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    Resumo IPEN-doc 31144
    Dose rate by distance for Au-198 nanoparticles in water
    2024 - ANGELOCCI, L.V.; SGRIGNOLI, S.S.; SOUZA, C.D.; TEODORO, L.E.H.; ZEITUNI, C.A.; ROSTELATO, M.E.C.M.
    Purpose: To evaluate dose as a function of depth in water medium by a source of Au-198 nanoparticles, both as a point source and as homogeneously distributed over a volume representing a prostate tumor. Dose over an unidirectional axis was estimated and presented according to distance from the source, highlighting nearby organs at risk. The aim of the work is the first step in the dosimetric characterization of a new source for nanobrachytherapy under development, consisting of Au-198 nanoparticles injected directly in tumoral mass. Methods: Simulations were carried using MCNP6.2 code by Los Alamos National Laboratory. Four different simulations were realized, for two different source configurations (point source and 0.4 cm radius spherical source, modeling a prostate tumor) each considering two different components for the dose (beta emission and photon (gamma/x-ray) emission from the source). Medium considered was infinite water homogeneous. Results: Dose curve as a function of distance from the source was evaluated and allowed a first estimative of dose at points of interest for treatment with a new nanobrachytehrapy source. Point source results are valuable for future extrapolation for complex tumor/organs geometry. Prostate tumor model presents data that allows to estimate dose at center of tumor, borders of tumor, and at other organs nearby, such as rectum and bladder. Conclusion: Being a beta-emitter, Au-198 shows a high deposition of energy near the source, with doses falling significantly with distance from the source. However, due to gamma and x-ray emission from the source, as well as secondary radiation originating from the beta particles, not-negligible dose was scored at significant distance. This quantitative study will be relevant for posterior dosimetry of more complex cases as well to develop protocols for dosimetry and clinical use, as nanobrachytherapy (with nanoparticles as sources) is a relatively new field with few specific works published.
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    Resumo IPEN-doc 31143
    Study of a new formulation for a phosphorus-32 polymeric source for use in brachytherapy
    2024 - TEODORO, L.E.H.; TALACIMON, C.F.; SILVA, A.C.K.D.S.; BURIN, A.L.; MEDEIROS, I.M.M.A.; RIGO, M.E.Z.; RODRIGUES, P.S.; TAVARES, P.V.D.S.; SGRIGNOLI, S.S.; ANGELOCCI, L.V.; VIEIRA, J.M.; ZEITUNI, C.A.; ROSTELATO, M.E.C.M.
    Purpose: To evaluate a new material for a phosphorus-32 polymeric film to use in brachytherapy for paraspinal and intracranial tumors and to analyze its activity distribution. Methods: As phosphorus-32 comes in the form of orthophosphoric acid, several tests were conducted to determine the best resin to encapsulate it. Initially, acid without radiation was used. Each test was repeated at least five times to ensure its result. Two variables were checked to evaluate the results: whether the resin cured or not, and if the final product was flexible. All tests were conducted with the selected resin being poured in molds of 5.0 x 5.0 x 0.04 cm. After selecting the considered suitable resins, acid with the active phosphorus-32 was used to produce the source. The film’s activity was measured on an ionization chamber detector. After measuring the activity from the whole film, it was cut into pieces of 1.0 x 1.0 cm and then measured again to verify the activity’s distribution. Results: From the resin tests, two of them stood out, for both their curing properties and malleability: silicone rubber with platinum catalyst and polyvinyl alcohol (PVA). Other resins evaluated whether did not cure or the film was considered not flexible. The activity measurements for the silicone rubber samples had a mean value of 227.92 ± 1.30 MBq (or 6.160 ± 0.005 mCi) and the distribution was acceptable. For the PVA, the activity mean value was 243.09 ± 1.39 MBq (or 6,573 ± 0.005 mCi) and the distribution was also acceptable. Conclusion: This work indicates a potential for a new flexible brachytherapy source, which could improve the surgical technique for central nervous system tumor resection and treatment. The activity results were promising according to the literature for a HDR source and further investigation on its dosimetry is needed to evaluate it.