No description available.

No description available.

No description available.

This thesis is an investigation of the biological effects of terahertz (THz) radiation at non-thermal power levels. One may loosely define the THz region of the electromagnetic spectrum spanning a range of frequencies between 0.1 and 10 THz. Recent advances in methods of generation and detection have made it possible to build instruments and perform experiments in this relatively unexplored part of he spectrum. Water represents an important constituent of biological systems and strongly absorbs in this frequency range. As a consequence, irradiation at THz frequencies can raise the temperature of biological material and temperature dependent processes can be influenced. THz radiation is non-ionising, with associated photon energies close to the thermal energy level of a metabolically active biological entity. At low power levels, however, a non-linear bio-effect relating to energy transfer from the field to the organism, which is not associated with a temperature rise, may be observed at specific frequencies. The current understanding of the interaction between THz radiation and biological material is. therefore, discussed within the framework of dielectric theory and is considered at both the macroscopic and microscopic levels. A discussion of important biological molecules, cells, tissues and a range of cellular processes is developed within this framework and the complexity of an interaction within a biological system is defined.

DNA-dependent protein kinase (DNA-PK) and poly(ADP-ribose) polymerase-1 (PARP-1) participate in non-homologous end joining and base excision repair respectively, and are key determinants of radio-resistance. The interactive effects of PARP-1 and DNA-PK in the cellular responses to DNA damage were investigated using novel specific inhibitors of DNA-PK (NU7026) and PARP-1 (AG14361) and cell lines proficient or deficient for DNA-PK or PARP-1. Enzyme deficient cell lines were 4-fold more sensitive to ionizing radiation (IR) alone, and showed reduced potentially lethal damage recovery (PLDR), compared to their proficient counterparts. NU7026 potentiated IR cytotoxicity in exponentially growing DNA-PK proficient, but not deficient cells. Similarly AG14361 potentiated IR in PARP-1 +/+ but not PARP-1-/- cells. When NU7026 and AG14361 were used in combination, their potentiating effects were additive. Both inhibitors reduced PLDR in the proficient cell lines. Furthermore, inhibitor combination completely abolished PLDR. Both inhibitors prevented IR-induced DNA double strand break repair, but only AG14361 prevented DNA single strand break repair The enzyme activities were investigated using purified enzymes and permeabilised cells. In cell-free assays, PARP- 1 activity was unaffected by the presence of DNA-PK, and vice versa, provided the enzyme substrates were present. DNA-PK inhibited PARP-1 when ATP was absent or NU7026 present. PARP-1 inhibited DNA-PK when NAD+ was absent or AG14361 present. Furthermore, PARP-1 inhibition increased with increasing ratio of DNA-PK to PARP-1, and vice versa. Similar results were obtained using the inhibitors in permeabilised cells. PARP-1 was inactive in the absence of histones, but activity was restored by the addition of DNA-PK. DNA-PK was inactive in the absence of its p53 peptide substrate unless PARP-1 was included. These data suggest reciprocal regulation of PARP-1 and DNA-PK, and co-operation in DSB repair and survival. Thus, individually, or in combination, the DNA-PK and PARP-1 inhibitors act as potent radio-sensitisers.

No description available.

Micro-irradiation systems are used to analyse the effect of ionizing radiation at the cellular and tissue level, targeting individual cells within a population with a controlled low dose. Cell survival experiments using micro-irradiation systems are limited by factors including: 1) the radiation attenuation and optical properties of the chosen cell dish substrate, 2) the registration of the cell dish before and after irradiation or between multiple imaging modalities and 3) the analysis of the cell or colony growth after irradiation. In this thesis, a set of tools have been developed to improve micro-irradiation experiments and to increase the accuracy of information provided by the cell survival data. The first contribution, the substrate cell dish evaluation, provides a set of characteristics defining the substrates used for micro-irradiation experiments based on minimal energy loss and optical clarity using unstained cell imaging. The second contribution was the development of a novel and low cost fiducial marking device for micro-irradiation experiments using an 808 nm laser and providing marks suitable for imaging with multiple modalities. The minimum focused spot diameter was calculated as 22.9 urn and the device was used to create fiducial marks with diameters ranging from 20 urn to 130 urn. The third contribution, the development of a cell counting methodology for use with a lens-free imaging device, has been shown to accurately count thousands of cells suitable for immediate analysis. Approximately 1000 cell colonies, containing 17 729 cells on 11 cell dishes were used for testing and training for automatic cell counting. Validation of the cell counting method showed that 76% and 89% of the cell colonies were counted within a ± 20% and ± 30% error of the ground truth, respectively. Further development of the fiducial marking device, by modifying the choice of laser and making it suitable for multiple types of cell dish substrates, would increase the applications of the device. Development of the cell counting methodology for different cells line, and for cells grown on multiple types of substrates, would make the system suitable for analysis of a wide variety of cell survival studies. The cell counting methodology, applied to the CyMap lens-free imaging device, has the potential to be an extremely useful and cost effective tool for cell survival studies.

The purpose of this study was to evaluate the effectiveness of the database system used at the South African Radiation Control Authority and compare it with RAIS (Regulatory Authority Information System). A radiation regulatory authority requires an adequate and effective data management system in order to carry out its regulatory control program efficiently and effectively. RAIS is a comprehensive system that includes all of the main functionality required to support a regulatory framework. A mixed methods approach, including a quantitative descriptive comparative evaluation research study was conducted to determine if the database system currently used by the South African Radiation Control Authority is effective as a data management tool for a regulatory body. Two analyses were conducted. Firstly, the specification records of the South African database system were compared with that of RAIS. Secondly, current database users were surveyed by means of a structured questionnaire. Both analyses reveal that RAIS performs better than the Radiation Control database in the main areas of the regulatory framework. The study results also highlight some of the shortcomings and strengths of the Radiation Control database / Medical Informatics / M.A. (Public Health)

Le risque potentiel de cancer induit par les irradiations mammographiques est sujet de santé publique majeur, d’intérêt médical et scientifique. Le but de ce travail a été de quantifier les cassures double-brin (CDB) de l’ADN en conditions exactes d’irradiations mammographiques. Cette quantification a été effectuée sur des cellules épithéliales mammaires non transformées issues de biopsies échoguidées en tissu sain en utilisant l’immunofluorescence de la protéine histone H2AX phosphorylée (γH2AX), avant, 10 min et 24 h après irradiation . Deux populations de patientes ont été incluses dans l’étude 19 sans antécédent familial de cancer du sein et/ou de l’ovaire (faible risque, FR) et 11 à haut risque identifié par le généticien avec ou sans mutation (haut risque, HR). En effet, les gènes mutés suppresseurs de tumeurs (BRCA1, BRCA2, CHK2, ATM, p53, PTEN) sont également impliqués dans la signalisation et/ou réparation des CDB. Spontanément, les patientes HR ont montré significativement plus de CDB spontanées que les LR. Trois effets radiobiologiques majeurs ont été mis en évidence : 1) Un effet de la dose, plus important chez les HR ; 2) Une augmentation significative du nombre de foci γH2AX entre 10 min et 24 h après irradiation ; 3) Un effet de répétition de dose, plus marqué chez les HR. Ces constatations devraient conduire à la ré-évaluation des séquences de dépistages mammographiques dans les populations où le bénéfice en terme de mortalité n’a pas été prouvé, comme dans la tranche d’âge des 40-49 ans et dans la surveillance des patientes où sont recommandées de façon annuelle IRM et mammographie dès l’âge de 30 ans ou 35 ans, les hauts risques et les femmes aux antécédents d’irradiation thoracique dans l’enfance, l’adolescence ou jeune adulte. Une seule incidence mammographique en dépistage pourrait être préconisée en dépistage dans l’attente de travaux radiobiologiques complémentaires évaluant la carcinogenèse éventuelle des irradiations mammographiques / The potential risk of cancer induced by radiation mammography is a major public health issue, medical and scientific interest. The purpose of this study was to quantify the double-strand break (DSB) DNA in exact terms of mammographic radiation. This quantification was performed on untransformed mammary epithelial cells from ultrasound-guided biopsies in healthy tissue using fluorescent protein phosphorylated histone H2AX (γH2AX) before, 10 min and 24 h after irradiation. Two patient populations were included in the study : 19 with no family history of breast cancer and/or ovarian cancer (low risk, LR) and 11 high-risk identified by the geneticist with or without mutation (high risk, HR). Indeed, mutated tumor suppressor genes (BRCA1, BRCA2, CHK2, ATM, p53, PTEN) are also involved in signaling and/or repair of DSBs. Spontaneously, patients showed significantly higher HR of DSBs that spontaneous LR. Three major radiobiological effects were highlighted : 1) A dose low effect, higher in HR; 2) A significant increase in the number of γH2AX foci from 10 min to 24 h after irradiation; 3) An effect of repeated doses more pronounced in HR. These findings should lead to re-evaluate mammographics procedures in screnning in populations where the benefit in term of mortality has not been proved, as women with high familial risk, in the age of group of 40-49 years, and in women treated with chest radiation for childhood, adolescent, or young adult cancer. A single mammographic view could be indicated. Further works assessing the possible carcinogenesis effects of mammographic irradiations will be necessary

The purpose of this study was to evaluate the effectiveness of the database system used at the South African Radiation Control Authority and compare it with RAIS (Regulatory Authority Information System). A radiation regulatory authority requires an adequate and effective data management system in order to carry out its regulatory control program efficiently and effectively. RAIS is a comprehensive system that includes all of the main functionality required to support a regulatory framework. A mixed methods approach, including a quantitative descriptive comparative evaluation research study was conducted to determine if the database system currently used by the South African Radiation Control Authority is effective as a data management tool for a regulatory body. Two analyses were conducted. Firstly, the specification records of the South African database system were compared with that of RAIS. Secondly, current database users were surveyed by means of a structured questionnaire. Both analyses reveal that RAIS performs better than the Radiation Control database in the main areas of the regulatory framework. The study results also highlight some of the shortcomings and strengths of the Radiation Control database / Medical Informatics / M.A. (Public Health)