Uso do código MCNP-4C para análise da curva de PDP em feixes de fótons de alta energia

Introdução: O método de Monte Carlo tem sido largamente aplicado para simulações de tratamentos e modelagem de feixes de radiação utilizados em radioterapia. As simulações envolvem características específicas do problema: geometria; composição; disposição dos elementos da simulação; especificações da fonte. Nestas simulações, um desafio é determinar o espectro da fonte de radiação, pois os fabricantes dos equipamentos não disponibilizam as informações específicas do feixe. O espectro pode ser obtido por um método empírico a partir da curva experimental de Porcentagem de Dose Profunda (PDP) e perfil de planura, obtidos nos procedimentos de dosimetria. Objetivos: Reconstruir as PDP experimentais dos feixes de 6 MV e 10 MV do acelerador linear Varian, modelo 2100C, através de simulações com o código MCNP-4C. Métodos: Os valores experimentais da PDP foram cedidos pelo Setor de Radioterapia do Hospital das Clínicas da UNESP de Botucatu. O MCNP-4C foi utilizado para simulações e reconstrução da curva de PDP. A modelagem geométrica considerou uma fonte plana de fótons, a 100cm da superfície de um fantoma cúbico de água contendo, em seu interior, 31 elipsoides (uma a cada 1cm). A energia depositada foi calculada para cada elipsoide e, com esses resultados, foram reconstruídas as curvas de PDP. Resultados: O desvio máximo encontrado para cada ponto foi de 1%, comprovando a consistência das medidas obtidas pelo MCNP-4C. A diferença máxima entre curvas experimentais e simuladas foi de 3,7% (feixe 6MV) e 4,6% (10MV). Conclusão: A concordância entre os resultados, para os feixes de fótons, valida a metodologia proposta

Monte Carlo studies on water and LiF cavity properties for dose-reporting quantities when using x-ray and brachytherapy sources

Model-based dose calculation algorithms (MBDCAs) are the current tools to estimate dose in brachytherapy, which takes into account heterogeneous medium, therefore, departing from water-based formalism (TG-43). One aspect associated to MBCDA is the choice of dose specification medium since it offers two possibilities to report dose: (a) dose to medium in medium, D-m,D-m; and (b) dose to water in medium, D-w,D-m. The discussion about the preferable quantity to be reported is underway. The dose conversion factors, DCF, between dose to water in medium, D-w,D-m, and dose to medium in medium, D-m,D-m, is based on cavity theory and can be obtained using different approaches. When experimental dose verification is desired using, for example, thermoluminescent LiF dosimeters, as in in vivo dose measurements, a third quantity is obtained, which is the dose to LiF in medium, D-LiF,D-m. In this case, DCF to convert from D-LiF,D-m to Dw, m or Dm, m is necessary. The objective of this study is to estimate DCFs using different approaches, present in the literature, quantifying the differences between them. Also, dose in water and LiF cavities in different tissue media and respective conversion factors to be able to convert LiF-based dose measured values into dose in water or tissue were obtained. Simple cylindrical phantoms composed by different tissue equivalent materials (bone, lung, water and adipose) are modelled. The phantoms contain a radiation source and a cavity with 0.002 69 cm(3) in size, which is a typical volume of a disc type LiF dosimeter. Three x-rays qualities with average energies ranging from 47 to 250 keV, and three brachytherapy sources, Co-60, Ir-192 and Cs-137, are considered. Different cavity theory approaches for DCF calculations and different cavity/medium combinations have been considered in this study. DCF values for water/bone and LiF/bone cases have strong dependence with energy increasing as the photon energy increases. DCF values also increase with energy for LiF/lung and water/lung cases but, they are much less dependent of energy. For LiF/adipose, water/adipose and LiF/water cases, the DCF values are also dependent of photon energy but, decreases as the energy increases. Maximum difference of 12% has been found compared to values in literature

Análise dosimétrica de perfis de distribuições radiais de doses relativas de um aplicador de betaterapia de 90Sr+90Y utilizando o código MCNP-4C e filmes raiocrômicos

Although they are no longer manufactured, the applicators of 90Sr +90Y acquired in the decades of 1990 are still in use, by having half-life of 28.5 years. These applicators have calibration certificate given by their manufacturers, where few have been recalibrated. Thus it becomes necessary to accomplish thorough dosimetry of these applicators. This paper presents a dosimetric analysis distribution radial dose profiles for emitted by an 90Sr+90Y betatherapy applicator, using the MCNP-4C code to simulate the distribution radial dose profiles and radiochromium films to get them experimentally . The results with the simulated values were compared with the results of experimental measurements, where both curves show similar behavior, which may validate the use of MCNP-4C and radiochromium films for this type of dosimetryApesar de não serem mais fabricados, os aplicadores de 90Sr+90Y adquiridos nas décadas de 90 ainda estão em uso, por possuírem uma meia-vida de 28,5 anos. Estes aplicadores possuem certificado de calibração dado pelos seus fabricantes, onde poucos foram recalibrados. Desta forma se torna necessário realizar uma meticulosa dosimetria destes aplicadores. Este trabalho aborda uma análise dosimétrica de perfis de distribuições radiais de doses relativas emitido por um aplicador de betaterapia de 90Sr+90Y, utilizando o código MCNP-4C para simular os perfis de distribuições radiais de doses relativas e os filmes radiocrômicos para obtê-los experimentalmente. Os resultados com os valores simulados foram comparados com os resultados das medidas experimentais, onde ambas as curvas apresentaram um comportamento semelhante, podendo validar o uso do MCNP-4C e dos filmes radiocrômicos para este tipo de dosimetria

The use of tetrahedral mesh geometries in Monte Carlo simulation of applicator based brachytherapy dose distributions

Submitted by Claudinei Pracidelli ([email protected]) on 2015-01-12T12:09:09Z No. of bitstreams: 1 20292.pdf: 3031678 bytes, checksum: 9ac1d39d7252b0f96ab00fbb863cac17 (MD5)Made available in DSpace on 2015-01-12T12:09:09Z (GMT). No. of bitstreams: 1 20292.pdf: 3031678 bytes, checksum: 9ac1d39d7252b0f96ab00fbb863cac17 (MD5

A new rectal model for dosimetry applications

A revised geometric representative model of the lower part of the colon, including the rectum, the urinary bladder and prostate, is proposed for use in the calculation of absorbed dose from injected radiopharmaceuticals. The lower segment of the sigmoid colon as described in the 1987 Oak Ridge National Laboratory mathematical phantoms does not accurately represent the combined urinary bladder/rectal/prostate geometry. In the revised model in this study, the lower part of the abdomen includes an explicitly defined rectum. The shape of sigmoid colon is more anatomically structured, and the diameters of the descending colon are modified to better approximate their true anatomic dimensions. To avoid organ overlap and for more accurate representation of the urinary bladder and the prostate gland (in the male), these organs are shifted from their originally defined positions. The insertion of the rectum and the shifting of the urinary bladder will not overlap with or displace the female phantom\u27s ovaries or the uterus. In the adult male phantom, the prostatic urethra and seminal duct are also included explicitly in the model. The relevant structures are defined for the newborn and 1-, 5-, 10- and 15-y-old (adult female) and adult male phantoms. METHODS: Values of the specific absorbed fractions and radionuclide S values were calculated with the SIMDOS dosimetry package. Results for 99mTc and other radionuclides are compared with previously reported values. RESULTS: The new model was used to calculate S values that may be crucial to calculations of the effective dose equivalent. For 131I, the S (prostate\u3c--urinary bladder contents) and S (lower large intestine [LLI] wall\u3c--urinary bladder contents) are 6.7 x 10(-6) and 3.41 x 10(-6) mGy/MBq x s, respectively. Corresponding values given by the MIRDOSE3 computer program are 6.23 x 10(-6) and 1.53 x 10(-6) mGy/MBq x s, respectively. The value of S (rectum wall\u3c--urinary bladder contents) is 4.84 x 10(-5) mGy/MBq x s. For 99mTc, we report S (testes\u3c--prostate) and S (LLI wall\u3c--prostate) of 9.41 x 10(-7) and 1.53 x 10(-7) mGy/MBq x s versus 1.33 x 10(-6) and 7.57 x 10(-6) mGy/MBq x s given by MIRDOSE3, respectively. The value of S (rectum wall\u3c--prostate) for 99mTc is given as 4.05 x 10(-6) mGy/MBq x s in the present model. CONCLUSION: The new revised rectal model describes an anatomically realistic lower abdomen region, thus giving improved estimates of absorbed dose. Due to shifting the prostate gland, a 30%-45% reduction in the testes dose and the insertion of the rectum leads to 48%-55% increase in the LLI wall dose when the prostate is the source organ

A medical image-based graphical platform-Features, applications and relevance for brachytherapy

Submitted by Claudinei Pracidelli ([email protected]) on 2014-12-23T11:24:06Z No. of bitstreams: 1 20236.pdf: 2337946 bytes, checksum: 965751ff4c83e256320509bdecb82e3d (MD5)Made available in DSpace on 2014-12-23T11:24:06Z (GMT). No. of bitstreams: 1 20236.pdf: 2337946 bytes, checksum: 965751ff4c83e256320509bdecb82e3d (MD5

Evaluation of the cytogenetic effects of I-131 preceded by recombinant human thyrotropin (rhTSH) in peripheral lymphocytes of Wistar rats

The present study was carried out to investigate the cytogenetic effects of therapeutic exposure to radioiodine preceded by rhTSH in an animal model. Three groups of Wistar rats (n = 6) were used: one group was treated only with I-131 (11.1 MBq/animal); the other two groups received rhTSH (1.2 mu g/rat of either Thyrogen or rhTSH-IPEN, respectively) 24 h before administration of radioiodine. The percentage of lymphocytes with chromosome aberrations and the average number of aberrations and of dicentrics per cell were determined on blood samples collected 24 h, 7 and 30 days after administration of I-131. The data show that the treatment with radioiodine alone or associated with rhTSH resulted in a greater quantity of chromosome alterations in relation to basal values after 24 h, with a gradual decline after 7 and 30 days of treatment. An increase in chromosome alterations was also seen after rhTSH treatment alone. Neither of the treatments, i.e., with I-131 alone or associated with hormone, resulted in an aneugenic effect or influenced the kinetics of cellular proliferation in rat blood lymphocytes. There was no significant difference between the cytogenetic effects of Thyrogen and rhTSH-IPEN treatment. These data suggest that the treatment with radioiodine, associated or not with rhTSH, affects to a limited extent a relatively small number of cells although the occurrence of late stochastic effects could not be discarded.FAPESP[02/09872-6