Exposure of aircraft crew to cosmic radiation: on-board intercomparison of various dosemeters

Cone Beam Computed Tomography in Orthodontics

Orthodontists treat malocclusions by applying three-dimensional forces. For years, the diagnosis of this three-dimensional condition and the related treatment plan has been based on two-dimensional imaging. Lateral and anteroposterior cephalometric, panoramic, and periapical radiographs are some of the two-dimensional radiographs routinely used in orthodontics. Despite being highly beneficial in evaluating skeletal and dental relations, these radiographs fail to provide sufficient two-dimensional information in certain cases. The purpose of this compilation is to review the use of cone-beam computed tomography in orthodontics.

Current Products and Practice

There has been an escalating interest in three-dimensional imaging devices over the last decade. Orthodontists are beginning to appreciate the advantages that the third dimension gives to clinical diagnosis, treatment planning and patient education. This article focuses on the cutting edge technology of cone beam CT, which utilizes conventional X-ray technology and computerized volumetric reconstruction to reproduce a three-dimensional image. A variety of applications and range of issues associated with this technology will be discussed.

Facial soft tissue thickness database for craniofacial reconstruction in Korean adults

One hundred Korean adults (50 men, 50 women) were scanned in the upright position using a cone-beam CT (CBCT) scanner. The soft tissue (ST) thicknesses were measured at 31 landmarks, 10 midline and 21 bilateral landmark sites, and the means and standard deviations were obtained for male and female subjects. While 18 of 31 landmarks showed sex differences, the majority showed higher values for male subjects with the exception of a few landmark sites corresponding to the zygoma area, which showed smaller values in men than in women. The mandibular area showed greater differences between the right and left sides. Overall, the ST thickness measurements obtained in this study can be used as a database for the forensic craniofacial reconstruction of Korean adult faces.

IASON-FREE: theory and experimental comparisons

A sophisticated flight code named FREE (acronym for Flight Route Effective Dose Estimation) was built for professional commercial usage. During its creation special precautions have been taken to take correctly into account all existing dependencies and details, so that the best possible result is achieved. Some of these factors are presented in detail and their effect on doses or dose rates is estimated. Detailed comparisons to more recent measurements for both quiescent as well as disturbed conditions are presented. The agreement at undisturbed conditions turns out to be excellent and also the comparisons to measured transient effects are very satisfactory.

Aircraft crew radiation workplaces: comparison of measured and calculated ambient dose equivalent rate data using the EURADOS in-flight radiation data base

In May 2000, the chairman of the European Radiation Dosimetry Group (EURADOS) invited a number of experts with experience of cosmic radiation dosimetry to form a working group (WG 5) on aircraft crew dosimetry. Three observers from the Article 31 Group of Experts as well as one observer from the Joint Aviation Authorities (JAA) were also appointed. The European Commission funded the meetings. Full meetings were organised in January 2001 and in November 2001. An editorial group, who are the authors of this publication, started late in 2002 to finalise a draft report, which was submitted to the Article 31 Group of Experts in June 2003. The methods and data reported are the product of the work of 26 research institutes from the EU, USA and Canada. Some of the work was supported by contracts with the European Commission, Directorate General XII, Science, Research and Development. A first overview of the EC report was published late in 2004. In this publication we focus on a comparison of measured and calculated ambient dose rate data using the EURADOS In-Flight Data Base. The evaluation of results obtained by different methods and groups, and comparison of measurement results and the results of calculations were performed in terms of the operational quantity ambient dose equivalent, H*(10). Aspects of measurement uncertainty are reported also. The paper discusses the estimation of annual doses for given flight hours and gives an outline of further research needed in the field of aircraft crew dosimetry, such as the influence of solar particle events.

Estimated neutron dose to embryo and foetus during commercial flight

A study has been carried out to assess the radiation exposure from cosmic-ray neutrons to the embryo and foetus of pregnant aircrew and air travellers in consideration of the radiation exposure from cosmic-ray neutrons to the embryo and foetus. A Monte Carlo analysis was performed to determine the equivalent dose from neutrons to the brain and body of an embryo at 8 weeks and to the foetus at the 3, 6 and 9 month periods. Neutron fluence-to-absorbed dose conversion coefficients for the foetal brain and for the entire foetal body (isotropic irradiation geometry) have been determined at the four developmental stages. The equivalent dose rate to the foetus during commercial flights has been further evaluated considering the fluence-to-absorbed dose conversion coefficients, a neutron spectrum measured at an altitude of 11.3 km and an ICRP-92 radiation-weighting factor for neutrons. This study indicates that the foetus can exceed the annual dose limit of 1 mSv for the general public after, for example, 15 round trips on commercial trans-Atlantic flights.

Aircrew dosimetry by means of experimental measurements and calculations: results obtained during the year 2003

The results of measurements performed during the year 2003 onboard aircraft, mostly during regular commercial flights of the Czech Airlines (CSA) are presented. The studies were performed during more than 30 individual flights, several dosemeters and equipments were used for both neutron and non-neutron components of the onboard radiation field. CSA colleagues submitted us for all flights with navigation data necessary for the calculation of onboard aircraft crew exposure with transport codes EPCARD and CARI. Direct readings of experimental equipments were corrected on the base of the calibration in CERN high-energy radiation fields. A reasonable agreement of measured and calculated data was observed. During one of the flights, a very deep Forbush decrease occurred. The experimental results confronted with calculation permitted to obtain new view on the influence of such events on aircraft crew exposure.

Aircrew exposure monitoring: results of 2001 to 2003 studies

Aircrew exposure represents one of the recent subjects of occupational individual dosimetry. Since 1991 many new results have been found; there is however a need to gather further data on this exposure and its variation with geomagnetic position, solar activity and flight route parameters. Since 2001, many individual and six long-term monitoring programmes have been conducted onboard aircraft of Czech Airlines (CSA). In these programmes, a Si-diode spectrometer was fixed in an aircraft. Together with it, passive dosemeters thermoluminescent detector, track-etch based neutron dosemeter linear energy transfer and spectrometer) were exposed. More than 700 regular commercial flights were monitored in this manner. CSA supplied us also with full navigation data, which allowed us to calculate the exposure levels using EPCARD 3.2 and CARI6 codes. Direct experimental readings obtained with the detectors mentioned above were interpreted on the basis of calibrations in on-Earth reference fields and compared with calculated data. A satisfactory correlation between all sets of data was observed.