JCO Interviews Dr. Alan G. Lurie on Risk/Benefit Considerations in Orthodontic Radiology
Orthodontists are becoming increasingly aware of the hazards to the patient from x-radiation. Every practitioner has an awesome responsibility to understand the risk factors involved every time a radiograph is prescribed and taken. It is difficult to acquire information about this problem. Dr. Alan Lurie is a graduate of UCLA School of Dentistry and at present is Associate Professor of Oral Diagnosis and Oral Radiology at the University of Connecticut School of Dental Medicine. Dr. Lurie is internationally known through his publications, lectures, and community activities; and is particularly well-qualified to discuss x-radiation and how it applies to orthodontic practice.--SIDNEY BRANDT, DDS, Interviews Editor
DR. BRANDT When an orthodontist takes diagnostic x-rays, is there a health hazard potential?
DR. LURIE There is always a health hazard potential to any human being who is exposed to diagnostic or any other type of x-radiation.
DR. BRANDT What is the principal risk to orthodontic patients from such x-rays?
DR. LURIE The principal risk to patients from diagnostic x-rays is probably the induction of a malignancy, although there is an extremely low but quantifiable risk of lasting genetic damage from such an exposure.
DR. BRANDT Is the need for orthodontic diagnostic purposes a valid reason for taking x-rays?
DR. LURIE The orthodontic diagnostic need In itself is not necessarily a valid reason for taking radiographs. However, there are many specific orthodontic problems which require specialized types of radiographs in order to diagnose and treatment plan the patient adequately.
DR. BRANDT Should orthodontists routinely take full mouth, panoramic, and cephalometric radiographs on all new patients?
DR. LURIE Sid, no general dentist or dental specialist should ever routinely complete any type of x-ray examination. Radiographs should be taken when there is a clinical indication that they are needed to provide information that cannot be obtained in a less hazardous manner. Full mouth radiographs and panoramic films are redundant; and, where a full mouth series is available, a panoramic film provides little, if any, additional information, while unnecessarily exposing the patient to excess radiation.
DR. BRANDT Many orthodontists routinely take serial head films during treatment to monitor progress. Is this subjecting the patient to unnecessary risks?
DR. LURIE Follow-up films should be taken when they will contribute diagnostic information that is not obtainable in any other way, which will affect the treatment of the patient. This should not be routine.
DR. BRANDT When a panoramic x-ray is substituted for a full mouth series (usually 14 periapical films), does this reduce or increase the radiation hazard?
DR. LURIE A correct answer to this question is very difficult, because it depends on the film/screen combination used for the panoramic film and the technique used for the intraoral films. However, if optimal technique is used with beam-guiding, field-size limiting devices, high KV, and ultraspeed film, then the risk from panoramic film is greater than the risk from the full mouth series. The critical aspect of risk from panoramic x-ray is the fact that it is a poor diagnostic film, replete with artifacts and distortions; and often results in the need for further radiographs, which could have been taken to begin with without a panoramic film. In a pragmatic sense, the panoramic film almost invariably will increase the radiation hazard to the patient.
DR. BRANDT Should a panoramic film be taken under any circumstances?
DR. LURIE There are occasions when a panoramic film is in order. Examples are: for post-surgical follow-ups of patients in intermaxillary fixation, patients who are simply not able to tolerate films in their mouths, and there is some evidence that panoramic film may be useful in diagnosing a suspected mandibular fracture.
DR. BRANDT Is the risk from exposure to diagnostic x-rays the same for children and adults?
DR. LURIE The risk factor is clearly greater for children than for adults. There is a variety of reasons for this, chief among them being that the cells in a child are much more actively dividing and, thus, more sensitive to the carcinogenic actions of radiation. This is particularly true in the thyroid gland. Not only are the cells dividing at a more rapid rate, but the anatomic position of the thyroid gland in a child is higher than in an adult, placing it more in the field of the primary beam than it would be in an adult. A final reason that children are at greater risk is that they have a longer time to develop radiogenic cancers, almost all of which have long latent periods.
DR. BRANDT Is there any way of telling in advance if some children are more highly sensitized and, therefore, at greater risk? If we cannot distinguish, is it wiser to include all children as high risks?
DR. LURIE At the present time, there are no specific criteria by which children who are more sensitive to radiogenic cancer can be identified, or if there are such cases. Thus, it is prudent to assume that all children are at maximum risk, and deal with ordering and taking radiographs on them accordingly.
DR. BRANDT Is it proper to state that most humans are susceptible to cancer with any radiation, no matter how small the dose?
DR. LURIE The statement as worded is not exactly correct. I think a more accurate statement would be that, with present knowledge, it is more likely that there is a degree of risk with any
radiation exposure no matter how small, and that the question at the present time is not whether or not a risk exists, but rather how large or small is the risk at the low doses which we employ in diagnostic dental radiology.
DR. BRANDT Now let's discuss the common uses of x-rays. Approximately how many dental x-rays are taken in the United States annually?
DR. LURIE There are approximately 100,000,000 dental radiographic examinations taken in the United States each year.
DR. BRANDT How does that number relate to the total taken in medico-dental examinations?
DR. LURIE The number is slightly smaller than all medical radiographs taken annually in the United States. Chest films are the major ones in medical examinations, with abdominal and extremity films comprising the bulk of the remainder.
DR. BRANDT Is it justifiable to x-ray deciduous dentitions to determine the presence or absence of permanent teeth, their size and location, and for supernumeraries or other anomalies?
DR. LURIE These are justifiable reasons for taking radiographs, because these are generally detectable only radiographically. The literature shows that approximately one child in fifteen will present with missing, supernumerary, fused, or peg-shaped teeth. Thus, there is a very favorable risk/benefit ratio in x-ray examination for these problems.
DR. BRANDT At what age should this type of x-ray survey be performed?
DR. LURIE I would recommend one examination for such anomalies early in the mixed dentition stage, somewhere between ages 6 and 8, where early interceptive treatment might be initiated.
DR. BRANDT What films would you recommend using?
DR. LURIE The most ideal examination for the detection of dental anomalies would be four posterior periapical films taken with size 2 film to demonstrate the developing premolar teeth, and two occlusal films to demonstrate the anterior arches, including the canine regions. If these films demonstrate the presence of anomalies, further films may be indicated to clarify their anatomy and position.
DR. BRANDT Again, you do not recommend a panoramic film for this purpose?
DR. LURIE This type of examination is preferable to a panoramic film, because the exposure is significantly lower, the detail and accuracy are considerably greater; and if a panoramic film showed such anomalies, these films would have to be taken anyway, to adequately define the nature of the problem.
DR. BRANDT What is your opinion of taking full mouth surveys routinely every six months for interproximal caries detection?
DR. LURIE Sid, a full mouth series of radiographs is unnecessary for interproximal caries evaluation. This is best accomplished by visual examination in the anterior regions and by bite wing films in the posterior regions. The frequency of the bite wing examination should be determined by the caries rate of that particular individual. In patients with a high caries index, this might be required every six months, while in well-fluoridated, caries-free patients such examinations may be appropriate at from one to three year intervals.
DR. BRANDT Do you approve of radiographic examination for third molars? Is there an optimum time for it?
DR. LURIE Yes, I approve of radiographic examination for third molars, as these teeth are known to cause very significant problems to large numbers of patients. An optimum time would be once between the ages of 14 and 17. If extraction is indicated, the teeth can be removed prior to complete development of the roots. The optimal film would be third molar periapical film.
DR. BRANDT How should dental infections be examined radiographically?
DR. LURIE If the infection is localized to a tooth-bearing area, a periapical film is frequently all that is required. However, more extensive infections involving fascial planes and large areas of the maxillofacial skeleton may require much more extensive radiographic examinations, which are best done in a radiology department.
DR. BRANDT How should patients be handled radiographically who present with traumatic injuries with dental overtones?
DR. LURIE These are generally dealt with in the dental office by examining the suspected fracture area with one centered and one eccentric periapical film, to determine the presence of crown, root, or alveolar fracture, with any further views as indicated clinically. Where more extensive fractures involving the midface or mandible are suspected, much more intensive and specialized radiographic examinations are required which, again, are best handled in a hospital or a dental radiology department.
DR. BRANDT We need to know much more about dosages of radiation. What are the radiation levels usually emitted by dental x-ray machines used by most dentists and orthodontists?
DR. LURIE The best way to answer that is by giving some dosage ranges. For intraoral periapical films, the range generally encountered is from 200 to 900 millirems, with the lower dose being achieved by the use of beam-guiding, field-size limiting, paralleling instruments. The dose to which the patient is exposed in panoramic radiography runs from 1000 to 1600 millirems, with the lower dose being achieved through the use of rare earth film/screen combinations. The total dose to the patient from lateral cephalometric films ranges from 5 to 110 millirems, with the lower dose again being accomplished through the use of rare earth film/screen combinations.
DR. BRANDT What is a millirem?
DR. LURIE A millirem is a thousandth of a rem. Rem stands for "roentgen-equivalent-man", and is a way of expressing the biological damage to a human from a given exposure to any type of radiation. For the type of radiation generally employed in dentistry, rem, rad, and roentgen are different ways of expressing approximately the same amount of radiation.
DR. BRANDT Is there a correlation between extremely high doses and the incidence of cancer?
DR. LURIE There is convincing evidence for a linear relationship between exposure to moderately high and high radiation doses and cancer induction in humans, although extremely high doses will generally kill the patient from the acute radiation syndrome, rather than cancer.
DR. BRANDT What about correlation between cancer and lower doses?
DR. LURIE The correlation between radiation exposure and cancer induction at low doses is not as clear as with higher doses. However, the bulk of the evidence indicates that there is risk, and the main argument now centers on the quantification of the risk, rather than its existence.
DR. BRANDT But, doesn't the incidence of cancer decrease at very low levels?
DR. LURIE When the dosage was reduced to very low levels, the incidence of malignant transformation, not cancer, decreased as the dose decreased. But, malignant transformation has been observed at all doses, including doses as small as 1R. The phenomenon cannot really be explained as yet, although there are numerous theories as to how low levels of radiation induce transformation. This may be a Nobel Prize type answer, if it ever comes.
DR. BRANDT If malignant transformation is not cancer, what is it?
DR. LURIE Malignant transformation is a term which generally refers to alterations in structure and function of cells in culture, which correspond to similar types of changes in human and animal cancer cells in vivo.
DR. BRANDT What cellular changes have been demonstrated?
DR. LURIE The answer to this question would require a book, but just briefly, there have been changes in numerous cytoplasmic organels, mitochondrial function, lipoprotein membranes, and cell proliferation, just to name a few.
DR. BRANDT What does all this mean for an orthodontist?
DR. LURIE What it means for an orthodontist is simply what we discussed before. He should take every step to reduce the exposure to his patients by taking radiographs only when there is a clear clinical indication for them, and by using optimum technique for the films he does take.
DR. BRANDT So, you would say that there is a carcinogenic risk at any level of radiation, no matter how small the dose?
DR. LURIE Almost all of the evidence from human epidemiological studies indicates that, in fact, there is a carcinogenic risk from any exposure to radiation, no matter how small.
DR. BRANDT What percentage of man-made radiation comes from medical and dental x-rays?
DR. LURIE Almost all man-made radiation comes from medical and dental x-rays. The 1977 BEIR (Biologic Effects of Ionizing Radiation) Committee report's health benefit/cost analysis showed that man-made radiation accounts for a total body exposure of approximately 78 millirems per year per person, with approximately 73 of these being from medical and dental diagnostic radiology, 4 from weapons testing fallout, and less than 1 from occupational exposure and nuclear power generation.
DR. BRANDT Can you explain the relationship of time, exposure, and KV to the amount of radiation that patients are exposed to?
DR. LURIE The longer the exposure time, the more radiation photons hit the patient. The higher the KV, the higher the percentage of. incoming beam photons will pass through the patient and take part in producing the image on the film, while a lower percentage of the incoming beam will be absorbed in the superficial tissues. Thus, higher kilovolt peak machines, used properly, deliver a lower dose to the patient. Such machines operate most effectively in the 70-90 KV range.
DR. BRANDT What is the significance of the shape of the tube head?
DR. LURIE X-rays should not be coming off a cone. Solid pointed cones are against the law in many states, as the radiation interacts with the matter of the cone, producing secondary delta radiation which is emitted omnidirectionally, thus exposing large areas of the patient to radiation that is not in the primary beam and does not contribute to the diagnostic image. A head with an open exit for the x-ray beam--be it square, rectangular, or circular--has the radiation photons exiting off the tungsten target and moving through openings in washers and collimeters, and then out the opening, not interacting with any material, and proceeding essentially in parallel lines until they interact with the patient and/or the film.
DR. BRANDT Are the washers and collimeters you mentioned intended to limit the diameter of the beam?
DR. LURIE Yes. Any technique that reduces the size of the beam, collimates it, and/or reduces the area of the patient which is exposed to the beam, affords protection to the patient.
DR. BRANDT Alan, let's get back to the issue of cancer induction via radiation. What are the statistical estimates of how many patients have had cancer induced by exposure to x-rays?
DR. LURIE There are too many statistical estimates on cancer induction by x-ray exposures to even begin to discuss them here. Specifically for dentistry, two recent papers--one by Bengtssen (Dentomaxillary Radiation, 7:5-14, 1978) and one by Danforth and Gibbs (J. Cal. Dent. Assn., June 1980)--discussed the risk to patients from dental exposures. These studies were done with extensive computer analysis of data gathered from both the BEIR report and the UNSCEAR report, and appear to be reasonably accurate, within the limits of present day knowledge. The overall risks in the Danforth/Gibbs paper are as follows: from a full mouth series with conventional intraoral and panoramic technique (not employing beam-guiding, field-limiting devices or rare earth screens) the risk estimate predicts the induction of 6-17 cancers per million mouth examinations, and 5-14 total cancers per million for panoramic film plus two bite wing examinations.
DR. BRANDT Which organs seem to be the most vulnerable?
DR. LURIE While attention as centered for many years on leukemia as the major risk from dental radiology, more recent evidence indicates that leukemia is one of the lower risk estimates in cancer induction by dental radiology. The most sensitive organ for tumor induction in the exposure field during dental x-ray examination is the thyroid gland, followed by the salivary glands, the brain, and then leukemia.
DR. BRANDT Are there statistics to indicate how often these occur?
DR. LURIE Estimates per million examinations with full mouth series are: thyroid 4-11, salivary glands 1-3, brain 0.2-1, leukemia 0.2-0.4, and gonads immeasurably small. Estimates per million examinations with panoramic film plus two bite wings are: thyroid 3-10, salivary glands 1.3-2.6, brain 0.2-1, and leukemia 0.14-0.26.
DR. BRANDT Alan, is there a method to know specifically that x-ray radiation was the definite cause for cancer in a specific individual?
DR. LURIE No.
DR. BRANDT What are the latent periods for tumors or other types of cancer symptoms following exposure to radiation? Do they differ for a child and an adult?
DR. LURIE The latent period for radiogenic cancer is generally quite long, ranging from 20 to 35 years. The one departure from this is leukemia, which has a 5-10 year latent period. The latent period does not appreciably differ between the child and the adult, although it might be shorter in a child. However, an adult may not have enough lifetime left to allow the latent period to result in a tumor. For example, a 70-year-old patient who receives irradiation for a brain tumor may die of natural causes or the brain tumor ten years later, while a squamous cell carcinoma of the scalp, induced by the radiation, wouldn't appear until he was 105 years old.
DR. BRANDT Is the greater risk of leukemia in children due to the latent period, with the disease manifesting itself in; adulthood, or can the leukemia appear in childhood?
DR. LURIE Leukemia is a greater risk in the child because the bone marrow is proliferating more rapidly and is more sensitive to the carcinogenic effects of radiation. Leukemias are generally induced 5-10 years after the radiation exposure, regardless of the age at exposure.
DR. BRANDT Are there indications that radiation may create genetic imbalances?
DR. LURIE There is clearly genetic damage that is induced by radiation.
DR. BRANDT Is there a resistance level to the carcinogenic effect?
DR. LURIE No.
DR. BRANDT Can the patient's diet affect cancer induction by radiation?
DR. LURIE That is a very controversial point and there is no concrete answer. However, there is data in animals to indicate that hydrocarbons related to those found in cigarette smoke, ethanol, and possibly some food additives, may have their carcinogenic actions enhanced by radiation, or they may enhance the carcinogenic effect of radiation.
DR. BRANDT Are there other agents that may behave in the same way?
DR. LURIE Several agents are now thought to interact with radiation in cancer induction, including alcohol and hydrocarbons; but there is only limited epidemiologic data on humans to support this.
DR. BRANDT Are all medical and dental x-rays cumulative? Does this mean over a long period of time--10 to 20 years?
DR. LURIE Radiation damage is cumulative to a certain degree. There is repair to radiation damage in mammalian cells. Exactly how much damage is repaired, how much is misrepaired, and how much remains unrepaired, is very much open to question at the present time. There seems to be evidence that there is a certain degree of cumulative radiation damage throughout a person's life. However, extensive studies following the atomic bombings in World War II demonstrated that these effects were not as formidable as had been thought earlier. However, the possibility of subtle, nonlethal genetic changes occurring as a result of low levels of radiation has recently begun to receive more attention. Better answers to this question may be forthcoming in the next decade.
DR. BRANDT Do you have confidence that laboratory studies and experimentation will help us understand the way cancer is induced in humans via radiation?
DR. LURIE I have reasonable confidence that, if research into radiogenic cancer receives considerably more support than it does now, ultimately we will be able to obtain reasonable answers as to its mechanism of action, and thus be able to deal with radiation protection and high yield criteria in a much more intelligent manner than we do at the present time.
DR. BRANDT What do you mean by high yield criteria?
DR. LURIE I define high yield criteria as those clinical or historical findings for which radiological examinations are likely to provide confirming or clarifying information. These radiological examinations should have a high probability of affecting the diagnosis and treatment of a problem which, if left untreated, poses a potential health hazard to the patient greater than that associated with the radiographic exposure.
DR. BRANDT Isn't it difficult to relate laboratory experiments on animals to humans?
DR. LURIE It is extremely difficult to relate data from animal experiments to humans, because the responses of different mammals to radiation are quite different. As an example, the LD-50 or radiation dose required to kill half of the exposed population, is almost twice as large for Syrian hamsters as it is for rats; and hamsters and rats are clearly more related to each other than are rats and humans. Nevertheless, general qualitative information on the nature of cancer induction and potential risks may be drawn from animal experimentation and applied in principle to human radiation protection guidelines and risk estimates.
DR. BRANDT In laboratory studies, in how many different organs has cancer been induced by radiation?
DR. LURIE Cancer has been induced in almost every single organ of laboratory animals, using x-radiation.
DR. BRANDT Is the radiation used the same as that emitted by the average dental x-ray machine?
DR. LURIE Most radiation carcinogenesis studies in the laboratory have employed radiation more in the nature of therapeutic radiation--high doses, KVP's of 300 and greater, and low dose rates. Recent evidence has indicated that the lower KVP's and higher dose rates employed in diagnostic radiology may be more efficient carcinogens than those employed in x-ray therapy. The cancer induction risk from diagnostic exposures may be more significant than we presently care to admit.
DR. BRANDT Now let's discuss protection. What are some methods of reducing patient x-ray exposure?
DR. LURIE Methods of reducing patient exposure to x-ray include ultra high speed films; shielding, beam-guiding, field-limiting devices, high kilovolt peak instruments; high yield criteria applied to the ordering and taking of radiographs; thyroid shields; arid quality assurance programs to maintain optimal machine and processing performance; plus numerous others that can be used in dental offices.
DR. BRANDT Should all dentists itemize every x-ray taken and record it on charts with specific details of the KV, exposure time, etc?
DR. LURIE Ideally, this should be done by all dentists. In fact, some states are now requiring it by law. It would be of significant value in attempting to study the induction of tumors in humans by diagnostic level x-rays, and would also be of considerable help to patients in documenting their radiation exposure. While this may seem to be a rather cumbersome thing to do, we have been doing it in our department for some time now, and it has been going on in several other places. It has proven to be rather speedy, once the dose estimates have been determined for the various procedures that are done, since the technique factors are generally fairly constant.
DR. BRANDT Should it be mandatory that dentists deliver x-rays to patients, so that if they move or change dentists, some x-rays might not have to be repeated?
DR. LURIE I don't believe so. The dentist should deliver radiographs to the patient if the patient requests the films in writing when they are moving or changing dentists. At least copies should be forwarded to the patient's next dentist, so that all of the films do not have to be repeated.
DR. BRANDT For every x-ray taken, should operators ask themselves, "Is this film absolutely necessary?"
DR. LURIE The objectives should be that the film is required to help provide a diagnosis significant to the planning and execution of treatment for that patient, and that the film is expected to have the required diagnostic information on it.
DR. BRANDT Is there any point in increasing the size of the individual films, so they cover a greater area; and perhaps fewer films might be needed?
DR. LURIE For intraoral films, yes. An example might be using a size 2 film rather than a size 1 film for posterior bite wings of the early mixed dentition. By using a size 2 film, all or part of the developing permanent premolars may be seen, obviating the need for additional films to study these teeth.
DR. BRANDT Are lead shields that cover the chest and gonads enough? Should there be lead coverage of the neck area too?
DR. LURIE When ideal intraoral techniques are used, lead shields that cover the chest and gonads do not appreciably diminish the radiation dose to the areas they cover, since these areas are not in the primary beam, and are exposed mainly by scatter radiation off the patient's cervical spine. However, there is exposure to the thyroid gland from the primary beam, and a thyroid collar (quite easy to place, comfortable to the patient, commercially available, and inexpensive) significantly reduces the thyroid dose and the overall cancer risk to that patient. Chest/gonad and thyroid shields should, of course, be used for extraoral films.
DR. BRANDT Are there just too many medical and dental films taken each year?
DR. LURIE Yes. Estimates are that anywhere from 30-60% of the medical and dental films are unnecessary. Not only do these films add significantly to the population radiation burden, but they also add an enormous amount to the constantly escalating cost of medical and dental care. Generalists, specialists, and radiologists carry an equal burden of guilt in this regard.
DR. BRANDT Alan, just how many rems is the population exposed to per annum from natural and from manmade x-ray sources?
DR. LURIE The population is exposed annually to approximately 200 millirems of radiation per year, about half of the that being natural background radiation and the other half man-made.
DR. BRANDT Do you approve of auxiliary help taking x-rays? In your opinion, will they perform their tasks adequately with instruction by the dentist or orthodontist who employs them?
DR. LURIE I approve of auxiliaries taking radiographs, if they are properly trained in machine operation, the physical nature of x-rays, and optimal technique. They should be closely supervised by the practicing dentist. I'm not entirely sure that they will perform adequately, simply if they are instructed by the person they work for. It is more reasonable for these people to have a certified radiology curriculum in their training, and probably that they be licensed by the appropriate state agency as being qualified to take radiographs on people.
DR. BRANDT Can the orthodontist modify his x-ray machine to provide better protection for himself and his patients?
DR. LURIE The orthodontist can modify his machine through the use of sliding aluminum wedge filters and collimators, which can reduce the dose to patients considerably, and also improve the quality of the films. He can also reduce the dose to patients by going to faster film/screen combinations, such as rare earths. All internal machine modifications must be approved by the appropriate state radiation protection agency.
DR. BRANDT Would this be a complicated and expensive project?
DR. LURIE No, Sid, it would be neither complicated nor expensive.
DR. BRANDT Would such modifications be equally useful for all dentists?
DR. LURIE They might not be useful or possible to general practitioners who do not take films of the skull. But, they can modify their equipment by using field-limiting, beam-guiding devices, which provide anywhere from 50 to 200 or 300 percent dose reduction per film, and this an inexpensive procedure.
DR. BRANDT Government is becoming involved in x-rays. What are some of the governmental agencies that are monitoring x-ray equipment and radiation dosages?
DR. LURIE There are numerous such government agencies. It is likely that there will be a significant monitoring operation through the Environmental Protection Agency in the various states, and there are several other agencies such as the Bureau of Radiologic Health, National Council on Radiation Protection, and the Nuclear Regulatory Commission.
DR. BRANDT Are these agencies making significant contributions toward solving the problems?
DR. LURIE These agencies have avoided trying to make a significant contribution towards solving our problems, because the government has felt the profession should take the responsibility to regulate itself.
DR. BRANDT A House Committee on Oversight and Investigation recently (8-23-80) released a report in which it recommended that Congress establish standards for the accreditation of school programs to train and certify radiologists. What is your opinion of that report?
DR. LURIE I fully support the establishment of standards for accreditation of school programs for training and certifying radiological personnel.
DR. BRANDT Only eleven states and Puerto Rico have adopted licensing requirements for operators of x-ray machines. Should all states require such licenses?
DR. LURIE I feel that all states should require licensing of operators and users of x-ray equipment. This would clearly aid in the protection of the consumer, as well as in his confidence in the medical and dental personnel treating him. It should also upgrade the clinical practice of radiology in dentistry.
DR. BRANDT In 1979, the Food and Drug Administration reported that one-third of dental x-ray machines were emitting unacceptable levels of radiation because of poor operation. Was this a valid charge? Is the American Dental Association involved properly?
DR. LURIE This is a touchy question. The charge is valid, as a very large number of machines were examined. The problem can be corrected by having radiation protection personnel in a particular state examine the machine and aid in upgrading it. In some instances, it may require the purchase of a new machine, which will cost anywhere from $1500 to $5000. I cannot guess at the involvement of the ADA but, in the past 10 years, the ADA has not exactly taken an aggressive stance in upgrading radiologic training and practice within the profession.
DR. BRANDT In July 1980, a panel chaired by Dr. Jacob Fabrikant of the University of California at Berkeley issued a report that cancer risks were perhaps about one-half of recent estimates. Are you familiar with this report, and what is your comment?
DR. LURIE This panel was reconstituted, following its 1979 report, with new members, because of intense disagreement among members of the BEIR Committee on whether to use a linear or a linear quadratic model for cancer induction at low doses, to generate their risk estimates. The bulk of the original committee felt that the risk estimates of the 1972 BEIR report were essentially correct, and that the linear hypothesis was basically right; while the minority report stated that they felt that this was too conservative an estimate and that, in fact, the risks were lower. The government reconvened the new panel and this report--that cancer risks were lower--was the result. The data, recently published, is extremely controversial. I must point out that the disagreement and controversy is not over the existence of risk, but over its quantification.
DR. BRANDT Was the disagreement substantially based on which model was used--a linear or a linear quadratic--and what are these models?
DR. LURIE Linear, linear quadratic, threshold, and convex upward are four different theoretical models which describe the induction of cancer in human beings by low levels of ionizing radiation. The linear hypothesis, most often cited by national and international radiation protection committees, holds that there is a linear relationship between increasing radiation dose and increasing cancer induction, and that this line extrapolates the origin at zero; thus implying that there is no safe radiation dose. The quadratic model is a slight variant of the linear model, which allows for the repair of radiation damage by mammalian cells, and implies that lower radiation doses are less effective at cancer induction than are higher ones; but still that there is no entirely safe dose. Recent epidemiological studies are beginning to suggest that this may be the most likely model for much carcinogenesis in human beings. The threshold hypothesis holds that there is a certain radiation dose below which there is no risk of cancer induction. The convex upward model implies that lower radiation doses are more effective in inducing cancer than are higher ones.
DR. BRANDT The American Cancer Society no longer advises cancer detection tests utilizing x-rays. Do you agree with this attitude, along with eliminating large population screening for TB, breast cancers, etc?
DR. LURIE I've been on the Board of Directors of the American Cancer Society for the last six years, and was fully aware of the new guidelines dealing with x-rays in the screening of potential cancer patients. I fully agree with the new guidelines, as there never has been any indication that massive radiographic screening has provided any benefit for large asymptomatic patient populations in the detection of occult malignant disease.
DR. BRANDT Some decades ago, many children were exposed to varying doses of x-ray to control tonsils, adenoids, etc. Within the past few years, many hospitals have attempted to locate these patients to learn if any of them developed complications as a result of that radiation. Have you learned what this investigation concluded?
DR. LURIE The patients were exposed to x-radiation, as well as to implants of radioisotopes, for tonsils, ringworm, acne, and enlarged thymus glands. This group has proven to be a population that has an abnormally high incidence of thyroid cancer. Patients with a history of such radiation exposure should be followed vigorously and regularly for the presence of nodules or enlargements in their thyroids. This is particularly important, since thyroid carcinoma is a very slow progressive disease, which is quite limited in its early stages and extremely well treated surgically.
DR. BRANDT Alan, would it be safer for the public and for orthodontists if all x-rays were performed in hospitals and radiology laboratories?
DR. LURIE I doubt that it would be much safer if all x-rays were made in hospitals and radiology laboratories. The major abuse of radiology from my point of view comes not from the way films are taken, but from ordering patterns. Moving the radiographs to the hospital would not change the prescribing modes. If high yield criteria were employed, this would be the most important factor in reducing population exposure to diagnostic radiology, since it would substantially reduce the number of films taken.
DR. BRANDT You have mentioned the use of rare earth screens. Could you enlighten us about them and their use?
DR. LURIE Rare earth screens and films are coated with different materials than the classic calcium tungstate screen. These materials are much more sensitive to radiation photons and much more efficient at emitting light. Therefore, a much smaller radiation dose is required to produce a usable image. At the same time, there is a minimal degradation of image quality. Thus, a large decrease in dose is achievable through the use of these film/screen combinations.
DR. BRANDT Is the use of laminagraphy increasing? Will it, in your opinion, continue expanding in clinical use, or will it be restricted to research and teaching?
DR. LURIE Laminagraphy, or tomography, has been in use in radiology for decades, and its curved surface form (the panoramic film) is finding a constantly increasing use in dentistry. I hope that the use of panoramic radiology in dentistry will significantly decrease in the future. The use of tomography, as is done in medicine, to look at structures that otherwise would be obscured by superimposed structures, is finding increased use in examinations of the temporomandibular joints, and probably will continue to do so.
DR. BRANDT When insurance carriers require additional films to substantiate dental treatment, which may result in additional exposure of patients to radiation, how should the dentist handle this situation?
DR. LURIE The FDA, in the Federal Register, has clearly stated that third party requirements for radiographs to prove treatment is specifically contraindicated. If an insurance carrier requires this, a copy of the statement in the Federal Register should be sent to them by the dentist.
DR. BRANDT Many dentists use x-rays as "defensive dentistry": due to apprehension that later claims may be made that x-rays would have disclosed latent conditions. Is this justified?
DR. LURIE Defensive dentistry, employing radiographs as a hedge against subsequent law suits is not justified. There is no benefit to the patient whatsoever from this procedure and, thus, it constitutes an unnecessary radiation exposure. Any dentist with knowledge of the incidence of oral disease and of the radiation risks should easily be able to defend an intelligent use of x-rays in a court of law. It may be that the unnecessary taking of radiographs may be used against the dentist in court, as an indication of his inability to practice his profession rationally.
DR. BRANDT Alan, we have discussed some very serious, almost frightening issues that must be of prime concern to conscientious orthodontists. Can you sermonize a bit and give our colleagues your thoughts as to how they should use x-rays from now on?
DR. LURIE I am not going to give a long sermon. I think my views are very straightforward. There is a radiation risk to anyone who is exposed to radiation, although the quantification of this risk is unclear at this time. Therefore, it is incumbent on any practitioner to have a good clinical reason for taking any film, as dictated by the patient's history and the presenting signs and symptoms. If the radiograph is expected to yield information which is necessary for treatment planning, or treatment progress, then the film should be prescribed, employing optimal techniques and as few films as possible. However, if the film is being taken to screen for unsuspected occult disease, for insurance purposes, for teaching purposes, for patient education, these are not reasons that accrue any benefit to the patient, and the films should not be taken under such circumstances.
DR. BRANDT Alan, on behalf of our readers, permit me to thank you for your time and effort on this project. I think we have all learned vital and timely information, which will make a major contribution to the way we will treat patients.
