Monte Carlo calculation of whole body counter efficiency factors for different computational phantoms.

Individual monitoring can provide an estimate of the radioactivity present in the body of the exposed individuals. Periodic monitoring of occupationally exposed individuals is of great importance in case of accidental incorporation. Computational phantoms and Monte Carlo codes are often used to complement the calibration method of counting systems in internal dosimetry. Here, counting efficiency (CE) factors for a WBC system were calculated using MC simulations. The WBC system with a NaI(Tl) detector and the BOMAB phantom was modeled using three MC codes. After validation, the models were used to obtain CE values for a wide range of energies, and a CE curve was generated for the WBC system. To estimate the effects of anatomical differences on the measurement process, two anthropomorphic voxel phantoms were modeled using the VMC code. For the detector position with the highest CE value, the differences when comparing BOMAB results with the MaMP and Yale results were (-1 ± 6)% and (-1 ± 3)%, respectively. The results confirm that the use of the BOMAB phantom is a good approach for the calibration of the whole-body counter system. Measurements should be made at detector position with the highest CE values, and it is recommended to use the mean Monte Carlo CE values calculated in this work.

Calculation of absorbed dose in paediatric phantoms using Monte Carlo techniques for 18F-FDG and 99mTc-DMSA and the new TIAC.

The radiopharmaceuticals most commonly used in nuclear medicine are 18F-FDG and 99mTc-DMSA, both of which are administered to paediatric and adult patients using the same time activity coefficient. However, the IAEA recommends specific paediatric dosimetry. The aim of this work (TW) was to estimate the absorbed dose for 18F-FDG and 99mTc-DMSA using two paediatric voxel phantoms (Baby and Child) by Monte Carlo techniques. Biokinetic data for both radiopharmaceuticals were obtained from ICRP 128. In addition, the new time-integrated activity coefficient (TIAC) values from a recent publication were examined for the following organs: Brain, urinary bladder wall, liver, heart wall, and lung. The absorbed dose per injected activity (AD/IA) and effective dose per injected activity (E/IA) values were calculated for both phantoms and the results were compared with simulated data of paediatric phantoms from ICRP 128, MIRDcalc software and available literature. Regarding AD/IA in organs, differences of up to 61% and 115% were found for the Baby phantom and 120% and 167% for the Child phantom using 18F-FDG and 99mTc-DMSA, respectively. For FDG using the new TIAC, a maximum difference of 244% was observed. For E/IA, the maximum differences were 27% and 31% for the Baby and Child phantoms, respectively, for FDG and DSMA. In this study, new dosimetric data were calculated using Baby and Child phantoms and the newly recommended TIAC.

Proposal of an algorithm to evaluate geometric distortion and artifact spreading in digital breast tomosynthesis.

BACKGROUND: According to the European Reference Organization for Quality Assurance Breast Screening and European Diagnostic Services, the spatial accuracy of reconstructed images and reconstruction artifacts must be evaluated in digital breast tomosynthesis (DBT) quality control procedures. PURPOSE: To propose a computational algorithm to evaluate the geometric distortion and artifact spreading (GDAS) in DBT images. MATERIAL AND METHODS: The proposed algorithm analyzed tomosynthesis images of a phantom that contains aluminum spheres (1 mm in diameter) arranged in a rectangular matrix spaced 5 cm apart that was inserted in 5-mm-thick polymethylmethacrylate (PMMA). RESULTS: The obtained results were compared with the values provided by the algorithm developed by the National Coordinating Center for the Physics of Mammography (NCCPM). In the comparison, the results depended on the dimensions of the region of interest (ROI). This dependence proves the benefit of the proposed algorithm because it allows the user to select the ROI. CONCLUSION: The computational algorithm proved to be useful for the evaluation of GDAS in DBT images, in the same way as the reference algorithm (NCCPM), as well as allowing the selection of the ROI dimensions that best suit the spreading of the artifact in the analyzed images.

Assessment of breast density in women from different regions of Brazil.

In many countries, there is an interest in determining the location of the women with the highest breast density. This investigation is important for optimize screening for breast cancer for women with dense breasts as other imaging modalities since 2D mammography is not very efficient on this type of breast. The objective of this study was to evaluate the variations in breast density in Brazilian women of different regions of Brazil. The mammographic images were taken from four regions of Brazil. The images, in the cranial caudal (CC) projection, were separated into intervals of compressed breast thickness (CBT) and patient age and were analysed by the software VolparaDensity, where volumetric breast density (VBD) calculations were performed. For each interval, null hypothesis tests for the mean difference between the VBD from the four regions of Brazil were performed. The paired tests indicated that there was a significant difference in the VBD of the women in the different regions of Brazil, with variations from 11.05% to 36.73%. Higher VBD was observed for women living in the Southeast region, followed by the Midwest, Northeast, and North regions. The Brazilian IBGE data show that the most urbanised region in Brazil is the Southeast, which coincides with the second highest rate of breast cancer in Brazil, according to the Brazilian National Cancer Institute (INCA). It is also known that breast cancer is strongly related to breast density; therefore, the results of this work support the data presented by federal agencies demonstrating that women living in the most urbanised region of Brazil (e.g., Southeast) present the highest breast density.

Backscatter factors calculation for intraoral dental radiology.

The dosimetry of intraoral radiography procedures is of great interest since dental examinations are among the most numerous radiological procedures. Usually, the surveys are performed using measurements free in air. The entrance surface air kerma (Ke) can be estimated from measurements of incident air kerma and the use of backscatter factors (BSF). The purpose of this work is to calculate BSF values suitable for intraoral radiography. In addition to specific intraoral radiography, a comprehensive reassessment of internationally recommended BSF values was performed through Monte Carlo simulations. Moreover, theKewas estimated using the calculated BSF values for a sample of 44 intraoral radiography systems. The interpolation of intraoral radiography BSF values from reference data can lead to an overestimation of up to 10% and 6% in comparison with the values calculated in this work for monoenergetic photons and x-ray spectra, respectively. Such discrepancy may be relevant when defining diagnostic reference levels (DRLs) or performing quality control tests. The calculations for a sample of 44 intraoral radiography systems showed that the majority of the equipment operates with an entrance surface air kerma higher than 3.5 mGy. In the case of adopting a single value to estimateKe, the use of BSF equal to 1.2 results in less dispersion compared to calculated values in this work and the use of 1.1 can underestimateKevalues up to 12%.

Determination of the dose rate constant through Monte Carlo simulations with voxel phantoms.

PURPOSE: The main goal of this study was to determine the dose rate constant of radionuclides used in Nuclear Medicine when they are biodistributed in humans. The secondary goal was to calculate the effective half-life for the same radionuclides in order to determine the realistic dose due to the incorporation of these nuclides for a variety of reasons. METHODS: Anthropomorphic voxel phantoms, with characteristics based on ICRP-110 were considered and the biodistributions of radionuclides were simulated using the Monte Carlo code MCNPX. In addition, the effective half-lives for all simulated radionuclides were calculated. RESULTS: The results for the dose rate constant, taking into account the patient body attenuation, showed no correlation between the biodistribution of the radionuclide and the energy of the radiation emitted. Body attenuation ranged between 6.7% and 94.1%. Also, the priority angle of radiation emission was determined. The values found for the body attenuation agree with the literature, corroborating the calculation of the body dose rate constant. CONCLUSIONS: The results for the body dose rate constant calculated in this work, for 30 radionuclides and 57 radiopharmaceuticals, and their effective half-lives, may be used to estimate the dose emitted by a person who has incorporated a radionuclide in the Nuclear Medicine activity range. This dose will be optimized when the body dose rate constant and the effective half-life determined in this study are used together with dose reduction factors.

Monte Carlo derivation of filtered tungsten anode X-ray spectra for dose computation in digital mammography / Derivação Monte Carlo de espectros filtrados de raios X de ânodo de tungstênio para determinação de dose em mamografia digital

Abstract Objective: Derive filtered tungsten X-ray spectra used in digital mammography systems by means of Monte Carlo simulations. Materials and Methods: Filtered spectra for rhodium filter were obtained for tube potentials between 26 and 32 kV. The half-value layer (HVL) of simulated filtered spectra were compared with those obtained experimentally with a solid state detector Unfors model 8202031-H Xi R/F & MAM Detector Platinum and 8201023-C Xi Base unit Platinum Plus w mAs in a Hologic Selenia Dimensions system using a direct radiography mode. Results: Calculated HVL values showed good agreement as compared with those obtained experimentally. The greatest relative difference between the Monte Carlo calculated HVL values and experimental HVL values was 4%. Conclusion: The results show that the filtered tungsten anode X-ray spectra and the EGSnrc Monte Carlo code can be used for mean glandular dose determination in mammography.

Resumo Objetivo: Derivar espectros filtrados de raios X de tungstênio utilizados em sistemas de mamografia digital por meio de simulações Monte Carlo. Materiais e Métodos: Espectros filtrados por filtro de ródio foram obtidos para potenciais do tubo entre 26 e 32 kV. Os valores de camada semirredutora (CSR) dos espectros filtrados simulados foram comparados aos valores obtidos experimentalmente com um detector de estado sólido Unfors modelo 8202031-H Xi R/F & MAM Detector Platinum e unidade base 8201023-C Xi Platinum Plus w mAs em um sistema Hologic Selenia Dimensions utilizado no modo radiografia direta. Resultados: Os valores de CSR calculados mostraram boa concordância quando comparados com os valores obtidos experimentalmente. A maior diferença relativa entre os valores de CSR calculados com Monte Carlo e os valores de CSR experimentais foi 4%. Conclusão: Os resultados demonstram que os espectros filtrados de raios X de ânodo de tungstênio e o código de Monte Carlo EGSnrc podem ser utilizados para determinar a dose glandular média em mamografia.

Monte Carlo derivation of filtered tungsten anode X-ray spectra for dose computation in digital mammography.

OBJECTIVE: Derive filtered tungsten X-ray spectra used in digital mammography systems by means of Monte Carlo simulations. MATERIALS AND METHODS: Filtered spectra for rhodium filter were obtained for tube potentials between 26 and 32 kV. The half-value layer (HVL) of simulated filtered spectra were compared with those obtained experimentally with a solid state detector Unfors model 8202031-H Xi R/F & MAM Detector Platinum and 8201023-C Xi Base unit Platinum Plus w mAs in a Hologic Selenia Dimensions system using a direct radiography mode. RESULTS: Calculated HVL values showed good agreement as compared with those obtained experimentally. The greatest relative difference between the Monte Carlo calculated HVL values and experimental HVL values was 4%. CONCLUSION: The results show that the filtered tungsten anode X-ray spectra and the EGSnrc Monte Carlo code can be used for mean glandular dose determination in mammography.

OBJETIVO: Derivar espectros filtrados de raios X de tungstênio utilizados em sistemas de mamografia digital por meio de simulações Monte Carlo. MATERIAIS E MÉTODOS: Espectros filtrados por filtro de ródio foram obtidos para potenciais do tubo entre 26 e 32 kV. Os valores de camada semirredutora (CSR) dos espectros filtrados simulados foram comparados aos valores obtidos experimentalmente com um detector de estado sólido Unfors modelo 8202031-H Xi R/F & MAM Detector Platinum e unidade base 8201023-C Xi Platinum Plus w mAs em um sistema Hologic Selenia Dimensions utilizado no modo radiografia direta. RESULTADOS: Os valores de CSR calculados mostraram boa concordância quando comparados com os valores obtidos experimentalmente. A maior diferença relativa entre os valores de CSR calculados com Monte Carlo e os valores de CSR experimentais foi 4%. CONCLUSÃO: Os resultados demonstram que os espectros filtrados de raios X de ânodo de tungstênio e o código de Monte Carlo EGSnrc podem ser utilizados para determinar a dose glandular média em mamografia.

Comparison of mean glandular dose values provided by a digital breast tomosynthesis system in Brazil.

Studies are needed to determine the radiation dose of patients that are undergoing Digital breast tomosynthesis (DBT) procedures. Mean glandular dose (DG) values were derived from the incident air kerma (Ki) measurements and tabulated conversion coefficients. Ki values were obtained through an ionization chamber positioned in a Hologic Selenia Dimensions system using appropriate exposure parameters. This work contributes to determine the reliable radiation dose received by the patients and compare DG values provided by this DBT system images.

Dosimetria e avaliação da qualidade da imagem em um sistema de radiografia direta / Dosimetry and image quality assessment in a direct radiography system

Objetivo: Avaliar a dose glandular média utilizando um detector de estado sólido e a qualidade da imagem de um sistema de radiografia direta a partir de objetos simuladores. Materiais e Métodos: Irradiações foram realizadas utilizando o controle automático de exposição e placas de polimetilmetacrilato com diferentes espessuras para o cálculo da dose glandular média. A qualidade da imagem foi avaliada por meio das estruturas visualizadas nas imagens dos objetos simuladores. Resultados: Considerando a incerteza das medições, os resultados de dose glandular média estão de acordo com os valores fornecidos pelo equipamento e com os níveis de referência adotados internacionalmente. Os resultados obtidos a partir das imagens dos objetos simuladores estavam em conformidade com os valores de referência. Conclusão: Este trabalho contribui para verificar a conformidade do equipamento em relação a dose e qualidade da imagem. .

Objective: To evaluate the mean glandular dose with a solid state detector and the image quality in a direct radiography system, utilizing phantoms. Materials and Methods: Irradiations were performed with automatic exposure control and polymethyl methacrylate slabs with different thicknesses to calculate glandular dose values. The image quality was evaluated by means of the structures visualized on the images of the phantoms. Results: Considering the uncertainty of the measurements, the mean glandular dose results are in agreement with the values provided by the equipment and with internationally adopted reference levels. Results obtained from images of the phantoms were in agreement with the reference values. Conclusion: The present study contributes to verify the equipment conformity as regards dose values and image quality. .

Dosimetry and image quality assessment in a direct radiography system.

OBJECTIVE: To evaluate the mean glandular dose with a solid state detector and the image quality in a direct radiography system, utilizing phantoms. MATERIALS AND METHODS: Irradiations were performed with automatic exposure control and polymethyl methacrylate slabs with different thicknesses to calculate glandular dose values. The image quality was evaluated by means of the structures visualized on the images of the phantoms. RESULTS: Considering the uncertainty of the measurements, the mean glandular dose results are in agreement with the values provided by the equipment and with internationally adopted reference levels. Results obtained from images of the phantoms were in agreement with the reference values. CONCLUSION: The present study contributes to verify the equipment conformity as regards dose values and image quality.

OBJETIVO: Avaliar a dose glandular média utilizando um detector de estado sólido e a qualidade da imagem de um sistema de radiografia direta a partir de objetos simuladores. MATERIAIS E MÉTODOS: Irradiações foram realizadas utilizando o controle automático de exposição e placas de polimetilmetacrilato com diferentes espessuras para o cálculo da dose glandular média. A qualidade da imagem foi avaliada por meio das estruturas visualizadas nas imagens dos objetos simuladores. RESULTADOS: Considerando a incerteza das medições, os resultados de dose glandular média estão de acordo com os valores fornecidos pelo equipamento e com os níveis de referência adotados internacionalmente. Os resultados obtidos a partir das imagens dos objetos simuladores estavam em conformidade com os valores de referência. CONCLUSÃO: Este trabalho contribui para verificar a conformidade do equipamento em relação a dose e qualidade da imagem.

Monte Carlo study of a new I-125 brachytherapy prototype seed with a ceramic radionuclide carrier and radiographic marker.

In prostate cancer treatment, there is an increasing interest in the permanent radioactive seeds implant technique. Currently, in Brazil, the seeds are imported with high prices, which prohibit their use in public hospitals. A ceramic matrix that can be used as a radioisotope carrier and radiographic marker was developed at our institution. The ceramic matrix is distinguished by the characteristic of maintaining the radioactive material uniformly distributed in its surface. In this work, Monte Carlo simulations were performed in order to assess the dose distributions generated by this prototype seed model, with the ceramic matrix encapsulated in titanium, in the same way as the commercial 6711 seed. The obtained data was assessed, as described in the TG-43U1 report by the American Association of Physicists in Medicine, for two seed models: (1) the most used model 6711 source - for validation and comparison, and (2) for the prototype model with the ceramic matrix. The dosimetric parameters dose rate constant, Λ, radial dose function, gL(r), and anisotropy function, F(r,θ), were derived from simulations by the Monte Carlo method using the MCNP5 code. A Λ 0.992 (± 2.33%) cGyh-1U-1 was found for the prototype model. In comparison with the 6711 model, a lower dose fall-off on transverse axis was found, as well as a lower dose anisotropy for the radius r = 0.25 cm. In general, for all distances, the prototype seed model presents a slightly larger anisotropy between 0° ≤ Θ < 50° and anisotropy similar to the 6711 model for Θ ≥ 50°. The dosimetric characteristics of the prototype model presented in this study suggest that its use is feasible. Because of the model's characteristics, seeds of lower specific activity iodine might be necessary which, on the other hand, would help to reduce costs. However, it has to be emphasized that the proposed source is a prototype, and the required (AAPM prerequisites) experimental study and tolerance manufacturer values are pending for future studies.