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.

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.

Dissertation (Ph.D.).--University of Texas Graduate School of Biomedical Sciences at San Antonio, 2006. / Vita. Includes bibliographical references.

Thesis--University of Utrecht. / Bibliography: p. 89-92.

Thesis--University of Utrecht. / Bibliography: p. 89-92.

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.

published_or_final_version / Clinical Oncology / Doctoral / Doctor of Philosophy

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

Graduation date: 1997

published_or_final_version / Radioisotope / Master / Master of Philosophy