In medical and health physics, we are interested in the effects of ionizing radiation on biological systems, in particular, human biology. The main process by which ionizing radiations causes damage to biological systems, is through the creation of radicals close to DNA strands. The radicals are very reactive and those created within close proximity to DNA will react with the DNA causing damage, in particular single strand or double strand breaks. This damage to the DNA can cause mutations that can kill the cell, either mitotically or apoptotically, or possibly lead to a cancerous formation. Therefore it is important to study how these radicals interact with DNA strands for a correlation between the resultant products of radical reactions and DNA strand breaks. For this study, we look at the most important radical, the OH radical and it's addition to DNA bases. We will study, through quantum chemistry, the thermodynamics of OH radical addition to the four bases, Adenine, Guanine, Cytosine and Thymine. The Jaguar program developed by Schrodinger was used for DFT calculations of the Gibbs free energy of the addition. In addition, calculations for the partial charge, HOMO's and Fukui indices were calculated and compared to experiment.

Checkpoint kinase 2 (CHK2) is an effector kinase of the DNA damage response pathway and although its mechanism of activation has been well studied, the attenuation of its activity following DNA damage has not been explored. Here, we identify the B'α subunit of protein phosphatase 2A (PP2A), a major protein serine/threonine phosphatase of the cell, as a CHK2 binding partner and show that their interaction is modulated by DNA damage. B'α binds to the SQ/TQ cluster domain of CHK2, which is a target of ATM phosphorylation. CHK2 is able to bind to many B' subunits as well as the PP2A C subunit, indicating that it can bind to the active PP2A enzyme. The induction of DNA double-strand breaks by ionizing radiation (IR) as well as treatment with doxorubicin causes dissociation of the B'α and CHK2 proteins, however, it does not have an effect on the binding of B'α to CHK1. IR-induced dissociation is an early event and occurs in a dose-dependent manner. CHK2 and B'α can re-associate hours after DNA damage and this is not dependent upon the repair of the DNA. Dissociation is dependent on ATM activity and correlates with an increase in the ATM-dependent phosphorylation of CHK2 at serines 33 and 35 in the SQ/TQ region. Indeed, mutating these sites to mimic phosphorylation increases the dissociation after IR. CHK2 is able to phosphorylate B'α in vitro; however, in vivo, irradiation has no effect on PP2A activity or localization. Alternatively, PP2A negatively regulates CHK2 phosphorylation at multiple sites, as well as its kinase activity and protein stability. These data reveal a novel mechanism for PP2A to keep CHK2 inactive under normal conditions while also allowing for a rapid release from this regulation immediately following DNA damage. This is followed by a subsequent reconstitution of the PP2A/CHK2 complex in later time points after damage, which may help to attenuate the signal. This mechanism of CHK2 negative regulation by PP2A joins a growing list of negative regulations of DNA damage response proteins by protein serine/threonine phosphatases.

Thyroid cancer constitutes about 1% of all malignant tumours and the incidence is increasing in Sweden. It is rare in children before the age of 10. During puberty the female to male ratio increases to be two to three times more common in females. The ratio remains constant until menopause and thereafter declines. The etiology of this gender-dependent incidence difference is unclear. Ionizing radiation is the only well-established risk factor for the disease, while the impact of other etiological factors is not clear. A retrospective study based upon medical records of 218 females and 91 males with papillary, mixed or follicular types of thyroid cancer was conducted. Prognostic factors were compared by multivariate analysis using Cox's semiparametric hazard model. Differences in prognosis between women and men were found. There was a higher relapse rate and mortality risk among men. Distant metastasis, age &gt;50 years, regional lymph node metastasis, low or moderate differentiation, and tumour related symptoms at diagnosis were also independent factors related to increased tumour mortality risk. A population-based case-control study including 180 cases and 360 controls was carried out to identify risk factors for thyroid cancer. Information on exposure was obtained by mailed questionnaires. The first part of the study investigated connections between medical ionizing radiation and thyroid cancer. The results showed that diagnostic X rays were a significant risk factor for papillary thyroid cancer in women between 20 and 50 years at diagnosis. Exposure to iodine-131 caused no increased risk for thyroid cancer. The result supports that external radiotherapy is a risk factor for thyroid cancer in women. The second part of the case-control study dealt with occupation and different exposures. Work with diagnostic X-ray investigations and work as a lineman was associated with thyroid cancer. Exposure to impregnating agents increased the risk. The third part of this study showed that one pregnancy increased the risk for papillary thyroid cancer. A medical history of asthma or allergy decreased the risk. Another case-control study using medical records as the source for assessment of exposure gave a non significantly increased risk for thyroid cancer in patients who had been treated with external radiotherapy including the thyroid gland. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1994, härtill 5 uppsatser.</p> / digitalisering@umu

iThemba LABS is a particle accelerator facility housing a radionuclide production facility that uses a 66 MeV proton beam to produce radionuclides for medical and industrial use. Ionising radiation is produced by a variety of sources at Themba LABS. Ionising is a health hazard. High doses can cause acute radiation syndrome, i.e. "radiation sickness". Lower doses cannot cause acute symptom, but carry a risk of radiation-related cancer. Ionising radiation is also detrimental to materials, and can damage polymers and lubricants e.g. Shielding is used to reduce radiation levels to values that should be safe for the intended level of human occupancy. Shield performance is vital to human health and the life expectancy of polymers and lubricants, so that quality management in shield design is very important. However, until 2003, there has been no formal system at iThemba LABS to evaluate and improve all radiation shield designs and layouts from a radiation protection perspective. This study deals with evaluating and redesigning radiation shielding in the radionuclide production facility of iThemba LABS. There are several designs and layouts in the radionuclide production building of iThemba LABS that lead to unnecessary exposure of personnel to ionising radiation. The shielding in these areas are sub-standard. Performance criteria for radiation shields are developed. Inadequate radiation shields are identified. The identified inadequate shields are: the processing hotcells, the target store room and the hotcells in the radiopharmaceutical dispensing laboratory, Point-Kernel radiation shielding calculations are done to specify materials and material thickness that will adequately protect workers against ionising radiation. / Thesis (MSc. ARST) North-West University, Mafikeng Campus, 2004

Our cells are constantly dealing with DNA damage generated by endogenous cellular activity (e.g. DNA replication) and exogenous agents (e.g. ultraviolet and ionizing radiation (IR)). The cellular stress response to DNA damage requires strict co-ordination between cell cycle checkpoint control and DNA repair. In response to DNA double-strand breaks (DNA-dsbs), members of the phosphatidylinositol 3-kinase–related kinase family (e.g. ATM and DNA-PKcs kinases) have been shown to redundantly phosphorylate substrates including the DNA-dsb marker, gamma-H2AX, and the p53 tumour suppressor protein. The p53 protein is best known as the guardian of the genome through its transcriptional-dependent and -independent functions. Despite a clear link between ATM-dependent phosphorylation of p53 with cell cycle checkpoint control and various modes of DNA damage repair, the intracellular biology and sub-cellular localization of p53 and specifically its phosphoforms during DNA damage induction and repair remains poorly characterized. Using G0/G1 confluent primary human diploid fibroblast cultures, this thesis shows that endogenous p53, phosphorylated at serine 15 (p53Ser15), accumulates as discrete, dose-dependent and chromatin-bound foci within 30 minutes following the induction of DNA breaks. This biologically distinct sub-pool of p53Ser15 is ATM-dependent and resistant to 26S-proteasomal degradation. p53Ser15 co-localizes and co-immunoprecipitates with gamma-H2AX with kinetics similar to that of biochemical DNA-dsb rejoining. Sub-nuclear microbeam irradiation studies confirm that p53Ser15 is recruited to sites of DNA damage containing gamma-H2AX, ATMSer1981 and DNA-PKcsThr2609 in vivo. Furthermore, studies using isogenic human and murine cells, which express Ser15 or Ser18 phosphomutant proteins, respectively, show defective nuclear foci formation, decreased induction of p21WAF, decreased gamma-H2AX-association and altered DNA-dsb kinetics following DNA damage. We further hypothesized that the non-specific DNA binding activity of the p53 carboxy-terminus mediates chromatin anchoring at sites of DNA damage. YFP-p53 fusion constructs expressing carboxy-terminus deletion mutants of p53 were transfected into p53-null H1299 cells to determine the role of the carboxy-terminus in chromatin-binding pre- and post-IR, independent of transcriptional activity. Within this isogenic human cell system, we observed exogenous YFP-p53WT associated with ATMSer1981 and 53BP1 within cellular chromatin in a dynamic manner. We confirmed that these associations also occurred between endogenous WTp53 with ATMSer1981 and 53BP1 within the chromatin of primary human diploid fibroblasts. YFP-p53del1-299 fusion proteins, which lack transcriptional activity and the Ser15-residue, also associated within chromatin. Ser15-phosphorylation was found not to be essential for DNA damage-induced association of p53 with chromatin or with ATMSer1981 and 53BP1. These data suggest a unique biology for p53Ser15 phosphoforms in the initial steps of DNA damage signaling and implicates ATM-p53-53BP1 chromatin-based interactions as mediators of cell cycle checkpoint control and DNA repair. And we propose a model whereby a pre-existing pool of p53 that constantly scans the genome, responds immediately to radiation-induced DNA damage by virtue of its association with chromatin through its carboxy-terminus. The consequences for these p53-ATMSer1981-53BP1 complexes following DNA damage remains to be investigated: could residual complexes be associated with decreased DNA-dsb rejoining or error-prone repair, or could these complexes signal for cell survival or cell death? Since altered p53 function and biology is an important factor in cellular carcinogenesis and response to cancer therapy, this study provides a step towards a greater understanding of WTp53 and MTp53 biology in tumour development and therapeutic resistance, in the hopes to contribute towards predicting therapeutic response and/or improving p53-targeted therapies.

The tumour suppressor p53-binding protein 1 (53BP1) is phosphorylated following DNA double strand breaks (DSBs); however, little is understood about the upstream signaling pathways that control this phosphorylation. Additionally, it is not known how these processes combine with 53BP1 to control the survival of cells following DNA damage such as that imparted by ionizing radiation (IR), which is the basis of radiotherapy. In this thesis, I have shown that 53BP1 is phosphorylated specifically in S-phase cells, but not relocalized to intranuclear foci, in response to severe oxygen stress. This occurs with only partial dependence on the ATM kinase (Chapter 2). Following IR, I find that both ATM and DNA-PKcs contribute to intranuclear phosphorylated 53BP1 foci, but that this phosphorylation is independent of proximal signaling molecules that control the localization of 53BP1 to initial DSBs (Chapter 3). Furthermore, I show that 53BP1 loss confers sensitivity to IR and this can be further augmented by inhibition of ATM and DNA-PKcs kinases suggesting that there are both 53BP1-dependent and -independent pathways of survival from IR (Chapter 4). These findings may have important implications for molecular pathology and personalized medicine as 53BP1 has recently been found to be activated or lost in subsets of human tumours. I have collaborated to initiate the development of a novel system to interrogate the implications of 53BP1 loss as traditional siRNA approaches in human cancer cells were not feasible (Chapter 5 and Appendix 2). This system can be used in vivo as tumour xenografts to further understand how 53BP1 and the tumour microenvironment interact endogenously and in response to IR. I also present the possibility and proof of concept for the use of 53BP1 as a biomarker in primary human prostate cancer tissue where little is known about 53BP1 biology (Chapter 5).

Thesis (M.Sc.) (Hons)-- University of Western Sydney, 2002. / "A thesis submitted in fulfillment of the requirements for the Degree of Master of Science (Honours) in Physics at the University of Western Sydney" "September 2002" "Kin Wa (Karl) Chan of Medical Physics Department of Westmead Hospital and the University of Western Sydney"-- t.p. Bibliography: leaves 100-105.

Thesis (M.Sc.) - Carleton University, 2007. / Includes bibliographical references (p. 67-73). Also available in electronic format on the Internet.

Ionizing radiation induces a range of different DNA lesions. In terms of mutation frequency and mammalian cell survival, the most critical of these lesions is the DNA double-strand break (DSB). DSB left unrepaired or mis-repaired may result in chromosomal aberrations that can lead to permanent genetic changes or cell death. The complexity of the DNA damage and the capacity to repair the DSB will determine the fate of the cell. This thesis focuses on the DNA damage formation, repair and signaling after irradiation of human cells. Radiation with high linear energy transfer (LET) produces clustered damaged sites in the DNA that are difficult for the cell to repair. Within these clustered sites, non-DSB lesions are formed that can be converted into a DSB and add to the damage complexity and affect DSB repair and the measurement. Heat-labile sites in DNA are converted into DSB at elevated temperatures. We show that heat-released DSB are formed post-irradiation with high-LET ions and increase the initial yield of DSB by 30%-40%, which is similar to yields induced by low-LET radiation. DNA-PKcs, a central player in non-homologous end-joining (NHEJ), the major mammalian DSB repair pathway, has been found to be both up- and downregulated in different tumor types. In Paper II we show that low levels of DNA-PKcs lead to extreme radiosensitivity but, surprisingly, had no effect on the DSB repair. However, the fraction of cells in G2/M phase increased two-fold in cells with low levels of DNA-PKcs. The study continued in Paper IV, where cells were synchronized to unmask potential roles of DNA-PKcs in specific cell cycle phases. Irradiation of DNA-PKcs suppressed cells in the G1/S phase caused a delay in cell cycle progression and an increase in accumulation of G2 cells. Further, these cells showed defects in DNA repair, where a significant amount of 53BP1 foci remained after 72 h. This further strengthens the hypothesis that DNA-PKcs has a role in regulation of mitotic progression. Several cellular signaling pathways are initiated in response to radiation. One of these downstream signaling proteins is AKT. We identified an interaction between DNA-PKcs and AKT. Knockouts of both AKT1 and AKT2 impaired DSB rejoining after radiation and low levels of DNA-PKcs increased radiosensitivity and decreased DNA repair further.

Submitted by Leonardo Silva Gomes null (drleonardosgomes@gmail.com) on 2018-01-22T00:28:55Z No. of bitstreams: 1 Dissertação corrigida.pdf: 2116172 bytes, checksum: f055c6caaf0bf0c28d76947eacf9e78c (MD5) / Approved for entry into archive by Silvana Alvarez null (silvana@ict.unesp.br) on 2018-01-23T19:48:52Z (GMT) No. of bitstreams: 1 kamezawa_lsg_me_sjc.pdf: 2116172 bytes, checksum: f055c6caaf0bf0c28d76947eacf9e78c (MD5) / Made available in DSpace on 2018-01-23T19:48:52Z (GMT). No. of bitstreams: 1 kamezawa_lsg_me_sjc.pdf: 2116172 bytes, checksum: f055c6caaf0bf0c28d76947eacf9e78c (MD5) Previous issue date: 2017-12-11 / A radioterapia é o uso da aplicação de radiação ionizante em áreas específicas, visando tratamento de tumores. Porém, a área irradiada e os tecidos normais circundantes estão sujeitos a danos agudos e crônicos. As injúrias no tecido ósseo variam desde osteopenia até osteorradionecrose e, devido a estas alterações, pacientes irradiados portadores de implantes vêm demonstrando maior taxa de insucesso. O objetivo deste estudo foi avaliar os efeitos da radioterapia, simulando uma dose total de um tratamento radioterápico convencional para pacientes oncológicos, na neoformação óssea e na osseointegração de implantes em fêmures de ratos. Foram utilizados neste estudo 66 ratos que receberam implantes cilíndricos de titânio comercialmente puro (TiCp) nos fêmures direito e esquerdo. Os animais foram divididos em 3 grupos: a) Grupo controle (C): cirurgia de colocação dos implantes (tecido sadio sem irradiação); b) Grupo irradiação precoce (Ip): cirurgia de colocação dos implantes seguido de irradiação após 24h; c) Grupo irradiado (I): irradiação e após 4 semanas, cirurgia de colocação dos implantes. Os animais dos grupos Ip e I foram submetidos a irradiação em 02 sessões de 15 Gy, totalizando a dose de 30 Gy. Os animais foram eutanasiados nos períodos de 2 e 7 semanas após o tratamento. Durante o experimento, os animais foram cuidadosamente monitorados quanto as alterações clínicas. Em cada período, 06 animais foram submetidos à análise histomorfométrica, visando avaliar a neoformação óssea e a interface osso-implante. Os outros 05 animais, dos períodos de 2 e 7 semanas após o tratamento, foram submetidos ao teste de torque reverso para avaliar a força de fixação osso-implante, obtida na osseointegração. Todos os dados foram estatisticamente analisados por meio da análise de variância de 2 fatores para torque reverso, porcentagem de área de formação óssea (BAFO) e porcentagem de superfície de contato osso implante (BIC) com nível de significância a 5%. O teste de Tukey foi realizado para determinação dos grupos homogêneos. A irradiação ionizante influenciou negativamente de maneira estatisticamente significante, retardando o processo de osseointegração, porém, não sendo capaz de inibí-lo. / The radiotherapy is ionizing radiation proceeding in specific areas, aiming at the treatment of tumors. However, the irradiated area and the surrounding normal tissue can develop acute and chronic damage. In bone tissue, injuries ranging from osteopenia to osteroadionecrosis and due to these changes patients irradiated with implants have shown higher failure rate. The objective of this study was to evaluate the effects of radiation, simulating a total dose of a conventional radiotherapy treatment for cancer, bone regeneration and osseointegration of implants in femurs of rats. It was used in this study 66 mice that receive cylindrical implants of commercially pure titanium (cpTi) on the right and left femurs. The animals were divided into 3 groups: a) control group (C): implant placement surgery (control group - healthy tissue without irradiation); b) Group early irradiation (Ip): placement of implants surgery followed by radiation after 24h; c) Group irradiated (I): irradiation and after 4 weeks of surgery implant placement. The animals of the Ip and I groups were subjected to irradiation in a double step at a dose of 15 Gy each, totalizing dose of 30 Gy. The animals were euthanized at periods of 2 and 7 weeks after treatment. During the experiment, the animals were carefully monitored for clinical changes. In each period 06 animals were submitted to histomorphometric analysis, to evaluate the bone formation and boneimplant interface. The other 05 animals, in periods of 2 and 7 weeks after treatment, were submitted to the reverse switch test to evaluate the strength of bone-implant fixation, obtained in osseointegration. All data were statistically analyzed by means of the 2-factor variance analysis for reverse torque, percentage of bone area fraction occupancy (BAFO) and percentage of bone implant contact (BIC) with significance level at 5%. The Tukey test was performed to determine the homogeneous groups. The ionizing radiation influenced negatively in a statistically significant way, delaying the process of osseointegration, but not being able to inhibit it.