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The success of a radiotherapy depends on the correct planning of the dose to be delivered to the target volume. In brachytherapy which is a radiotherapy mode where intracavitary or interstitial implants of a sealed radioisotope are used, there are less computational advances in treatment planning systems than in teletherapy, more widely used in typical medical services. However, brachytherapy, where applicable, is preferable for sparing neighboring healthy tissues from unnecessary dose. The AMIGOBrachy is a treatment planning system (TPS) with an user-friendly interface for brachytherapy, compatible with other commercial systems, and integrated with MCNP6 code (Monte Carlo N-Particle Transport Code v. 6). It was developed in the Nuclear Engineering Center of the Instituto de Pesquisas Energéticas e Nucleares (CEN-IPEN), São Paulo, Brasil, and is currently in a validation process. This work contributed to this process, evaluating three different clinical cases with the TG43 formalism by AAPM (American Association of Medical Physics), a protocol for dosimetry in brachytherapy, and comparing their results with the dose distributions calculated by other well-known commercial systems: Varian BrachyVision TM (Varian Medical Systems; Palo Alto, CA, USA) and Nucletron Oncentra® (Elekta; Stockholm, Sweden). The results obtained are within a ±10% range of agreement, being more discrepant in regions very near to the applicator, where commercial planning systems and AMIGOBrachy differ due to different calculation methods. However, the dose agreed in a range of ±3% for at least two thirds of the region of interest, for all three cases. Also, simulations were performed using the TG186 formalism of AAPM, which considers heterogeneities in the tissue, to assess their impact on the dose. In addition to the validation process, a study in ophthalmic brachytherapy for future insertion of an additional module to AMIGOBrachy was performed; for this, a human eye model was developed using UM (Unstructured Mesh) geometry, for validation with MCNP6 code, that only in this version shows a new resource capable of simulating a hybrid geometry: partly analytical, partly UM. Ten different structures of the human eye were modeled: sclera, choroid, retina, vitreous body, cornea, anterior chamber, lens, optic nerve, optic nerve wall, and a tumor defined arbitrarily growing from the external surface of the eyeball toward its center. The results were compared with a purely analytical model eye modeled with MCNP6 and used as a reference. The results were satisfactory in all performed simulations, except for the optic nerve and its wall, mainly because of their small size and distance from the source, showing larger relative errors, but still lower than 10%, which, however, does not represent clinical concern problem since they receive very small doses. The problems encountered in this new resource of MCNP code to simulate hybrid geometries were also discussed, since it was implemented recently and still display deficiencies that were overcome in the present work.

Estudo de casos clínicos em radioterapia através do sistema de planejamento AMIGOBrachy