Breast dose heterogeneity in CT-based radiotherapy treatment planning

The aim of this study was to evaluate the breast dose heterogeneity in CT-based radiotherapy treatment planning and to correlate with breast parameters. Also, the number of slices required for treatment planning in breast cancer by tangential field technique has been assessed by comparing the treatment plans according to International Commission on Radiation Units and Measurement (ICRU) 50 guidelines (1993) for single-slice, three-slice, and multi-slice (3D) planning . Sixty women who underwent isocentric tangential field breast radiotherapy were included in this study. The plans were optimized and analyzed with dose volume histograms. Sixty-three percent of the single-slice plans and 26.7% of the three-slice plans showed poor dose homogeneity as compared to the 3D plans. Dose inhomogeneity correlated better with breast volume (r(2) = 0.43) than the chest wall separation (r(2) = 0.37) and breast area product (r(2) = 0.36). Similarly, breast volume correlated better with breast area product (r(2) = 0.80) than with chest wall separation (r(2) = 0.56). Breast volume can be approximated to breast area product from the relation, breast volume = [(breast area product x 8.85) - 120.05]. The results of this study showed that most of the cases require 3D planning for breast cancer. It also showed that patients with large breast are prone to have more dose inhomogeneity with standard tangential field radiotherapy. In centers where 3D planning is not possible due to lack of facilities or workload, three slices-based planning can be performed to approximate the dosimetric advantage of 3D planning.