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Leaded shields for thyroid dose reduction in intraoral dental radiography
Leaded shields for thyroid dose reduction in intraoral dental radiography Bruce L. Whitcher, B.A., * Barton M. Gratt, D.D.S., ** and Edward A. Sickles, M.D., *** San Francisco, Cal$. UNIVERSITY
OF CALIFORNIA
SCHOOLS
OF DENTISTRY
AND
MEDICINE
This study evaluated the radiation dose reduction, operator acceptance, and patient acceptance of two types of leaded thyroid shields designed for use during intraoral dental radiography. Exposure levels were measured with thermoluminescent dosimeters on three groups of 20 patients undergoing complete mouth (20-film) surveys. Skin entrance dose to the thyroid was 20 mR per complete mouth survey without a shield in place, 12 mR per complete mouth survey with the experimental shield in place, and 9 mR with the commercial shield. Patients and radiologic technologist were surveyed to determine patient comfort and operator acceptability. Patient and operator acceptability were higher for the experimental shield than for the commercial shield.
I
ntraoral dental radiography is the most widely used technique for the x-ray diagnosis of oral pathoses. This technique produces highly detailed films of the teeth and their supporting structures with relatively low patient radiation dose. Fewer than 7 percent of the dental radiographic units in use produce an x-ray beam greater than 3 inches in diameter at skin entrance.’ In addition, rectangular collimators may be used to restrict the beam to a film-sized field, but these devices require precise alignment of the beam and film and at present are not widely used. Most dental x-ray units produce an x-ray beam diameter at least % inch larger than the largest periapical film.’ This oversized beam is a source of unnecessary radiation exposure, and a means for reducing this exposure is highly desirable. Shields of leaded material are used in medical and dental radiography to protect radiation-sensitive areas from undesirable and potentially harmful exposure. This study was supported in part by funds from Biomedical Research Support Grant 5 S07-RR05305-17, National Institutes of Health, United States Public Health Service, Bethesda, Md. *Second year Dental Student, Summer Student Research Fellowship Program, Oral Radiology, School of Dentistry. **Assistant Professor, Oral Radiology; Sponsor, Summer Student Research Fellowships, Division of General Dentistry, School of Dentistry. ***Chief, Mammography Section, Department of Radiology, School of Medicine. 0030-4220/79/120567+04$00.40/0
0
1979 The C. V. Mosby CO.
Block and Goepp3 used a leaded collar draped around the neck to protect the thyroid gland during cephalometric radiography and suggested its use during intraoral radiography as well. Protection of the thyroid gland is necessary because of its sensitivity to the oncogenic effects of radiation. Studies have suggested an increased incidence of thyroid neoplasms with radiation levels as low as 6 rads .4, 5 Estimates of dose to the thyroid from intraoral dental radiography vary from 5.7 mR6 to 113 mR7 per 18 to 20-film complete mouth survey. Exposure factors (amperage, voltage), cone length, beam diameter, beam filtration, film speed, film position, and patient anatomy all affect thyroid dose measurements.8’ 9 This study evaluated two different types of leaded thyroid shields for intraoral dental radiography. The reduction in skin dose and the patient and operator acceptance of each shield were determined. METHODS
The study population consisted of 60 consecutive adult dental patients ( 18 to 68 years old, mean age 39) requiring 20-film complete mouth surveys. After informed consent was granted, patients were sequentially assigned to one of three groups. Patients in group 1 served as controls and were radiographed without a thyroid shield; group 2 patients wore an experimental thyroid shield (0.25 mm. lead equivalent) constructed to our specifications for easy placement and patient 567
568
Whitcher, Gratt, and Sickles
Oral Surg.
December,1979
Fig. 1. A, Cervi-Shield commercial thyroid shield. B, Experimental thyroid shield.
I ce
J
Position of lithium fluoride thermoluminescent dosimeterswith respectto patient anatomy.
Fig. 2.
comfort (Fig. 1, B); group 3 patients wore a commercially available thyroid shield* (Fig. 1, A). All patients were draped with a conventional leaded apron (0.25 mm. lead equivalent) during radiography, and all films produced for the study were used during each patient’s subsequent dental treatment. Dental radiologic technologists at the University of California, San Francisco Dental Clinic performed the complete mouth (20-film) surveys using the long-cone paralleling principle and D-speed film.? Radiographs were taken with G.E. 100 dental x-ray units,$ total * Cerv-Shield,DunvaleRadiographic,Hoffman Estates, Ill. +Eastman Kodak Co.. Rochester, N. Y. iGenera Electric Co., Milwaukee, Wis.
filtration of 2.5 mm aluminum equivalent, and a minimum target-film distance of 16 inches. Tube voltage varied from 70 to 100 kVp, depending on the anatomic region; all radiographs were taken using 10 mA and %-second exposure (30 impulses). All films were processed according to the manufacturer’s recommendations. Radiation exposure measurements were made by thermoluminescent dosimetry (TLD) with polyethylene capsules containing lithium fluoride.* TLD capsules were used in pairs to give duplicate measurements at each site and were accurate to 210 mR below 100 mR and i 10 percent above 100 mR. The capsules were taped to the skin at three different locations on the neck using micropore tape (Fig. 2). Previously reported estimates of radiation dose to the thyroid per complete mouth survey have been as low as 5.7 mR.“’ To reduce dosimeter error, TLD capsules were exposed to 20 consecutive complete mouth (20-film) surveys. One set of six TLD capsules was evaluated for each group of 20 patients by successively positioning the set of capsules on each patient in the group undergoing a complete mouth survey (Fig. 3). Patients wearing thyroid shields were asked to comment on shield comfort, while radiologic technologists were asked to evaluate ease of shield placement; their responses were recorded as experimental data. *Radiation Detection Co., Sunnyvale. Calif.
Leaded shields for thyroid dose reduction
Volume 48 Number 6
569
Fig. 3. A, Patient without thyroid shield, showing placement of thermoluminescent dosimeters. B. Patient wearing experimental thyroid shield. C, Patient wearing Cervi-Shield thyroid shield. Table I. Dosimetric measurements of thyroid gland exposure (skin entrance dose) Group
No. patients
Shield
1
20
None
2 3
20 20
Dosimeter location*
Exposure (n%wv) 380 390 440 260 250 230 180 170 170
Experiment&i: Commercial@
2 2 2 2 2 k + i 2
50 50 60
40 40 30 30 20 20
Exposure (mRisurvey)t 19 + 3 19 2 22 2 13 + 12 2 12 + 921 821 9&l
3 3 2 2 2
*See Fig. 2. tObtained from group exposure data by dividing by 20. Shield constructedto our design from leaded apron (0.25 mm. Iead equivalent) material. PCervi-Shield.
RESULTS
DISCUSSION
TLD dosimetry measurements are reported in Table I. The mean skin exposure without use of a thyroid shield was 20 mR per complete mouth (20-film) survey. With the experimental shield (Fig. 1, B), skin dose was 12 mR per complete mouth survey, a reduction of 40 percent; skin dose with the commercially available shield (Fig. 1, A), was 9 mR per complete mouth survey, a reduction of 55 percent. Only one patient (5 percent) reported that the experimental shield was uncomfortable, while seven patients (35 percent) reported the commercial shield to be uncomfortable. All four technologists stated that the experimental shield was easy to use, but they found the commercial collar difficult to use on patients with large or short necks.
Results demonstrated that thyroid shields substantially reduce the radiation dose to the thyroid gland. Nevertheless, some exposure was still detectable at the skin surface of the neck. The doses reported with the shields in place were probably due to a combination of primary beam exit radiation, scattered radiation, and entrance dose radiation due to occasional incomplete coverage of the neck. The commercial shield often fit the patient’s neck more closely than the experimental collar and therefore gave greater dose reduction; however, the commercial shield was too small to fit some patients, and on others it was uncomfortably tight and restricted head movements. Technologists found the experimental thyroid
570
Whitcher,
Grutt,
and Sickles
Oral Surg. December, 1979
shield easy to use and indicated that it did not interfere with intraoral radiographic procedures.
6. Weissman, D. D., and Sobkowski, F. J.: Comparative Thermoluminescent Dosimetry of Intraoral Periapical Radiography,
ORALSKJRG. 29: 376-386, 1970. 7. Bushong, S. C., Galbreath, J. C., Garvis, R., and Merritt, E.:
REFERENCES I. Fess, L. R., McDowell, R. B., Jameson, W. R., and Alcox, R. W.: Results of 33,911 X-ray Protection Surveys of Facilities With Medical and Dental Diagnostic X-ray Equipment, Fiscal Years 1961-1968, Radiol. Health Data and Reports 11: 581,
1970. 2. Wuehrmann, A. H., and Manson-Hing, L. R.: Dental Radiology, ed. 4, St. Louis, 1977, The C. V. Mosby Company, pp. 71-72.
Reduction of Patient Exposure During Dental Radiography, Health Phys. 21: 281-286, 1971. 8. Alcox, R. W., and Jameson, W. R.: Patient Exposures From Intraoral Radiographic Examinations, J. Am. Dent. Assoc. 88:
568-579, 1974. 9. Frey, N. W., and Wuehrmann,A. H.: Radiation Dosimetry and Intraoral Radiographic Techniques, ORAL SURG.38: 639-652, 1974.
_3 Block, A. J., Goepp, R. A., and Manson, E. W.: Thyroid Radiation Dose During Panoramic and Cephalometric Dental X-ray Examinations, Angle Orthod. 47: 17-24, 1977. 4. Silverman. C., and Hoffman, D. A.: Thyroid Tumor Risk From Radiation During Childhood, Prev. Med. 4: 100.105, 1975. 5. Modan, B., Mart, H., Baidatz, D., Stemietz. R.. and Levin. S.: Radiation Induced Head and Neck Tumors. Lancet I: 277.279.
Rqwitrt
r~yuem
IO:
Dr. Barton M. Gratt UCLA Dental School Los Angeles, Calif. 90024
1974.
INFORMATION
FOR AUTHORS
Most of the provisions of the Copyright Act of 1976 became effective on January I, 1978. Therefore, all manuscripts must be accompanied by the following written statement, signed by one author: “The undersigned author transfers all copyright ownership of the manuscript entitled (title of article) to The C. V. Mosby Company in the event the work is published. The undersigned author warrants that the article is original, is not under consideration by another journal, and has not been previously published. I sign for and accept responsibility for releasing this material on behalf of any and all co-authors.” Authors will be consulted, when possible, regarding republication of their material.
OF CALIFORNIA
SCHOOLS
OF DENTISTRY
AND
MEDICINE
This study evaluated the radiation dose reduction, operator acceptance, and patient acceptance of two types of leaded thyroid shields designed for use during intraoral dental radiography. Exposure levels were measured with thermoluminescent dosimeters on three groups of 20 patients undergoing complete mouth (20-film) surveys. Skin entrance dose to the thyroid was 20 mR per complete mouth survey without a shield in place, 12 mR per complete mouth survey with the experimental shield in place, and 9 mR with the commercial shield. Patients and radiologic technologist were surveyed to determine patient comfort and operator acceptability. Patient and operator acceptability were higher for the experimental shield than for the commercial shield.
I
ntraoral dental radiography is the most widely used technique for the x-ray diagnosis of oral pathoses. This technique produces highly detailed films of the teeth and their supporting structures with relatively low patient radiation dose. Fewer than 7 percent of the dental radiographic units in use produce an x-ray beam greater than 3 inches in diameter at skin entrance.’ In addition, rectangular collimators may be used to restrict the beam to a film-sized field, but these devices require precise alignment of the beam and film and at present are not widely used. Most dental x-ray units produce an x-ray beam diameter at least % inch larger than the largest periapical film.’ This oversized beam is a source of unnecessary radiation exposure, and a means for reducing this exposure is highly desirable. Shields of leaded material are used in medical and dental radiography to protect radiation-sensitive areas from undesirable and potentially harmful exposure. This study was supported in part by funds from Biomedical Research Support Grant 5 S07-RR05305-17, National Institutes of Health, United States Public Health Service, Bethesda, Md. *Second year Dental Student, Summer Student Research Fellowship Program, Oral Radiology, School of Dentistry. **Assistant Professor, Oral Radiology; Sponsor, Summer Student Research Fellowships, Division of General Dentistry, School of Dentistry. ***Chief, Mammography Section, Department of Radiology, School of Medicine. 0030-4220/79/120567+04$00.40/0
0
1979 The C. V. Mosby CO.
Block and Goepp3 used a leaded collar draped around the neck to protect the thyroid gland during cephalometric radiography and suggested its use during intraoral radiography as well. Protection of the thyroid gland is necessary because of its sensitivity to the oncogenic effects of radiation. Studies have suggested an increased incidence of thyroid neoplasms with radiation levels as low as 6 rads .4, 5 Estimates of dose to the thyroid from intraoral dental radiography vary from 5.7 mR6 to 113 mR7 per 18 to 20-film complete mouth survey. Exposure factors (amperage, voltage), cone length, beam diameter, beam filtration, film speed, film position, and patient anatomy all affect thyroid dose measurements.8’ 9 This study evaluated two different types of leaded thyroid shields for intraoral dental radiography. The reduction in skin dose and the patient and operator acceptance of each shield were determined. METHODS
The study population consisted of 60 consecutive adult dental patients ( 18 to 68 years old, mean age 39) requiring 20-film complete mouth surveys. After informed consent was granted, patients were sequentially assigned to one of three groups. Patients in group 1 served as controls and were radiographed without a thyroid shield; group 2 patients wore an experimental thyroid shield (0.25 mm. lead equivalent) constructed to our specifications for easy placement and patient 567
568
Whitcher, Gratt, and Sickles
Oral Surg.
December,1979
Fig. 1. A, Cervi-Shield commercial thyroid shield. B, Experimental thyroid shield.
I ce
J
Position of lithium fluoride thermoluminescent dosimeterswith respectto patient anatomy.
Fig. 2.
comfort (Fig. 1, B); group 3 patients wore a commercially available thyroid shield* (Fig. 1, A). All patients were draped with a conventional leaded apron (0.25 mm. lead equivalent) during radiography, and all films produced for the study were used during each patient’s subsequent dental treatment. Dental radiologic technologists at the University of California, San Francisco Dental Clinic performed the complete mouth (20-film) surveys using the long-cone paralleling principle and D-speed film.? Radiographs were taken with G.E. 100 dental x-ray units,$ total * Cerv-Shield,DunvaleRadiographic,Hoffman Estates, Ill. +Eastman Kodak Co.. Rochester, N. Y. iGenera Electric Co., Milwaukee, Wis.
filtration of 2.5 mm aluminum equivalent, and a minimum target-film distance of 16 inches. Tube voltage varied from 70 to 100 kVp, depending on the anatomic region; all radiographs were taken using 10 mA and %-second exposure (30 impulses). All films were processed according to the manufacturer’s recommendations. Radiation exposure measurements were made by thermoluminescent dosimetry (TLD) with polyethylene capsules containing lithium fluoride.* TLD capsules were used in pairs to give duplicate measurements at each site and were accurate to 210 mR below 100 mR and i 10 percent above 100 mR. The capsules were taped to the skin at three different locations on the neck using micropore tape (Fig. 2). Previously reported estimates of radiation dose to the thyroid per complete mouth survey have been as low as 5.7 mR.“’ To reduce dosimeter error, TLD capsules were exposed to 20 consecutive complete mouth (20-film) surveys. One set of six TLD capsules was evaluated for each group of 20 patients by successively positioning the set of capsules on each patient in the group undergoing a complete mouth survey (Fig. 3). Patients wearing thyroid shields were asked to comment on shield comfort, while radiologic technologists were asked to evaluate ease of shield placement; their responses were recorded as experimental data. *Radiation Detection Co., Sunnyvale. Calif.
Leaded shields for thyroid dose reduction
Volume 48 Number 6
569
Fig. 3. A, Patient without thyroid shield, showing placement of thermoluminescent dosimeters. B. Patient wearing experimental thyroid shield. C, Patient wearing Cervi-Shield thyroid shield. Table I. Dosimetric measurements of thyroid gland exposure (skin entrance dose) Group
No. patients
Shield
1
20
None
2 3
20 20
Dosimeter location*
Exposure (n%wv) 380 390 440 260 250 230 180 170 170
Experiment&i: Commercial@
2 2 2 2 2 k + i 2
50 50 60
40 40 30 30 20 20
Exposure (mRisurvey)t 19 + 3 19 2 22 2 13 + 12 2 12 + 921 821 9&l
3 3 2 2 2
*See Fig. 2. tObtained from group exposure data by dividing by 20. Shield constructedto our design from leaded apron (0.25 mm. Iead equivalent) material. PCervi-Shield.
RESULTS
DISCUSSION
TLD dosimetry measurements are reported in Table I. The mean skin exposure without use of a thyroid shield was 20 mR per complete mouth (20-film) survey. With the experimental shield (Fig. 1, B), skin dose was 12 mR per complete mouth survey, a reduction of 40 percent; skin dose with the commercially available shield (Fig. 1, A), was 9 mR per complete mouth survey, a reduction of 55 percent. Only one patient (5 percent) reported that the experimental shield was uncomfortable, while seven patients (35 percent) reported the commercial shield to be uncomfortable. All four technologists stated that the experimental shield was easy to use, but they found the commercial collar difficult to use on patients with large or short necks.
Results demonstrated that thyroid shields substantially reduce the radiation dose to the thyroid gland. Nevertheless, some exposure was still detectable at the skin surface of the neck. The doses reported with the shields in place were probably due to a combination of primary beam exit radiation, scattered radiation, and entrance dose radiation due to occasional incomplete coverage of the neck. The commercial shield often fit the patient’s neck more closely than the experimental collar and therefore gave greater dose reduction; however, the commercial shield was too small to fit some patients, and on others it was uncomfortably tight and restricted head movements. Technologists found the experimental thyroid
570
Whitcher,
Grutt,
and Sickles
Oral Surg. December, 1979
shield easy to use and indicated that it did not interfere with intraoral radiographic procedures.
6. Weissman, D. D., and Sobkowski, F. J.: Comparative Thermoluminescent Dosimetry of Intraoral Periapical Radiography,
ORALSKJRG. 29: 376-386, 1970. 7. Bushong, S. C., Galbreath, J. C., Garvis, R., and Merritt, E.:
REFERENCES I. Fess, L. R., McDowell, R. B., Jameson, W. R., and Alcox, R. W.: Results of 33,911 X-ray Protection Surveys of Facilities With Medical and Dental Diagnostic X-ray Equipment, Fiscal Years 1961-1968, Radiol. Health Data and Reports 11: 581,
1970. 2. Wuehrmann, A. H., and Manson-Hing, L. R.: Dental Radiology, ed. 4, St. Louis, 1977, The C. V. Mosby Company, pp. 71-72.
Reduction of Patient Exposure During Dental Radiography, Health Phys. 21: 281-286, 1971. 8. Alcox, R. W., and Jameson, W. R.: Patient Exposures From Intraoral Radiographic Examinations, J. Am. Dent. Assoc. 88:
568-579, 1974. 9. Frey, N. W., and Wuehrmann,A. H.: Radiation Dosimetry and Intraoral Radiographic Techniques, ORAL SURG.38: 639-652, 1974.
_3 Block, A. J., Goepp, R. A., and Manson, E. W.: Thyroid Radiation Dose During Panoramic and Cephalometric Dental X-ray Examinations, Angle Orthod. 47: 17-24, 1977. 4. Silverman. C., and Hoffman, D. A.: Thyroid Tumor Risk From Radiation During Childhood, Prev. Med. 4: 100.105, 1975. 5. Modan, B., Mart, H., Baidatz, D., Stemietz. R.. and Levin. S.: Radiation Induced Head and Neck Tumors. Lancet I: 277.279.
Rqwitrt
r~yuem
IO:
Dr. Barton M. Gratt UCLA Dental School Los Angeles, Calif. 90024
1974.
INFORMATION
FOR AUTHORS
Most of the provisions of the Copyright Act of 1976 became effective on January I, 1978. Therefore, all manuscripts must be accompanied by the following written statement, signed by one author: “The undersigned author transfers all copyright ownership of the manuscript entitled (title of article) to The C. V. Mosby Company in the event the work is published. The undersigned author warrants that the article is original, is not under consideration by another journal, and has not been previously published. I sign for and accept responsibility for releasing this material on behalf of any and all co-authors.” Authors will be consulted, when possible, regarding republication of their material.