Dosimetric aspects of permanent radioactive implants for the treatment of prostate cancer

Understanding how an initial planning dose distribution provides a proper dose coverage after a permanent prostate implant is crucial to the outcome of the treatment of prostate cancer with permanent radioactive implants, both in term of success rate and in minimizing adverse effects of the radiation to normal tissues. Although there exist several approaches to obtain an initial dose distribution, either manually or with the use of an optimization routine, they are not equally robust to the effect of seed misplacement. After a brief review of the criteria considerations that must be met to achieve a good dose distribution, we present an optimization algorithm that was developed for dose planning. We also present a mathematical simulation model of source misplacement to predict post-implant dosimetry. Simulations were used to guide the development of the optimization algorithm and to select among various planning scenarios, the one offering the best post-implant dose coverage. (author)