Improved dose homogeneity to the intact breast using three-dimensional treatment planning: technical considerations

The current consensus is that breast-conservative treatment is superior to mastectomy because it provides survival equivalent to total mastectomy and axillary dissection while preserving the breast. This technique still has several technical issues that can adversely influence the successful outcome of breast-conservative treatment. Specifically, dose coverage and homogeneity must be maintained throughout the breast while reducing the hot-volume magnitude and normal tissue complications. A random retrospective three-dimensional treatment-planning study was conducted using computed tomography scans of 20 female patients with early-stage breast cancer. Two- and three-dimensional homogenous and heterogeneous treatment planning was conducted using all possible hard-wedge combinations and effective photon energies, with the goal of reducing the hot volumes in the breast below 110 percent of the prescribed dose. The hard-wedge combination that minimized the hot volumes uses either 15-degree wedges on the medial and lateral beams or a 30-degree wedge on the medial beam and a 15-degree wedge on the lateral beam. For patients with bridge distances less than 20 cm, this wedge combination reduces the hot volumes below 110 percent of the prescribed dose. For patients with bridge distances greater than 20 cm, low- and high-energy photon beams must be mixed to lower the maximum dose below 110 percent of the prescribed dose. The hot volumes in the breasts of 20 random patients was reduced below 110 percent of the prescribed dose without a significant reduction in tumor coverage.