Purpose: A method for designing partly wide tangential fields that irradiate the superiorly placed internal mammary nodes, yet exclude the inferiorly placed internal mammary nodes and the cardiac tissue, is described for patients receiving tangential radiation for breast cancer.
Methods and materials: Patients are immobilized in hemibody foam cradles. A CT study is performed with a series of fiducial markers. The CT data set can then either be transferred to the three-dimensional treatment planning computer for sophisticated treatment planning, or can be viewed to design partly wide tangential fields "by hand." This latter method is far less time consuming and, we believe, usually adequate, given the uncertainties in identifying the location of the internal mammary nodes.
Results: This technique has been implemented in our clinic and has been used to treat approximately 15 patients. In four of these patients, a formal dose-volume histogram analysis revealed that these partly wide tangential fields can adequately exclude the cardiac volume and include the superiorly placed internal mammary nodes. Modest reductions in the pulmonary volume that is incidentally irradiated are seen compared to conventional wide tangents that irradiate the entire length of the internal mammary chain.
Conclusion: While controversy remains regarding the appropriateness of internal mammary nodal irradiation for patients with breast cancer, the technique described represents an attractive compromise. Selective irradiation of the superiorly placed internal mammary nodes (which are those at greatest risk for involvement) with customized "partly wide" tangential fields is possible. This treatment technique may provide the survival advantage that might be seen with internal mammary node irradiation, yet avoid the possible cardiac morbidity.