Thesis (M.Med. (Diagnostic Radiology)) -- University of Limpopo, 2022 / BACKGROUND: Ionizing radiation is detrimental to growing cells. The potential risk of any dose of radiation in growing cells can lead to permanent damage of basic cellular structure resulting in a high risk of developing cancer in children. Therefore, paediatric doctors need sufficient knowledge to protect their patients from late effects of radiation resulting from medical use. Most studies report poor knowledge of radiation safety measures among doctors. PURPOSE: The purpose of this study is to assess the knowledge of radiation safety and radiation doses among paediatric doctors in Pietersburg and Mankweng Hospitals, Limpopo province, South Africa. OBJECTIVE: To assess the paediatric doctors’ knowledge of radiation doses used in radiological diagnostic imaging examinations, as well as their knowledge of radiation safety measures. METHODOLOGY: This is a survey of paediatric doctors in the paediatrics general ward, paediatric oncology, intensive care and neonatal units, and paediatric surgery department, at Pietersburg and Mankweng Hospitals. A self-administered questionnaire with 23 items on knowledge of radiation safety and radiation doses emitted during normal radiological examinations is used to collect the data in May 2021. Data are analysed using Statistical Package for Social Sciences (SSPS) version 26.0 software. Chi-squared test is used to analyse the relationship between variables. Analysis of variance (ANOVA) is used to analyse the differences between variables. A p value of <0.05 is considered statistically significant. A total score of 50% in each section is used to denote adequate knowledge. The result are presented in charts and tables. RESULTS: Out of 52 paediatric doctors, 47 completed the questionnaire achieving a 90.4% response rate. Majority of participants were females (n = 31; 66%). Overall, only 10 (21.2%) of the participants scored 50% and above, including three consultants, two registrars, two medical officers and one medical officer intern. Twenty-five (53.1%) participants scored 50% and above on knowledge of radiation safety. Nearly half (44.7%) of the doctors were familiar with the concept of ALARA principle in radiation dose optimisation. Three participants scored more than 50% in the knowledge of radiation doses section. Only five (10.6%) and 17 (36%) participants correctly identified MRI and ultrasound, respectively, as the radiological diagnostic modalities that do not utilize ionizing radiation. CONCUSION: The level of knowledge of radiation safety and radiation doses among the paediatric doctors are poor. A very small number of the paediatric doctors were able to identify non-ionizing radiation modalities that can be used as an alternative to reduce radiation exposure to paediatrics during radiological investigations. Paediatric doctors will benefit from courses on radiation safety and radiation doses to improve their knowledge and/or eliminate unwarranted exposure of their patients to ionizing radiation.

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)

89 Abstract The topic of the thesis concerns Czech nuclear law. Nuclear law can be defined as a set of special legal norms adjusting the terms of the nuclear energy and ionizing radiation usage, protection of population and environment against ionizing radiation, radiation accidents solving and treatment of radioactive waste. As such, nuclear law fully adjust the behaviour of all the natural and legal persons who are concerned with activities connected to the nuclear materials, ionizing radiation and natural resources of ionizing radiation. The field of nuclear law is closely connected to the branches of science dealing with the nuclear energy and ionizing radiation usage; therefore, the factual issues of which at least the fundamental knowledge is necessary for the understanding of nuclear law are given space at the beginning of the thesis. In its provisions, Czech nuclear law adjustment also reflect a number of international treaties and European Union regulations. On account of this, the next part of the thesis deals briefly with the international and European nuclear law adjustment. Important international organizations of the field are mentioned as well. The core of the paper consists in the part concerning the outline and analysis of the present adjustment of Czech nuclear law. The taxonomy of this...

The aim of this diploma thesis is to analyse health and safety system in department of nuclear medicine in Kolín hospital and evaluate its compliance with czech legislation. The thesis is compsed of four chapters. Chapter One gives a general introduction to health and safety issues and describes most important aspect of general health and safety legislation. Chapter Two explains the basic terms of ionizing radiation and radioactivity and focuses mainly on radiation protection, which is closely linked to the health and safety area. Chapter Three defines the legislative and institutional framework of health and safety in the area of ionizing radiation. This chapter is a starting point for Chapter Four, which analyzes the health and safety system in department of nuclear medicine in Kolín hospital, compares it with legislation requirements and evaluates the compliance.

A dosimetria de pacientes associada à avaliação das condições de funcionamento dos equipamentos médicos e aos procedimentos empregados na realização dos exames, desempenha um papel fundamental no sistema de proteção radiológica das exposições médicas. Nesse sentido, foi realizado um levantamento em grande escala das doses recebidas pelos pacientes submetidos a exames radiológicos convencionais realizados em uma amostra representativa de estabelecimentos de saúde do estado de São Paulo. Nesse levantamento foi empregado um kit dosimétrico postal originalmente desenvolvido, que permitiu a determinação da dose de entrada na pele (DEP) através da técnica de dosimetria termoluminescente. Paralelamente foram realizadas visitas in-loco a uma sub-amostra de estabelecimentos, onde as condições de funcionamento dos equipamentos de raios X médicos e do sistema de imagem foram avaliadas empregando-se procedimentos e equipamentos já estabelecidos em protocolos de controle de qualidade. O estudo completou-se com a elaboração de um catálogo de espectros na faixa de energia do radiodiagnóstico, que, através de procedimento desenvolvido, permitiu inferir espectros equivalentes em equipamentos médicos. Na determinação dos espectros foi empregado um detector semicondutor de telureto de cádmio e zinco (CdZnTe), cujas curvas de eficiência e escape foram determinadas experimentalmente para realização do processo de correção dos espectros (stripping procedure). O processo de amostragem de estabelecimentos de saúde realizado neste estudo permitiu verificar a distribuição de equipamentos de diagnóstico por imagem e a freqüência de exames radiológicos no estado de São Paulo. A partir desses resultados foram escolhidos os exames de tórax, crânio (e seios da face) e coluna para avaliação de DEP, uma vez que os mesmos apresentam as maiores freqüências anuais de exames por 1.000 habitantes: 100, 46 e 29, respectivamente. Na técnica de amostragem dos estabelecimentos de saúde incluídos neste estudo foi empregado como critério de estratificação a quantidade anual de exames radiológicos associados ao município de localização do estabelecimento. Do total de 200 estabelecimentos sorteados, 50 participaram da primeira etapa e 38 da segunda. Um total de 83 salas de exames (ou equipamentos) e 868 pacientes foram incluídos, e um conjunto de 1415 valores de DEP foi determinado. O resultado da distribuição dos valores de DEP permitiu determinar os chamados níveis de referência, que, no caso de pacientes adultos, se mostraram bastante semelhantes aos encontrados em outros estudos internacionais. No caso de pacientes infantis, a situação é bem diferente, obtendo-se valores pelo menos 2 vezes superiores a outros recomendados internacionalmente para a radiografia infantil mais freqüente (tórax). Esse fato sugere que as práticas empregadas na realização dos exames devem ser revisadas e que recomendações específicas a esse grupo de pacientes, a partir de estudos dirigidos, sejam publicadas. Constatou-se também alguns casos de DEP elevada pelo uso desnecessário de radioscopia de localização. Os testes de desempenho dos equipamentos e a avaliação das imagens realizadas sugerem que há possibilidade de melhoria das condições de realização dos exames, sem perda de informação diagnóstica presente na imagem e com redução das doses. Alguns espectros de raios X determinados experimentalmente apresentaram divergência em relação a outros catálogos já estabelecidos, numa faixa específica de energia do espectro (entre 25 e 40 keV). Para a sua utilização em situações práticas há necessidade de algumas correções na curva de eficiência, o que não inviabiliza a metodologia e os procedimentos estabelecidos. De forma geral, os resultados encontrados neste estudo permitem traçar um panorama das exposições médicas em radiologia convencional no estado de São Paulo, contribuindo para o aperfeiçoamento de futuras pesquisas que sejam realizadas na área, ou mesmo, para a implementação de políticas públicas. / Patients dosimetry, associated with the assessment of the performance of the radiological equipment and of the series of procedures employed in the accomplishment of the examinations, plays fundamental role in the radiation protection system of medical exposures. Therefore, a large-scale survey of absorbed doses was carried out in health services localized in the state of São Paulo, including patients submitted to conventional radiological examinations. In this survey a postal dosimetric kit, originally developed, was employed. It allows the evaluation of the entrance surface dose (ESD) to patients with thermoluminescence dosimeters. Also a series visits to a sub-sample of services was carried out, giving rise to the in-loco evaluation of the performance of the medical x-ray equipment and of the image system, using procedures and equipments already established in protocols of quality control. The study is completed with the elaboration of a catalogue of x-ray spectra, which provides means to infer the spectra generated by medical x-ray equipments. Measurements of x-ray spectra were carried out with a cadmium zinc telluride detector (CdZnTe), and the stripping procedure was performed taking into account both the contributions of efficiency and x-ray escape fraction, experimentally determined in this work. The stratified sampling technique furnished important data on the distribution of equipments and the annual frequency of examinations performed in the state of São Paulo. From these results radiological examinations of the chest, skull and sinus, and spine were selected for the evaluation of ESD, as their annual frequencies are the highest observed: 100, 46 and 29 per thousand inhabitants, respectively. The number of x-ray examinations carried out annually in the cities of the state was employed as the stratification criterion to construct the sample. From a total of 200 health services sampled, 50 agreed to participate of the first stage, and 38 of the second. A total of 83 rooms (or x-ray equipments) and 868 patients was included, and a set of 1415 values of ESD was measured. Diagnostic reference levels were determined with the outcomes of the distribution of ESD. For adult patients, the reference levels achieved are very similar to others obtained in international surveys. However, as far as pediatric patients are concerned, the situation is very different: the values found in this survey are twice larger than the international recommendations to chest radiography of children. This points out that the practices need to be revised and that specific recommendations to this patient group, following specific surveys, should be provided. Also, a series of high ESD values due to unnecessary localizing radioscopy were detected among our data. The results of the equipment performance tests and of the evaluation of image quality suggest that it is possible to improve the conditions of the examinations and to reduce doses to patients, without impairment of the diagnostic information. Some of the experimentally determined x-ray spectra show a discrepancy, when compared to other catalogue spectra, in a particular energy range 25 to 40 keV. The practical application of them will require some corrections in the efficiency curve, but the established methodology and procedures remain legitimate. In an extensive approach, the results of this study supply a panorama of medical exposures in conventional radiology in the state of São Paulo, contributing with resources to future research in the field and also to governmental actions.

Neste trabalho foram avaliados aventais de proteção e blindagens de ovário de cinco fabricantes segundo as normas NBR / IEC 61331-1 e NBR / IEC 61331-3 de 2004. Para a determinação da espessura equivalente de atenuação foram aplicadas três metodologias diferentes (interpolação linear, modelo de Archer e somatório de exponenciais), uma vez que a norma não indica como este valor deve ser obtido. Além disso, foram estimadas as incertezas associadas a cada método e a influência do número de medições na incerteza combinada. As características de confecção avaliadas foram: documento acompanhante, projeto, materiais, dimensões e marcação da etiqueta. Para esta avaliação foi elaborado um formulário que contemplava todas as exigências da NBR / IEC 61331-3. Os resultados mostraram uma grande diferença entre os valores de espessura equivalente de atenuação declarados e medidos. A comparação dos resultados das três metodologias aplicadas mostrou que há pouca variação entre os valores obtidos e entre as incertezas associadas nas diferentes metodologias. Foi possível observar também que o número de medições não contribui significativamente para o aumento da incerteza nas três metodologias. A metodologia que melhor se adequou à rotina do laboratório foi a metodologia da interpolação linear com cinco medições da taxa de kerma no ar. A discrepância entre os resultados apresentados neste trabalho e as exigências das normas estudadas mostra a necessidade de tornar compulsória a certificação dos dispositivos de proteção, contribuindo assim para o aumento da proteção radiológica do usuário. / In this work protective devices of five manufacturers were evaluated according to the NBR/IEC 61331-1 and NBR/IEC 61331-3 standards. Three different methodologies (linear interpolation, Archer model and sum of exponentials) were applied for the determination of the attenuation equivalent, since the standard does not indicate how it must be determined. Moreover, the uncertainties associated to each method, and the influence of the number of measurements in the combined uncertainty were estimated. The evaluated manufacture characteristics were: accompanying document, design, materials, dimensions and label marking. For this evaluation a check list about the requirements of the NBR/IEC 61331-3 standard was elaborated. The results showed a great difference between nominal and measured attenuation equivalent values. The comparison of the results using the three methodologies showed small variations among the obtained values and among the associated uncertainties in the different methodologies. It was possible to observe that the number of measurements does not contribute significantly for the increase of the uncertainty in all three methodologies. The best methodology for the laboratory routine is the linear interpolation methodology, with five measurements for each air kerma rate value. The discrepancy between the results obtained in this work and the requirements of the applied standards show the need to adopt a compulsory certification process for protective devices, thus contributing for the increase of the radiation protection of the users.

No presente trabalho foram determinadas as concentrações de radônio em seis cavernas do Parque Estadual Turístico do Alto Ribeira (PETAR) e foi estimada a dose efetiva anual recebida pelos guias turísticos da região. O PETAR apresenta quatro núcleos de visitação: Santana, Ouro Grosso, Caboclos e Casa de Pedra e recebe anualmente cerca de 40 mil visitantes. As cavernas escolhidas foram Couto, Água Suja, Laje Branca, Morro Preto e Santana, do núcleo Santana e a caverna Alambari de Baixo do núcleo Ouro Grosso, por receberem o maior número de turistas. Os níveis de radônio foram determinados utilizando detectores de traços nucleares do estado sólido Makrofol E expostos trimestralmente por um período de 26 meses, entre Outubro de 2003 e Novembro de 2005. As concentrações de 222Rn variaram na faixa de 153 Bq.m-3 a 6607 Bq.m-3, sendo observado que, de uma maneira geral, os níveis de radônio diminuem nos períodos frios. A dose efetiva anual, considerando os cenários mais realistas, com média geométrica das concentrações, fator de equilíbrio 0,5 e tempo de exposição anual para cada caverna, variou entre 0,2 mSv.a-1 para a caverna Couto, bastante ventilada e 4,0 mSv.a-1 para a caverna Santana, a mais visitada, com galerias sem comunicação externa. Para o pior cenário, com média aritmética das concentrações, fator de equilíbrio 1 e tempo de exposição anual para todas as cavernas, a dose efetiva anual total foi 16,1 mSv.a-1. Todas as estimativas da dose efetiva anual estão abaixo de 20 mSv.a-1, sugerido como o valor limite para dose efetiva anual para exposição ocupacional pela Comissão Internacional de Proteção Radiológica (ICRP 60, 1990). / In the present work, radon concentrations in six caves of PETAR - Parque Estadual Turístico do Alto Ribeira (High Ribeira River Turistic State Park) were carried out with Makrofol E solid state nuclear track detectors (SSNTD) and used to assess the annual effective dose received by regional tour guides. The park has four visitation centers: Santana, Ouro Grosso, Caboclos e Casa de Pedra and receives nearly 40,000 people annually. The caves evaluated were Couto, Água Suja, Laje Branca, Morro Preto and Santana, from Santana center and Alambari de Baixo from Ouro Grosso center, for being the most frequently visited caves. The exposure period of the SSNTD was, at least, three months, over a period of 26 months, from October 2003 to November 2005. The 222Rn concentrations lay in a range from 153 Bq.m-3 to 6607 Bq.m-3 and we observed that, in general, for chilly weather, the radon levels decrease. The annual effective dose, considering the most realistic scenario, with geometric mean concentrations, an equilibrium factor of 0.5 and annual exposure time for each cave, varied from 0.2 mSv.a-1 for the Couto cave, strongly ventilated, to 4.0 mSv.a-1 for the Santana cave, the most frequently visited and no external communication. For the worst scenario, with arithmetic mean concentrations, equilibrium factor 1 and annual exposure time for all caves, the annual effective dose was 16.1 mSv.a-1. All assessed effective doses received by the tour guides are bellow 20 mSv.a-1, suggested as an annual effective dose limit for occupational exposure by the International Commission of Radiological Protection (ICRP 60, 1990).

Neste trabalho foram avaliados aventais de proteção e blindagens de ovário de cinco fabricantes segundo as normas NBR / IEC 61331-1 e NBR / IEC 61331-3 de 2004. Para a determinação da espessura equivalente de atenuação foram aplicadas três metodologias diferentes (interpolação linear, modelo de Archer e somatório de exponenciais), uma vez que a norma não indica como este valor deve ser obtido. Além disso, foram estimadas as incertezas associadas a cada método e a influência do número de medições na incerteza combinada. As características de confecção avaliadas foram: documento acompanhante, projeto, materiais, dimensões e marcação da etiqueta. Para esta avaliação foi elaborado um formulário que contemplava todas as exigências da NBR / IEC 61331-3. Os resultados mostraram uma grande diferença entre os valores de espessura equivalente de atenuação declarados e medidos. A comparação dos resultados das três metodologias aplicadas mostrou que há pouca variação entre os valores obtidos e entre as incertezas associadas nas diferentes metodologias. Foi possível observar também que o número de medições não contribui significativamente para o aumento da incerteza nas três metodologias. A metodologia que melhor se adequou à rotina do laboratório foi a metodologia da interpolação linear com cinco medições da taxa de kerma no ar. A discrepância entre os resultados apresentados neste trabalho e as exigências das normas estudadas mostra a necessidade de tornar compulsória a certificação dos dispositivos de proteção, contribuindo assim para o aumento da proteção radiológica do usuário. / In this work protective devices of five manufacturers were evaluated according to the NBR/IEC 61331-1 and NBR/IEC 61331-3 standards. Three different methodologies (linear interpolation, Archer model and sum of exponentials) were applied for the determination of the attenuation equivalent, since the standard does not indicate how it must be determined. Moreover, the uncertainties associated to each method, and the influence of the number of measurements in the combined uncertainty were estimated. The evaluated manufacture characteristics were: accompanying document, design, materials, dimensions and label marking. For this evaluation a check list about the requirements of the NBR/IEC 61331-3 standard was elaborated. The results showed a great difference between nominal and measured attenuation equivalent values. The comparison of the results using the three methodologies showed small variations among the obtained values and among the associated uncertainties in the different methodologies. It was possible to observe that the number of measurements does not contribute significantly for the increase of the uncertainty in all three methodologies. The best methodology for the laboratory routine is the linear interpolation methodology, with five measurements for each air kerma rate value. The discrepancy between the results obtained in this work and the requirements of the applied standards show the need to adopt a compulsory certification process for protective devices, thus contributing for the increase of the radiation protection of the users.

No presente trabalho foram determinadas as concentrações de radônio em seis cavernas do Parque Estadual Turístico do Alto Ribeira (PETAR) e foi estimada a dose efetiva anual recebida pelos guias turísticos da região. O PETAR apresenta quatro núcleos de visitação: Santana, Ouro Grosso, Caboclos e Casa de Pedra e recebe anualmente cerca de 40 mil visitantes. As cavernas escolhidas foram Couto, Água Suja, Laje Branca, Morro Preto e Santana, do núcleo Santana e a caverna Alambari de Baixo do núcleo Ouro Grosso, por receberem o maior número de turistas. Os níveis de radônio foram determinados utilizando detectores de traços nucleares do estado sólido Makrofol E expostos trimestralmente por um período de 26 meses, entre Outubro de 2003 e Novembro de 2005. As concentrações de 222Rn variaram na faixa de 153 Bq.m-3 a 6607 Bq.m-3, sendo observado que, de uma maneira geral, os níveis de radônio diminuem nos períodos frios. A dose efetiva anual, considerando os cenários mais realistas, com média geométrica das concentrações, fator de equilíbrio 0,5 e tempo de exposição anual para cada caverna, variou entre 0,2 mSv.a-1 para a caverna Couto, bastante ventilada e 4,0 mSv.a-1 para a caverna Santana, a mais visitada, com galerias sem comunicação externa. Para o pior cenário, com média aritmética das concentrações, fator de equilíbrio 1 e tempo de exposição anual para todas as cavernas, a dose efetiva anual total foi 16,1 mSv.a-1. Todas as estimativas da dose efetiva anual estão abaixo de 20 mSv.a-1, sugerido como o valor limite para dose efetiva anual para exposição ocupacional pela Comissão Internacional de Proteção Radiológica (ICRP 60, 1990). / In the present work, radon concentrations in six caves of PETAR - Parque Estadual Turístico do Alto Ribeira (High Ribeira River Turistic State Park) were carried out with Makrofol E solid state nuclear track detectors (SSNTD) and used to assess the annual effective dose received by regional tour guides. The park has four visitation centers: Santana, Ouro Grosso, Caboclos e Casa de Pedra and receives nearly 40,000 people annually. The caves evaluated were Couto, Água Suja, Laje Branca, Morro Preto and Santana, from Santana center and Alambari de Baixo from Ouro Grosso center, for being the most frequently visited caves. The exposure period of the SSNTD was, at least, three months, over a period of 26 months, from October 2003 to November 2005. The 222Rn concentrations lay in a range from 153 Bq.m-3 to 6607 Bq.m-3 and we observed that, in general, for chilly weather, the radon levels decrease. The annual effective dose, considering the most realistic scenario, with geometric mean concentrations, an equilibrium factor of 0.5 and annual exposure time for each cave, varied from 0.2 mSv.a-1 for the Couto cave, strongly ventilated, to 4.0 mSv.a-1 for the Santana cave, the most frequently visited and no external communication. For the worst scenario, with arithmetic mean concentrations, equilibrium factor 1 and annual exposure time for all caves, the annual effective dose was 16.1 mSv.a-1. All assessed effective doses received by the tour guides are bellow 20 mSv.a-1, suggested as an annual effective dose limit for occupational exposure by the International Commission of Radiological Protection (ICRP 60, 1990).

La scanographie est une technique d’imagerie médicale performante offrant des bénéfices considérables pour le diagnostic et le suivi médical des patients. Néanmoins, la question des effets adverses potentiels induits par l’exposition aux rayons-X se pose, tant au niveau individuel qu’en termes de santé publique du fait de la fréquence du recours à cette procédure. Des premières études épidémiologiques suggèrent une augmentation du risque de cancer associée à l’exposition à la scanographie durant l’enfance ou l’adolescence. Néanmoins, l’interprétation de ces résultats reste controversée et les connaissances sur le risque de cancer radio-induit à ce niveau d’exposition et pendant l’enfance demeurent limitées.En France, la cohorte « Enfant Scanner » est mise en place par l’IRSN pour étudier l’incidence de cancer dans une population de près de 110 000 enfants ayant reçu des examens par scanographie avant l’âge de 10 ans dans 21 centres hospitaliers universitaires. Cette étude participe au projet européen Epi-CT, coordonné par le Centre International de Recherche sur le Cancer, intégrant neuf cohortes nationales sur la base d’un protocole commun. A partir de la cohorte française, cette thèse s’intéresse à caractériser les expositions des enfants recevant des examens diagnostiques par scanographie et à fournir des éléments de quantification du risque de cancer associé.Une évaluation dosimétrique est réalisée à partir des protocoles radiologiques utilisés en pédiatrie entre 2000 et 2011 dans les services hospitaliers participant. Cette étude présente l’évolution des expositions au cours de la période ainsi que la variabilité des pratiques dans les services. Les résultats montrent l’existence d’une marge d’optimisation des protocoles utilisés pour limiter l’exposition des patients, en particulier pour des explorations de la tête qui sont les examens les plus fréquents en pédiatrie.Une évaluation du risque de cancer potentiellement induit par des actes de scanographie pédiatrique a été réalisée, sur la base d’estimations de risque obtenues pour d’autres contextes d’exposition aux rayonnements ionisants. Les résultats montrent que chaque examen pourrait être associé à un excès de risque de tumeur du système nerveux central (SNC), de cancer du sein, de la thyroïde ou de leucémies compris entre 0,01‰ et 5‰. Le risque de cancer serait jusqu’à 7 fois supérieur pour des patients âgés de 1 an par rapport à des enfants de 10 ans. Les incertitudes attachées à ces prédictions de risque ont été quantifiées par simulations.A partir du suivi d’incidence de la cohorte, la relation dose-réponse a été étudiée entre le risque de tumeurs du SNC, de leucémies et de lymphome, et les doses cumulées aux organes d’intérêt reçues lors d’examens par scanographie. Aucune augmentation significative de risque n’a été mise en évidence. En 2011, le suivi dans la cohorte – 4 ans en moyenne– était en effet très court. Les analyses ont néanmoins caractérisé l’impact de syndromes d’immunodéficiences et d’autres facteurs génétiques de prédisposition au cancer sur les estimations de risque, et mis en évidence l’importance de prendre en compte l’indication des examens dans ce type d’étude.Le suivi de la cohorte doit être poursuivi afin de fournir des estimations de risque plus robustes. L’extension de la durée de suivi de cette population ainsi que les résultats attendus à partir d’autres études, notamment dans le cadre du projet Epi-CT, devraient constituer, dans les 5 prochaines années, une avancée tout à fait significative sur la question des risques associés à la scanographie. A ce jour, les prédictions réalisées dans le cadre d’évaluations de risque demeurent incertaines, en particulier pour les tumeurs du SNC, mais constituent une aide pour orienter le recours à la scanographie. Des efforts d’optimisation des procédures radiologiques demeurent, par ailleurs, encore nécessaires pour réduire les doses délivrées en pédiatrie ainsi que les risques possiblement associés / Computed tomography (CT) is a powerful imaging technique that provides great benefits for diagnosis and medical management of patients. Nonetheless, the widespread use of this procedure raises many concerns about the potential adverse effects induced by X-rays exposure, both in clinical practice and in terms of public health. First epidemiological studies have suggested an increased risk of cancer associated with CT scan exposures in childhood or adolescence. The interpretation of these results is, however, controversial, and evidence about radiation-induced risks of cancer is still limited at this level of exposure and during childhood.In France, the "Enfant Scanner" cohort was set up by IRSN to study the incidence of cancer among more than 100,000 children who received CT scans before the age of 10 in 21 university hospitals. This study is part of the European Epi-CT project – coordinated by the International Agency for Research on Cancer – which includes nine national cohorts set up on the basis of a common protocol. The current thesis, based on the French cohort, focuses on characterizing the exposure of children receiving diagnostic CT scans and quantifying the risk of cancer associated with these exposures.Dosimetric assessment was performed from the radiological protocols used in paediatrics between 2000 and 2011 in the participating hospitals. This study presents the evolution of the exposures during the period and the variability of practices in the radiology departments. The results show that there is a leeway for optimizing the procedures and limiting the exposure of patients, especially for scans of the head that account for most of the examinations in paediatrics.From these exposure measurements, a quantitative assessment of cancer risk potentially induced by CT scans in paediatrics was performed – on the basis of estimates of risk in other contexts of ionizing radiation exposure. The results show that each CT scan could be associated with an excess risk of tumours of the central nervous system, breast cancer, thyroid cancer or leukaemia ranging from 0.01‰ to 5‰. Cancer risks may be up to 7 times higher for patients aged 1 year compared to 10 year olds. Uncertainties attached to these risk predictions were quantified by simulations.From the follow-up of cancer incidence in the cohort, the dose-response relation was studied between the risk of tumors of the central nervous system, leukaemia and lymphoma, and cumulative X-ray doses to the organs of interest from CT scans. No significant increased risk was observed. Indeed, in 2011, the duration of the follow-up, i.e. 4 years on average, was very short. The analyzes have nevertheless characterized the impact of (acquired or hereditary) immunodeficiencies and other genetic factors predisposing to cancer on the risk estimates, and highlighted the importance of considering the indication of examinations in studies on CT scans.The follow-up of the cohort should be extended to provide more robust risk estimates. Extension of this study as well as expected results from other cohorts, particularly within the Epi-CT project, would provide, in the next 5 years, significant progresses on the issue of the potential adverse effects of CT. To date, risk predictions from quantitative risk assessment are still uncertain, especially for cerebral tumours, but should help to guide the use of CT. In addition, efforts for optimizing the radiological procedures are still needed to reduce the doses delivered in paediatrics and the potential associated risks.