Os órgãos de saúde internacionais e nacionais, como o Ministério da Saúde na portaria 453/98 da Vigilância Sanitária, exigem que a Dose de Entrada na Pele seja avaliada para cada equipamento mamográfico através da leitura de um sistema câmara de ionização-eletrómetro corrigida pelo fator de retroespalhamento. Ao não existir menção explícita na portaría de valores utilizáveis para o fator de retroespalhamento, este trabalho visa à determinação experimental do fator de retroespalhamento, através da utilização dos dosímetros termoluminescentes TLD-100. No estudo são verificadas as dependências geométricas e espectrais do fator de retroespalhamento, assim como do valor da Dose de Entrada na Pele, e da Dose em Profundidade, correspondentes com as técnicas radiográficas empregadas nos exames mamográficos convencionais de rotina. Foram avaliados feixes na faixa de 0,35 mmAl até 0,43 mmAl, tensões do tubo de 25kV, 28kV, 30kV, e 32kV, assim como os três tamanhos de campo disponíveis no Mamógrafo Senographe DMR utilizado, e distancias focofilme iguais a 56cm, 61cm e 66cm. Os resultados obtidos foram comparados com publicações existentes, as quais apresentam resultados obtidos através de Simulação Monte Carlo, câmaras de ionização, e dosímetros TLD-100. Os resultados obtidos neste trabalho permitem estabelecer e discutir as dependências das grandezas dosimétricas estudadas com a Camada Semi-Redutora, tensão do tubo, combinação ânodo-filtro, tamanho de campo, distância foco-filme e espessura da mama. / National and international health organizations such as the Brazilian Ministry of Health, through its Secretary of Health Surveillance establishes in the publication Nº 453/98 that in all mammographic equipments must be evaluated the entrance-skin dose through the readings of an ionization chamber-electrometer system corrected by the backscatter factor, among others factors. Nevertheless, there is no explicit mention for useful values of backscatter factor in this document; the main aim of this work is the experimental determination of backscatter factor through the use of TLD-100 dosimeters. In this study, the geometric and spectral dependencies of the backscatter factor, entrance-skin dose and the in-depth dose were evaluated, corresponding to the most radiographic techniques employed in conventional mammographic procedures, i.e., beam qualities in the range of 0.35 mmAl to 0.43 mmAl, tube voltages from 25kV to 32kV, focus-film distances from 56cm to 66cm, and three field sizes were evaluated. Our results were compared with those previously published obtained through Monte Carlo simulation, ionization chambers and TLD dosimeters. The results obtained in this work allow studying the dependency of the mentioned dosimetric quantities with the half-value layer, tube voltage, anode-filter combination, field size, focusfilm distance and breasting thickness of the breast.

Os órgãos de saúde internacionais e nacionais, como o Ministério da Saúde na portaria 453/98 da Vigilância Sanitária, exigem que a Dose de Entrada na Pele seja avaliada para cada equipamento mamográfico através da leitura de um sistema câmara de ionização-eletrómetro corrigida pelo fator de retroespalhamento. Ao não existir menção explícita na portaría de valores utilizáveis para o fator de retroespalhamento, este trabalho visa à determinação experimental do fator de retroespalhamento, através da utilização dos dosímetros termoluminescentes TLD-100. No estudo são verificadas as dependências geométricas e espectrais do fator de retroespalhamento, assim como do valor da Dose de Entrada na Pele, e da Dose em Profundidade, correspondentes com as técnicas radiográficas empregadas nos exames mamográficos convencionais de rotina. Foram avaliados feixes na faixa de 0,35 mmAl até 0,43 mmAl, tensões do tubo de 25kV, 28kV, 30kV, e 32kV, assim como os três tamanhos de campo disponíveis no Mamógrafo Senographe DMR utilizado, e distancias focofilme iguais a 56cm, 61cm e 66cm. Os resultados obtidos foram comparados com publicações existentes, as quais apresentam resultados obtidos através de Simulação Monte Carlo, câmaras de ionização, e dosímetros TLD-100. Os resultados obtidos neste trabalho permitem estabelecer e discutir as dependências das grandezas dosimétricas estudadas com a Camada Semi-Redutora, tensão do tubo, combinação ânodo-filtro, tamanho de campo, distância foco-filme e espessura da mama. / National and international health organizations such as the Brazilian Ministry of Health, through its Secretary of Health Surveillance establishes in the publication Nº 453/98 that in all mammographic equipments must be evaluated the entrance-skin dose through the readings of an ionization chamber-electrometer system corrected by the backscatter factor, among others factors. Nevertheless, there is no explicit mention for useful values of backscatter factor in this document; the main aim of this work is the experimental determination of backscatter factor through the use of TLD-100 dosimeters. In this study, the geometric and spectral dependencies of the backscatter factor, entrance-skin dose and the in-depth dose were evaluated, corresponding to the most radiographic techniques employed in conventional mammographic procedures, i.e., beam qualities in the range of 0.35 mmAl to 0.43 mmAl, tube voltages from 25kV to 32kV, focus-film distances from 56cm to 66cm, and three field sizes were evaluated. Our results were compared with those previously published obtained through Monte Carlo simulation, ionization chambers and TLD dosimeters. The results obtained in this work allow studying the dependency of the mentioned dosimetric quantities with the half-value layer, tube voltage, anode-filter combination, field size, focusfilm distance and breasting thickness of the breast.

The ability to accurately predict dose from electron backscatter created by internal lead shielding utilized during various superficial electron beam treatments (EBT), such as lip carcinoma, is required to avoid the possibility of an overdose. Methods for predicting this dose include the use of empirical equations or physically measuring the electron backscatter factor (EBF) and upstream electron backscatter intensity (EBI). The EBF and upstream EBI are defined as the ratio of dose at, or upstream, from the shielding interface with and without the shielding present respectively. The accuracy of these equations for the local treatment machines was recognised as an area that required verification; in addition the ability of XiO's electron Monte Carlo (eMC) treatment planning algorithm to handle lead interfaces was examined. A Monte Carlo simulation using the EGSnrc package of a Siemens Artiste Linac was developed for 6, 9, 12, and 15 MeV electron energies and was verified against physical measurements to within an accuracy of 2 % and 2 mm. Electron backscatter dose distributions were predicated using the MC model, Gafchromic film, and XiO eMC, which when compared showed that XiO's eMC could not accurately calculate dose at the lead interface. Several MC simulations of lead interfaces at different depths, corresponding to energies of 0.2-14 MeV at the interfaces, were used to validate the accuracy of the equations, with the results concluding that the equation could not accurately predict EBF and EBI values, especially at low energies. From this data, an equation was derived to allow estimation of the EBF and upstream EBI, which agreed to within 1.3 % for the EBF values and can predict the upstream EBI to a clinically acceptable level for all energies.