Monte Carlo evaluation of the dose sparing and dose enhancement by combination of Gd-infused tumor and 241 Am source for an endocavitary brachytherapy geometry

In this work, the benefits in terms of dose enhancement and dose sparing via radiation shielding are evaluated, for a combined irradiation scheme with sources of Am and tumor-infused with Gd agents, regarding conventional Ir treatment. Monte Carlo simulations using PENELOPE code were implemented for endocavitary brachytherapy geometries, configuring a pelvis phantom of 15 cm radius and 30 cm length. Inside, it was defined cylindrical tumor phantoms of 2 cm radius and 4 cm-6 cm length (simulating initial stages) as well as tumors of extensive volume (2.5 and 3.0 cm radius) and difficult coverage. Tumor phantoms were doped with 68 mM and 138 mM of Gd in order to assess the effects of enhancement and protection based on the concentration and emission energy of the isotope. Obtained results for the first tumor group, shown the feasibility of achieving dose enhancements of 94.3%-117% and 160%-194% for 68 mM and 138 mM of Gd infused into the tumor and irradiation with Am, respectively. Similarly, reduced dose enhancements of 3.5-5.7% y 8.9%-11.2% for 68 mM and 138 mM of Gd are attained with Ir. In terms of dose sparing outer the tumor, the radiation shielding and dose enhancement allowed a higher reduction in the dose by Am of 17%-24% for 68 mM and 21%-32% for 138 mM of Gd, and non-negligible dose sparing are produced too by Ir of 2% and 5% for the same concentration of Gd. For the second tumors group, the combined use of 241Am and Gd agents simultaneously allowed to improve coverage and reduce the healthy tissue dose, showing the obtained results the possibility of achieving coverage of 95% of the prescribed dose in 100% of tumor volume together with dose sparing factor of 6-21% reduction in isodose of the studied point and dose enhancements of 75%-158% at the prescription point.