Optimisation of patient doses in programmable dental panoramic radiography

Sensitive Fibre-Based Thermoluminescence Detectors for High Resolution In-Vivo Dosimetry

With interest in the potential of optical fibres as the basis of next-generation thermoluminescence dosimeters (TLDs), the development of suitable forms of material and their fabrication has become a fast-growing endeavour. Present study focuses on three types of Ge-doped optical fibres with different structural arrangements and/or shapes, namely conventional cylindrical fibre, capillary fibre, and flat fibre, all fabricated using the same optical fibre preform. For doses from 0.5 to 8 Gy, obtained at electron and photon energies, standard thermoluminescence (TL) characteristics of the optical fibres have been the subject of detailed investigation. The results show that in collapsing the capillary fibre into a flat shape, the TL yield is increased by a factor of 5.5, the yield being also some 3.2 times greater than that of the conventional cylindrical fibre fabricated from the same perform. This suggests a means of production of suitably sensitive TLD for in-vivo dosimeter applications. Addressing the associated defects generating luminescence from each of the optical fibres, the study encompasses analysis of the TL glow curves, with computerized glow curve deconvolution (CGCD) and 2^nd order kinetics.

Efficacy of lead foil for reducing doses in the head and neck: a simulation study using digital intraoral systems

OBJECTIVES

To assess the efficacy of lead foils in reducing the radiation dose received by different anatomical sites of the head and neck during periapical intraoral examinations performed with digital systems.

METHODS

Images were acquired through four different manners: phosphor plate (PSP; VistaScan(®) system; Dürr Dental GmbH, Bissingen, Germany) alone, PSP plus lead foil, complementary metal oxide semiconductor (CMOS; DIGORA(®) Toto, Soredex(®), Tuusula, Finland) alone and CMOS plus lead foil. Radiation dose was measured after a full-mouth periapical series (14 radiographs) using the long-cone paralleling technique. Lithium fluoride (LiF 100) thermoluminescent dosemeters were placed in an anthropomorphic phantom at points corresponding to the tongue, thyroid, crystalline lenses, parotid glands and maxillary sinuses.

RESULTS

Dosemeter readings demonstrated the efficacy of the addition of lead foil in the intraoral digital X-ray systems provided in reducing organ doses in the selected structures, approximately 32% in the PSP system and 59% in the CMOS system.

CONCLUSIONS

The use of lead foils associated with digital X-ray sensors is an effective alternative for the protection of different anatomical sites of the head and neck during full-mouth periapical series acquisition.

The reduction of dose in paediatric panoramic radiography: the impact of collimator height and programme selection

OBJECTIVES

The aim of this work was to estimate the doses to radiosensitive organs in the head of a young child undergoing panoramic radiography and to establish the effectiveness of a short collimator in reducing dose.

METHODS

Thermoluminescent dosemeters were used in a paediatric head phantom to simulate an examination on a 5-year-old child. The panoramic system used was an Instrumentarium OP200 D (Instrumentarium Dental, Tuusula, Finland). The collimator height options were 110 and 140 mm. Organ doses were measured using exposure programmes intended for use with adult and child size heads. The performance of the automatic exposure control (AEC) system was also assessed.

RESULTS

The short collimator reduced the dose to the brain and the eyes by 57% and 41%, respectively. The dose to the submandibular and sublingual glands increased by 32% and 20%, respectively, when using a programme with a narrower focal trough intended for a small jaw. The effective dose measured with the short collimator and paediatric programme was 7.7 μSv. The dose to the lens of the eye was 17 μGy. When used, the AEC system produced some asymmetry in the dose distribution across the head.

CONCLUSIONS

Panoramic systems when used to frequently image children should have programmes specifically designed for imaging small heads. There should be a shorter collimator available and programmes that deliver a reduced exposure time and allow reduction of tube current. Programme selection should also provide flexibility for focal trough size, shape and position to match the smaller head size.

Effective dose from direct and indirect digital panoramic units

Purpose

This study aimed to provide comparative measurements of the effective dose from direct and indirect digital panoramic units according to phantoms and exposure parameters.

Materials and Methods

Dose measurements were carried out using a head phantom representing an average man (175 cm tall, 73.5 kg male) and a limbless whole body phantom representing an average woman (155 cm tall, 50 kg female). Lithium fluoride thermoluminescent dosimeter (TLD) chips were used for the dosimeter. Two direct and 2 indirect digital panoramic units were evaluated in this study. Effective doses were derived using 2007 International Commission on Radiological Protection (ICRP) recommendations.

Results

The effective doses of the 4 digital panoramic units ranged between 8.9 µSv and 37.8 µSv. By using the head phantom, the effective doses from the direct digital panoramic units (37.8 µSv, 27.6 µSv) were higher than those from the indirect units (8.9 µSv, 15.9 µSv). The same panoramic unit showed the difference in effective doses according to the gender of the phantom, numbers and locations of TLDs, and kVp.

Conclusion

To reasonably assess the radiation risk from various dental radiographic units, the effective doses should be obtained with the same numbers and locations of TLDs, and with standard hospital exposure. After that, it is necessary to survey the effective doses from various dental radiographic units according to the gender with the corresponding phantom.

Cone-beam computed tomography and radiographs in dentistry: aspects related to radiation dose

Introduction. The aim of this study was to discuss the radiation doses associated with plain radiographs, cone-beam computed tomography (CBCT), and conventional computed tomography (CT) in dentistry, with a special focus on orthodontics. Methods. A systematic search for articles was realized by MEDLINE from 1997–March 2011. Results. Twenty-seven articles met the established criteria. The data of these papers were grouped in a table and discussed. Conclusions. Increases in kV, mA, exposure time, and field of view (FOV) increase the radiation dose. The dose for CT is greater than other modalities. When the full-mouth series (FMX) is performed with round collimation, the orthodontic radiographs transmit higher dose than most of the large FOV CBCT, but it can be reduced if used rectangular collimation, showing lower effective dose than large FOV CBCT. Despite the image quality, the CBCT does not replace the FMX. In addition to the radiation dose, image quality and diagnostic needs should be strongly taken into account.

Absorbed and effective doses from cone beam volumetric imaging for implant planning

OBJECTIVES

Volumetric CT using a cone beam has been developed by several manufacturers for dentomaxillofacial imaging. The purpose of this study was to measure doses for implant planning with cone beam volumetric imaging (CBVI) in comparison with conventional multidetector CT (MDCT).

METHODS

The two CBVI systems used were a 3D Accuitomo (J. Morita), including an image-intensifier type (II) and a flat-panel type (FPD), and a CB MercuRay (Hitachi). The 3D Accuitomo operated at 80 kV, 5 mA and 18 s. The CB MercuRay operated at 120 kV, 15 mA, 9.8 s. The MDCT used was a HiSpeed QX/i (GE), operated at 120 kV, 100 mA and 0.7 s, and its scan length was 77 mm for both jaws. Measurement of the absorbed tissue and organ doses was performed with an Alderson phantom, embedding the radiophotoluminescence glass dosemeter into the organs/tissues. The values obtained were converted into the absorbed dose. The effective dose as defined by the International Commission on Radiological Protection was then calculated.

RESULTS

The absorbed doses of the 3D Accuitomo of the organs in the primary beam ranged from 1-5 mGy, and were several to ten times lower than other doses. The effective dose of the 3D Accuitomo ranged from 18 muSv to 66 muSv, and was an order of magnitude smaller than the others. In conclusion, these results show that the dose in the 3D Accuitomo is lower than the CB MercuRay and much less than MDCT.

Radiation doses in examination of lower third molars with computed tomography and conventional radiography

OBJECTIVES

To measure organ doses and calculate effective doses for pre-operative radiographic examination of lower third molars with CT and conventional radiography (CR).

METHODS

Measurements of organ doses were made on an anthropomorphic head phantom with lithium fluoride thermoluminescent dosemeters. The dosemeters were placed in regions corresponding to parotid and submandibular glands, mandibular bone, thyroid gland, skin, eye lenses and brain. The organ doses were used for the calculation of effective doses according to proposed International Commission on Radiological Protection 2005 guidelines. For the CT examination, a Siemens Somatom Plus 4 Volume Zoom was used and exposure factors were set to 120 kV and 100 mAs. For conventional radiographs, a Scanora unit was used and panoramic, posteroanterior, stereographic (scanogram) and conventional spiral tomographic views were exposed.

RESULTS

The effective doses were 0.25 mSv, 0.060 mSv and 0.093 mSv for CT, CR without conventional tomography and CR with conventional spiral tomography, respectively.

CONCLUSIONS

The effective dose is low when CT examination with exposure factors optimized for the examination of bone structures is performed. However, the dose is still about four times as high as for CR without tomography. CT should therefore not be a standard method for the examination of lower third molars. In cases where there is a close relationship between the tooth and the inferior alveolar nerve the advantages of true sectional imaging, such as CT, outweighs the higher effective dose and is recommended. Further reduction in the dose is feasible with further optimization of examination protocols and the development of newer techniques.

Dosimetry of digital panoramic imaging. Part I: patient exposure

OBJECTIVES

To measure patient radiation dose during panoramic exposure with various panoramic units for digital panoramic imaging.

METHODS

An anthropomorphic phantom was filled with thermoluminescent dosemeters (TLD 100) and exposed with five different digital panoramic units during ten consecutive exposures. Four machines were equipped with a direct digital CCD (charge coupled device) system, whereas one of the units used storage phosphor plates (indirect digital technique). The exposure settings recommended by the different manufacturers for the particular image and patient size were used: tube potential settings ranged between 64 kV and 74 kV, exposure times between 8.2 s and 19.0 s, at fuse current values between 4 mA and 7 mA. The effective radiation dose was calculated with inclusion of the salivary glands.

RESULTS

Effective radiation doses ranged between 4.7 microSv and 14.9 microSv for one exposure. Salivary glands absorbed the most radiation for all panoramic units. When indirect and direct digital panoramic systems were compared, the effective dose of the indirect digital unit (8.1 microSv) could be found within the range of the effective doses for the direct digital units (4.7-14.9 microSv).

CONCLUSIONS

A rather wide range of patient radiation doses can be found for digital panoramic units. There is a tendency for lower effective doses for digital compared with analogue panoramic units, reported in previous studies.

Radiation doses of collimated vs non-collimated cephalometric exposures

OBJECTIVES

The aim of the study was to compare organ and effective radiation doses for collimated and non-collimated cephalometric radiographs made by a multipurpose extraoral radiation unit.

METHODS

Cephalometric exposures were made from a Rando head phantom representing an average man with the Cranex Tome multipurpose radiation unit. A collimator was fabricated from a 3-mm thick piece of lead. The collimator was designed so that structures relevant for orthodontic diagnosis were not shielded, whereas the thyroid gland and the major part of the skull were shielded. Absorbed organ doses were measured using thermoluminescent dosimeters. The effective dose was calculated both with (E(sal)) and without (E) inclusion of the salivary glands.

RESULTS

Use of a wedge-shaped lead collimator yielded a reduction in field size of 55% and a reduction in E from 3.0 micro Sv to 1.6 micro Sv (47%) and in E(sal) from 3.7 micro Sv to 2.2 micro Sv (41%).

CONCLUSIONS

Use of a wedge-shaped collimator should be advocated in all cases where depiction of the thyroid gland and the neurocranium is not required. The resulting reduction in effective dose using our collimator was 47% (41% when the salivary glands are included), which is of clinical importance, especially in children.