Study of dose deposition for two different geometries of iodine seeds in a solid water phantom

The OncoSeed 6711 is among the most used models in brachytherapy of prostate cancer. These seeds are implanted and positioned near the tumor following a plan. During this procedure, and with the natural movement of the body, these sources undergo small displacements. This work aimed to study the differences in the dose distribution, in a solid water phantom for two symmetric arrays of 4 seeds OncoSeed 6711. The phantom was machined to receive the sources and dosimeters LiF-100 Rod type. In this procedure, were made concentric circles around the seed configurations with radii of 1cm to 4cm and a central hole in each arrangement of seeds. The results showed a 35.8% difference in dose deposited in the center and significant differences in the radii of 1 cm and 2 cm, for the same irradiation time. After 3 cm this effect is showed negligible. Another note is that, although symmetrical distribution of the dose does not happen in this way. Thus, we conclude that changes in the seed placement caused differences in dose distribution and that this fact should be considered in planning for treatment. (author)