An Evaluation of Treatment Planning Strategies to Improve Dose Homogeneity in Permanent Breast Seed Implant

Abstract

There is no evidence in the literature that the seed activity and implantation pattern recommended for permanent breast seed implant (PBSI) are optimal. These planning parameters were systematically evaluated to determine an optimal planning strategy for PBSI. A simple model was used to investigate planning strategies incorporating various Pd-103 seed activities, needle and seed spacings, and implants in which seed positions are either restricted to or permitted outside of spherical target volumes. To address more realistic geometries, model parameters were used to re-plan a 5-patient cohort in MIM Symphony. The results confirm that the current clinical needle-to-needle and seed-to-seed spacing provides the most favourable dose distributions, given the limitations imposed by the implant apparatus. However, a drastic improvement in dose homogeneity, with equivalent coverage and conformity, can be achieved by implanting seeds beyond the PTV within a 0.3 – 0.5 cm margin, and optimizing seed activity on a per patient basis.