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Thesis (doctoral)--Freie Universität Berlin, 1979.

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PhD - Science / Screening of asymptomatic women using X-ray mammography technique is very common in many parts of the world in view of the prevalence of breast cancer among women. Mammography X-ray procedures are well established; with radiation dose measurements usually carried out using air ionisation chamber despite its inherent disadvantages. In this study, the various parameters necessary for accurate dose calculations from mammography X-ray energies and their effect on the calculated dose values, the relationship between dose, breast size, image quality and X-ray tube parameters as well as an alternative method for dose measurements, were systematically investigated. A method is presented for calculating accurately the mass attenuation and mass-energy coefficients for any energy bin of interest in the photon energy region 1-20 keV from existing mass attenuation and mass-energy coefficients data. Data fitting procedure was used for the study using an established equation. The results of the study showed that when data points containing high and low energies such as 1 - 200 keV are fit together with a single set of parameters, an overestimation of about 20% at the lower energies with far greater deviations at higher energies can result. It has been shown that grouping data into smaller energy regions when fitting would lead to accurate calculations of the mass attenuation or mass energy-absorption data. This is especially important if the data were to be used in low energy photon calculations such as would be the case for mammography beams. An investigation into the effect of pressure, temperature and humidity in air on photon fluence at a typical mammography, low bremsstrahlung energy (25 kVp), has been carried out. The results of the investigation showed that air kerma values from an X-ray spectrum that has significant lower energy components is likely to be more sensitive to changes in pressure, temperature and humidity than the air kerma from an X-ray spectrum with lower energy components less pronounced. Mean glandular dose (MGD) values had been calculated for various tube potentials and tube loadings (TL) using direct measurements of the incident entrance air kerma (ESAK) at the surface of a standard breast phantom and also from spectral measurements acquired with a solid-state detector. Detailed presentations of dose measurements from direct measurements and also from X-ray spectral data employing the established methods are given. Comparisons of the MGD values thus derived are presented and the relationship between MGD, phantom thickness, image quality and tube operating parameters is discussed. The possibility of evaluating radiation dose from mammography X-ray beams using constructed probes with diamond as the active radiation sensing material has been studied. Diamond has been used in the conduction mode whereby electrodes are connected to it and the resulting current from the interaction of the ionizing radiation with the diamond detected. Single crystal diamonds produced under high pressure and temperature (HPHT), as well as polycrystalline diamonds manufactured by the chemical vapour deposition (CVD) method were used. Suitable diamond stones were carefully selected for the study using various techniques. The probe was constructed entirely using tissue equivalent materials. In current practice diamond in the form of thin plates are used in the “flat-on” geometry, where the radiation beam to be monitored or measured, impinges on the flat face of the diamond. In this work it was found that using diamond plates in a side-on, or “edgeon”, geometry improves the collection efficiency of the diamond. The probe has been designed for radiation detection in both “edge-on” and “flat-on” sensor geometry profiles without having firstly to unseat the diamond sensor element from its original position within the probe housing before taking measurements. The study has shown that with the “edge-on” geometry configuration, radiation from impinging photons with energies below 30 keV can be made to deposit almost all (about 90%) of their energy into the sensor. The probe was designed for use in combination with commercially available electrometer systems. The response of the diamond probe to changes in radiation dose correlated well with that obtained from a secondary standard ionization chamber at the same X-ray tube settings.

Masters Research - Master of Medical Science / Introduction: Between 6-10% of women attending breast screening are recalled to investigate an unclear area on the mammogram. Image quality is known to affect image interpretation and it has been suggested that the number of recalls could be reduced with improved image quality. Aim: This study aimed to investigate the effect image quality has on recall rates, to assess reader consistency using the PGMI classification system and to establish factors leading to recall. Materials and Methods: A six member panel assessed 904 sets of images (698 recalled; 206 non-recalled) through a BreastScreening Program during three separate phases (pilot, main and non-recall). The pilot study was conducted without additional training in PGMI. Levels of agreement and Kappa statistics were calculated to assess intra- and inter-consistency. The percentage of and reasons for inadequate images was calculated; while a case-control study was conducted to establish factors increasing the likelihood of a client being recalled. Results: The level of agreement between panel members significantly increased from the pilot to the main study (45.5% to 57.7%) before decreasing slightly for the non-recall (57.7% to 52.2%). Overall, 3.3% of the 904 sets of images were classed as inadequate; the most common PGMI reason was exposure (31%); the left MLO was considered the most common inadequate projection (30%), with more privately produced (66%) images considered inadequate compared to public images (34%). Inadequate image quality did not hinder the cancer detection rates. The case-control component demonstrated current and previous HRT use, increased breast density, better image quality and images being taken at a public site all contributed to a client being recalled. Conclusion: The results of this study demonstrated that inadequate image quality was not a major factor leading to recall; although twice the number of recalled images were considered inadequate compared to the non-recalled images. The use of the PGMI classification system is highly subjective, with low levels of agreement amongst users. The use of HRT, breast density, imaging site and image quality all contribute to a client being recalled.

Breast cancer is a leading cause of mortality among women in the United States. Women with chronic disabling conditions such as multiple sclerosis (MS) are less likely to participate in routine mammography screening than women without disabilities due to multiple barriers. Underuse of mammography screening may lead to a diagnosis of a later stage breast cancer and consequently higher breast cancer mortality rate. This study examined the influence of several factors including, severity of MS-related functional limitations, demographic characteristics, family history of breast cancer, beliefs related to mammography screening and breast cancer, and personal resources on usual screening mammography in a sample of women with MS. The conceptual framework guiding this study was synthesized from The Explanatory Model of Health Promotion and Quality of Life in Chronic and Disabling Conditions and the Health Belief Model. Data from an ongoing longitudinal study (R01NR003195) focused on health promotion of persons with MS were combined with primary data for this prospective descriptive correlational study. The nonprobability sample consisted of 274 women ages 39-85 years who were primarily White (92%), married (66.1%), and unemployed (64.1%) with a 22 year average length of diagnosis with MS. Data were collected over two years using a mailed survey. Descriptive statistics and hierarchical logistic regression analyses were used to address the research questions. The annual mammography rate in this sample was 62%. Perceived susceptibility to breast cancer (AOR = 3.0, p < .05), family history (AOR = 2.5, p < .05), economic adequacy (AOR = 1.6, p < .05), and perceived barriers to mammography (AOR = .98, p < .05) significantly predicted mammography use, adjusted for severity of functional limitations. Though severity of limitations was negatively associated with mammography, it was not a significant predictor in the overall model. These findings suggest that for women with chronic disabling conditions, health beliefs, family history, and personal resources influence mammography screening. Clinicians need to continue to eliminate the barriers to mammography screening to improve screening and reduce overall breast cancer mortality rate in this vulnerable population. / text

The mean glandular dose (MGD) was measured for a breast phantom by using molybdenum/molybdenum and molybdenum/rhodium target/filter combinations, at different kVp 26, 28 and 32 kilovolts. The phantom thickness was 7.5cm and was made of BR12 material. The change of dose was studied as a function of depth inside the phantom at different depths from the surface, namely 3.3, 4.3 and 5.3cm, by using TLDs. It was found that the MGD value for different combinations of beam quality (HVL) and energy (kVp) did not exceed the recommended values given by different protocols. The Mo/Rh target/filter required lower doses to achieve the same or better results compared with the Mo/Mo target/filter. The change in the surface dose as a function of kVp was more significant for Mo/Rh than for the Mo/Mo. Studying the change in dose within the breast, as a function of depth gives a better understanding of the interactions between radiation and tissue inside the breast. It should be noted that the MGD is a tool for optimization of the mammography parameters. However, the MGD should not be used directly to estimate the risk of determinable health effects from mammography. This will ultimately help to determine limits for the breast surface dose and a better understanding of cancer risk. In future work, we will try to measure the change of the dose as a function of depth by using more kVp, HVL, different breast composition and different target/filter combinations to give a wider picture for different situations.

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