Dosimetria da braquiterapia por Califórnio-252 associada à captura de nêutrons pelo Boro com balão moderador aplicada ao Glioblastoma multiforme

Abstract

Glioblastoma multiforme is a highly infiltrative tumor and, even with technological advances, the treatment for the control of infiltrations and local metastases is still a challenge. In order to evaluate alternatives for its treatment, this work aimed to conduct dosimetric studies for 252Cf brachytherapy combined with boron neutron capture therapy (BNCT) and to propose the coupling of a balloon moderator to this association. Dosimetric studies were conducted through computational simulation in MCNP5 code, using a voxel model of a human head, in which a hypothetical brain tumor and infiltrations were incorporated. The model was constructed on the SISCODES software that was also used as an interface for the MCNP5 simulations. 252Cf brachytherapy, 252Cf brachytherapy combined with BNCT, 252Cf brachytherapy combined with BNCT and a moderator balloon of heavy water, 252Cf brachytherapy combined with BNCT and a moderator balloon of light water, and 125I balloon brachytherapy cases were simulated. In 252Cf brachytherapy combined with BNCT, simulations were performed for boron concentration ratios to normal tissue:tumor of 1:1, 1:3,5, 1:5, 1:10, 1:20 e 1:50, even as no boron concentration. Comparative dosimetric analysis among the mentioned techniques was performed. Considering a boron concentration ratio of 1:3,5 and 72Ýg of 252Cf, results showed that would be necessary a cumulative exposure time of 9,6 h to reach a dose of 60 RBE.Gy in the tumor bed, at 1 cm of the source center, both in 252Cf brachytherapy as in 252Cf brachytherapy combined with BNCT. But in the last, the dose in the infiltration would be 2 to 5 times larger than in the first. In balloon brachytherapy cases, both 125I balloon brachytherapy and 252Cf brachytherapy combined with BNCT and heavy water balloon would require a cumulative time of 54 h to reach a dose of 60 RBE.Gy in the tissue adjacent to the balloon, for example 9 fractions of 6 h. However, with the 125I balloon the dose in the bone would reach 114.6 RBE.Gy, which requires a reassessment of this type of therapy. Whereas in 252Cf source, BNCT and balloon of heavy water association, the dose in the infiltration closer to the balloon would reach 91.4 RBE.Gy, meaning a dose of 50% larger than in the periphery of the balloon. The results showed that the association of 252Cf source with a balloon moderator may be an alternative for increasing the viability and effectiveness of the BNCT technique in Brazilians radiotherapy centers.