| Περίληψη: | The aim of this thesis, is the measurement of secondary radiation in a conventional radiographic room, in terms of the dose rate, and the study of the influence of different radiographic exposure factors (tube voltage, tube current, distance), with the field size kept constant. This thesis can be of importance in optimizing the radiation protection of people and medical personnel, which have to be present in an X-ray room during typical radiography or fluoroscopy procedures. In addition the inclusion of X-ray filtration, as an exposure parameter for 100 kVp tube voltage, can make the presented results applicable to clinical exposure conditions, like coronary angiography, whereby, added filtration and increased tube voltage is utilized for heavy patients. Except from shielding calculations, current X-ray practices consider calculation of secondary radiation, in the proximity area to the X-ray tube, as mandatory to be necessary.
Such knowledge should be of assistance to technical staff. Such requirements of this thesis are of value during exposure of people not protected by shielding materials such as radiographers, and patients during the use of mobile X-ray units, since it has demonstrated that the choice of the tube voltage and filtration affects of the dose rate from the scatter radiation.
In the first experimental, it was found that the dose rate decrease in air is larger than 40.0%, for every half meter away from the phantom, while its angular distribution remained almost stable given the symmetry of the phantom. The added filtration of 2.0 mmAl, further reduced the scattered dose rate by 21.4%, because of the related decrease in the X-ray tube output. These results can be of value for an estimation of ambient dose rate equivalent H*(10), for various X-ray tube voltages and 2.5 s exposure time, provided the X-ray output and H*(10) is linear with respect to mA. A more detailed account regarding the measured dose rate can be observed in Table 9, where the dose rate for the X-ray tube voltages at 60, 80 and 100 kVp, with irradiation conditions of 25 mA and 2.5 s is demonstrated, for distances of 1.0, 1.5 and 2.0 m from the phantom. It is interesting to notice that at 315o at distance of 1.0 m, the dose rate increases significantly compared to the other angles. In Table 10, the corresponding results for the 100 kVp with an additional 2.0 mmAl filtration are shown. It can be observed that the dose rates are lower in respect to the 100 kVp tube voltage and the same exposure conditions. The proportionality of dose rate with mA is verified.
Dental and veterinary radiography is one of the most valuable tools used in modern dental health care. It enables the diagnosis of physical conditions that would otherwise be difficult to identify, and thus. Ιts judicious use is of considerable benefit to the patient. However, the use of dental radiological procedures must be carefully managed, because radiation has the potential for damaging cells and tissues. The aim of radiation protection in dentistry and veterinary is to obtain the desired clinical information with minimum radiation exposure to patients, dental and veterinary personnel, and the public. The most popular material for radio protection is lead, however it is known to be toxic and expensive. For these reasons it might be interest to use common building materials, such as a) single ceramic tile, b) reinforced ceramic tile, c) double reinforced ceramic tile, d) glass block, e) single plasterboard (or gypsumboard wall) and f) double plasterboard, for radiation protection especially to adjacent areas, where small thicknesses of lead may be required and the workload of the equipment is small.
In the second experimental showed that the secondary radiation and the energy spectrum are different, using different irradiation fields. It has been shown the secondary radiation and the dose rate (mSv/hr) was reduced at 16 cm x 2 cm irradiation field with respect to the 7.5 cm x 7.5 cm irradiation field. At 16 cm x 2 cm irradiation field, the secondary radiation of glass block was 100.0 μSv/hr, lower than the other materials, with a transmission of 30.0%. In the same irradiation field, double plasterboard and double reinforced in thickness ceramic tile have similar transmission 30.0%. In addition the average transmitted X-ray energy and the dose area was reduce in 16 cm x 2 cm irradiation field compared to 7.5 cm x 7.5 cm irradiation field. In both irradiation fields, the glass block at first and then, the double reinforced in thickness ceramic tile and the double plasterboard provided lower transmission (%) and better radiation protection, from any other common building material for low energies.
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