| dc.description.abstract | Exposure to ionizing radiation is associated With the possibility that harmful health effects may be induced in the irradiated individuals, or in their descendants. In order to obtain quantitative assessments
of such hazards, it is necessary to determine the radiation absorbed doses, or some related quantities, from various sources of radiation exposure. Medical irradiation during x-ray diagnosis is an important source because it contributes the largest proportion of the collective population dose from man-made sources of radiation exposure.
This thesis is based on studies of the radiation doses received by patients from a sample of diagnostic x-ray examinations at the Withington Hospital, Manchester, United Kingdom, between 1982 and 1983, and at six different x-ray centres in Kenya between 1984 and 1986. A survey of the frequency of radiological examinations at x-ray departments in Kenya during 1986 is also incorporated into the thesis.
The objectives of the studies conducted in Kenya were to provide a data base of patient doses during dome diagnostic x-ray examinations, to examine which factors were important in influencing the magnitudes
of patient doses, to indicate priority areas for dose reduction, and to make an assessment of the
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current annual radiological workload in the country. Attention has previously been drawn to the scarcity
of data from the developing countries on both the
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frequency of radiological examinations and on the magnitudes of patient doses (UNSCEAR, 1982). The major motivation in conducting these studies was to help fill this gap in knowledge.
The studies at the hospital in the United Kingdom were aimed at providing patient dose data over an extended period of time from examinations of relatively low frequency, following a national survey which had yielded few data for these particular types of examination (gastro-intestinal investigations).
Radiation dose measurements were based on thermoluminescence dosimetry (TLD) techniques, using the laboratory facilities of the Christie Hospital and Holt Radium Institute, Manchester, U.K., and the Kenyatta National Hospital, Nairobi, Kenya.
The types of radiological examination for which dose surveys were conducted included barium meal, barium enema, chest radiography and photo- fluorography, hysterosalpingography, and pelvimetry. The studies involved monitoring some 912 patients,
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on whom a total of 1,558 dose measurements were made. Preliminary reports of these studies have recently been published in the radiological literature (Tole,
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1984, 1985, 1987, 1988).
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The introductory chapters (1 & 2 ) review the literature on the hazards of low-level exposure to ionizing radiation and the methodologies employed in patient dosimetry studies, and consider the rationale behind patient dosimetry research.
Chapter 3 reviews the theoretical background of TLD, and examines some of the characteristics of the TLD system used in these studies.
An extensive survey of patient doses during chest radiography and photofluorography is reported in Chapter 4. Mass miniature technigues without image intensification are found to deliver high patient doses. Comparisons between direct dose measurements (TLD) and indirect estimates from technical exposure factors gave reasonable agreement, within a factor of about 2.
Chapters 5 and 6 report data on patient exposures during pelvimetry and hysterosalpingography, respectively. The dose reduction effect of using Y2°2^ ‘ Tk rare-earth intensifying screens in place of CaWO^ screens is demonstrated. Estimates are made of the risks of pelvimetry for the induction of juvenile leukaemia.
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Studies of patient dose during gastrointestinal
radiology/ with special reference to intrahospital
dose variations/ are reported in Chapter 7. They indicate that overcouch fluoroscopy equipment may have an adverse effect on doses to organs outside the useful x-ray beam. Logistical constraints during national dose surveys are found to make such surveys unsuitable for detailed analyses of patient dose variations.
In Chapter 8/ a statistical analysis of dose data from barium meal investigations suggests that depth dose relations derived from plain radiography
should not be used for computing organ doses
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during fluoroscopic examinations.
A survey of the frequency of radiological examinations at x-ray departments in Kenya during 1986 is reported in Chapter 9. The results indicate that the current frequency of radiological examinations
is about 32 examinations per thousand population. Examinations of the limbs and the chest were the most frequently performed routine investigations/
while studies of the gastro-intestinal tract dominated the special examinations.
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Chapter 10 presents an appraisal of the hazards of x-ray diagnosis in Kenya/ on the basis of
the scope of radiological services, levels of patient dose, and age distribution in the population.
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An overview of the main findings, observations, and recommendations appears in Chapter 11. The recommendations
touch on restrictions in the use of photof1uorographic equipment, the use of sensitive image receptors, wider dissemination of knowledge on patient referal criteria for radiological investigations,
and a greater commitment to improving the status of radiological equipment in Kenya.
The limitations of the present studies are also discussed in Chapter 11, and suggestions made for further research. Further studies are indicated in the areas of patient dose measurements, quality assurance, and radiological manpower utilization.
This thesis makes some important contributions to the subject matter of patient dosimetry in diagnostic
radiology. The studies in Kenya provide the first set of patient dose data from the Eastern Africa region. They indicate priority areas for the application of radiation protection measures.
The frequency survey provides an insight into the current scope of radiological services in both government and private institutions. The studies in the United Kingdom provide a critical analysis of
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some aspects of patient dosimetry methodology. They point out limitations in the analysis of patient dose variations within and between hospitals during national surveys. They examine the problems of relating measured skin doses to organ doses during fluoroscopic examinations.
Based on the findings and observations from these studies/ some recommendations are made on measures to improve the radiation protection of the patient during x-ray | en_US |
