Brachytherapy partial breast irradiation: analyzing effect of source configurations on dose metrics relevant to toxicity.

Abstract

Recently, the use of partial breast irradiation (PBI) for patients with early-stage breast cancer with low-risk factors has increased. The volume of the high-dose regions has been correlated with toxicity in interstitial treatment. Although no such associations have been made in applicator-based experience, new applicators are being developed that use complex noncentered source configurations. This work studied the effect of noncentered source placements on the volume of the high-dose regions around a spherical applicator. Many applicator configurations were numerically simulated for a range of inflation radii. For each configuration, a dose homogeneity index was used as a dose metric to measure the volume of the high-dose region. All multisource configurations examined resulted in an increase of the high-dose region compared with a single-center source. The resulting decrease in the prescription dose homogeneity index was more pronounced for sources further from the center of the applicator, and the effect was reduced as the number of dwell locations was increased. The geometries of particular applicators were not considered to achieve a more general result. On the basis of the calculations of this work, it would appear that treatment using noncentered dwell locations will lead to an increase in the volume of the high-dose regions.