OBJECTIVE: The present paper is aimed at presenting a comparative dosimetric study of prostate brachytherapy with I-125 and Pd-103 seeds. MATERIALS AND METHODS: A protocol for both implants with 148 seeds was simulated on a heterogeneous three-dimensional pelvic phantom by means of the SISCODES/MCNP5 codes. Dose-volume histograms on prostate, rectum and bladder, dose indexes D₁₀, D₃₀, D₉₀, D_0.5cc, D_2cc and D_7cc, and representations of the spatial dose distribution were evaluated. RESULTS: For a D₉₀ index equivalent to the prescription dose, the initial activity of each I-125 seed was calculated as 0.42 mCi and of Pd-103 as 0.94 mCi. The maximum dose on the uretra was 90% and 108% of the prescription dose for I-125 and Pd-103, respectively. The D_2cc for I-125 was 30 Gy on the rectum and 127 Gy on the bladder; for Pd-103 was 29 Gy on the rectum and 189 Gy on the bladder. The D₁₀ on the pubic bone was 144 Gy for I-125 and 66 Gy for Pd-103. CONCLUSION: The results indicate that Pd-103 and I-125 implants could deposit the prescribed dose on the target volume. Among the findings of the present study, there is an excessive radiation exposure of the pelvic bones, particularly with the I-125 protocol.

Keywords: Radiotherapy; Dosimetry; Prostate cancer; Brachytherapy; SISCODES; MCNP.