Objective: The present paper is aimed at presenting a comparative dosimetric study of prostate brachytherapy with I-125 and Pd-103 seeds. Materials and Methods: A protocol for both implants with 148 seeds was simulated on a heterogeneous three-dimensional pelvic phantom by means of the SISCODES/MCNP5 codes. Dose-volume histograms on prostate, rectum and bladder, dose indexes D 10 , D 30 , D 90 , D 0.5cc , D 2cc and D 7cc , and representations of the spatial dose distribution were evaluated. Results: For a D 90 index equivalent to the prescription dose, the initial activity of each I-125 seed was calculated as 0.42 mCi and of Pd-103 as 0.94 mCi. The maximum dose on the uretra was 90% and 108% of the prescription dose for I-125 and Pd-103, respectively. The D 2cc for I-125 was 30 Gy on the rectum and 127 Gy on the bladder; for Pd-103 was 29 Gy on the rectum and 189 Gy on the bladder. The D 10 on the pubic bone was 144 Gy for I-125 and 66 Gy for Pd-103. Conclusion: The results indicate that Pd-103 and I-125 implants could deposit the prescribed dose on the target volume. Among the findings of the present study, there is an excessive radiation exposure of the pelvic bones, particularly with the I-125 protocol. Keywords: Radiotherapy; Dosimetry; Prostate cancer; Brachytherapy; SISCODES; MCNP.Objetivo: O presente artigo visa apresentar um estudo dosimétrico comparativo de braquiterapia de próstata com sementes de I-125 e Pd-103. Materiais e Métodos: Um protocolo adotado para ambos os implantes com 148 sementes foi simulado em um fantoma tridimensional heterogêneo de pelve por meio dos códigos SISCODES/MCNP5. Histogramas dose-volume na próstata, bexiga e reto, índices de doses D 10 , D 30 , D 90 , D 0,5cc , D 2cc e D 7cc , e representações de distribuição espacial de dose foram avaliados. Resultados: A atividade inicial de cada semente de I-125, para que D 90 seja equivalente à dose de prescrição, foi calculada em 0,42 mCi, e de Pd-103, em 0,94 mCi. A dose máxima na uretra foi 90% e 108% da dose de prescrição para I-125 e Pd-103, respectivamente. A D 2cc para I-125 foi 30 Gy no reto e 127 Gy na bexiga, e para Pd-103 foi 29 Gy no reto e 189 Gy na bexiga. A D 10 no osso do púbis foi 144 Gy para I-125 e 66 Gy para Pd-103. Conclusão: Os resultados indicam que os implantes de Pd-103 e I-125 puderam depositar a dose prescrita no volume alvo. Entre os achados, observou-se excessiva exposição de radiação nos ossos da pelve, principalmente no protocolo com I-125. Unitermos: Radioterapia; Dosimetria; Câncer de próstata; Braquiterapia; SISCODES; MCNP. AbstractResumo
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