Paediatric absorbed doses from rotational panoramic radiography

OBJECTIVES: To determine the paediatric doses in rotational panoramic radiography with film/screen and photostimulable phosphor receptors. STUDY DESIGN: A paediatric anthropomorphic head and neck phantom was used. Absorbed doses were measured for two panoramic systems, the Orthophos (Sirona Dental Systems, Bensheim, Germany) and the PM 2002 CC (Planmeca Oy, Helsinki, Finland), with and without programmable child settings, using both screen/film and photostimulable phosphor receptors. RESULTS: Absorbed doses to the eye ranged from 5 to 24 micro Gy. Doses to the dental arches with the Orthophos unit ranged from 50 to 555 micro Gy with the adult and from 27 to 436 micro Gy with the child program; using the PM 2002 CC unit, doses ranged from 56 to 1040 micro Gy using the adult settings, and from 60 to 890 micro Gy with the paediatric settings. The paediatric exposure settings reduced doses at most locations for both panoramic systems. The highest doses were measured near the rotational axes of the X-ray beam. Paediatric settings with the Orthophos P10 resulted in the dose reduction more than 50% to the thyroid but not with the PM 2002 CC. When lower kVcp or mA settings were used, absorbed doses were effectively reduced for all combinations of machines, programs and detectors. CONCLUSIONS: Specific program settings for children reduced the absorbed doses from panoramic radiography irrespective of the machine or receptor used.     

Influence of lead apron shielding on absorbed doses from panoramic radiography

Objectives:

This study investigated the absorbed doses in a full anthropomorphic body phantom from two different panoramic radiography devices, performing protocols with and without applying a lead apron.

Methods:

A RANDO^® full body phantom (Alderson Research Laboratories Inc., Stamford, CT) was equipped with 110 thermoluminescent dosemeters at 55 different sites and set up in two different panoramic radiography devices [SCANORA^® three-dimensional (3D) (SOREDEX, Tuusula, Finland) and ProMax^® 3D (Planmeca, Helsinki, Finland)] and exposed. Two different protocols were performed in the two devices. The first protocol was performed without any lead shielding, whereas the phantom was equipped with a standard adult lead apron for the second protocol.

Results:

A two-tailed paired samples t-test for the SCANORA 3D revealed that there is no difference between the protocol using lead apron shielding (m = 87.99, s = 102.98) and the protocol without shielding (m = 87.34, s = 107.49), t(54) = −0.313, p > 0.05. The same test for the ProMax 3D showed that there is also no difference between the protocol using shielding (m = 106.48, s = 117.38) and the protocol without shielding (m = 107.75, s = 114,36), t(54) = 0.938, p > 0.05.

Conclusions:

In conclusion, the results of this study showed no statistically significant differences between a panoramic radiography with or without the use of lead apron shielding.     

Techniques for measurement of dose width product in panoramic dental radiography

Dose width product (DWP) is the quantity recommended for assessment of patient dose for panoramic dental radiography. It is the product of the absorbed dose in air in the X-ray beam integrated over an exposure cycle and the width of the beam, both measured at the receiving slit. A robust method for measuring the DWP is required in order to facilitate optimization of practices and enable comparison of dose levels at different centres. In this study, three techniques for measuring the DWP have been evaluated through comparison of results from 20 orthopantomographic units. These used a small in-beam semiconductor detector and X-ray film, a pencil ionization chamber and an array of thermoluminescent dosemeters (TLDs). The mean results obtained with the three techniques agreed within +/-6%. The technique employing a pencil ionization chamber of the type used for dose assessment of CT scanners is the simplest and most reliable method. The in-beam detector and film method has larger errors both from positioning the radiation detector and from measurement of X-ray beam width, which should be the full width at half maximum obtained from a scan of the film optical density. The TLD array method was accurate, but more time consuming to carry out. The mean DWP for the units studied was 65 mGy mm and the mean dose-area product was 89 mGy cm2. The DWP for 30% of the units tested exceeded the diagnostic reference dose of 65 mGy mm, recommended by the National Radiological Protection Board.     

Organ doses and subjective image quality of indirect digital panoramic radiography

OBJECTIVES: To determine if slight variations in exposure will affect diagnostic image quality and absorbed radiation doses for digital and analogue panoramic radiography. METHODS: Thermoluminescent dosimeters were placed in the thyroid gland, eyes, submandibular glands, parotid glands and skin of two human cadaver heads. Three different exposure settings were used: 70 kV, 120 mAs; 77 kV, 75 mAs; and 81 kV, 60 mAs. Subjective image quality was assessed using a phantom head. Storage phosphor (SP) images were printed on film and both analogue and SP images were assessed for their subjective image quality on a five-point rating scale. The results were statistically analysed using logistic regression analysis and chi(2) tests. RESULTS: Highest organ doses were measured for the submandibular glands, followed by the parotid glands. Salivary gland doses tended to be higher at lower kV settings. Image quality was not statistically different for the different exposure settings. Imaging technique did not seem to influence diagnostic image quality, except for the periapical status of upper premolars where SP was better. The main reason for any differences appeared to be interobserver variation. CONCLUSIONS: Analogue and SP panoramic radiography performed equally well for subjective diagnostic image quality. No significant differences could be found at the exposure settings used in this study. Radiation doses were highest for the salivary glands, especially at lower kV settings.     

National reference doses for dental cephalometric radiography

Objectives

Diagnostic reference levels (DRLs) are an important tool in the optimisation of clinical radiography. Although national DRLs are provided for many diagnostic procedures including dental intra-oral radiography, there are currently no national DRLs set for cephalometric radiography. In the absence of formal national DRLs, the Health Protection Agency (HPA) has previously published National Reference Doses (NRDs) covering a wide range of diagnostic X-ray examinations. The aim of this study was to determine provisional NRDs for cephalometric radiography.

Methods

Measurements made by the Dental X-ray Protection Service (DXPS) of the HPA, as part of the cephalometric X-ray equipment testing service provided to dentists and dental trade companies throughout the UK, were used to derive provisional NRDs.

Results

Dose–area product measurements were made on 42 X-ray sets. Third quartile dose–area product values for adult and child lateral cephalometric radiography were found to be 41 mGy cm² and 25 mGy cm², respectively, with individual measurements ranging from 3 mGy cm² to 108 mGy cm².

Conclusion

This report proposes provisional NRDs of 40 mGy cm² and 25 mGy cm² for adult and child lateral cephalometric radiographs, respectively; these doses could be considered by employers when establishing their local DRLs.Since the introduction of the Ionising Radiation (Medical Exposure) Regulations in 2000 (IR(ME)R 2000) [1], employers responsible for the use of dental and medical X-ray equipment have been required to establish local diagnostic reference levels (DRLs) for each common radiographic procedure undertaken. Reviews of their radiography practices are required if DRLs are consistently exceeded. In effect, a diagnostic reference level can be considered the level of dose expected not to be exceeded for a standard procedure when good and normal practice regarding diagnostic and technical performance is applied. Local DRLs should be established by the employer in consultation with the appointed medical physics expert (MPE).To assist employers to set appropriate local DRLs, the Department of Health adopted national DRLs for many common X-ray examinations [2]. National DRLs are normally set at the third quartile value of the patient dose distribution observed for a particular type of X-ray examination during a widescale survey (i.e. the patient dose value that only 25% of assessed X-ray sets exceed).The national DRLs adopted by the Department of Health were primarily based on the Health Protection Agency’s (HPA) 2000 review of the National Patient Dose Database (NPDD) [3]. However, at the time of the review, dental X-ray examinations were not included in the NPDD. Subsequently, the national DRL for dental intra-oral examinations was based on separate patient dose data published by the HPA in 1999 [4].The NPDD was designed to collate measurements of patient radiation doses from common diagnostic X-ray examinations carried out throughout the UK and to provide a major source of information for the review and adoption of new national DRLs. In July 2007, the HPA published the 2005 review of the NPDD [5]; this time, the review included dose data from dental X-ray examinations and proposed new National Reference Doses (NRDs) for intra-oral and panoramic examinations, which updated those first proposed in 1999 [4]. Although these NRDs for intra-oral and panoramic examinations have not been formally adopted by the Department of Health as national DRLs, the data collected are representative of current practice.When setting a local DRL, national DRLs and NRDs should be considered and it would be expected that the local DRL should not normally exceed the national level. However, just ensuring that patient doses are below the national DRL or NRD does not mean that local practices are being optimised. Dental surgeries using modern equipment and techniques should be able to set a local DRL significantly lower than the national level, based on their local circumstances.A national review of doses arising from dental cephalometric examinations has never been undertaken in the UK and cephalometric doses have not, to date, been included in the NPDD. For many years, however, the Dental X-ray Protection Service (DXPS) of the HPA has carried out the commissioning and routine quality assurance testing of cephalometric equipment installed throughout the UK. As part of the testing procedures, measurements are made of representative patient doses. This report proposes a patient dose measurement method together with rounded third quartile dose values for adult and child lateral cephalometric radiography based on the patient dose measurements made by DXPS.Owing to the specialist applications of cephalometric radiography, there are only a relatively small number of units in use in the UK compared with intra-oral or panoramic equipment; consequently, the sample size considered in this report is fairly small. However, the dose measurements are considered reasonably representative of UK practice so that the third quartile values can be considered as provisional NRDs and provide a useful guide to employers when establishing their local DRLs. Furthermore, it is anticipated that the patient dose data presented in this report and any data subsequently collected on cephalometric radiography doses will be included in the NPDD so that future reviews of the database can propose NRDs for cephalometric radiography.     

Cleidocranial dysplasia: radiological appearances on dental panoramic radiography.

OBJECTIVE: To report the effectiveness of dental panoramic radiography in identifying features pathognomonic for cleidocranial dysplasia. METHODS: Panoramic radiographs of nine male Caucasian patients with cleidocranial dysplasia are analysed. RESULTS: In addition to the established dental complications of failure of eruption of the permanent dentition and multiple supernumerary teeth, morphological abnormalities of the maxilla and mandible, particularly in the ascending ramus and coronoid process were present. CONCLUSION: Dental panoramic radiography is a valuable adjunct in confirming the diagnosis of cleidocranial dysplasia.     

The use of panoramic radiography in a dental accident and emergency department

OBJECTIVES: To determine the rate of appropriate requests for panoramic radiography (PR) in a Dental Accident and Emergency Department and the implications for patient dose. METHODS: Two hundred and seventy-one requests for PR during July 1998 were assessed by two dental radiologists and categorised as appropriate or inappropriate based on established selection criteria. Incidental findings that might alter patient management were also noted. RESULTS: One hundred and fifty-seven requests (58%) were considered appropriate and 114 (42%) inappropriate. The most common inappropriate request was to assess disease localised to one or two teeth. Dental students were involved in 186 requests and 76 of these (41%) were inappropriate. The estimated saving in collective radiation dose over the month of the study if appropriate radiographs had been taken, would have been approximately 540 microSv, a reduction of 70%. Three out of 114 (3%) inappropriate, PRS showed minor incidental findings. CONCLUSIONS: A considerable proportion of requests for PR were inappropriate. In most of these cases, periapical radiographs would have provided more detail with less radiation dose. The large number of inappropriate requests involving dental students has implications for educators. The use of local selection criteria based on currently accepted guidelines would have reduced the dose substantially.     

Effect of dose reduction in digital dental panoramic radiography on image quality.

OBJECTIVES: To investigate the effect of dose reduction in digital panoramic radiography on subjective image quality and diagnostic performance. METHODS: Two digital panoramic radiographs were obtained with the Orthophos DS(Sirona, Bensheim, Germany) of patients (n=100) receiving dental care. The first image was taken at the standard exposure setting. For the second image the tube current was reduced by between 48 and 53%, 63 and 69%, 75 and 80% and 80 and 81% respectively. Ten observers rated both images for 21 specific anatomical details and 30 pathological findings. RESULTS: All radiographs taken at reduced mA levels had a significantly inferior score (P<0.01) for anatomical details. There was no difference in the scores for pathological findings. CONCLUSION: Radiographs obtained at reduced mA had inferior subjective image quality, but there was no difference in diagnostic performance. Thus, a reduction in tube current of approximately 50% is recommended. In certain circumstances such as follow-up radiographic examinations, a reduction of up to 65% should be considered.     

Exposure reduction in panoramic radiography

Increased receptor speed in panoramic radiography is useful in reducing patient exposure if it doesn't substantially decrease the diagnostic quality of the resultant image. In a laboratory investigation four rare earth screen/film combinations were evaluated ranging in relative speed from 400 to 1200. The results indicated that an exposure reduction of approximately 15 percent can be achieved by substituting a 1200 speed system for a 400 speed system without significantly affecting the diagnostic quality of the image.     

Genotoxic effects of X-rays on keratinized mucosa cells during panoramic dental radiography

OBJECTIVES: The aim of this study was to evaluate the genotoxic effects of X-rays on epithelial gingival cells during panoramic dental radiography using a differentiated protocol for the micronucleus test. METHODS: 40 healthy individuals who underwent this procedure for diagnostic purposes on request from their dentists agreed to participate in this study. All of them answered a questionnaire before the examination. Epithelial gingival cells were obtained from the keratinized mucosa of the upper dental arcade by gentle scraping with a cervical brush immediately before exposure and 10 days later. Cytological preparations were stained according to the Feulgen-Rossenbeck reaction, counterstained with fast green 1% for 1 min and analysed under a light microscope. Micronuclei, nuclear projections (broken eggs) and degenerative nuclear alterations (pyknosis, karyolysis, karyorrhexis and condensed chromatin) were scored. RESULTS: The frequency of micronuclei was significantly higher after exposure (P < 0.05), as were the frequencies of nuclear alterations indicative of apoptosis (P < 0.001). CONCLUSIONS: These results indicate that X-ray radiation emitted during panoramic dental radiography induces a genotoxic effect on epithelial gingival cells that increases the frequency of chromosomal damage and nuclear alterations indicative of apoptosis.     

Object position and image magnification in dental panoramic radiography: a theoretical analysis

Objectives

The purpose of our study was to investigate how image magnification and distortion in dental panoramic radiography are influenced by object size and position for a small round object such as a ball bearing used for calibration.

Methods

Two ball bearings (2.5 mm and 6 mm in diameter) were placed at approximately the same position between the teeth of a plastic skull and radiographed 21 times. The skull was replaced each time. Their images were measured by software using edge detection and ellipse-fitting algorithms. Using a standard definition of magnification, equations were derived to enable an object''s magnification to be determined from its position and vice versa knowing the diameter and machine parameters.

Results

The average magnification of the 2.5 mm ball bearing was 1.292 (0.0445) horizontally and 1.257 (0.0067) vertically with a mean ratio of 1.028 (0.0322); standard deviations are in parentheses. The figures for the 6 mm ball bearing were 1.286 (0.0068), 1.255 (0.0018) and 1.025 (0.0061), respectively. Derived positions of each ball bearing from magnification were more consistent horizontally than vertically. There was less variation in either direction for the 6 mm ball bearing than the 2.5 mm one.

Conclusions

Automatic measurement of image size resulted in less variation in vertical magnification values than horizontal. There are only certain positions in the focal trough that achieve zero distortion. Object location can be determined from its diameter, measured magnification and machine parameters. The 6 mm diameter ball bearing is preferable to the 2.5 mm one for more reliable magnification measurement and position determination.     

Validation of dental panoramic radiography measures for identifying postmenopausal women with spinal osteoporosis

OBJECTIVE: Measurements of mandibular inferior cortical shape and width detected on dental panoramic radiographs may be a useful screening tool for spinal osteoporosis in postmenopausal women. The purposes of this study were to clarify whether these measures are validated compared with simple screening tools based on questionnaires, such as the osteoporosis self-assessment tool (OST) and whether these measures can be used in postmenopausal women with histories of hysterectomy, oophorectomy, or estrogen use. SUBJECTS AND METHODS: We calculated the diagnostic performances of panoramic measurements and the OST for identifying women with spinal osteoporosis in both 159 healthy postmenopausal and 157 postmenopausal women with histories of hysterectomy, oophorectomy, or estrogen use. Spinal osteoporosis was defined as a bone mineral density T score of -2.5 or less at the lumbar spine. Cortical shape and width were evaluated on dental panoramic radiographs. Receiver operating characteristic curve analyses were used to determine the optimal cutoff thresholds for cortical width and the OST in healthy postmenopausal women. RESULTS: The sensitivity and specificity, respectively, for identifying women with spinal osteoporosis were 89.5% and 33.9% for cortical width, 86.8% and 57.8% for the OST, and 86.8% and 63.6% for cortical shape in healthy postmenopausal women. Sensitivity and specificity, respectively, were 92.5% and 35.0% for cortical width, 72.5% and 58.1% for the OST, and 80.0% and 64.1% for cortical shape in postmenopausal women with histories of hysterectomy, oophorectomy, or estrogen use. CONCLUSION: Dentists may be able to refer postmenopausal women with suspected spinal osteoporosis for bone densitometry on the basis of dental panoramic radiographs with diagnostic performance similar to that of osteoporosis screening tools based on questionnaires.     

X射线摄影所致受检者器官剂量-入射体表剂量转换系数的研究

目的 比较简单程式化数学模型(MIRD)与体素模型在常见X射线摄影下得到的器官剂量-入射体表剂量的转换系数差异。方法 利用蒙特卡罗模拟技术,分别模拟计算体素模型的5种常见摄影下受检者的器官剂量与入射体表剂量,并计算两者的转换系数,与MIRD模型所得结果进行比较。结果 体素模型得到射野内器官的转换系数分别是,胸部后前位0.149~0.650,胸部左侧位0.067~0.382,胸部右侧位0.023~0.374,腹部前后位0.035~0.431,腰椎前后位0.083~0.432。在胸部后前位下,两种模型模拟肺的剂量转换系数结果相差最大约54.3%;胸部左侧位照射的肝脏剂量转换系数差异最大为54.5%;胸部右侧位照射胃剂量转换系数差异最大为63.8%;而腹部前后位,两种模型模拟脾脏的剂量转换系数差异最大为65.0%;腰椎前后位发现胃的剂量转换系数相差最大约43.7%。结论 利用两种模型模拟得到的器官剂量转换系数偏差可达50%以上,由于MIRD模型的解剖结构过于简化,计算误差较大。利用体素模型得到的转换系数数据更加科学合理。     

Applicability of simultaneous rotational panoramic radiography

The position of the image layer in simultaneous multilayer rotational panoramic radiography using films placed parallel in one cassette was calculated for curved and flat cassettes. Parallel films do not result in parallel layers. The use of a flat cassette results in minor shifts in layer position compared with a curved cassette. The position of the film required to produce parallel curved layers was calculated. Using curved cassettes, extraordinary modifications of the film position would be needed for the anterior region. The use of flat cassettes appears to be practically impossible. Routine use of this technique is therefore unlikely.     

Transition from screen-film to digital radiography: evolution of patient radiation doses at projection radiography

PURPOSE: To retrospectively evaluate patient radiation doses in projection radiography after the transition to computed radiography (CR) in the authors' hospital. MATERIALS AND METHODS: The hospital's ethical committee approved the study and waived informed consent. In 2001, a dose reduction initiative was implemented, which involved collecting radiographic parameters, calculating patient entrance doses, and monitoring changes with an online computer, and a training program for radiographers was conducted. A database with 204 660 patient dose values was used to compute changes in patient doses over time. Sample sizes ranged from 1800 to 23 000 examinations. Doses were compared with European and American reference values. Kruskal-Wallis and Mann-Whitney tests were used for statistical analysis. RESULTS: Median values for patient entrance doses increased 40%-103% after implementation of CR. Initial increases were corrected during the 1st year, and additional dose decreases were achieved after the dose reduction initiative was launched. At present, doses range between 15% and 38% of the European diagnostic reference levels established for screen-film radiography and between 28% and 41% of the reference values recommended by the American Association of Physicists in Medicine, representing an effective 20%-50% reduction in the initial values for CR. CONCLUSION: Though patient doses can increase considerably during the transition from conventional screen-film radiography to CR, dose management programs, including specific training of radiographers and patient dose audits, allow for reductions of the previous values.     

Quality of film-based and digital panoramic radiography

OBJECTIVES: To compare the image quality of panoramic radiographs obtained with storage phosphor plate and screen-film systems. METHODS: Panoramic radiographs were taken in 60 patients both with film and with a storage phosphor plate system (30 with DenOptix (Dentsply/Gendex) and 30 with Digora PCT). The images were obtained with either the Cranex Tome or the Scanora multimodal X-ray unit. The screen-film combination was Lanex medium/Curix Ortho HT-G. The digital images were displayed as 8-bit images with a 300 dpi resolution on a 19" monitor and the film images were placed on a light box adjacent to the screen. Ten observers evaluated diagnostic image quality by means of visual grading analysis of different anatomical structures. The structures were scored as being visualized much better (5), better (4), equal (3), worse (2) or much worse (1) in the digital images than in the film images. The mean number of patients receiving the different scores was calculated. Statistical methods used were Wilcoxon sign rank test and Mann-Whitney test. RESULTS: On average, visualization was equal in 19 of the 30 patients imaged using Digora PCT; in 10 it was worse. The corresponding values for DenOptix were 20 and 9. The difference between the film-based and the digital images was small but statistically significant (P<0.0001). The difference between the two image plate systems was not statistically significant (P>/=0.17). CONCLUSIONS: It was concluded that digital panoramic radiographs are equivalent to film-based images for most purposes.