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Effective dose from radiation absorbed during a panoramic examination with a new generation machine
Vol. 89 No. 2 February 2000
ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY ORAL AND MAXILLOFACIAL RADIOLOGY
Editor: Sharon L. Brooks
Effective dose from radiation absorbed during a panoramic examination with a new generation machine Robert A. Danforth, DDS,a and Dennis E. Clark, DDS, MS,b Los Angeles and Loma Linda, California UNIVERSITY OF SOUTHERN CALIFORNIA SCHOOL OF DENTISTRY AND LOMA LINDA UNIVERSITY SCHOOL OF DENTISTRY
Objectives. The purpose of this investigation was to measure the tissue-absorbed dose and to calculate the whole-body effective dose (E) for a new generation panoramic machine (Planmeca PM 2002 CC Proline), operating in the panoramic examination mode. Comparisons could then be made with historical panoramic and intraoral radiographic dose measurement values and effective dose estimates. Study Design. Thermoluminescent dosimeters were embedded in a humanoid, tissue-equivalent phantom at anatomically significant sites, representing key tissues. Absorbed dose measurements were obtained after every 5 panoramic exposures of a 25-exposure total. The measured average tissue-absorbed doses from a single panoramic exposure were used in the calculation of the whole-body E. Results. The whole-body E for the PM 2002 CC Proline panoramic examination is 3.85 µSv. This is below the panoramic average of 6.7 µSv. The PM 2002 CC Proline panoramic examination delivers approximately 5% to 12% of the E of a complete mouth intraoral radiographic examination. Conclusions. The effective dose from the PM 2002 CC Proline examination is at the low end of the range for other panoramic machines and is far below either a D-speed or E-speed film intraoral radiographic examination.
(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:236-43)
Paatero1,2 and Hudson et al3 developed panoramic radiography for clinical use during the 1940s and 1950s. From inception, one of the many advantages reported for panoramic radiography was a reduction of the radiation dose as a result of the use of a fluorescent intensifying screen or film combinations and machine technology.4 Some reports suggested that the panoramic dose was one tenth of that received from a complete mouth survey5 and compared favorably with a single periapical radiograph.6 In 1966, Van Aken and Van der Linden7 reported the integral absorbed dose for the conventional complete mouth series (CMS) to be 700 to 1300 gram rads and 100 gram rads for a aAssistant Professor of Clinical Dentistry, Director of Oral Radiology, Department of Oral and Maxillofacial Imaging, University of Southern California. bProfessor, Radiology Section Chief, Department of Oral Diagnosis, Radiology, and Pathology, Loma Linda University. Received for publication Oct 30, 1998; returned for revision Jan 31, 1999; accepted for publication July 30, 1999. Copyright © 2000 by Mosby, Inc. 1079-2104/2000/$12.00 + 0 7/16/103526
236
panoramic examination. Jerman et al,8 when comparing the dose from a combination of panoramic and bitewings to the traditional CMS dose, found the exposure for the panoramic bitewing combination to be an 82% smaller dose than that of the CMS. Unfortunately, many of the early dosimetry studies, which attempted to further verify these reports, were inconsistent in their methodologies, resulting in disagreement.9 Both Weissman and Longhurstl0 and Manson-Hing and Greer11 when comparing their findings with those of others, stated that these differences in methodologies made equivalent comparisons difficult and suggested increased conformity for future studies. After these suggestions were made, a series of panoramic examinations and other related dental radiographic studies were conducted, which had more comparable results.12-16 These results were used in the 1992 comparative study reported by White,17 which has become a standard reference for panoramic and intraoral radiographic examinations. White17 used the effective dose (E) to report the risk associated with both panoramic and intraoral dental
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Fig 1. Representative panoramic radiograph made of exposure phantom.
Table I. Measured tissue absorbed dose (average µGy) from a panoramic examination Proline PM 2002 CC Bone marrow
Salivary glands
C-spine
Mandible
Calvaria†
Parotid
198
311 90-170‡
0
291
Eye†
Submandibular Sublingual 183 400-700‡
104
Thyroid
Sella*
Right
Left
41 17-22‡
9
0 Not reported‡
0
*Dose
detected during 2 of 5 series only. dose detected. ‡Hayakawa et al22 data for comparison. †No
radiography. The use of E is a concept and approach recommended by the International Commission on Radiological Protection (ICRP)18 to estimate damage from radiation to an exposed population. In contrast to the early reports, which simply measured a dose value, the calculation of E takes into account not only specific site measurements but also type, quantity, sensitivity, and carcinogenic potential of the irradiated tissues. Differences in radiation energy and form, including those found in particle beams, radiations from naturally occurring sources, and those used for medical or dental procedures, are also factored in to the calculation of E. Significant innovations continue to produce faster film and screen combinations and new generations of panoramic machines that claim improved panoramic technology for imaging and further reduction of patient exposure. These claims are reminiscent of historic statements regarding dose reduction in particular. For example, Planmeca Corporation (Helsinki, Finland) states in the promotional material for their PM 2002 CC Proline unit that the use of direct current technology provides a 25% dose reduction when compared with those panoramic machines that still use alter-
nating current. In certain modes of operation, a 90% reduction in patient exposure is claimed, as compared with a CMS. This approximates the dose of a single periapical film. The purpose of this investigation was to measure the tissue-absorbed dose and to calculate the E for a newgeneration panoramic machine operating in the panoramic examination mode. Such data for the PM 2002 CC Proline were not available at the time of White’s17 report or for the other classic studies on panoramic dose. We intended for our methods to closely parallel those of Gibbs,12 Underhill,14 White,17 and the ICRP Publication 6019 so that comparisons could be made with those reports. We also intended that our findings would be included in future investigations involving panoramic effective doses.
MATERIAL AND METHODS The Planmeca PM 2002 CC Proline was selected for the measurements of tissue-absorbed dose and E during panoramic radiography. This unit is representative of the features common to the newest generation of panoramic machines. The PM 2002 CC Proline is marketed by
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Table II. Equivalent dose (µSv) per tissue or organ from a panoramic examination, Proline PM 2000 CC
Table III. E per tissue/organ from a panoramic examination (µSv) Proline PM 2000 CC
Bone marrow
Salivary glands
Thyroid
Sella*
Eye†
Tissue or organ
WT, 1990*
HT
11
237
41
9
0
Bone marrow (red) Bone surface Thyroid Remainder Total
0.12 0.01 0.05 0.05
11 50† 41 0.9‡
*Dose †No
detected during 2 of 5 series only. dose detected.
*ICRP
Planmeca as the most innovative panoramic system available. It uses a microprocessor control system and is designed to improve image quality by providing a patientpositioning light beam alignment system, an adjustable improved-image–geometry focal trough, a smaller focal spot, and a rigid film or screen cassette. In addition, different imaging options are easily accessed, and a direct current power generator is claimed to reduce patient dose approximately 25% from the traditional alternating current systems. We evaluated the operation of the unit in the panoramic mode at a constant potential frequency of 80 kHz and measured an 18-second exposure cycle, an average of 1.19 × 10–5 coulombs per kilogram at machine settings of 60 kilovolts peak (kVp) and 4 mA, and a halfvalue layer of 2.47 mm of aluminum. A humanoid tissue-equivalent dosimetry phantom (Humanoid Systems, Torrance, Calif) represented the patient for the purpose of measuring the absorbed radiation dose. The phantom consists of a human skull with complete dentition and cervical vertebrae C1 through C5 all embedded in a tissue-equivalent material molded into the shape of the human head. The phantom could be separated into 10 transverse sections for the placement of radiation dosimetry measuring devices into reservoirs, which had been prepared to correspond to the anatomic sites of interest. One hundred lithium fluoride thermoluminescent dosimeters (TLD) were supplied in 2 × 2 mm chips (Siemens Medical Systems, Inc; Dosimetry Service, Hoffman Estates, Ill) for placement within and on the phantom. The phantom was prepared for exposure by placing dosimeters in anatomic locations corresponding to bone marrow sites within the calvaria, mandible, and cervical spine; the salivary glands; upper and lower thyroid gland; pituitary fossa of sella turcica; and eyes. Multiple sites were used within each tissue area, and each site contained from 1 to 3 dosimeters as determined by space available. ICRP19 does not currently recommend the use of pituitary, eye, and salivary gland locations, but these sites were included here for the purpose of comparison with historical references, which did include them. For detection of eye exposure, dosimeters wrapped in plastic were taped to the external surface of the phantom’s eyes. An additional TLD chip was kept outside the examination room to serve as a control for background levels of radiation.
E, 1990 1.3 0.5 2.0 0.045 E = 3.85
60, 199019 bone surface dose = Bone marrow dose 11 × 4.64 (White,17 Table
†Calculated
IX). ‡Average dose to 10 remainder tissue or organs. Sella, 9 µSv.
The phantom was supported in the PM 2002 CC Proline unit on a camera tripod with the lower jaw positioned on the chin rest and secured with elastic bands to the head holder. Lines were drawn on the phantom to correspond with the light-alignment system so that similar alignment was possible for each exposure series. A panoramic radiograph was made at the beginning of each exposure series with Kodak Lanex regular screens and T-Mat G film (Eastman Kodak Co, Rochester, NY) to verify the accuracy of anatomic positioning and exposure suitability (Fig 1). The film was developed with a Konica Qx-70 medical film processor (Tokyo, Japan) at 92°F for 90 seconds. The film density in the resultant panoramic image confirmed an acceptable patient exposure setting for the remainder of the series. Five series of panoramic exposures were conducted on the humanoid phantom described earlier. A single series consisted of 5 panoramic exposures, 18 seconds each, for a total exposure time of 90 seconds. The panoramic exposures were performed by using machine settings designated for an examination of an averagesized adult. These included a 68 to 70 kV(p) and 6 to 7 mA. A total of 25 individual radiographic examinations were represented in the 5 series. After each exposure series, the dosimeters were removed from the phantom and sent to the dosimetry service for reading and a dose report. The report listed the dose in millirads absorbed by each individual dosimeter. The doses were then converted to micrograys by the authors. By using the values obtained from the 5 reports, an average absorbed dose per panoramic examination was calculated for each dosimeter location. Such calculations are site-specific and do not represent the dose absorbed by some tissues, such as the exposed bone marrow and salivary glands, which are represented by multiple anatomic locations. Calculations of absorbed dose to these tissues must take into account the weighted dose contribution from each location to properly express the average absorbed-tissue dose. For bone
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Table IV. Comparison of E values (µSv) with other panoramic radiography values reported in the literature E
Bone marrow Bone surface Thyroid Remainder tissues Total E
Planmeca (current) White17
1.3 0.5 2.0 0.045 3.85
1.4 0.6 3.8 0.3 6.1
Gibbs12
Underhill14
Panoral
OP5
Oralix
Panoura
Panoral
Oralix
Panelips
OP5
1.2 0.5 2.2 0.4 4.3
1.7 0.8 6.0 1.1 9.6
1.4 0.6 3.0 0.7 5.7
1.6 0.6 3.0 0.1 5.3
0.8 0.3 1.7 0.1 2.9
1.7 0.6 2.0 0.1 4.5
1.2 0.6 2.0 0.1 3.9
1.9 0.7 2.5 0.1 5.2
Critical organ values not measured in this study (lung, skin, esophagus) were also deleted from White,17 Gibbs,12 and Underhill14 data in constructing this table for a more direct comparison.
Table V. Comparison between effective dose (µSv) for Planmeca Proline PM 2002 CC and intraoral radiography examinations Intraoral radiographic examination 20 film CMS, D-speed film, round collimation, White17 20 film CMS, E-speed film, rectangular collimation, Goaz and White24* 20 film CMS, E-speed film, round collimation, Underhill14 4 Bitewings, E-speed film, round collimation, Underhill14 Single bitewing film, D-speed film, round collimation, 75 kVp, Velders23 *Goaz
Reported E 84 33 73.3 21 2.3
PM 2002 CC Proline E (3.85 µSv) as a percentage of intraoral procedure 5% 12% 5% 18% 167%
and White,24 Table 3-3, p. 53.
marrow, exposure to any site is expressed as a proportional effect to the whole-body bone marrow. Bone marrow site proportions in the head and neck region are calvaria, 11.8%; mandible, 1.3%; and cervical spine, 3.4%. The bone marrow dose for each site was determined by using these percentages with the method described by White and Rose.20 The salivary gland dose was calculated in a manner similar to that described by others14,21 to reflect the weighted exposure from parotid, submandibular, and sublingual gland sites. These values were used to calculate the equivalent dose (HT) with the equation HT = Σ WR × DT18, where the equivalent dose (HT) for a given tissue or organ is the product of the radiation weighting factor (WR), which for x-ray photons is 1, and the average absorbed dose (DT) measured for that specific tissue or organ. The equivalent dose (HT) compares different types of radiation effects on tissues or organs. For this study, only x-ray photon-type radiation was used, which has a WR of 1. Therefore, actual value for both absorbed and equivalent doses is the same, but the measurement unit is changed from micrograys to the equivalent unit expressed as microsieverts (µSv). E, as described in the introduction, was calculated by means of the equation E = Σ WT × HT18 and is also expressed in µSv units. E is a product of the tissue or organ equivalent dose (HT) and the tissue or organweighting factor (WT). Summation of the products for all tissues or organs exposed expresses the entire whole-body risk caused by radiation exposure.18
Tissue-weighting factors are values that represent the contribution each specific tissue or organ makes to the overall risk. Sources of these values are the ICRP Publication 26, 197718 and a more recent update, ICRP Publication 60, 1990.19
RESULTS The measured tissue-absorbed dose from a PM 2002 CC Proline panoramic examination appears in Table I. The values represent micrograys of the dose for a single panoramic exposure, obtained by dividing the total dosimeter readings (5 series, 25 exposures) by 25. For comparison, Table I also includes the absorbeddose values reported by Hayakawa et al22 for the PM 2002 CC Proline panoramic examination. Table II shows the equivalent dose in microsieverts to the exposed tissues. The whole-body effect to the bone marrow from head and neck radiation is represented by a summation of calculated dose values only for the cervical spine and mandible because the calvaria had no measurable dose. The salivary gland dose is a single value based on the average exposure to multiple glands. Dose for thyroid and sella are directly from Table I. E in microsieverts is shown in Table III. In keeping with the ICRP Publication No. 60 recommendations, the salivary gland dose was not used and the Sella dose, representing the brain in our study, was calculated as a remainder organ. The remainder category as identified by the ICRP consists of 10 organs, including the brain,
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Fig 2. Manufacturer’s diagram (Planmeca Oy). Light-shaded area represents projection of x-ray beam and exposed anatomy. Note that calvaria, eye, sella, and thyroid are outside the area of primary exposure.
believed to contribute negligible effects from radiation exposure. The remainder dose is an average of the doses received by all organs in this category. Nine of the remainder organs were assumed to have received negligible doses, because they are all located outside of the primary beam used for intraoral and panoramic radiography. The brain, represented by our Sella site, was the only organ in the remainder category that we measured because of its proximity to the field of exposure. The measured value was 9 µSv. This value was divided by the number of remainder organs (10), leaving an average remainder dose of 0.9 µSv. The resulting E to the whole body for the PM 2002 CC Proline panoramic examination is 3.85 µSv. Table IV compares E for PM 2002 CC Proline, determined by this study, with those reported by White,17 Gibbs,12 and Underhill14 for several other panoramic machines. A comparison between E for the PM 2002 CC Proline panoramic examination and that previously reported for intraoral radiographic examinations14, 17, 23, 24 is shown in Table V.
DISCUSSION Measuring dose has been one of the basic methods for comparing differences among forms of radiation and radiographic examinations and for developing associated risk estimations. How these data have been reported, interpreted, and used for risk determinations has
changed over the decades under the influence of 3 agencies: the ICRP,18,19 the Committee on the Biological Effects of Ionizing Radiations of the US National Research Council,25 and the United Nations Scientific Committee on the Effects of Atomic Radiation.26 The concept of the E is the current approach recommended by the ICRP to estimate detriment from radiation to an exposed population. White17 used this approach in 1992 when assessing the radiation risk from various dental radiographic examinations. In this study we measured the tissue-absorbed dose for a new generation panoramic machine, the PM 2002 CC Proline, when conducting a panoramic examination, and calculated E to enable comparisons with the values reported by White17 and others. Our methods for determining an E of 3.85 µSv for the Planmeca have been described in the preceding section for Tables I, II, and III. Dosimeters placed in the calvaria and eyes received no measurable dose for any of the exposure series. The sella received no measurable dose during 3 of the 5 exposure series. We believe the manufacturer’s diagram of beam vertical collimation (Fig 2) offers an explanation for these nonmeasurable results. It shows these regions to be effectively collimated from primary beam exposure. Our findings of no measurable dose for these locations support the current ICRP guideline recommendations.
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Hayakawa22 has previously reported some absorbed doses for the PM 2002 CC Proline. The inclusion of Hayakawa’s data in Table I allows comparisons to be made with our data. Despite some similarities, the number of TLDs and the anatomic locations used were notably dissimilar to the methods used either in this study or in the studies referenced by White.17 Because of these differences, we did not include these data in the additional comparisons made in other tables. When ICRP Publications No. 2618 and No. 6019 were used to obtain tissue-weighting values for Table III, differences were found between the values contained in these reports. For example, some tissues, such as salivary glands, were deleted as risk organs in the 1990 report. Other tissues, such as brain tissue, were assigned to the lesser risk “remainder” category. These deletions and changes ignore or reduce the dose contributions of these organs and therefore minimize their effect on the final determination of E. In spite of these deletions, we felt compelled to collect data for a salivary gland dose in keeping with historical patterns to allow comparisons with those earlier reports.12,14,22,23 In fact the salivary gland tissues received the highest dose of any tissue for which we gathered data. These values appear in Tables I and II for use by those who have an interest in salivary gland dose and who want to compare the current findings with historical references. However, to follow the ICRP Publication No. 60 recommendations and to make direct study comparisons in Table IV, we found it necessary to make some adjustments not only to our data, but to that in the reference study reported by White.17 The significance of White’s report is that he used dose data from 5 previous studies12-16 and summarized it to conform to current ICRP 1990 guidelines. White’s approach modified those other reports by deleting the salivary gland dose, placing brain or pituitary gland dose in the remainder category, and reporting values to other critical organs (gonads, breast, lung, skin, and esophagus) not regularly associated with dental radiography or measured by traditional methods. As a result, the average panoramic examination E of 6.7 µSv, as reported by White,17 represents all panoramic radiography and has been established by some data dating back to the 1970s. However, most of the data White used came primarily from the more recent comparable studies of Gibbs12 and Underhill.14 Data from the studies of Wall and Kendall,13 Bengstsson,15 and Antoku et al16 were included in White’s report but were incomplete, reported data collected by others or were for much earlier equipment. Therefore, we decided to limit our comparisons with White’s study to the average E for panoramic radiography and E as determined for the studies of Gibbs12 and Underhill.24 For these compar-
isons, we used the same modified approach with the exception of reporting values to other critical organs, for which we did not attempt to measure dose, in the calculation of the total E in Table III. It was the inclusion by White17 of other critical organ doses in the average E for a panoramic examination that made direct data comparisons between our studies somewhat difficult. Doses to the gonads and breasts, as reported in earlier studies,13,15 were not included in White’s average, but lung, skin, and esophagus doses did contribute. Gibbs’ study provided most of the other critical organ dose for lung, skin, and esophagus. To resolve these differences in handling the other critical organ doses, we decided to confine our comparisons to common measured values and deleted the other critical organ values from White’s and Gibbs’ data. Although the deletion the other critical organ doses would tend to underestimate E, we believe that the overall effect on our comparisons is negligible. The data of Underhill et al14 did not include any measurements of doses to other critical organs and therefore did not have to be modified for this category. This modified the average panoramic examination E to 6.1 µSv and lowered the study range of 2.9 to 9.6 µSv reported in Table IV. When we compared our resultant E of 3.85 for the PM 2002 CC Proline with modified E for other units in Table IV, we found this unit to deliver an E approximately 37% less than the modified average panoramic examination and at the low end of the modified study range. This finding is consistent with low-dose results previously reported by Hayakawa22 for the PM 2002 CC Proline. Hayakawa has offered an explanation for the lower dose, based on the rotational axes of the x-ray beam of the PM 2002 CC Proline, which are located farther apart and more posterior, relative to the mandible, than the axes of other machines. E comparisons between the PM 2002 CC Proline panoramic examination and intraoral radiographic examinations are found in Table V. The comparison between panoramic and intraoral radiographic examinations is common and has been reported in the literature for nearly as long as panoramic technology has been available.7,8,14,17 There are those who advocate the use of a panoramic examination for circumstances in which others would currently prescribe a CMS. Langlais,27 for example, states: “We now believe that when a dentist decides to take a radiograph in an asymptomatic patient, or when the physical findings suggest that a radiograph(s) should be taken, then the initial radiograph should be a panoramic view. All other radiographs should be considered supplemental views, including periapical, bitewing, occlusal, extraoral plain views, tomography including CT, and other more advanced imaging techniques such as MR.” Langlais makes this statement based
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in part on the diagnostic adequacy of panoramic radiographs produced by modern equipment. However, the more important part of his argument is that a panoramic examination delivers a reduced radiation dose, compared with intraoral radiographic examinations. White17 reports that the panoramic average E (6.7 µSv) is less than 10% of a CMS taken with D-speed film when using round collimation (84 µSv). We found the PM 2002 CC Proline examination delivers approximately 5% of the reported E associated with a D-speed, round collimation CMS, or 12% of the reported E associated with an E-speed, rectangular collimation CMS. Underhill’s14 data, modified to remove salivary gland values, yield E values of 21 and 73.3 µSv for E-speed round collimation interproximal (4 bitewings) and complete mouth (20 film) examinations, respectively. When comparing the PM 2002 CC Proline panoramic examination with Underhill’s data in this manner, the E is 18% of the bitewing and 5% of the complete mouth examination. A representative E for a single film has been reported by Velders23 to be 2.3 µSv for a single bitewing with of Dspeed film, round collimation, and 75 kVp. The E of 3.85 µSv for the PM 2002 CC Proline examination is 167% of a single bitewing. The E of 3.85 µSv for the PM 2002 CC Proline examination is approximately 95% less than that of a D-speed film CMS and supports the manufacturer’s claim of a 90% reduction in patient exposure. This is also slightly less than the E associated with 2 D-speed bitewing radiographs. Comparisons with naturally occurring background radiation are another way to express equivalent risks and are helpful when discussing radiation risks with patients. White17 has reported that the traditional 20film CMS is equivalent to 1 week of background radiation, and the 4-film bitewing series is equivalent to 1 day. For an E speed film, rectangular collimated CMS, background equivalency is 1 day and the 4-film bitewing series is 7 hours. Current average panoramic techniques are equivalent to 12 hours of background radiation. When one uses this approach, the PM 2002 CC Proline examination is equivalent to approximately 7 hours of background radiation. Such favorable dose findings for panoramic radiography raise the question of why the panoramic examination is not the survey of choice when examining patients. In fact, the question is not current. Jerman8 et al, in 1973, supported the use of a panoramic and bitewing examination as complying with a cited American Dental Association House of Delegates 1965 resolution, passed with the intent of developing devices and methods for reducing radiation exposure. Now, 3 decades later, with the development of digital imaging (including digital panoramic radiography), dentistry
may again have to reassess its view about the role of the panoramic examination. In conclusion, our findings are consistent with some of the manufacturers’ claims regarding reduced radiation dose, although we cannot prove whether the dose reduction is caused by the use of direct current technology or improved beam collimation. Our findings are also in agreement with earlier published reports and the study by White.17 We believe the Planmeca PM 2002 CC Proline examination and other similar “new generation” panoramic machines provide very low-dose radiography for dental patients. We thank Planmeca USA, Inc for their assistance in funding the expense of the dosimetry service. REFERENCES 1. Paatero YV. A new tomographical method for radiographing curved outer surfaces. Acta Radiol 1949;32:177-84. 2. Paatero YV. Pantomography and orthopantomography. Oral Surg Oral Med Oral Pathol 1961;14:947-53. 3. Hudson DC, Kumpula JW, Dickson G. A panoramic dental x-ray machine. US Armed Forces Med J. 1957;8:46-55. 4. Mitchell LD Jr. Panoramic roentgenography. J Am Dent Assoc 1963:66:777-86. 5. XRM Panorex Dental X-ray Machine [Catalogue No. 2411]. 6. Gilbert SG. Orthodontics and the panorex dental x-ray. Bull Philadelphia D Soc 1962;28:11, 14-5. 7. Van Aken J, Van der Linden L. The integral absorbed dose in conventional and panoramic complete-mouth examinations. Oral Surg Oral Med Oral Pathol 1966;22:603-16. 8. Jerman AC, Kinsley EL, Moms CR. Absorbed radiation from panoramic plus bitewing exposures vs full-mouth periapical plus bitewing exposures. J Am Dent Assoc 1973;86:420-3. 9. Kuba RK, Beck JO. Radiation dosimetry in Panorex roentgenography. III. Radiation dose measurements. Oral Surg Oral Med Oral Pathol 1968;25:393-404. 10. Weissman DD, Longhurst GE. Comparative absorbed doses in periapical radiography. II. Panorex. Oral Surg Oral Med Oral Pathol 1972:33:661-8. 11. Manson-Hing LR, Greer DF. Radiation exposure and distribution measurements for three panoramic x-ray machines. Oral Surg Oral Med Oral Pathol 1977;44:313-21. 12. Gibbs SJ, Pujol A, McDavid WD, Welander U, Tronje C. Patient risk from rotational panoramic radiography. Dentomaxillofac Radiol 1988;17:25-32. 13. Wall BF, Kendall GM. Collective doses and risks from dental radiology in Great Britain. Br J Radiol 1983;56:511-6. 14. Underhill TE, Chilvarquer I, Kimura K, Langlais RP, McDavid WD, Preece JW, et al. Radiobiological risk estimations from dental radiology. Part I. Absorbed doses to critical organs. Oral Surg Oral Med Oral Pathol 1988;66:111-20. 15. Bengstsson G. Maxillofacial aspects of radiation protection, focused on recent research regarding critical organs. Dentomaxillofac Radiol 1978;7:5-14. 16. Antoku S, Hoshi M, Russell WJ, Kihara K, Sawada S, Takeshita K, et al. Dental radiography exposure of the Hiroshima and Nagasaki populations. Oral Surg Oral Med Oral Pathol 1989;67:354-60. 17. White SC. Assessment of radiation risk from dental radiography. Dentomaxillofac Radiol 1992;21:118-26. 18. International Commission on Radiological Protection. Annals ICRP 1977. Oxford: Pergamon Press; 1977. Publication 26. 19. 1990 Recommendations of the International Commission of Radiological Protection. Annals ICRP 1990. Oxford: Pergamon Press; 1990. Publication 60. 20. White SC, Rose TC. Absorbed bone marrow dose in certain dental techniques. J Am Dent Assoc 1979;98:553-8.
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21. Clark DE, Danforth RA, Barnes RW, Burtch ML. Radiation absorbed dose from implant dental radiography: a comparison of linear tomography, CT scan, and panoramic and intraoral techniques. J Implantol 1990;16:156-64. 22. Hayakawa Y, Kobayashi N, Kousuge Y, Fujimori H, Kuroyangi K. Absorbed doses modified by exposure settings with rotational panoramic radiography. Bull Tokyo Dent Coll 1994;35:121-5. 23. Velders XL, van Aken J, van der Stelt PF. Risk assessment from bitewing radiography. Dentomaxillofac Radiol 1991;20:209-13. 24. Goaz PW, White SC. Oral radiology: principles and interpretation. 3rd ed. St Louis: Mosby; 1994. 25. National Research Council. Health effects of exposure to low levels of ionizing radiation. BEIR V. Washington (DC): National Academy Press; 1990.
26. United Nations Scientific Committee on the Effects of Atomic Radiation. Sources, effects and risks of ionizing radiation. New York: United Nations; 1988. 27. Langlais RP, Langland OE, Nortje CJ. Decision making in dental radiography. In: Langlais RP, Langland OE, Nortje CJ, editors. Diagnostic imaging of the jaws. Baltimore: Williams & Wilkins; 1995. p. 1-17. Reprint requests: Robert A. Danforth, DDS Department of Oral and Maxillofacial Imaging School of Dentistry, University of Southern California Los Angeles, CA 90089-0641
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ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY ORAL AND MAXILLOFACIAL RADIOLOGY
Editor: Sharon L. Brooks
Effective dose from radiation absorbed during a panoramic examination with a new generation machine Robert A. Danforth, DDS,a and Dennis E. Clark, DDS, MS,b Los Angeles and Loma Linda, California UNIVERSITY OF SOUTHERN CALIFORNIA SCHOOL OF DENTISTRY AND LOMA LINDA UNIVERSITY SCHOOL OF DENTISTRY
Objectives. The purpose of this investigation was to measure the tissue-absorbed dose and to calculate the whole-body effective dose (E) for a new generation panoramic machine (Planmeca PM 2002 CC Proline), operating in the panoramic examination mode. Comparisons could then be made with historical panoramic and intraoral radiographic dose measurement values and effective dose estimates. Study Design. Thermoluminescent dosimeters were embedded in a humanoid, tissue-equivalent phantom at anatomically significant sites, representing key tissues. Absorbed dose measurements were obtained after every 5 panoramic exposures of a 25-exposure total. The measured average tissue-absorbed doses from a single panoramic exposure were used in the calculation of the whole-body E. Results. The whole-body E for the PM 2002 CC Proline panoramic examination is 3.85 µSv. This is below the panoramic average of 6.7 µSv. The PM 2002 CC Proline panoramic examination delivers approximately 5% to 12% of the E of a complete mouth intraoral radiographic examination. Conclusions. The effective dose from the PM 2002 CC Proline examination is at the low end of the range for other panoramic machines and is far below either a D-speed or E-speed film intraoral radiographic examination.
(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:236-43)
Paatero1,2 and Hudson et al3 developed panoramic radiography for clinical use during the 1940s and 1950s. From inception, one of the many advantages reported for panoramic radiography was a reduction of the radiation dose as a result of the use of a fluorescent intensifying screen or film combinations and machine technology.4 Some reports suggested that the panoramic dose was one tenth of that received from a complete mouth survey5 and compared favorably with a single periapical radiograph.6 In 1966, Van Aken and Van der Linden7 reported the integral absorbed dose for the conventional complete mouth series (CMS) to be 700 to 1300 gram rads and 100 gram rads for a aAssistant Professor of Clinical Dentistry, Director of Oral Radiology, Department of Oral and Maxillofacial Imaging, University of Southern California. bProfessor, Radiology Section Chief, Department of Oral Diagnosis, Radiology, and Pathology, Loma Linda University. Received for publication Oct 30, 1998; returned for revision Jan 31, 1999; accepted for publication July 30, 1999. Copyright © 2000 by Mosby, Inc. 1079-2104/2000/$12.00 + 0 7/16/103526
236
panoramic examination. Jerman et al,8 when comparing the dose from a combination of panoramic and bitewings to the traditional CMS dose, found the exposure for the panoramic bitewing combination to be an 82% smaller dose than that of the CMS. Unfortunately, many of the early dosimetry studies, which attempted to further verify these reports, were inconsistent in their methodologies, resulting in disagreement.9 Both Weissman and Longhurstl0 and Manson-Hing and Greer11 when comparing their findings with those of others, stated that these differences in methodologies made equivalent comparisons difficult and suggested increased conformity for future studies. After these suggestions were made, a series of panoramic examinations and other related dental radiographic studies were conducted, which had more comparable results.12-16 These results were used in the 1992 comparative study reported by White,17 which has become a standard reference for panoramic and intraoral radiographic examinations. White17 used the effective dose (E) to report the risk associated with both panoramic and intraoral dental
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Fig 1. Representative panoramic radiograph made of exposure phantom.
Table I. Measured tissue absorbed dose (average µGy) from a panoramic examination Proline PM 2002 CC Bone marrow
Salivary glands
C-spine
Mandible
Calvaria†
Parotid
198
311 90-170‡
0
291
Eye†
Submandibular Sublingual 183 400-700‡
104
Thyroid
Sella*
Right
Left
41 17-22‡
9
0 Not reported‡
0
*Dose
detected during 2 of 5 series only. dose detected. ‡Hayakawa et al22 data for comparison. †No
radiography. The use of E is a concept and approach recommended by the International Commission on Radiological Protection (ICRP)18 to estimate damage from radiation to an exposed population. In contrast to the early reports, which simply measured a dose value, the calculation of E takes into account not only specific site measurements but also type, quantity, sensitivity, and carcinogenic potential of the irradiated tissues. Differences in radiation energy and form, including those found in particle beams, radiations from naturally occurring sources, and those used for medical or dental procedures, are also factored in to the calculation of E. Significant innovations continue to produce faster film and screen combinations and new generations of panoramic machines that claim improved panoramic technology for imaging and further reduction of patient exposure. These claims are reminiscent of historic statements regarding dose reduction in particular. For example, Planmeca Corporation (Helsinki, Finland) states in the promotional material for their PM 2002 CC Proline unit that the use of direct current technology provides a 25% dose reduction when compared with those panoramic machines that still use alter-
nating current. In certain modes of operation, a 90% reduction in patient exposure is claimed, as compared with a CMS. This approximates the dose of a single periapical film. The purpose of this investigation was to measure the tissue-absorbed dose and to calculate the E for a newgeneration panoramic machine operating in the panoramic examination mode. Such data for the PM 2002 CC Proline were not available at the time of White’s17 report or for the other classic studies on panoramic dose. We intended for our methods to closely parallel those of Gibbs,12 Underhill,14 White,17 and the ICRP Publication 6019 so that comparisons could be made with those reports. We also intended that our findings would be included in future investigations involving panoramic effective doses.
MATERIAL AND METHODS The Planmeca PM 2002 CC Proline was selected for the measurements of tissue-absorbed dose and E during panoramic radiography. This unit is representative of the features common to the newest generation of panoramic machines. The PM 2002 CC Proline is marketed by
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Table II. Equivalent dose (µSv) per tissue or organ from a panoramic examination, Proline PM 2000 CC
Table III. E per tissue/organ from a panoramic examination (µSv) Proline PM 2000 CC
Bone marrow
Salivary glands
Thyroid
Sella*
Eye†
Tissue or organ
WT, 1990*
HT
11
237
41
9
0
Bone marrow (red) Bone surface Thyroid Remainder Total
0.12 0.01 0.05 0.05
11 50† 41 0.9‡
*Dose †No
detected during 2 of 5 series only. dose detected.
*ICRP
Planmeca as the most innovative panoramic system available. It uses a microprocessor control system and is designed to improve image quality by providing a patientpositioning light beam alignment system, an adjustable improved-image–geometry focal trough, a smaller focal spot, and a rigid film or screen cassette. In addition, different imaging options are easily accessed, and a direct current power generator is claimed to reduce patient dose approximately 25% from the traditional alternating current systems. We evaluated the operation of the unit in the panoramic mode at a constant potential frequency of 80 kHz and measured an 18-second exposure cycle, an average of 1.19 × 10–5 coulombs per kilogram at machine settings of 60 kilovolts peak (kVp) and 4 mA, and a halfvalue layer of 2.47 mm of aluminum. A humanoid tissue-equivalent dosimetry phantom (Humanoid Systems, Torrance, Calif) represented the patient for the purpose of measuring the absorbed radiation dose. The phantom consists of a human skull with complete dentition and cervical vertebrae C1 through C5 all embedded in a tissue-equivalent material molded into the shape of the human head. The phantom could be separated into 10 transverse sections for the placement of radiation dosimetry measuring devices into reservoirs, which had been prepared to correspond to the anatomic sites of interest. One hundred lithium fluoride thermoluminescent dosimeters (TLD) were supplied in 2 × 2 mm chips (Siemens Medical Systems, Inc; Dosimetry Service, Hoffman Estates, Ill) for placement within and on the phantom. The phantom was prepared for exposure by placing dosimeters in anatomic locations corresponding to bone marrow sites within the calvaria, mandible, and cervical spine; the salivary glands; upper and lower thyroid gland; pituitary fossa of sella turcica; and eyes. Multiple sites were used within each tissue area, and each site contained from 1 to 3 dosimeters as determined by space available. ICRP19 does not currently recommend the use of pituitary, eye, and salivary gland locations, but these sites were included here for the purpose of comparison with historical references, which did include them. For detection of eye exposure, dosimeters wrapped in plastic were taped to the external surface of the phantom’s eyes. An additional TLD chip was kept outside the examination room to serve as a control for background levels of radiation.
E, 1990 1.3 0.5 2.0 0.045 E = 3.85
60, 199019 bone surface dose = Bone marrow dose 11 × 4.64 (White,17 Table
†Calculated
IX). ‡Average dose to 10 remainder tissue or organs. Sella, 9 µSv.
The phantom was supported in the PM 2002 CC Proline unit on a camera tripod with the lower jaw positioned on the chin rest and secured with elastic bands to the head holder. Lines were drawn on the phantom to correspond with the light-alignment system so that similar alignment was possible for each exposure series. A panoramic radiograph was made at the beginning of each exposure series with Kodak Lanex regular screens and T-Mat G film (Eastman Kodak Co, Rochester, NY) to verify the accuracy of anatomic positioning and exposure suitability (Fig 1). The film was developed with a Konica Qx-70 medical film processor (Tokyo, Japan) at 92°F for 90 seconds. The film density in the resultant panoramic image confirmed an acceptable patient exposure setting for the remainder of the series. Five series of panoramic exposures were conducted on the humanoid phantom described earlier. A single series consisted of 5 panoramic exposures, 18 seconds each, for a total exposure time of 90 seconds. The panoramic exposures were performed by using machine settings designated for an examination of an averagesized adult. These included a 68 to 70 kV(p) and 6 to 7 mA. A total of 25 individual radiographic examinations were represented in the 5 series. After each exposure series, the dosimeters were removed from the phantom and sent to the dosimetry service for reading and a dose report. The report listed the dose in millirads absorbed by each individual dosimeter. The doses were then converted to micrograys by the authors. By using the values obtained from the 5 reports, an average absorbed dose per panoramic examination was calculated for each dosimeter location. Such calculations are site-specific and do not represent the dose absorbed by some tissues, such as the exposed bone marrow and salivary glands, which are represented by multiple anatomic locations. Calculations of absorbed dose to these tissues must take into account the weighted dose contribution from each location to properly express the average absorbed-tissue dose. For bone
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Table IV. Comparison of E values (µSv) with other panoramic radiography values reported in the literature E
Bone marrow Bone surface Thyroid Remainder tissues Total E
Planmeca (current) White17
1.3 0.5 2.0 0.045 3.85
1.4 0.6 3.8 0.3 6.1
Gibbs12
Underhill14
Panoral
OP5
Oralix
Panoura
Panoral
Oralix
Panelips
OP5
1.2 0.5 2.2 0.4 4.3
1.7 0.8 6.0 1.1 9.6
1.4 0.6 3.0 0.7 5.7
1.6 0.6 3.0 0.1 5.3
0.8 0.3 1.7 0.1 2.9
1.7 0.6 2.0 0.1 4.5
1.2 0.6 2.0 0.1 3.9
1.9 0.7 2.5 0.1 5.2
Critical organ values not measured in this study (lung, skin, esophagus) were also deleted from White,17 Gibbs,12 and Underhill14 data in constructing this table for a more direct comparison.
Table V. Comparison between effective dose (µSv) for Planmeca Proline PM 2002 CC and intraoral radiography examinations Intraoral radiographic examination 20 film CMS, D-speed film, round collimation, White17 20 film CMS, E-speed film, rectangular collimation, Goaz and White24* 20 film CMS, E-speed film, round collimation, Underhill14 4 Bitewings, E-speed film, round collimation, Underhill14 Single bitewing film, D-speed film, round collimation, 75 kVp, Velders23 *Goaz
Reported E 84 33 73.3 21 2.3
PM 2002 CC Proline E (3.85 µSv) as a percentage of intraoral procedure 5% 12% 5% 18% 167%
and White,24 Table 3-3, p. 53.
marrow, exposure to any site is expressed as a proportional effect to the whole-body bone marrow. Bone marrow site proportions in the head and neck region are calvaria, 11.8%; mandible, 1.3%; and cervical spine, 3.4%. The bone marrow dose for each site was determined by using these percentages with the method described by White and Rose.20 The salivary gland dose was calculated in a manner similar to that described by others14,21 to reflect the weighted exposure from parotid, submandibular, and sublingual gland sites. These values were used to calculate the equivalent dose (HT) with the equation HT = Σ WR × DT18, where the equivalent dose (HT) for a given tissue or organ is the product of the radiation weighting factor (WR), which for x-ray photons is 1, and the average absorbed dose (DT) measured for that specific tissue or organ. The equivalent dose (HT) compares different types of radiation effects on tissues or organs. For this study, only x-ray photon-type radiation was used, which has a WR of 1. Therefore, actual value for both absorbed and equivalent doses is the same, but the measurement unit is changed from micrograys to the equivalent unit expressed as microsieverts (µSv). E, as described in the introduction, was calculated by means of the equation E = Σ WT × HT18 and is also expressed in µSv units. E is a product of the tissue or organ equivalent dose (HT) and the tissue or organweighting factor (WT). Summation of the products for all tissues or organs exposed expresses the entire whole-body risk caused by radiation exposure.18
Tissue-weighting factors are values that represent the contribution each specific tissue or organ makes to the overall risk. Sources of these values are the ICRP Publication 26, 197718 and a more recent update, ICRP Publication 60, 1990.19
RESULTS The measured tissue-absorbed dose from a PM 2002 CC Proline panoramic examination appears in Table I. The values represent micrograys of the dose for a single panoramic exposure, obtained by dividing the total dosimeter readings (5 series, 25 exposures) by 25. For comparison, Table I also includes the absorbeddose values reported by Hayakawa et al22 for the PM 2002 CC Proline panoramic examination. Table II shows the equivalent dose in microsieverts to the exposed tissues. The whole-body effect to the bone marrow from head and neck radiation is represented by a summation of calculated dose values only for the cervical spine and mandible because the calvaria had no measurable dose. The salivary gland dose is a single value based on the average exposure to multiple glands. Dose for thyroid and sella are directly from Table I. E in microsieverts is shown in Table III. In keeping with the ICRP Publication No. 60 recommendations, the salivary gland dose was not used and the Sella dose, representing the brain in our study, was calculated as a remainder organ. The remainder category as identified by the ICRP consists of 10 organs, including the brain,
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Fig 2. Manufacturer’s diagram (Planmeca Oy). Light-shaded area represents projection of x-ray beam and exposed anatomy. Note that calvaria, eye, sella, and thyroid are outside the area of primary exposure.
believed to contribute negligible effects from radiation exposure. The remainder dose is an average of the doses received by all organs in this category. Nine of the remainder organs were assumed to have received negligible doses, because they are all located outside of the primary beam used for intraoral and panoramic radiography. The brain, represented by our Sella site, was the only organ in the remainder category that we measured because of its proximity to the field of exposure. The measured value was 9 µSv. This value was divided by the number of remainder organs (10), leaving an average remainder dose of 0.9 µSv. The resulting E to the whole body for the PM 2002 CC Proline panoramic examination is 3.85 µSv. Table IV compares E for PM 2002 CC Proline, determined by this study, with those reported by White,17 Gibbs,12 and Underhill14 for several other panoramic machines. A comparison between E for the PM 2002 CC Proline panoramic examination and that previously reported for intraoral radiographic examinations14, 17, 23, 24 is shown in Table V.
DISCUSSION Measuring dose has been one of the basic methods for comparing differences among forms of radiation and radiographic examinations and for developing associated risk estimations. How these data have been reported, interpreted, and used for risk determinations has
changed over the decades under the influence of 3 agencies: the ICRP,18,19 the Committee on the Biological Effects of Ionizing Radiations of the US National Research Council,25 and the United Nations Scientific Committee on the Effects of Atomic Radiation.26 The concept of the E is the current approach recommended by the ICRP to estimate detriment from radiation to an exposed population. White17 used this approach in 1992 when assessing the radiation risk from various dental radiographic examinations. In this study we measured the tissue-absorbed dose for a new generation panoramic machine, the PM 2002 CC Proline, when conducting a panoramic examination, and calculated E to enable comparisons with the values reported by White17 and others. Our methods for determining an E of 3.85 µSv for the Planmeca have been described in the preceding section for Tables I, II, and III. Dosimeters placed in the calvaria and eyes received no measurable dose for any of the exposure series. The sella received no measurable dose during 3 of the 5 exposure series. We believe the manufacturer’s diagram of beam vertical collimation (Fig 2) offers an explanation for these nonmeasurable results. It shows these regions to be effectively collimated from primary beam exposure. Our findings of no measurable dose for these locations support the current ICRP guideline recommendations.
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Hayakawa22 has previously reported some absorbed doses for the PM 2002 CC Proline. The inclusion of Hayakawa’s data in Table I allows comparisons to be made with our data. Despite some similarities, the number of TLDs and the anatomic locations used were notably dissimilar to the methods used either in this study or in the studies referenced by White.17 Because of these differences, we did not include these data in the additional comparisons made in other tables. When ICRP Publications No. 2618 and No. 6019 were used to obtain tissue-weighting values for Table III, differences were found between the values contained in these reports. For example, some tissues, such as salivary glands, were deleted as risk organs in the 1990 report. Other tissues, such as brain tissue, were assigned to the lesser risk “remainder” category. These deletions and changes ignore or reduce the dose contributions of these organs and therefore minimize their effect on the final determination of E. In spite of these deletions, we felt compelled to collect data for a salivary gland dose in keeping with historical patterns to allow comparisons with those earlier reports.12,14,22,23 In fact the salivary gland tissues received the highest dose of any tissue for which we gathered data. These values appear in Tables I and II for use by those who have an interest in salivary gland dose and who want to compare the current findings with historical references. However, to follow the ICRP Publication No. 60 recommendations and to make direct study comparisons in Table IV, we found it necessary to make some adjustments not only to our data, but to that in the reference study reported by White.17 The significance of White’s report is that he used dose data from 5 previous studies12-16 and summarized it to conform to current ICRP 1990 guidelines. White’s approach modified those other reports by deleting the salivary gland dose, placing brain or pituitary gland dose in the remainder category, and reporting values to other critical organs (gonads, breast, lung, skin, and esophagus) not regularly associated with dental radiography or measured by traditional methods. As a result, the average panoramic examination E of 6.7 µSv, as reported by White,17 represents all panoramic radiography and has been established by some data dating back to the 1970s. However, most of the data White used came primarily from the more recent comparable studies of Gibbs12 and Underhill.14 Data from the studies of Wall and Kendall,13 Bengstsson,15 and Antoku et al16 were included in White’s report but were incomplete, reported data collected by others or were for much earlier equipment. Therefore, we decided to limit our comparisons with White’s study to the average E for panoramic radiography and E as determined for the studies of Gibbs12 and Underhill.24 For these compar-
isons, we used the same modified approach with the exception of reporting values to other critical organs, for which we did not attempt to measure dose, in the calculation of the total E in Table III. It was the inclusion by White17 of other critical organ doses in the average E for a panoramic examination that made direct data comparisons between our studies somewhat difficult. Doses to the gonads and breasts, as reported in earlier studies,13,15 were not included in White’s average, but lung, skin, and esophagus doses did contribute. Gibbs’ study provided most of the other critical organ dose for lung, skin, and esophagus. To resolve these differences in handling the other critical organ doses, we decided to confine our comparisons to common measured values and deleted the other critical organ values from White’s and Gibbs’ data. Although the deletion the other critical organ doses would tend to underestimate E, we believe that the overall effect on our comparisons is negligible. The data of Underhill et al14 did not include any measurements of doses to other critical organs and therefore did not have to be modified for this category. This modified the average panoramic examination E to 6.1 µSv and lowered the study range of 2.9 to 9.6 µSv reported in Table IV. When we compared our resultant E of 3.85 for the PM 2002 CC Proline with modified E for other units in Table IV, we found this unit to deliver an E approximately 37% less than the modified average panoramic examination and at the low end of the modified study range. This finding is consistent with low-dose results previously reported by Hayakawa22 for the PM 2002 CC Proline. Hayakawa has offered an explanation for the lower dose, based on the rotational axes of the x-ray beam of the PM 2002 CC Proline, which are located farther apart and more posterior, relative to the mandible, than the axes of other machines. E comparisons between the PM 2002 CC Proline panoramic examination and intraoral radiographic examinations are found in Table V. The comparison between panoramic and intraoral radiographic examinations is common and has been reported in the literature for nearly as long as panoramic technology has been available.7,8,14,17 There are those who advocate the use of a panoramic examination for circumstances in which others would currently prescribe a CMS. Langlais,27 for example, states: “We now believe that when a dentist decides to take a radiograph in an asymptomatic patient, or when the physical findings suggest that a radiograph(s) should be taken, then the initial radiograph should be a panoramic view. All other radiographs should be considered supplemental views, including periapical, bitewing, occlusal, extraoral plain views, tomography including CT, and other more advanced imaging techniques such as MR.” Langlais makes this statement based
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in part on the diagnostic adequacy of panoramic radiographs produced by modern equipment. However, the more important part of his argument is that a panoramic examination delivers a reduced radiation dose, compared with intraoral radiographic examinations. White17 reports that the panoramic average E (6.7 µSv) is less than 10% of a CMS taken with D-speed film when using round collimation (84 µSv). We found the PM 2002 CC Proline examination delivers approximately 5% of the reported E associated with a D-speed, round collimation CMS, or 12% of the reported E associated with an E-speed, rectangular collimation CMS. Underhill’s14 data, modified to remove salivary gland values, yield E values of 21 and 73.3 µSv for E-speed round collimation interproximal (4 bitewings) and complete mouth (20 film) examinations, respectively. When comparing the PM 2002 CC Proline panoramic examination with Underhill’s data in this manner, the E is 18% of the bitewing and 5% of the complete mouth examination. A representative E for a single film has been reported by Velders23 to be 2.3 µSv for a single bitewing with of Dspeed film, round collimation, and 75 kVp. The E of 3.85 µSv for the PM 2002 CC Proline examination is 167% of a single bitewing. The E of 3.85 µSv for the PM 2002 CC Proline examination is approximately 95% less than that of a D-speed film CMS and supports the manufacturer’s claim of a 90% reduction in patient exposure. This is also slightly less than the E associated with 2 D-speed bitewing radiographs. Comparisons with naturally occurring background radiation are another way to express equivalent risks and are helpful when discussing radiation risks with patients. White17 has reported that the traditional 20film CMS is equivalent to 1 week of background radiation, and the 4-film bitewing series is equivalent to 1 day. For an E speed film, rectangular collimated CMS, background equivalency is 1 day and the 4-film bitewing series is 7 hours. Current average panoramic techniques are equivalent to 12 hours of background radiation. When one uses this approach, the PM 2002 CC Proline examination is equivalent to approximately 7 hours of background radiation. Such favorable dose findings for panoramic radiography raise the question of why the panoramic examination is not the survey of choice when examining patients. In fact, the question is not current. Jerman8 et al, in 1973, supported the use of a panoramic and bitewing examination as complying with a cited American Dental Association House of Delegates 1965 resolution, passed with the intent of developing devices and methods for reducing radiation exposure. Now, 3 decades later, with the development of digital imaging (including digital panoramic radiography), dentistry
may again have to reassess its view about the role of the panoramic examination. In conclusion, our findings are consistent with some of the manufacturers’ claims regarding reduced radiation dose, although we cannot prove whether the dose reduction is caused by the use of direct current technology or improved beam collimation. Our findings are also in agreement with earlier published reports and the study by White.17 We believe the Planmeca PM 2002 CC Proline examination and other similar “new generation” panoramic machines provide very low-dose radiography for dental patients. We thank Planmeca USA, Inc for their assistance in funding the expense of the dosimetry service. REFERENCES 1. Paatero YV. A new tomographical method for radiographing curved outer surfaces. Acta Radiol 1949;32:177-84. 2. Paatero YV. Pantomography and orthopantomography. Oral Surg Oral Med Oral Pathol 1961;14:947-53. 3. Hudson DC, Kumpula JW, Dickson G. A panoramic dental x-ray machine. US Armed Forces Med J. 1957;8:46-55. 4. Mitchell LD Jr. Panoramic roentgenography. J Am Dent Assoc 1963:66:777-86. 5. XRM Panorex Dental X-ray Machine [Catalogue No. 2411]. 6. Gilbert SG. Orthodontics and the panorex dental x-ray. Bull Philadelphia D Soc 1962;28:11, 14-5. 7. Van Aken J, Van der Linden L. The integral absorbed dose in conventional and panoramic complete-mouth examinations. Oral Surg Oral Med Oral Pathol 1966;22:603-16. 8. Jerman AC, Kinsley EL, Moms CR. Absorbed radiation from panoramic plus bitewing exposures vs full-mouth periapical plus bitewing exposures. J Am Dent Assoc 1973;86:420-3. 9. Kuba RK, Beck JO. Radiation dosimetry in Panorex roentgenography. III. Radiation dose measurements. Oral Surg Oral Med Oral Pathol 1968;25:393-404. 10. Weissman DD, Longhurst GE. Comparative absorbed doses in periapical radiography. II. Panorex. Oral Surg Oral Med Oral Pathol 1972:33:661-8. 11. Manson-Hing LR, Greer DF. Radiation exposure and distribution measurements for three panoramic x-ray machines. Oral Surg Oral Med Oral Pathol 1977;44:313-21. 12. Gibbs SJ, Pujol A, McDavid WD, Welander U, Tronje C. Patient risk from rotational panoramic radiography. Dentomaxillofac Radiol 1988;17:25-32. 13. Wall BF, Kendall GM. Collective doses and risks from dental radiology in Great Britain. Br J Radiol 1983;56:511-6. 14. Underhill TE, Chilvarquer I, Kimura K, Langlais RP, McDavid WD, Preece JW, et al. Radiobiological risk estimations from dental radiology. Part I. Absorbed doses to critical organs. Oral Surg Oral Med Oral Pathol 1988;66:111-20. 15. Bengstsson G. Maxillofacial aspects of radiation protection, focused on recent research regarding critical organs. Dentomaxillofac Radiol 1978;7:5-14. 16. Antoku S, Hoshi M, Russell WJ, Kihara K, Sawada S, Takeshita K, et al. Dental radiography exposure of the Hiroshima and Nagasaki populations. Oral Surg Oral Med Oral Pathol 1989;67:354-60. 17. White SC. Assessment of radiation risk from dental radiography. Dentomaxillofac Radiol 1992;21:118-26. 18. International Commission on Radiological Protection. Annals ICRP 1977. Oxford: Pergamon Press; 1977. Publication 26. 19. 1990 Recommendations of the International Commission of Radiological Protection. Annals ICRP 1990. Oxford: Pergamon Press; 1990. Publication 60. 20. White SC, Rose TC. Absorbed bone marrow dose in certain dental techniques. J Am Dent Assoc 1979;98:553-8.
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21. Clark DE, Danforth RA, Barnes RW, Burtch ML. Radiation absorbed dose from implant dental radiography: a comparison of linear tomography, CT scan, and panoramic and intraoral techniques. J Implantol 1990;16:156-64. 22. Hayakawa Y, Kobayashi N, Kousuge Y, Fujimori H, Kuroyangi K. Absorbed doses modified by exposure settings with rotational panoramic radiography. Bull Tokyo Dent Coll 1994;35:121-5. 23. Velders XL, van Aken J, van der Stelt PF. Risk assessment from bitewing radiography. Dentomaxillofac Radiol 1991;20:209-13. 24. Goaz PW, White SC. Oral radiology: principles and interpretation. 3rd ed. St Louis: Mosby; 1994. 25. National Research Council. Health effects of exposure to low levels of ionizing radiation. BEIR V. Washington (DC): National Academy Press; 1990.
26. United Nations Scientific Committee on the Effects of Atomic Radiation. Sources, effects and risks of ionizing radiation. New York: United Nations; 1988. 27. Langlais RP, Langland OE, Nortje CJ. Decision making in dental radiography. In: Langlais RP, Langland OE, Nortje CJ, editors. Diagnostic imaging of the jaws. Baltimore: Williams & Wilkins; 1995. p. 1-17. Reprint requests: Robert A. Danforth, DDS Department of Oral and Maxillofacial Imaging School of Dentistry, University of Southern California Los Angeles, CA 90089-0641
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