The Role of Postmastectomy Radiation in the Treatment of Early Stage Breast Cancer: Back to the Future

Actual computer-generated dosimetry from CT of a 38-year-old woman with T₁N₁M₀ subareolar breast cancer and 10 positive axillary nodes. A. Standard left-breast tangential RT fields include a portion of the anterior wall of the left ventricle and fail to encompass the IM lymphatics. B. Broad tangential fields encompass IM lymphatics but also include a substantial portion of the left ventricle and 3.5 cm of the lung. C. The 5-field technique covers the IM lymphatics with minimal dosage to a very small volume of the heart and lung. The separate IM fields mix 5 anterior 6 MV photon with 23 oblique electron beam fractions of 180 cGy. The usual cold triangle beneath the IM/tangent junction is eliminated by overlapping the antero-posterior IM photons into the medial tangent field by 1 cm, and angling the IM electrons 5° less than the tangents. By choosing an electron energy (here 12 MV) that places the 80% isodose at the pleural surface, the IM nodes are typically at the prescription isodose (90%), and the dose falls off rapidly as it reaches the lung and heart. Multiplane CT planning is a necessity. CT=computerized tomography, RT= radiotherapy, IM=internal mammary [Reprinted by permission of Lippincott, Williams and Wilkins from Journal of Clinical Oncology 1998. 16:2581]