Monte-Carlo dosimetry simulations of mono- and bi-isotopic radioactive sources used in prostate brachytherapy

Brachytherapy designs of sources have evolved during the past ten years. However, besides the type of radio-isotope (Pd-103, I-125 and recently Cs-131), no fundamental innovation have been proposed. The present work proposes an original seed loaded with two different isotopes in order to take the advantages of both. Theoretical dosimetry studies by Monte Carlo simulations have been performed to study the dose distribution of a combination of Pd-103 and I-125 in an InterSource-TM seed. It demonstrates advantages in comparison to mono-isotopic sources. Adjusting the relative activity of Pd-103 and I-125, one can get a higher dose at short distance avoiding Pd-103 cold spot and a smaller dose at long distances avoiding I-125 morbidity.