Comparison of two treatment techniques for breast irradiation including internal mammary nodes.

Techniques to treat breast cancer inclusive of the internal mammary lymph node chain (IMC) vary. This study compared a presently accepted technique implemented at the Radiation Oncology Department at Barnes-Jewish Hospital/Washington University School of Medicine (BJ/WU) to a proposed technique for irradiation of breast tissue and the IMC. The present technique consists of parallel-opposed breast tangential beams in combination with photon and electron IMC fields angled along the chest wall. The proposed method involves a wide medial tangent field covering the IMC, with an angled electron IMC field for a portion of the treatment regimen and an opposed lateral breast-only tangent. This technique uses a multileaf collimation (MLC) reduction to treat the IMC aspect following the wide medial tangent, to supplement the IMC to a tumorcidal dose. These techniques were compared by reviewing isodoses with subsequent isodensity confirmation. Computerized tomography imaging sets of patients with various body types (chest wall, small and large breasts) for left-sided tumors were planned using a three-dimensional treatment planning system (FOCUS, Computerized Medical Systems). The plans were evaluated by comparing irradiated heart and lung volumes and the respective dose distribution at the IMC field/medial tangent junction. Specific treatment aids and photon/electron energies were employed to produce desirable isodose distributions, with a dose prescription of 4680-cGy total dose. The efficiency of the radiation treatments itself was also evaluated. The proposed technique decreases treatment time by eliminating an additional IMC field that involves repositioning and placement of a block. Phantom-based film isodensity measurements were evaluated to validate the calculated dosimetry for these techniques.