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A comparison of radiation doses to selected vital organs in the maxillo-facial region using three different settings on the Galileos CBCT machine housed in the Wits Dental HospitalDimtchev, Dimcho Lubomirov 21 April 2015 (has links)
A research report submitted to the Faculty of Health Sciences, University of the
Witwatersrand, Johannesburg in partial fulfillment of the requirements for the degree of MSc
(Dent) / A comparison of radiation doses to selected vital organs in the maxillo-facial region at
three different settings on the Galileos cone-beam computed tomography (CBCT)
machine in the Wits Dental Hospital, was conducted with the courtesy of the Department
of Medical Physics of the Charlotte Maxeke Johannesburg Academic Hospital. The study
made use of the RANDO phantom and TLD- 100 detector chips, which provided detailed
mapping of the dose distribution from the Galileos CBCT machine. Sixty-two Sanford®
lithium fluoride dosimeters- (TLD- 100) were irradiated using a calibrated known x-ray
source after having undergone a recommended annealing cycle.
The data showed great consistency in the results. Association between the different
imaging modalities was further investigated using Kruskal-Wallis equality-of-populations
rank test and Chi-squared test. A p-value of <0.05 was considered statistically significant.
Since there do not appear to be major differences between the radiation doses for the
different settings of the Galileos CBCT machine, the author recommends the use of the
combined setting at all times for optimum image quality.
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Effective dose of radiation on the eye, thyroid and pelvic region resulting from exposures to the Galileos comfort cone beam computerized tomographic scannerPhanzu, Bwanga 21 April 2015 (has links)
Degree of Master of Science in Dentistry by coursework and dissertation
A research report submitted to the Faculty of Health Sciences, University of the Health Sciences. University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Dentistry
Johannesburg, 2014 / Introduction: Dental Cone beam CT has encountered great success in diagnostics and treatment planning in dentistry. However, it makes use of ionizing radiation. Lots of concern on the effects of x-rays on vital organs of the head and neck region has been raised. Clarity on the amount of radiation received on these specific organs will be a contribution to a better use of the emergent technology.
Aim: The aim of this study is to determine the potential dose of radiation received on the eye and thyroid and to quantify the amount of potential scatter on the gonads during CBCT examinations.
Material and Methods: Calibrated Lithium- Fluoride thermoluminescent dosimeters were inserted inside an anthropomorphic phantom, on sites of the eye, thyroid and the gonads. After its submission to a CBCT examination, using the high and standard resolution for a similar scanning protocol, the dose of radiation received on each organ was calculated according to the ICRP guidelines.
Results: An equivalent dose of 0.059 mGy was calculated for the eye. Compared to the threshold dose of 0.5 Gy fixed by the ICRP 2007, this can be considered as relatively low. The thyroid with an effective dose of 23.5 μSv represented 20% of the full body effective dose existing in literature. The gonads absorbed an effective dose of 0.05 μSv, which was considered as negligible. Conclusion: The doses calculated were considered as relatively low. However, dentists must be aware of risks of cumulative exposure. Therefore adherence to the ALARA principle and consideration of clinical indication for CBCT remain a priority.
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Comparison of MCNPX and measured doses at interfaces for photon and electron beams : a dissertation /Campos, Robin L. January 2006 (has links)
Dissertation (Ph.D.).--University of Texas Graduate School of Biomedical Sciences at San Antonio, 2006. / Vita. Includes bibliographical references.
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Radiation effects and after-effects in the clear polymethyl methacrylate dosimeterChadwick, K. H. January 1971 (has links)
Thesis--University of Utrecht. / Bibliography: p. 89-92.
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Radiation effects and after-effects in the clear polymethyl methacrylate dosimeterChadwick, K. H. January 1971 (has links)
Thesis--University of Utrecht. / Bibliography: p. 89-92.
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Measurement of absorbed dose for paediatric patients for the purpose of developing dose guidelines in paediatric radiologySwart, Gillian January 2004 (has links)
Thesis (MTech (Radiography))--Peninsula Technikon, 2004 / The radiation risks associated with children are higher than the risk for adults.
Children have growing organs and they have a longer life expectancy than that of
adults. As a consequence the effects of damage from radiation could be greater than
in adults. Children who receive radiation damage may pass genetic damage onto
future generations.
This study was carried out to investigate the optimal effective x-ray dose young
children need to receive who have radiographic examination to the chest at Tygerberg
Hospital, South Africa. Chest radiographs are documented as being the most common
radiographic examination done on children. The age groups of children participating
in this study were 0-1 year, 1-5 years and 5-10 years. A total of 67 children were
involved and the absorbed doses for 134 views of the anterior-posteria (AP) chest and
lateral chest were measured.
Entrance surface dose (ESD) values were determined, and measured mean ESD
(mGy) and the ESD range was reported for each age group. This was done by
attaching thermolurninescent dosirneters (TLD pellets) to the patients skin at the
entrance point of the x-ray beam. The results were compared to similar studies done
in Ireland and Nigeria From the ESD values obtained the absorbed doses ofthe eyes,
heart, liver, thyroid and genitals could be calculated by using the "Childdose"
programme ofthe NRPB.
The ESD dose levels for South Africa compare favourably with Ireland. However the
Nigerian values differed greatly from those of Ireland and South Africa It was very
encouraging to note the comparative results achieved at Tygerberg Hospital especially
due to the fact that this was the first time such study had been conducted in the
Tygerberg Hospital Radiology Department. The results also compare favourable with
that achieved by a group working in the United Kingdom. This group does similar
surveys every five years as part of their radiation protection programme. The results
were also in line with the UNSCEAR document of2000.
v
This study could serve as a valuable source of reference to radiographers and
radiologists when performing paediatric radiology especially as the radiation absorbed
dose could be used as a baseline to create awareness of size of dose received, and to
limit deleterious radiation doses to patients and to prevent unnecessary exposures.
A second significant outcome of the study was the effect that added filters had on the
x-ray beam generated. Experiments were done in which the filtration filters were
added sequentially. It was found that if the filtration was increased to 2mmAl the dose
to the patient decreased by more than 20%. At 50 and 60 kV the density of the x-ray
image on film only increased by 2%. From these results it may be concluded that an
increase in filtration thickness used for paediatric chest x-rays should be giVIng
reduced dose readings and assisting with radiation protection ofthe patient.
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Inverse planning in three-dimensional conformal and intensity modulated radiotherapyWu, Wing-cheung, Vincent, 胡永祥 January 2004 (has links)
published_or_final_version / Clinical Oncology / Doctoral / Doctor of Philosophy
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A survey on doctors' awareness and attitude of radiation dose of imaging examination in Hong KongKam, Chi-kong., 甘志江. January 2005 (has links)
published_or_final_version / Medical Sciences / Master / Master of Medical Sciences
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Investigation of depleted uranium migration offsite from a military ordnance range : potential concentrations and radiological dosesRynders, David G. 10 January 1997 (has links)
Graduation date: 1997
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Exposures to artificial sources of ionising radiation in Hong Kong陳木華, Chan, Mok-wah. January 1989 (has links)
published_or_final_version / Radioisotope / Master / Master of Philosophy
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