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No kilovoltage dilemma
No kilovoltage dilemma Robert E. Buchholz, WRIGHT-PATTERSON
Lieutenant AIR
FORCE
Colonel, USAF
BASE,
(DC)*
OHIO
I
n a recent article by Pentel and Goren,l it was implied that I was alone in my belief that with radiographic techniques utilizing either high or low kilovoltages the patient’s exposure to ionizing radiation is essentially similar. Pentel a.nd Goren said that my opinion was cofntrary to research findings on the subject, and/ they found it difficult to appreciate how I calculated an equivalence. The purpose of this a,rticle is to substantiate the validity of the original quotation in question for any of the profession who may now be confused. The original quotation is: “It is now known that the sum of primary and secondary radiation is almost identical for exposures made at both high and low kilovoltage. The use of high kilovoltage has been greatly overemphasized. ‘U The scientific world generally agrees that only those variables in question within a specific study should be manipulated if the results are to be valid. In a determination of the dose effects of high and low kilovoltages as they rela,te to intraoral radiographic techniques, it seems reasonable to assume that only the kilovoltage will be changed (along with necessary adljustments in the milliampere-seconds to produce radiographs of similar usable density). No other variable can be justified when the study is designed to determine the dose of radiaCon the patient receives from techniques using either high or low kilovoltages. Use of a medium-speed film with one kilovoltage and an ultrafast film with another kilovoltage invalidates the integrity of the experiment. The additional factor of film speed is not a part of the original premise or thesis. There should be no dilemma about the effects of high- or low-kilovoltage techniques upon the total dose of primary and secondary radiation received by the dental patient. Adequate valid research has been reported to substantiate the opinion that the sum of primary and secondary ra,diation is almost identical *Chief, Oral Diagnosis Section, Dental Division, USAF Hospital Wright-Patterson, Wright-Patterson AFB, Ohio. The opinions and assertions contained in this presentation are the private ones of the author and are not to be construed as official or reflecting the views of the Department of the Air Force.
459
460
Buchholz
OS, O.Jl. 8 0.1’. April,
1987
for dental radiographs of similar dens,ities made a,t Iroth high and low kilovoltages. The studies cited in the paragraphs that I’ollow directly rclate to the question without the addition of such superfluous variables as film speed, filtration, collimation, resulta,nt film dens’ity, or target-film distance, each of which will influence the absorbed dose if altered. Whereas Pentel and Gorenl interpreted selected studies to imply a 90 per cent reduction in patdent exposure by changing to the higher kilovoltages, the American Academy of Oral Roentgenology states, as policy” tha,t the difference in patient irradiation by techniques of high or low kilovoltages is greatly overemphasized. Certainly, a 90 per cent, reduction could not be overemphasized if it were fact. The reason for t.his divergence of opinion will become apparent during later discussion. Wainwright and Villanyi” reported the results of data appearing in the literature in 1958.5-7 It was shown that, all other factors remaining equal, the change from low to high kilovoltage will reduce the gonadal dose by only 13 per cent, even with a prima,ry beam of the large diameter in general use at that time. Similarly, all other factors remaining unchanged, the simple change from medium-speed film to ultrafast film reduces the gonadal dose by more tha,n 90 per cent. Therefore, as Pentel and Goren reported, it is reasonable to expect that a 90 per cent reduct.ion would be noted when the factors were changed from medium-speed film and low kilovoltage to ultraspeed film and high kilovoltage. Contrary to their conclusion, however, t.he expected 90 per cent reduction is due to the change in film used rather than to the change in kilo’voltage. In 1962 Richards8 reported a, study in which his attention was directed primarily to the effect of va,rious cones (pointed, open-end, and shielded open-end) on the reduction of gonadal irradiation of dental patients. The data showed a difference between the various co’nes a.,t low kilovoltage; a simila,r difference was noted between cones at high kilo8volta,ge. The accumula,tcdl dat’a also showed that for each cone tested the dos,c to the gonads was, in fact, smaller during the 65 kilovolt exposures tha,n during the 90 kilovolt exposures. Richards and Webberg reported a st,udy designed specifically to measure the radiation received by numerous organs of the head and neck during a fourteenfilm periapical examinatio’n and during a.,bitewing examination. Their find,ings indicated that the doses wit.11 high and low kilovoltages were compa.rable, with few exceptions. The exceptions were at. the sit.es of the pituitary and other more distant glands, where the 90 kilovolt exposure resulted in a measurably higher dose bhan exposure at low kilovoltagr. This study is in agreement with essentially similar experiments reported by Bjarngard and co-workers.1” DISCUSSION
When all factors that are not relevant to the quest.ion of patient irradiation from exposure techniques using high and low kilovoltages are removed from the context of the investigation, the literature substantiates the thesis that the sum of primary and second!ary radiation is almost identical for both. This substantiation is what should be expected from a review of depth dme data in any standard textbook.
1’olume 23 Number 4
No kilovoltage
d&mma
461
It behooves the researcher, who reports, and the practitioner, who reads the reports, to evaluate what is written for validity of the study, authenticity of the ideas extracted from other authors, and integrity of the comparisons and conclusions made. Errors in any of these aSeas are misleading to the reader and may perpetuate misconceptions of importance to the normal progression of professional knowledge. For the discriminate reader such errors will tend to invalidate the remainder of the report. REFERENCES 1. Pental,
2. 3. 4. 5. 6. 7.
L., and Goren, A.: Tone Scale and Separation in Dental X-ray Emulsions, ORAL SURG., ORAL MED. & ORAL PATH. 21: 748-739, 1966. Buchholz, R. : Radiographic Interpretation of Proximal Carious Lesions, D. Radiog. & Photog. 38: 9-12, 1965. American Academy of Oral Roentgenology : The Effective Use of X-ray Radiation in Dentistry, ORAL SURG.,ORAL MED. & ORAL PATH. 16: 294-304, 1963. Wainwright, W., and Villanyi, A.: Film Speed-Greatest Single Factor in the Reduction of Radiation to Dentist and Patient, J. South. California State D. A. 26: 429-430, 1958. Richards, A. : Roentgen-Ray Doses in Dental Roentgenography, J. Am. Dent. A. 56: 351-368, 1958. Richards, A., Nelsen, R., Fitzgerald, G., Wald, S., and Spangenberger, H.: X-ray Protection in the Dental Office, J. Am. Dent. A. 56: 514-521, 1958. Wainwright, W., and Villa@, A.: Radiation Hazards-Reduction of Dental X-ray Exp;yQres to Meet the Changing Conditions of the Atomic Age, PDM, pp. l-31, January,
8. Richards,
A.: New Method for Reduction of Gonadal Irradiation of Dental Patients, J. Am. Dent. A. 65: 15-25, 1962. 9. Richards, A., and Webber, R.: Dental X-ray Expoeure of Sites Within the Head and Neck, ORAL SURG., ORAL MED. & ORAL PATH. 18: 752-756, 1964, 10. Bjarngard, B., and others: Radiation Doses in Oral Radiography. I. Measurements of Doses to Gonads and Certain Parts of Head and Neck During Full Mouth Roentgenography, Odont. revy 10: 355, 1959. II. The Influence of Technical Factors on the Dose to the Patient in Full Mouth Roentgenography, Odont. revy 11: 100, 1960.
Lieutenant AIR
FORCE
Colonel, USAF
BASE,
(DC)*
OHIO
I
n a recent article by Pentel and Goren,l it was implied that I was alone in my belief that with radiographic techniques utilizing either high or low kilovoltages the patient’s exposure to ionizing radiation is essentially similar. Pentel a.nd Goren said that my opinion was cofntrary to research findings on the subject, and/ they found it difficult to appreciate how I calculated an equivalence. The purpose of this a,rticle is to substantiate the validity of the original quotation in question for any of the profession who may now be confused. The original quotation is: “It is now known that the sum of primary and secondary radiation is almost identical for exposures made at both high and low kilovoltage. The use of high kilovoltage has been greatly overemphasized. ‘U The scientific world generally agrees that only those variables in question within a specific study should be manipulated if the results are to be valid. In a determination of the dose effects of high and low kilovoltages as they rela,te to intraoral radiographic techniques, it seems reasonable to assume that only the kilovoltage will be changed (along with necessary adljustments in the milliampere-seconds to produce radiographs of similar usable density). No other variable can be justified when the study is designed to determine the dose of radiaCon the patient receives from techniques using either high or low kilovoltages. Use of a medium-speed film with one kilovoltage and an ultrafast film with another kilovoltage invalidates the integrity of the experiment. The additional factor of film speed is not a part of the original premise or thesis. There should be no dilemma about the effects of high- or low-kilovoltage techniques upon the total dose of primary and secondary radiation received by the dental patient. Adequate valid research has been reported to substantiate the opinion that the sum of primary and secondary ra,diation is almost identical *Chief, Oral Diagnosis Section, Dental Division, USAF Hospital Wright-Patterson, Wright-Patterson AFB, Ohio. The opinions and assertions contained in this presentation are the private ones of the author and are not to be construed as official or reflecting the views of the Department of the Air Force.
459
460
Buchholz
OS, O.Jl. 8 0.1’. April,
1987
for dental radiographs of similar dens,ities made a,t Iroth high and low kilovoltages. The studies cited in the paragraphs that I’ollow directly rclate to the question without the addition of such superfluous variables as film speed, filtration, collimation, resulta,nt film dens’ity, or target-film distance, each of which will influence the absorbed dose if altered. Whereas Pentel and Gorenl interpreted selected studies to imply a 90 per cent reduction in patdent exposure by changing to the higher kilovoltages, the American Academy of Oral Roentgenology states, as policy” tha,t the difference in patient irradiation by techniques of high or low kilovoltages is greatly overemphasized. Certainly, a 90 per cent, reduction could not be overemphasized if it were fact. The reason for t.his divergence of opinion will become apparent during later discussion. Wainwright and Villanyi” reported the results of data appearing in the literature in 1958.5-7 It was shown that, all other factors remaining equal, the change from low to high kilovoltage will reduce the gonadal dose by only 13 per cent, even with a prima,ry beam of the large diameter in general use at that time. Similarly, all other factors remaining unchanged, the simple change from medium-speed film to ultrafast film reduces the gonadal dose by more tha,n 90 per cent. Therefore, as Pentel and Goren reported, it is reasonable to expect that a 90 per cent reduct.ion would be noted when the factors were changed from medium-speed film and low kilovoltage to ultraspeed film and high kilovoltage. Contrary to their conclusion, however, t.he expected 90 per cent reduction is due to the change in film used rather than to the change in kilo’voltage. In 1962 Richards8 reported a, study in which his attention was directed primarily to the effect of va,rious cones (pointed, open-end, and shielded open-end) on the reduction of gonadal irradiation of dental patients. The data showed a difference between the various co’nes a.,t low kilovoltage; a simila,r difference was noted between cones at high kilo8volta,ge. The accumula,tcdl dat’a also showed that for each cone tested the dos,c to the gonads was, in fact, smaller during the 65 kilovolt exposures tha,n during the 90 kilovolt exposures. Richards and Webberg reported a st,udy designed specifically to measure the radiation received by numerous organs of the head and neck during a fourteenfilm periapical examinatio’n and during a.,bitewing examination. Their find,ings indicated that the doses wit.11 high and low kilovoltages were compa.rable, with few exceptions. The exceptions were at. the sit.es of the pituitary and other more distant glands, where the 90 kilovolt exposure resulted in a measurably higher dose bhan exposure at low kilovoltagr. This study is in agreement with essentially similar experiments reported by Bjarngard and co-workers.1” DISCUSSION
When all factors that are not relevant to the quest.ion of patient irradiation from exposure techniques using high and low kilovoltages are removed from the context of the investigation, the literature substantiates the thesis that the sum of primary and second!ary radiation is almost identical for both. This substantiation is what should be expected from a review of depth dme data in any standard textbook.
1’olume 23 Number 4
No kilovoltage
d&mma
461
It behooves the researcher, who reports, and the practitioner, who reads the reports, to evaluate what is written for validity of the study, authenticity of the ideas extracted from other authors, and integrity of the comparisons and conclusions made. Errors in any of these aSeas are misleading to the reader and may perpetuate misconceptions of importance to the normal progression of professional knowledge. For the discriminate reader such errors will tend to invalidate the remainder of the report. REFERENCES 1. Pental,
2. 3. 4. 5. 6. 7.
L., and Goren, A.: Tone Scale and Separation in Dental X-ray Emulsions, ORAL SURG., ORAL MED. & ORAL PATH. 21: 748-739, 1966. Buchholz, R. : Radiographic Interpretation of Proximal Carious Lesions, D. Radiog. & Photog. 38: 9-12, 1965. American Academy of Oral Roentgenology : The Effective Use of X-ray Radiation in Dentistry, ORAL SURG.,ORAL MED. & ORAL PATH. 16: 294-304, 1963. Wainwright, W., and Villanyi, A.: Film Speed-Greatest Single Factor in the Reduction of Radiation to Dentist and Patient, J. South. California State D. A. 26: 429-430, 1958. Richards, A. : Roentgen-Ray Doses in Dental Roentgenography, J. Am. Dent. A. 56: 351-368, 1958. Richards, A., Nelsen, R., Fitzgerald, G., Wald, S., and Spangenberger, H.: X-ray Protection in the Dental Office, J. Am. Dent. A. 56: 514-521, 1958. Wainwright, W., and Villa@, A.: Radiation Hazards-Reduction of Dental X-ray Exp;yQres to Meet the Changing Conditions of the Atomic Age, PDM, pp. l-31, January,
8. Richards,
A.: New Method for Reduction of Gonadal Irradiation of Dental Patients, J. Am. Dent. A. 65: 15-25, 1962. 9. Richards, A., and Webber, R.: Dental X-ray Expoeure of Sites Within the Head and Neck, ORAL SURG., ORAL MED. & ORAL PATH. 18: 752-756, 1964, 10. Bjarngard, B., and others: Radiation Doses in Oral Radiography. I. Measurements of Doses to Gonads and Certain Parts of Head and Neck During Full Mouth Roentgenography, Odont. revy 10: 355, 1959. II. The Influence of Technical Factors on the Dose to the Patient in Full Mouth Roentgenography, Odont. revy 11: 100, 1960.