collimating dcviccs, reported that they had modified their machines bccausc of that program. Apparently, that program was successful. Sixty-three independent practitioners, that is, those who either owned the equipment or were responsible for it,, reported att.ending a short course in radiologic health sponsored by the Public Health Service State Hea,lth Department, and State Dental Society, and 84 per cent of these dentists thought that the course had been beneficial. When asked if they thought they would attend a more advanced course on the subject, 53 per cent gave an unqualified affirmative answer. Another 10 per cent gave a qualified affirmative reply lo the same question. Pathologic Changes Z’hought 1’0 Be Related to X-radiation.--Two dentists of the 206 who practiced in offices in which there was x-ray equipment reported noticing changes which they thought were related to excessive exposures to x-radiation. Each of these men had had a digit amputated because of pathologic changes. One had held films for patients routinely for 2 years before the changes were noticed. The other man had done so for 18 years before the changes were noticed. Three other practitioners reported having held the films routinely for periods of 1 month, 10 years, and 39 yea.rs, but no evidence of pathologic changes had been noticed. Another man had held the films to obtain pictures of the molars for 7 years. and ho evidently expected to continue to hold them. Equipnlext Surceyed.--Most, of the x-ray machines-144 of 22% (64.9 per cent)-had been bought within the last 10 years; however, these machines were not all new when purchased. Only 104 of the independent practitioners had graduated from dental school in the last 10 years. Thirty-six independent practitioners had owned other machines which were no longer used; it is apparent that an appreciable proportion of the dentists had been interested in obtaining newer x-ray equipment. The machines which had been replaced had been owned for I month to 3-L years before they were replaced; the average period of ownership had been 10.7 years. Nine (4.1 prr cent) of the machines had been bought more than 30 years before the survey. None of the offices contained either radionucleids or other sources of appreciable amounts of ionizing radiation. Darkroom Facilities and Developing Techniyues:-The information obtained about the darkrooms and developing techniques indicated that many practitioners probably did not obtain maximum roentgenographic information with minimum exposure of the patient. Fourteen per cent used a sight developing technique. While 86 per cent professed to use a t,ime-temperature technique, only 21 per cent of the darkrooms had an arrangement of running water which permitted control of solution temperature by adjustment of the flow of water. Furthermore, only 52 per cent of the darkrooms had a solution thermometer.
Volume 16 Number
X-RADIATION
8
IS
DENTAL
OFFICES
933
Of the 191 darkrooms examined, seventy-four were judged to have inadequate safelighting. Of these, seven had no safelight; in the remainder, the safelighting was either excessive or white light was allowed to escape. Only twenty-five darkrooms had no apparent light leaks. Roentgenographic Surceys rind Techniques.-One hundred eighty-six of the dentists questioned routineI)* obtained “complete” roentgenographic surreys of their patients. However, the number of intraoral films per survey varied from four to twenty, with the majority of dentists using fourteen. Policies of periodic retaking of periapical and bitewing films varied greatly among the practitioners. Almost all dentists use the bisecting-the-angle technique and the short pointed cone; approximately 40 per cent of the dentists use the fastest intraoral film available. Operators.--One hundred sixty-one of the 204 dentists reported that they ordinarily operated the machine. Thirty-six of the other forty-three delegated this work to assistants, and seven delegated it to dental hygienists. Fifty-three of the 161 dentists were the exclusive operators of the machines, eighty-one used assistants, and twenty-seven used hygienists secondarily. All of the assistants and hygienists and one of the 161 dentists were women. Of the 151 women who ordinarily operated the machines or assisted in roentgenography, seventy-two were older than 30 years, sixty-five were 30 or younger, and age was not ascertained for the other thirteen. Ten of the eighteen dentists who were younger than 30 years ordinarily operated their machines without an assistant present, and eight of these young dentists used assistants during roentgenographic examinations. Roentgenogrnphic Work Lo&.--Estimates of the roentgenographic work load were based on replies from 193 practitioners. Sufficient information was not available from the remainder of those contacted to warrant inclusion in the survey report, The weekly work loads ranged from 13 to 9,020 milliampereseconds and were distributed as shown in Table I. TABLE WEEKLY
WORK (MA.%)
7,000
to
5,000 4,000 3,000 2,000 1,000 900 800 700
to to to to to to to to
LOAD
9,999 6,999 4,999 3,999 2,999 1,999 999 899 799
The work loads nineteen of the 193 estimate to be made. extraoral work loads
NUMBER OF PRACTITIONERS
2 0 1 2 10 19 6
I WEEKLY
WORK (MA.S.)
600 500 400 300 200 100 50 1
to to to to to to to to
699 599 499 399 299 199 99 49
LOAD
NUMBER OF PRACTITIONERS
11 :t 19 20 30 15 13
were composed chiefly of intraoral roentgenography. Only practitioners had a suficient extraoral work load for an One work load was 112 Ma.S. weekly. The other eighteen are shown in Table II.
Exposure of Personnel.--The estimated annual whole-body exposure of one operator exceeded 2,000 mr and nine other operators and/or assistants received annual exposures in excess of 1,000 mr. Sixty-nine per cent of the operators and assistants received less than 100 mr annually. It, is pert,inent to note that users of radiation are limited to (N - 18) x 5 roentgens during their lifetimes. N equals the age of the individual. Kvery effort should he made to minimize this exposure as much as possible. In industry OS research environments, the activities of anyone receiving more than 25 per cent of this amount would be critically evaluated. l’ube-IIousing Leakage.-The housings of the x-ray tubes were scanned for detectable leakage of radiation. The location of any leakage was determined first, and then the rate was measured at a distance of 25 cm. For three of the machines surveyed, measurements greater than 50,000 mr per hour were obtained. These machines had very low work loads; they were purchased in 1.925, 1927, and 19%. One other machine yielded a measurement of 15,000 mr per hour. The other measurements are shown in Table III. TABLE RATE
OF LEAKAGE
(MR/HR.)
Greater than 50,000 15,000 1,000 to 1,999 .500 to 999 100 to 499 10 to 99 Detectable and less Sot detectable
III NUMBER
-_I_-- I
OF AlACHIh'ES
a 1 39 70 4x 61
than
10
14 46
In t,he three machines which yielded rates exceeding 50,000 mr per hour, a location for the leakage could not, be determined. Uniform measurements also were observed around the housing of 20 other tubes. The location of the leakage in the other 153 machines is shown in Table IV.
LOCATION
OF LEAKAGE
Not determined Around housing At end of housing At bottom of housing At top of housing No leakage
1
-i&BER
OF hzi= --__
3
.___-
f9 52 8 46
Volume Number
X-RADIATlON
IG 8
IS
DENTAL
935
OFFICES
Accuracy of Timers.-The accuracy of timers was expressed as a ratio of the timer setting to the actual time as determined by a stop watch and the cyclic electrical current. Therefore, a ratio of less than 1 revealed that the machine operated longer than indicated by the timer setting, and a ratio larger than 1 revealed the opposite situation. The ratios for timer settings of less than 1 second varied from 0.3 to 5.0, as shown in Table V. TABLE RATIOS FOR TIMER OF LESS THAN
5.0 4.0 3.0 2.0 1.5
to to to to
SETTINGS 1 SECOND
NUMBER MACHINES
OF
V RATIOS FOR TIMER SETTINGS OF LESS THAN 1 SECOND
1.01 to 1.49 1.00 0.50 to 0.99 0.3 to 0.5 Not ascertained
1 ii
4.9 3.9 2.9 1.9
25 24
NUMBER MACHINES
OF
56 3 74 2 27
When set at 4 seconds, the timers were more accurate than when set at less than 1 second. The range of ratios was shorter and there were greater proportions at and near one than for the other setting. For one machine a ratio was not obtained. Only one ratio exceeded 2 ; it was 2.86. The other ratios are shown in Table VI. TABLE RATIOS
OF TIMER SETTINGS AT 4 SECONDS
Not obtained Greater than 1.80 to 1.89 1.70 to 1.79 1.60 to 1.69 1.50 to 1.59 1.40 to 1.49 1.30 to 1.39 1.20 to 1.29
2.00
NUMBER MACHINES
1 1 1 0 0 0 1 4 7
OF
VI RATIOS
OF AT
4
TIMER SETTINGS SECONDS
1.10 to 1.01 to Exactly 0.90 to 0.80 to 0.70 to 0.60 to 0.50 to 0.40 to
1.19 1.09 1.00 0.99 0.89 0.79 0.69 0.59 0.49
NlJMBER MACHINES
OF
2 50 52 37
ii 3 1
The Primary X-ray Beam.-The primary beam from twenty-seven of the 222 machines appeared to be ovoid ; the others appeared to be round. Thirteen of the twenty-seven ovoid beams seemed off center, while only forty-seven of the round beams seemed off center. The greatest dimension of sixteen of the twenty-seven ovoid beams was 2.75 inches or less. For the other eleven ovoid beams the approximate greatest dimensions were 3 inches in seven, 4 inches in one, and 5 inches in three. The least dimension of six of the seven ovoid beams which had a greatest dimension of approximately 3 inches was 2.75 inches or less. The remaining small ovoid beam was almost round. The 4 and 5 inch ovoid beams were also almost round. One hundred forty-seven of the 195 round beams were 2.75 inches or less in diameter. Thirty-nine were approximately 3 inches, six were approximately 4 inches, and three were approximately 6 inches in diameter. The line voltage to the x-ray machines often varied appreciably from 110 volts. Most of the variation of line voltage from 110 volts was toward higher
voltage; almost 90 per cent of the machines wre receiving 115 or mow ~011s. E’or 36 per cent of the machines this voltage fluctuated 3 volts or mow when the machines were operated for ‘L seconds. Almost 5 per cent of the machines needed both additional tiltcrs and collimating diaphragms to conform to the accepted st>andards. Another I!) pet cent needed additional filters only, and almost 11 per cent needed collimating diaphragms only. Except for three machines (one needing a filter and two necding collimators), all of thcsc modifications were made at, the t,imc of the survey. Hodifications of il~a~hines.-8dditional filters were prepared and installed in fifty-two machines as follows: 2.0 mm. aluminum in two, 1.5 mm. aluminum in seven, 1.0 mm. aluminum in twcnt,y-four and 0.5 mm. aluminum in ninot~ecn. Another machine needed added filtration to conform to the accepted standards; however, the dentist said that he would retire soon and did not grant his permission for the modification. lt was apparent that t,his machine was used only occasionally. Collimating diaphragms designed to reduce the beam to 2.75 inches vvcre prepared and installed in thirty-two machines. Ten of these machines also had filters added by tho survey team. Tvvo other machines needed collimating diaphragms to reduce the size of their primary beams to conform to accepted standards, hut) the owners refused to permit such modificat,ion. CTorrelations of Estinmtes Obtained by Surpaks wcl Instrunlents.--Estimates of total filtration and half-value layer obtained by the Surpak method were correlated with such estimates obtained through the survey. Although thr correlations between methods wrc not, \-cry high, they provided evidence of consistency within the two methods.
An intensive radiologic health survey in the dental offices of Jefferson County, Alabama, has been described. The survey included personal interviews, inspection of each facility, and detailed monitoring procedures. The results of the survey have been outlined in general terms. A more detailed report, involving specific aspects of the survey, will be published in the immediate future.
Academy
Arthur H. Wwhmuznn,
.
.
.
.
.
X-RADIATION
ALABAMA.
of Oral Roentgenology Editor
.
.
.
.
IN DENTAL
.
.
.
OFFICES
.
.
.
.
.
.
IN JEFFERSON
.
.
.
.
of
.
COUNTY,
I.
A. H. Jvuehrmann, LB., D.M.D.,’ I,. R. Munson-Hing, D.M.D., M.fi.,'* H. C. Jamison, B.A., D.D.S., M.P.H., Dr.P.H.,*” Birmingham, 4la. Dniz;ersity
.
Alabama
School
and
of Dentistry
INTRODUCTION
T
HE professions of medicine and dent,istry are said to contribute to the population’s whole-body radiation dose an amount exceeding that of background radiation. In view of the anticipated increased peace-time use of radiation and radioactive materials of all types, it is increasingly important that welldocumented information be obtained concerning the use of s-radiation in dental offices. On the basis of such data, it should be possible to decide whether or not it would be in the public interest to take any action toward modifying the present dental ofice procedures in so far as radiation usage is concerned. It was with this concept in mind that t,he administration of the Ncdical Center and the School of Dentistry of the University of Ala.bama agreed to participate in a survey of the dental offices of Jefferson County. This survey was performed during the summer of 1961 at the request of the Alabama State Health Department and in cooperation with the Jefferson County Department of Health. Financial arrangements were made between the State Health Department and the Division of R,adiological Health, United States Public Health Service, on the basis of a contract grantt which, at the request of t,hc State Health Department, was administered by the comptroller of the IJniversity of Alabama Medical Center. *Professor of Dentistry, University of Alabama School of Dentistry. **Associate Professor of Dentistry, University of Alabama School of Dentistry. tContract No. SAph 78332, Department of Health, Education, and Welfare, TJnited Public Health Service. Division of Radiological Health. 926
States
Volullle 16 Number 8
X-RADIATION
IN
DENTAL
OFFICES
927
The survey was carried out by means of a carefully designed questionnaire which was divided into three parts and used for the following three purposes: 1. Consultation with the dentist and, when necessary, with the dental assistant or hygienist. 2. Observation of the physical facilities related to the x-ray machine, x-radiation protection measures, and darkroom facilities and procedures. 3. Recording of physical measurements concerned with radiation characteristics and protection factors. The survey was conducted by dental students following an intensive period of training. Three teams of two members each participated. One of us accompanied each survey team during the initial ofice visits in order to be certain that all procedures were being followed faithfully and that there were no misunderstandings on the part of the team members. It was soon apparent that further surveillance was unnecessary. The completed questionnaires were returned to the Medical Center each day. They were checked by one of us for completeness; when necessary, the survey teams made subsequent visits to dental offlees and obtained missing information. The survey teams were instructed t,o code the information for transcription onto tabulating cards in accord with previously planned work codes. The coded information was key-punched and verified. Editing for inconsistent entries and computation of parametric statistics were accomplished by means of an IBM 1620 computer. Distributions for the preparation of tables were obtained by means of an IBM 082 sorter with counters for all possible numeric entries. OFFICE
PROCEDURES
The person interviewed in most offices was the dentist, but in a few oftices a dental hygienist or assistant supplied the information. After the interview was completed, the interviewer examined the darkroom while the other member of the team examined the x-ray machine and started radiat,ion survey procedures. Activation of the x-ray tube had to be done with care not to exceed tube capacity. The individual team member’s work schedule allowed for maximum tube cooling time. The survey was made with exposure factors that were less than 50 per cent of the duty cycle of the tube, thus minimizing the chances of damage to the x-ray tube. The duty cycles of the various tubes were obtained prior to the survey from the manufacturers of dental x-ray tubes. When the interview and the darkroom examination were completed, the two team members completed the radiation survey together ; some procedures called for one member to operate the machine while the other operated the monitoring instruments. Necessary x-ray machine modifications were made when feasible. X-ray psotection of the team members was obtained mainly by using distance. The rate meter used could be read at distances greater than 6 feet. However, to ensure the safety of the team members, leaded aprons were used during the monitoring procedures. Instruments necessary for monitoring the offices were obtained through purchase with funds allocated for this purpose
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The Inter&x<.-The intervicaw was carried out t,o obtain information about the operation of the x-ra,v installation. la the main, data were collected 1.0 determine ( 1) who owned the machinc~, (2) who was b&g interviewed, (3 1 the age, training, and type of practice of the doctor, (4) the age, type, and number of s-ray marhincs or radiation sources in the off&, (5) cvidtlnce of s-ray damage to persons taking roc~ntgenograms, (6) present or past radiation monitoring or survc’y activities and the result,s of such procedures, (7 j tlic type of roentgenographic surveys made on l)aticnts, (Si the type and numbers of’ films used, (!I) the sex, title, ago, and radiation csposurc of persons operating the s-ray machines, (10) the locations oi’ operators during film c:xposarc iilld their relationship to the primar’,v beam of radiation, ( 1 1 1 machine modifications and the reason for this change, ( 12) the: rorntgenographic technique or tcchniques used, (13) the work load of the s-ray machine, C14) thth use of shields, and (15) film-processing techniquc~s. When an office contained more than one machine, the rclcl-ant portions of additional questionnaires were filled out for each machine. In most instances, the information gathered in that intrrvie\v &ended into the past,. Changes in alld work load WVI’C noted by the interpersonnel, machines. technique, films, viewer, and a historical r~ord ot’ s-radiation use was accumulated whcncver possible. The Darkroont ~‘sanzinntion.-Tht: condition of the darkroom was graded subjectively on a three-point scale. In addition, the observer recorded his comments as to the adequacy of the room for processing films. The presence or absence of a thermometer and thermostatically controlled running water was noted. The room was observed from within for light leaks. The adequacy of the safelight was tested. This test was accomplished by ( 1) unwrapping an intraoral film with the safelight off, (2) placing the film with a coin upon it on the work bench for 10 minutes with the safelight on, and (3) t,urning off the safelight and processing the film in darkness. If an image of t,he coin was seen on the processed film, the safelight was judged to be inadequate, provided the darkroom was light tight. The X-ray Room Exan~incction.-A diagram of the s-ray room was drawn, and notations were made as to approximate dimensions, location of the machine, beam direction, occupancy of adjacent areas, and wall, floor, and ceiling construction. The s-ray loom was esamincd for accessory warning signals and shields for the operator. When shields were present, they mrre examined for ease of use during t,he t,aking of roentgenograms. 7%~ li,‘xamimtion of t/w d’i’-rtr~/ .llccchinr.-Thtl tJ-pc> of tnachinc~ in the dent,al office was recorded as h&g cithrr mohilt~ or fixed. The make, model, and serial number of bot,h the tube head and the console were noted. The type and stability of the tube head were ~rorded. The machine was examined for the kiloroltage and milliamperage ranges when these meters were present. The cone on t,he x-rav machine was removed, and the presence or absence and type and thickness of an; added filter material was recorded. The method of collimation
Volume Number
16 8
X-RADIATION
Ix
DEKTAL
929
OFFICES
of the x-ray beam was noted. The type of cone on the machine and the one usually used were observed. The timing mechanism was classified as being mechanical, electrical, electronic, or other. The timer cord was measured and the timer was examined to determine if it had a “dead-man” type of switch and if this switch terminated the exposure. When the machine had a voltmeter or a KVP meter, a 2 second exposure was made and fluctuations were classified as being less than 5, 5 to 10, or more than 10 KVP or volts. A voltmeter was placed in the electric line leading to the x-ray machine and observed for a period of 2 minutes with the x-ray machine turned off. Fluctuations in the line current were recorded. The machine was then activated for 2 seconds and fluctuations in the line voltage were noted. Machines with milliameters were activated and the milliamperage was read. Another reading was taken 2 minutes later, and any variation between the two readings was classified as being less than 1 Ma., 1 to 2 Ma., or more than 2 Ma. XONITORING
PROCEDURES
Measurements were made which would permit an evaluation radiation, scattered radiation, radiation leakage, timer accuracy, efficiency.
of primary and barrier
Primary Radiation.-A 14 by 17 inch fluorescent screen, separated from the observer by leaded glass and built into the side of a light-tight box, was used to examine the size of the primary x-ray beam.* The shape and position of the beam were observed through a small hole in the opposite side of the box. The diameter of the beam was measured on the screen at two different targetto-screen distances. The position of the tube target within the head of the x-ray machine was calculated from these measurements. To estimate the quality of the x-ray beam, the machine was set, when possible, at 65 KVP and 10 Ma. Machines possessing no variable KVP and/or milliampere meters were assumed to be set at 65 KVP and 10 Ma. Two Victoreen 25 R chambers, Model 70-5, were used to make “cap-on/cap-off” measurements. This technique will be described in a later publication. In addition to the routine survey, an exposure was made of’ a Surpak (a survey film package provided by the Division of Radiological Health) for the purpose of comparing the Surpak findings with the more extensive examination of the dental office. The Surpaks were exposed according to the directions supplied. The serial number of the Surpak was noted and the Surpaks were shipped to the Division of Radiological Health, United States Public Health Service, for evaluation. Scattered Ra.diation.-A Nucor Survey Meter, Model CS-40, was used to make measurements of scattered radiation while the x-ray machine irradiated a phantom. The phantom consisted of a skull embedded in a wax-paraffin mixture molded in the shape of the soft tissues of a human face. The wax-paraffin mixture had a density of one. The phantom head was placed in the patient’s head *This larger screen was used provided by the Division of Radiological to examine the areas immediately around the collimators.
by
the investigators Health. United the primary
outside
instead States beam
of the Slh Public Health of radiation
by 9 inch screen Service, in order for leaks in 0~
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position, and the s-~;IJ- beam TTilS tlircvtcd ni the anl(~t~iol~, left, posterior, and right, postwior teeth of the phantom. Five second oxposnrcs were made with t hr beam directed at each of thcsc, posit ions. I)osr rate n~ras~tremenls i II nril liroentgcns per hour were made in the operator’s position, the assist,anl’s I)osition, and the position of any other persons usually present in the room during the making of S-IX\- cxposurc~~. ( Positions were tlet.crmined through thtx interview. ) 1~‘rom t,licse ill(‘ilsUi’clllelits, the milliroentgens per inilliartlpcrc-second and millirocntgens per I\-crk dose rates of the operator, assistant, iltld Othch?* personnel present in the s-raj- room were calculated. Similar Ill(~ilslII’~~Irlcllts and c~irlculations wcrc ills0 Inadr llndcr tllcW SNIlle conditions lvith the rat,e meter positionctl in the I\-ait,ing room, on the rcceptionist ‘s desk. and in other positions in the oficc \vhcrc~ pc~rsonncl might be SitUiltCd for prolonged periods of time. Hadiatio?~ Lcrrkn!/c.-Radiat,iorl leaking from the head of the s-rag machine was measured b\- scanning the tube housing with the rate meter at a distance of 25 cm. from the t,ubc housing. Before the machine was activated for these measurements, the primary beam VW blocked by removing the cone and placing a lead wafer r/4 inch thick in the diaphragm’s position. Maximum. leakage and its location were recordrd as the machine operated at 65 KVP and 10 Ma. Maximum lcakagc was corrected for distance (1 meter) and fract,ional operating time imposed by the duty cyclr of the x-ray tube. Where leakage was greater than 100 mr per hour, the excessive leakage was calculatjed. Timer Accuracy.-The accuracy of the timer was tested with a stop watch at 2 and 4 seconds. The accnracy of the timer at tither $$,I, j/s, and/or l/z second also was determined. A narrow strip of unexposed x-ray film was placed in a light-tight box. This box was placed within nnot,hcr box that was lead-lined in such a manner that the film box could be moved backward or forward smoothly. The x-ray beam was dircctcd at a small hole placed in the middle of the lead-lined box The film 110s was moved within the lead-lined box by means of ;I string attached to it, starting before and ending after the x-ray c~xposurc. The cycle of the electric current supplying the x-ray machine was recorded (60 cycles per second in all cases). The film strip was processed, and the number of black images of the hole in tlw Ired hs seen on tlw film was recorded. The accuracy of the timer was then calculated; for example, in l,G,, second an accurate timer will produce sis impulses of radiation or black images on the film when the machine uses a 60 cycle alternating current. Ba,rriej* E~ciency.--I2arricrs were classified as being (1) a protective apron ; (‘2) a primary barrier (for example, a wall shield, leaded glass, or ordinary wall) ; and (3) others, such as gonadal shields. When feasible, barriers were examined 1)~ directing the primary beam of radiation at the barrier with the machine set at 65 KVP and 10 Ma. The distance from the x-rag tube head to the barrier was that of the cone ordinarily used on t hc machine. Exit dose rates mere measured behind the barrichr with the rate mctcr .1 cm. from the barrier.
Volume Number MACHINE
16 8
X-RADIATION
Ilj
DEW’AL
OFFICES
931
MODIl?ICIC$TIONS
Machines that did not meet the specifications of Regulations Series 7, Radiological Health Service, Jefferson County Department of Health, Birmingham, Alabama, which are essentially identical with those included in Nntionnl Bureau of Standards Handboolc #76, were modified to meet the necessary requirements whenever possible. This was done only with the consent of the dentist responsible for the machine. The x-ray beam was collimated properly with lead diaphragms, and filtration requirements were met using commercially pure aluminum. Other needed modifications, such as adjustment of the head supports, were noted. Whenever a machine was modified, the beam diameter at the tip of the cone was re-examined using the fluorescent screen, and the output of the machine was remeasured at the tip of the cone in roentgens per second. A Surpak was also exposed after the machine had been modified. RESULTS
The results of this study were considered under the following general categories : ( 1) the population studied ; (2) attitudes toward ionizing radiation ; (3) pathologic changes thought to be related to x-radiation ; (4) equipment surveyed ; (5) darkroom facilities and developing techniques ; (6) roentgenographic surveys and techniques; (7) operators ; (8) roentgenographic work load; (9) exposure of personnel; (10) tube-housing leakage; (11) accuracy of timers ; (12) the primary x-ray beam; (13) x-ray machine modifications; and (14) correlations of estimates obtained using Surpaks and conventional measuring instruments. In the interest of brevity, this article will comment superficially on each of the above 14 categories. Publications to follow in this JOURNAL mill expand on most of these results. Th.e Population Studie&-All dental practitioners in Jefferson County, Alabama, participated in the survey. We surveyed 195 private offices and industrial clinics in which 206 dentists used 222 x-ray machines. An additional seventeen machines were surveyed in public dental clinics supervised by personnel with extreme interest in radiologic health. Because of the unusual interest of supervisors of public clinics, they were excluded from the analysis, except that some data about these machines were included in the correlation of results obtained from Surpaks and by the cap-on/cap-off met,hod. There were sixteen other dentists practicing in the county who did not use x-ray equipment. Except for six specialists whose roentgenographic examinations were done in other offices, the practitioners who did not use x-ray equipment mere past 50 years of age and had graduated from dental school at least 30 years before the survey. Half of the practitioners who used x-ray machines had graduated from dental school during the 10 year period preceding the survey. Attitudes Toward Ionizing Radiation.-Considerable educational efforts had been directed toward the dentists whose offices were surveyed. Apparently, these efforts had favorably influenced the attitudes toward ionizing radiation. Eightptwo per cent of the independent practitioners who were at liberty to take action
!l32
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toward better conditions had either obtained a radiologic safety snrvcg, used some typo of personnel monitoring, modified their machines, arrangrd for t ht operator and assistant to be shielded, or sought positions at least 6 feet away from the machine when it was operated. Almost 53 per cent of the 178 dentists who practiced in the county in 1!)58, when t,he State Health I)epartment provided filters and collimating dcviccs, reported that they had modified their machines bccausc of that program. Apparently, that program was successful. Sixty-three independent practitioners, that is, those who either owned the equipment or were responsible for it,, reported att.ending a short course in radiologic health sponsored by the Public Health Service State Hea,lth Department, and State Dental Society, and 84 per cent of these dentists thought that the course had been beneficial. When asked if they thought they would attend a more advanced course on the subject, 53 per cent gave an unqualified affirmative answer. Another 10 per cent gave a qualified affirmative reply lo the same question. Pathologic Changes Z’hought 1’0 Be Related to X-radiation.--Two dentists of the 206 who practiced in offices in which there was x-ray equipment reported noticing changes which they thought were related to excessive exposures to x-radiation. Each of these men had had a digit amputated because of pathologic changes. One had held films for patients routinely for 2 years before the changes were noticed. The other man had done so for 18 years before the changes were noticed. Three other practitioners reported having held the films routinely for periods of 1 month, 10 years, and 39 yea.rs, but no evidence of pathologic changes had been noticed. Another man had held the films to obtain pictures of the molars for 7 years. and ho evidently expected to continue to hold them. Equipnlext Surceyed.--Most, of the x-ray machines-144 of 22% (64.9 per cent)-had been bought within the last 10 years; however, these machines were not all new when purchased. Only 104 of the independent practitioners had graduated from dental school in the last 10 years. Thirty-six independent practitioners had owned other machines which were no longer used; it is apparent that an appreciable proportion of the dentists had been interested in obtaining newer x-ray equipment. The machines which had been replaced had been owned for I month to 3-L years before they were replaced; the average period of ownership had been 10.7 years. Nine (4.1 prr cent) of the machines had been bought more than 30 years before the survey. None of the offices contained either radionucleids or other sources of appreciable amounts of ionizing radiation. Darkroom Facilities and Developing Techniyues:-The information obtained about the darkrooms and developing techniques indicated that many practitioners probably did not obtain maximum roentgenographic information with minimum exposure of the patient. Fourteen per cent used a sight developing technique. While 86 per cent professed to use a t,ime-temperature technique, only 21 per cent of the darkrooms had an arrangement of running water which permitted control of solution temperature by adjustment of the flow of water. Furthermore, only 52 per cent of the darkrooms had a solution thermometer.
Volume 16 Number
X-RADIATION
8
IS
DENTAL
OFFICES
933
Of the 191 darkrooms examined, seventy-four were judged to have inadequate safelighting. Of these, seven had no safelight; in the remainder, the safelighting was either excessive or white light was allowed to escape. Only twenty-five darkrooms had no apparent light leaks. Roentgenographic Surceys rind Techniques.-One hundred eighty-six of the dentists questioned routineI)* obtained “complete” roentgenographic surreys of their patients. However, the number of intraoral films per survey varied from four to twenty, with the majority of dentists using fourteen. Policies of periodic retaking of periapical and bitewing films varied greatly among the practitioners. Almost all dentists use the bisecting-the-angle technique and the short pointed cone; approximately 40 per cent of the dentists use the fastest intraoral film available. Operators.--One hundred sixty-one of the 204 dentists reported that they ordinarily operated the machine. Thirty-six of the other forty-three delegated this work to assistants, and seven delegated it to dental hygienists. Fifty-three of the 161 dentists were the exclusive operators of the machines, eighty-one used assistants, and twenty-seven used hygienists secondarily. All of the assistants and hygienists and one of the 161 dentists were women. Of the 151 women who ordinarily operated the machines or assisted in roentgenography, seventy-two were older than 30 years, sixty-five were 30 or younger, and age was not ascertained for the other thirteen. Ten of the eighteen dentists who were younger than 30 years ordinarily operated their machines without an assistant present, and eight of these young dentists used assistants during roentgenographic examinations. Roentgenogrnphic Work Lo&.--Estimates of the roentgenographic work load were based on replies from 193 practitioners. Sufficient information was not available from the remainder of those contacted to warrant inclusion in the survey report, The weekly work loads ranged from 13 to 9,020 milliampereseconds and were distributed as shown in Table I. TABLE WEEKLY
WORK (MA.%)
7,000
to
5,000 4,000 3,000 2,000 1,000 900 800 700
to to to to to to to to
LOAD
9,999 6,999 4,999 3,999 2,999 1,999 999 899 799
The work loads nineteen of the 193 estimate to be made. extraoral work loads
NUMBER OF PRACTITIONERS
2 0 1 2 10 19 6
I WEEKLY
WORK (MA.S.)
600 500 400 300 200 100 50 1
to to to to to to to to
699 599 499 399 299 199 99 49
LOAD
NUMBER OF PRACTITIONERS
11 :t 19 20 30 15 13
were composed chiefly of intraoral roentgenography. Only practitioners had a suficient extraoral work load for an One work load was 112 Ma.S. weekly. The other eighteen are shown in Table II.
Exposure of Personnel.--The estimated annual whole-body exposure of one operator exceeded 2,000 mr and nine other operators and/or assistants received annual exposures in excess of 1,000 mr. Sixty-nine per cent of the operators and assistants received less than 100 mr annually. It, is pert,inent to note that users of radiation are limited to (N - 18) x 5 roentgens during their lifetimes. N equals the age of the individual. Kvery effort should he made to minimize this exposure as much as possible. In industry OS research environments, the activities of anyone receiving more than 25 per cent of this amount would be critically evaluated. l’ube-IIousing Leakage.-The housings of the x-ray tubes were scanned for detectable leakage of radiation. The location of any leakage was determined first, and then the rate was measured at a distance of 25 cm. For three of the machines surveyed, measurements greater than 50,000 mr per hour were obtained. These machines had very low work loads; they were purchased in 1.925, 1927, and 19%. One other machine yielded a measurement of 15,000 mr per hour. The other measurements are shown in Table III. TABLE RATE
OF LEAKAGE
(MR/HR.)
Greater than 50,000 15,000 1,000 to 1,999 .500 to 999 100 to 499 10 to 99 Detectable and less Sot detectable
III NUMBER
-_I_-- I
OF AlACHIh'ES
a 1 39 70 4x 61
than
10
14 46
In t,he three machines which yielded rates exceeding 50,000 mr per hour, a location for the leakage could not, be determined. Uniform measurements also were observed around the housing of 20 other tubes. The location of the leakage in the other 153 machines is shown in Table IV.
LOCATION
OF LEAKAGE
Not determined Around housing At end of housing At bottom of housing At top of housing No leakage
1
-i&BER
OF hzi= --__
3
.___-
f9 52 8 46
Volume Number
X-RADIATlON
IG 8
IS
DENTAL
935
OFFICES
Accuracy of Timers.-The accuracy of timers was expressed as a ratio of the timer setting to the actual time as determined by a stop watch and the cyclic electrical current. Therefore, a ratio of less than 1 revealed that the machine operated longer than indicated by the timer setting, and a ratio larger than 1 revealed the opposite situation. The ratios for timer settings of less than 1 second varied from 0.3 to 5.0, as shown in Table V. TABLE RATIOS FOR TIMER OF LESS THAN
5.0 4.0 3.0 2.0 1.5
to to to to
SETTINGS 1 SECOND
NUMBER MACHINES
OF
V RATIOS FOR TIMER SETTINGS OF LESS THAN 1 SECOND
1.01 to 1.49 1.00 0.50 to 0.99 0.3 to 0.5 Not ascertained
1 ii
4.9 3.9 2.9 1.9
25 24
NUMBER MACHINES
OF
56 3 74 2 27
When set at 4 seconds, the timers were more accurate than when set at less than 1 second. The range of ratios was shorter and there were greater proportions at and near one than for the other setting. For one machine a ratio was not obtained. Only one ratio exceeded 2 ; it was 2.86. The other ratios are shown in Table VI. TABLE RATIOS
OF TIMER SETTINGS AT 4 SECONDS
Not obtained Greater than 1.80 to 1.89 1.70 to 1.79 1.60 to 1.69 1.50 to 1.59 1.40 to 1.49 1.30 to 1.39 1.20 to 1.29
2.00
NUMBER MACHINES
1 1 1 0 0 0 1 4 7
OF
VI RATIOS
OF AT
4
TIMER SETTINGS SECONDS
1.10 to 1.01 to Exactly 0.90 to 0.80 to 0.70 to 0.60 to 0.50 to 0.40 to
1.19 1.09 1.00 0.99 0.89 0.79 0.69 0.59 0.49
NlJMBER MACHINES
OF
2 50 52 37
ii 3 1
The Primary X-ray Beam.-The primary beam from twenty-seven of the 222 machines appeared to be ovoid ; the others appeared to be round. Thirteen of the twenty-seven ovoid beams seemed off center, while only forty-seven of the round beams seemed off center. The greatest dimension of sixteen of the twenty-seven ovoid beams was 2.75 inches or less. For the other eleven ovoid beams the approximate greatest dimensions were 3 inches in seven, 4 inches in one, and 5 inches in three. The least dimension of six of the seven ovoid beams which had a greatest dimension of approximately 3 inches was 2.75 inches or less. The remaining small ovoid beam was almost round. The 4 and 5 inch ovoid beams were also almost round. One hundred forty-seven of the 195 round beams were 2.75 inches or less in diameter. Thirty-nine were approximately 3 inches, six were approximately 4 inches, and three were approximately 6 inches in diameter. The line voltage to the x-ray machines often varied appreciably from 110 volts. Most of the variation of line voltage from 110 volts was toward higher
voltage; almost 90 per cent of the machines wre receiving 115 or mow ~011s. E’or 36 per cent of the machines this voltage fluctuated 3 volts or mow when the machines were operated for ‘L seconds. Almost 5 per cent of the machines needed both additional tiltcrs and collimating diaphragms to conform to the accepted st>andards. Another I!) pet cent needed additional filters only, and almost 11 per cent needed collimating diaphragms only. Except for three machines (one needing a filter and two necding collimators), all of thcsc modifications were made at, the t,imc of the survey. Hodifications of il~a~hines.-8dditional filters were prepared and installed in fifty-two machines as follows: 2.0 mm. aluminum in two, 1.5 mm. aluminum in seven, 1.0 mm. aluminum in twcnt,y-four and 0.5 mm. aluminum in ninot~ecn. Another machine needed added filtration to conform to the accepted standards; however, the dentist said that he would retire soon and did not grant his permission for the modification. lt was apparent that t,his machine was used only occasionally. Collimating diaphragms designed to reduce the beam to 2.75 inches vvcre prepared and installed in thirty-two machines. Ten of these machines also had filters added by tho survey team. Tvvo other machines needed collimating diaphragms to reduce the size of their primary beams to conform to accepted standards, hut) the owners refused to permit such modificat,ion. CTorrelations of Estinmtes Obtained by Surpaks wcl Instrunlents.--Estimates of total filtration and half-value layer obtained by the Surpak method were correlated with such estimates obtained through the survey. Although thr correlations between methods wrc not, \-cry high, they provided evidence of consistency within the two methods.
An intensive radiologic health survey in the dental offices of Jefferson County, Alabama, has been described. The survey included personal interviews, inspection of each facility, and detailed monitoring procedures. The results of the survey have been outlined in general terms. A more detailed report, involving specific aspects of the survey, will be published in the immediate future.