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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

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 Hospital

Dimtchev, 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.

Effective dose of radiation on the eye, thyroid and pelvic region resulting from exposures to the Galileos comfort cone beam computerized tomographic scanner

Phanzu, 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.

Determination and use of radiobiological response parameters in radiation therapy optimization /

Mavroidis, Panayiotis, January 1900 (has links)
Diss. (sammanfattning) Stockholm : Karolinska institutet, 2001. / Härtill 7 uppsatser.

ESR dosimetry in the radiation therapy dose range : development of dosimetry systems and sensitive dosimeter materials /

Olsson, Sara, January 2001 (has links) (PDF)
Diss. (sammanfattning) Linköping : Univ., 2001. / Härtill 5 uppsatser.

Accurate description of heterogeneous tumors for biologically optimized radiation therapy /

Nilsson, Johan, January 2004 (has links)
Diss. (sammanfattning) Stockholm : Univ., 2004. / Härtill 4 uppsatser.

Safety limit estimation for cataract induced by ultraviolet radiation /

Dong, Xiuqin, January 2005 (has links)
Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 5 uppsatser.

Radon in natural waters : analytical methods, correlation to environmental parameters, radiation dose estimation, and GIS applications /

Isam Salih, M. Musa, January 2003 (has links) (PDF)
Diss. (sammanfattning) Linköping : Univ., 2003. / Härtill 6 uppsatser.

Evaluation of optically stimulated luminescence A1₂O₃:C detectors for use in diagnostic computed tomography

Kalavagunta, Chaitanya. January 2008 (has links) (PDF)
Thesis--University of Oklahoma. / Bibliography: leaves 81-83.

Effects of tissue density on organ dose in accelerated partial breast electronic brachytherapy

Walters, Andrew W. January 2009 (has links) (PDF)
Thesis--University of Oklahoma. / Bibliography: leaves 78-79.

The analysis of radiation-induced micronuclei in peripheral blood lymphocytes for purpose of biological dosimetry

Le Roux, Jacques January 1995 (has links)
In the investigation of radiation accidents, it is of great importance to estimate the dose absorbed by exposed persons in order to plan their therapy. Although occasionally in these situations physical dose measurements are possible, most often biological methods are required for dose estimation. The aim of this investigation was to assess the suitability of the cytokinesis blocked (CB) micronucleus assay as a biodosimetric method using lymphocytes irradiated in vivo. The approach adopted to achieve this was to estimate whole body doses by relating micronuclei yields in patients undergoing radiotherapy treatment with an in vitro radiation dose-response curve. These biologically derived estimates were then compared with the corresponding doses obtained by physical measurement and calculation. As a first approach a study was performed of the in vitro dose-response of gamma-ray induced micronuclei following cytokinesis-block in the lymphocytes of peripheral blood samples obtained from 4 healthy donors. The results indicated that the distribution of the induced micronuclei were overdispersed. Furthermore, a linear dose-response relationship was established when a curve was fitted to the data by an iteratively reweighted least squares method. By means of an analysis of covariance it was demonstrated that this result is in agreement with the dose-response relationships found by various other workers (Fenech et al., 1985; Fenech et al., 1986; Fenech et al., 1989; Balasem et al., 1992, and Slabbert, 1993). To assess the suitability and accuracy of dose assessment using the CB micronucleus assay for in vivo exposure of lymphocytes, blood samples obtained from 8 patients undergoing radiotherapy before, during and after treatment were examined. The physical doses of these patients were determined according to conventional radiation treatment plans and cumulative dose-volume histograms. The dose-volume histograms permitted calculation of integral doses and subsequently the estimate of equivalent whole-body doses. The results of the CB micronucleus assay applied to peripheral blood lymphocytes of 6 patients undergoing fractionated partial-body irradiation showed a dose-related increase in micronucleus frequency in each of the patients studied. This demonstrated that micronuclei analysis may serve as a quantitative biological measure of such exposures. The pooled data of these patients compared to the pooled data of the healthy donors show that there was no statistically significant difference between in vitro and in vivo results, however a slightly lower induced micronuclei frequency was observed after in vivo exposure. When the biological dose estimates for equivalent whole-body doses obtained from the in vitro dose response curve were compared with calculated physical doses, it was found that: biologically estimated dose = 0.936 physical dose. However, there was inadequate statistical evidence to discard the hypothesis that the gradient of the equation was equal to one. Therefore, the analysis of micronuclei induced in lymphocytes in vivo yields highly quantitative information on the equivalent whole-body dose. The negative binomial method was used for analysing the micronucleus data from two patients who received single, relatively larger tumour doses of 10 Gy each, with the objective to obtain estimates of the exposed body fraction and the dose to this fraction. The dose estimates to the irradiated volume were found to be within 30% of the physical tumour dose. The irradiated volume estimates seemed to be higher than the physically calculated volumes but by discarding the correction for the loss of cells due to interphase death the agreement was good between the physically and biologically determined integral doses. This study has revealed that the CB micronucleus assay appears to offer a reliable, consistent and relatively rapid biological method of whole body dose estimation. It is recognised that further corroborative work using the techniques described in this thesis is required for estimating localized exposure.

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