Dados do Trabalho

Título

Evaluation of teletherapy and brachytherapy scenarios in three materials comparing two Monte Carlo simulation systems

Introdução

Radiotherapy aims to eradicate tumor volume while preserving healthy adjacent cells as much as possible. If the irradiation source is close to the tumor region, the treatment is called brachytherapy and if the source is far from the patient, teletherapy. Due to the high dose gradient and experimental difficulties, the use of simulation for dosimetric determination in regions close to the source is recommended.

Objetivo

In this work, we analyzed the response of two Monte Carlo simulation packages, PENELOPE and TOPAS, in the comparison of teletherapy and brachytherapy scenarios in three materials.

Método

In all simulations, a cubic phantom with 30 cm side was used, filled with three different materials: liquid water, solid water and perspex. The number of particles remained constant at 5x10⁸. In brachytherapy, the Palladium source, model IR06-103Pd, was modeled in the center of the phantom and in teletherapy the source was positioned 40 cm from the surface of the phantom, with a quadratic irradiation field of 5 cm on the side. Photon and electron beams, both of 6 MeV, were analyzed.

Resultados

For the evaluation of the packages, percent depth dose was analyzed for teletherapy, for which the maximum uncertainty found, in both beams, was less than 4.5%. The biggest difference found, in photons, was 9.9% bigger for TOPAS, in the simulation with perspex. While for the electron beam, a 12% greater difference was obtained for PENELOPE, in the simulation with water. For the brachytherapy scenario, the relative dose was analyzed, in the radial direction of the source, with a maximum relative uncertainty of less than 5% for all materials, in accordance with the recommendations of the American Association of Physicists in Medicine.

Conclusão

The percent depth dose profiles are in agreement with what was experimentally expected, considering the sharper drop for the electron beam than for the photon beam. Furthermore, the simulators presented similar performances for the two teletherapy scenarios. However, for the brachytherapy scenario, the simulators showed different performances. Thus, the analysis presented in this work showed that the simulation packages PENELOPE and TOPAS have high agreement in the teletherapy results, however for the brachytherapy results they did not agree, due to the physical implementation of the computational packages.

Palavras-chave

Dosimetry, PENELOPE, TOPAS.